golang http transport源码分析
前言
Golang http库在日常开发中使用会很多。这里通过一个demo例子出发，从源码角度梳理golang http库底层的数据结构以及大致的调用流程
例子
package main
import (
"fmt"
"net/http"
"net/url"
"time"
"net"
)
func send_http_request(addr string, port int) error {
client := &http.Client{
Transport: &http.Transport{
Proxy: http.ProxyFromEnvironment,
DialContext: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
DualStack: true,
}).DialContext,
MaxIdleConns: 100,
MaxIdleConnsPerHost: 100,
IdleConnTimeout: 90 * time.Second,
},
}
// construct encoded endpoint
Url, err := url.Parse(fmt.Sprintf("http://%s:%d", addr, port))
if err != nil {
return err
}
Url.Path += "/index"
endpoint := Url.String()
req, err := http.NewRequest("GET", endpoint, nil)
if err != nil {
return err
}
// use httpClient to send request
rsp, err := client.Do(req)
if err != nil {
return err
}
// close the connection to reuse it
defer rsp.Body.Close()
// check status code
if rsp.StatusCode != http.StatusOK {
return fmt.Errorf("get rsp error: %v", rsp)
}
return err
}
func main() {
send_http_request("xxx", 8080)
}
源码分析
先看看http.Client结构体，如下：
// A Client is an HTTP client. Its zero value (DefaultClient) is a
// usable client that uses DefaultTransport.
//
// The Client's Transport typically has internal state (cached TCP
// connections), so Clients should be reused instead of created as
// needed. Clients are safe for concurrent use by multiple goroutines.
//
// A Client is higher-level than a RoundTripper (such as Transport)
// and additionally handles HTTP details such as cookies and
// redirects.
//
// When following redirects, the Client will forward all headers set on the
// initial Request except:
//
// • when forwarding sensitive headers like "Authorization",
// "WWW-Authenticate", and "Cookie" to untrusted targets.
// These headers will be ignored when following a redirect to a domain
// that is not a subdomain match or exact match of the initial domain.
// For example, a redirect from "foo.com" to either "foo.com" or "sub.foo.com"
// will forward the sensitive headers, but a redirect to "bar.com" will not.
//
// • when forwarding the "Cookie" header with a non-nil cookie Jar.
// Since each redirect may mutate the state of the cookie jar,
// a redirect may possibly alter a cookie set in the initial request.
// When forwarding the "Cookie" header, any mutated cookies will be omitted,
// with the expectation that the Jar will insert those mutated cookies
// with the updated values (assuming the origin matches).
// If Jar is nil, the initial cookies are forwarded without change.
//
type Client struct {
// Transport specifies the mechanism by which individual
// HTTP requests are made.
// If nil, DefaultTransport is used.
Transport RoundTripper
// CheckRedirect specifies the policy for handling redirects.
// If CheckRedirect is not nil, the client calls it before
// following an HTTP redirect. The arguments req and via are
// the upcoming request and the requests made already, oldest
// first. If CheckRedirect returns an error, the Client's Get
// method returns both the previous Response (with its Body
// closed) and CheckRedirect's error (wrapped in a url.Error)
// instead of issuing the Request req.
// As a special case, if CheckRedirect returns ErrUseLastResponse,
// then the most recent response is returned with its body
// unclosed, along with a nil error.
//
// If CheckRedirect is nil, the Client uses its default policy,
// which is to stop after 10 consecutive requests.
CheckRedirect func(req *Request, via []*Request) error
// Jar specifies the cookie jar.
//
// The Jar is used to insert relevant cookies into every
// outbound Request and is updated with the cookie values
// of every inbound Response. The Jar is consulted for every
// redirect that the Client follows.
//
// If Jar is nil, cookies are only sent if they are explicitly
// set on the Request.
Jar CookieJar
// Timeout specifies a time limit for requests made by this
// Client. The timeout includes connection time, any
// redirects, and reading the response body. The timer remains
// running after Get, Head, Post, or Do return and will
// interrupt reading of the Response.Body.
//
// A Timeout of zero means no timeout.
//
// The Client cancels requests to the underlying Transport
// as if the Request's Context ended.
//
// For compatibility, the Client will also use the deprecated
// CancelRequest method on Transport if found. New
// RoundTripper implementations should use the Request's Context
// for cancellation instead of implementing CancelRequest.
Timeout time.Duration
}
- Transport：http client实际发送请求结构体
- Timeout：http client请求超时设置(后续在详细分析)
在看Transport结构体(net/http/client.go)：
// RoundTripper is an interface representing the ability to execute a
// single HTTP transaction, obtaining the Response for a given Request.
//
// A RoundTripper must be safe for concurrent use by multiple
// goroutines.
type RoundTripper interface {
// RoundTrip executes a single HTTP transaction, returning
// a Response for the provided Request.
//
// RoundTrip should not attempt to interpret the response. In
// particular, RoundTrip must return err == nil if it obtained
// a response, regardless of the response's HTTP status code.
// A non-nil err should be reserved for failure to obtain a
// response. Similarly, RoundTrip should not attempt to
// handle higher-level protocol details such as redirects,
// authentication, or cookies.
//
// RoundTrip should not modify the request, except for
// consuming and closing the Request's Body. RoundTrip may
// read fields of the request in a separate goroutine. Callers
// should not mutate or reuse the request until the Response's
// Body has been closed.
//
// RoundTrip must always close the body, including on errors,
// but depending on the implementation may do so in a separate
// goroutine even after RoundTrip returns. This means that
// callers wanting to reuse the body for subsequent requests
// must arrange to wait for the Close call before doing so.
//
// The Request's URL and Header fields must be initialized.
RoundTrip(*Request) (*Response, error)
}
从注释可以看到RoundTripper负责HTTP请求的建立，发送，接收HTTP应答以及关闭；但是不应该对HTTP应答进行额外处理，例如：redirects, authentication, or cookies等上层协议细节。另外RoundTripper也是goroutines-safe的
其中RoundTrip方法的Request和Response参数如下(net/http/request.go)：
// A Request represents an HTTP request received by a server
// or to be sent by a client.
//
// The field semantics differ slightly between client and server
// usage. In addition to the notes on the fields below, see the
// documentation for Request.Write and RoundTripper.
type Request struct {
// Method specifies the HTTP method (GET, POST, PUT, etc.).
// For client requests, an empty string means GET.
//
// Go's HTTP client does not support sending a request with
// the CONNECT method. See the documentation on Transport for
// details.
Method string
// URL specifies either the URI being requested (for server
// requests) or the URL to access (for client requests).
//
// For server requests, the URL is parsed from the URI
// supplied on the Request-Line as stored in RequestURI. For
// most requests, fields other than Path and RawQuery will be
// empty. (See RFC 7230, Section 5.3)
//
// For client requests, the URL's Host specifies the server to
// connect to, while the Request's Host field optionally
// specifies the Host header value to send in the HTTP
// request.
URL *url.URL
...
// Body is the request's body.
//
// For client requests, a nil body means the request has no
// body, such as a GET request. The HTTP Client's Transport
// is responsible for calling the Close method.
//
// For server requests, the Request Body is always non-nil
// but will return EOF immediately when no body is present.
// The Server will close the request body. The ServeHTTP
// Handler does not need to.
Body io.ReadCloser
...
}
...
// Response represents the response from an HTTP request.
//
// The Client and Transport return Responses from servers once
// the response headers have been received. The response body
// is streamed on demand as the Body field is read.
type Response struct {
Status string // e.g. "200 OK"
StatusCode int // e.g. 200
Proto string // e.g. "HTTP/1.0"
ProtoMajor int // e.g. 1
ProtoMinor int // e.g. 0
...
}
这里Request和Response就是我们熟悉的HTTP请求和应答结构体
这里我们看demo对Transport的使用如下(net/http/transport.go)：
client := &http.Client{
Transport: &http.Transport{
Proxy: http.ProxyFromEnvironment,
DialContext: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
DualStack: true,
}).DialContext,
MaxIdleConns: 100,
MaxIdleConnsPerHost: 100,
IdleConnTimeout: 90 * time.Second,
},
}
...
// Transport is an implementation of RoundTripper that supports HTTP,
// HTTPS, and HTTP proxies (for either HTTP or HTTPS with CONNECT).
//
// By default, Transport caches connections for future re-use.
// This may leave many open connections when accessing many hosts.
// This behavior can be managed using Transport's CloseIdleConnections method
// and the MaxIdleConnsPerHost and DisableKeepAlives fields.
//
// Transports should be reused instead of created as needed.
// Transports are safe for concurrent use by multiple goroutines.
//
// A Transport is a low-level primitive for making HTTP and HTTPS requests.
// For high-level functionality, such as cookies and redirects, see Client.
//
// Transport uses HTTP/1.1 for HTTP URLs and either HTTP/1.1 or HTTP/2
// for HTTPS URLs, depending on whether the server supports HTTP/2,
// and how the Transport is configured. The DefaultTransport supports HTTP/2.
// To explicitly enable HTTP/2 on a transport, use golang.org/x/net/http2
// and call ConfigureTransport. See the package docs for more about HTTP/2.
//
// Responses with status codes in the 1xx range are either handled
// automatically (100 expect-continue) or ignored. The one
// exception is HTTP status code 101 (Switching Protocols), which is
// considered a terminal status and returned by RoundTrip. To see the
// ignored 1xx responses, use the httptrace trace package's
// ClientTrace.Got1xxResponse.
//
// Transport only retries a request upon encountering a network error
// if the request is idempotent and either has no body or has its
// Request.GetBody defined. HTTP requests are considered idempotent if
// they have HTTP methods GET, HEAD, OPTIONS, or TRACE; or if their
// Header map contains an "Idempotency-Key" or "X-Idempotency-Key"
// entry. If the idempotency key value is an zero-length slice, the
// request is treated as idempotent but the header is not sent on the
// wire.
type Transport struct {
idleMu sync.Mutex
closeIdle bool // user has requested to close all idle conns
idleConn map[connectMethodKey][]*persistConn // most recently used at end
idleConnWait map[connectMethodKey]wantConnQueue // waiting getConns
idleLRU connLRU
reqMu sync.Mutex
reqCanceler map[*Request]func(error)
altMu sync.Mutex // guards changing altProto only
altProto atomic.Value // of nil or map[string]RoundTripper, key is URI scheme
connsPerHostMu sync.Mutex
connsPerHost map[connectMethodKey]int
connsPerHostWait map[connectMethodKey]wantConnQueue // waiting getConns
// Proxy specifies a function to return a proxy for a given
// Request. If the function returns a non-nil error, the
// request is aborted with the provided error.
//
// The proxy type is determined by the URL scheme. "http",
// "https", and "socks5" are supported. If the scheme is empty,
// "http" is assumed.
//
// If Proxy is nil or returns a nil *URL, no proxy is used.
Proxy func(*Request) (*url.URL, error)
// DialContext specifies the dial function for creating unencrypted TCP connections.
// If DialContext is nil (and the deprecated Dial below is also nil),
// then the transport dials using package net.
//
// DialContext runs concurrently with calls to RoundTrip.
// A RoundTrip call that initiates a dial may end up using
// a connection dialed previously when the earlier connection
// becomes idle before the later DialContext completes.
DialContext func(ctx context.Context, network, addr string) (net.Conn, error)
// Dial specifies the dial function for creating unencrypted TCP connections.
//
// Dial runs concurrently with calls to RoundTrip.
// A RoundTrip call that initiates a dial may end up using
// a connection dialed previously when the earlier connection
// becomes idle before the later Dial completes.
//
// Deprecated: Use DialContext instead, which allows the transport
// to cancel dials as soon as they are no longer needed.
// If both are set, DialContext takes priority.
Dial func(network, addr string) (net.Conn, error)
// DialTLS specifies an optional dial function for creating
// TLS connections for non-proxied HTTPS requests.
//
// If DialTLS is nil, Dial and TLSClientConfig are used.
//
// If DialTLS is set, the Dial hook is not used for HTTPS
// requests and the TLSClientConfig and TLSHandshakeTimeout
// are ignored. The returned net.Conn is assumed to already be
// past the TLS handshake.
DialTLS func(network, addr string) (net.Conn, error)
// TLSClientConfig specifies the TLS configuration to use with
// tls.Client.
// If nil, the default configuration is used.
// If non-nil, HTTP/2 support may not be enabled by default.
TLSClientConfig *tls.Config
// TLSHandshakeTimeout specifies the maximum amount of time waiting to
// wait for a TLS handshake. Zero means no timeout.
TLSHandshakeTimeout time.Duration
// DisableKeepAlives, if true, disables HTTP keep-alives and
// will only use the connection to the server for a single
// HTTP request.
//
// This is unrelated to the similarly named TCP keep-alives.
DisableKeepAlives bool
// DisableCompression, if true, prevents the Transport from
// requesting compression with an "Accept-Encoding: gzip"
// request header when the Request contains no existing
// Accept-Encoding value. If the Transport requests gzip on
// its own and gets a gzipped response, it's transparently
// decoded in the Response.Body. However, if the user
// explicitly requested gzip it is not automatically
// uncompressed.
DisableCompression bool
// MaxIdleConns controls the maximum number of idle (keep-alive)
// connections across all hosts. Zero means no limit.
MaxIdleConns int
// MaxIdleConnsPerHost, if non-zero, controls the maximum idle
// (keep-alive) connections to keep per-host. If zero,
// DefaultMaxIdleConnsPerHost is used.
MaxIdleConnsPerHost int
// MaxConnsPerHost optionally limits the total number of
// connections per host, including connections in the dialing,
// active, and idle states. On limit violation, dials will block.
//
// Zero means no limit.
MaxConnsPerHost int
// IdleConnTimeout is the maximum amount of time an idle
// (keep-alive) connection will remain idle before closing
// itself.
// Zero means no limit.
IdleConnTimeout time.Duration
// ResponseHeaderTimeout, if non-zero, specifies the amount of
// time to wait for a server's response headers after fully
// writing the request (including its body, if any). This
// time does not include the time to read the response body.
ResponseHeaderTimeout time.Duration
// ExpectContinueTimeout, if non-zero, specifies the amount of
// time to wait for a server's first response headers after fully
// writing the request headers if the request has an
// "Expect: 100-continue" header. Zero means no timeout and
// causes the body to be sent immediately, without
// waiting for the server to approve.
// This time does not include the time to send the request header.
ExpectContinueTimeout time.Duration
// TLSNextProto specifies how the Transport switches to an
// alternate protocol (such as HTTP/2) after a TLS NPN/ALPN
// protocol negotiation. If Transport dials an TLS connection
// with a non-empty protocol name and TLSNextProto contains a
// map entry for that key (such as "h2"), then the func is
// called with the request's authority (such as "example.com"
// or "example.com:1234") and the TLS connection. The function
// must return a RoundTripper that then handles the request.
// If TLSNextProto is not nil, HTTP/2 support is not enabled
// automatically.
TLSNextProto map[string]func(authority string, c *tls.Conn) RoundTripper
// ProxyConnectHeader optionally specifies headers to send to
// proxies during CONNECT requests.
ProxyConnectHeader Header
// MaxResponseHeaderBytes specifies a limit on how many
// response bytes are allowed in the server's response
// header.
//
// Zero means to use a default limit.
MaxResponseHeaderBytes int64
// WriteBufferSize specifies the size of the write buffer used
// when writing to the transport.
// If zero, a default (currently 4KB) is used.
WriteBufferSize int
// ReadBufferSize specifies the size of the read buffer used
// when reading from the transport.
// If zero, a default (currently 4KB) is used.
ReadBufferSize int
// nextProtoOnce guards initialization of TLSNextProto and
// h2transport (via onceSetNextProtoDefaults)
nextProtoOnce sync.Once
h2transport h2Transport // non-nil if http2 wired up
tlsNextProtoWasNil bool // whether TLSNextProto was nil when the Once fired
// ForceAttemptHTTP2 controls whether HTTP/2 is enabled when a non-zero
// Dial, DialTLS, or DialContext func or TLSClientConfig is provided.
// By default, use of any those fields conservatively disables HTTP/2.
// To use a custom dialer or TLS config and still attempt HTTP/2
// upgrades, set this to true.
ForceAttemptHTTP2 bool
}
http.Transport实现了http.RoundTripper，支持HTTP，HTTPS以及HTTP Proxy(for either HTTP or HTTPS with CONNECT)
http.Transport默认实现了TCP连接池，会复用底层TCP连接。所以推荐的做法是初始化一次http.Transport，然后重复使用
http Transport对HTTP URLs使用HTTP/1.1协议；对HTTPS URLs使用HTTP/1.1 or HTTP/2，具体使用哪种协议要取决于Transport的配置以及服务端是否支持HTTP/2协议
Transport默认支持HTTP/2；如果要强制开启HTTP/2，使用ConfigureTransport，详细参考golang.org/x/net/http2
Transport只有在遇到网络故障的情况下会重试幂等的请求。另外，http Transport实现了goroutine-safe
接下来我们分析一下Transport各字段：
- closeIdle：关闭所有空闲的连接
- idleConn：空闲连接池
- Proxy：对特定的请求返回代理
- DialContext：指定底层TCP连接的创建函数
- Dial(Deprecated)：和DialContext一样的功能，区别在于DialContext多了一个context.Context参数，用于取消dials功能
- DialTLS：为non-proxied HTTPS requests创建TLS connections
- TLSHandshakeTimeout：TLS handshake超时时间
- DisableKeepAlives：禁止HTTP keep-alives，一个连接只用于一次请求(注意区分TCP keep-alives。HTTP keep-alives用于连接复用；TCP keep-alives用于连接保活)
- MaxIdleConns：控制所有hosts的空闲连接最大数目(Zero means no limit.)
- MaxIdleConnsPerHost：控制某个host的空闲连接(keep-alives)最大数目(设置为0，则默认DefaultMaxIdleConnsPerHost=2)
- MaxConnsPerHost：控制某个host的所有连接，包括创建中，正在使用的，以及空闲的连接(including connections in the dialing, active, and idle states)。一旦超过限制，dial会阻塞(Zero means no limit)
- IdleConnTimeout：空闲连接(keep-alives)超时时间
- h2transport：HTTP/2协议对应的transport
- ForceAttemptHTTP2：当Dial, DialTLS, or DialContext func or TLSClientConfig提供时，默认情况下会禁止HTTP/2协议。当使用自定义的这些配置时，需要设置ForceAttemptHTTP2字段开启HTTP2
我们看一下DefaultTransport配置：
// DefaultTransport is the default implementation of Transport and is
// used by DefaultClient. It establishes network connections as needed
// and caches them for reuse by subsequent calls. It uses HTTP proxies
// as directed by the $HTTP_PROXY and $NO_PROXY (or $http_proxy and
// $no_proxy) environment variables.
var DefaultTransport RoundTripper = &Transport{
Proxy: ProxyFromEnvironment,
DialContext: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
DualStack: true,
}).DialContext,
ForceAttemptHTTP2: true,
MaxIdleConns: 100,
IdleConnTimeout: 90 * time.Second,
TLSHandshakeTimeout: 10 * time.Second,
ExpectContinueTimeout: 1 * time.Second,
}
重点看DialContext实例，展开net.Dialer结构体(net/dial.go)：
// A Dialer contains options for connecting to an address.
//
// The zero value for each field is equivalent to dialing
// without that option. Dialing with the zero value of Dialer
// is therefore equivalent to just calling the Dial function.
type Dialer struct {
// Timeout is the maximum amount of time a dial will wait for
// a connect to complete. If Deadline is also set, it may fail
// earlier.
//
// The default is no timeout.
//
// When using TCP and dialing a host name with multiple IP
// addresses, the timeout may be divided between them.
//
// With or without a timeout, the operating system may impose
// its own earlier timeout. For instance, TCP timeouts are
// often around 3 minutes.
Timeout time.Duration
// Deadline is the absolute point in time after which dials
// will fail. If Timeout is set, it may fail earlier.
// Zero means no deadline, or dependent on the operating system
// as with the Timeout option.
Deadline time.Time
// LocalAddr is the local address to use when dialing an
// address. The address must be of a compatible type for the
// network being dialed.
// If nil, a local address is automatically chosen.
LocalAddr Addr
// DualStack previously enabled RFC 6555 Fast Fallback
// support, also known as "Happy Eyeballs", in which IPv4 is
// tried soon if IPv6 appears to be misconfigured and
// hanging.
//
// Deprecated: Fast Fallback is enabled by default. To
// disable, set FallbackDelay to a negative value.
DualStack bool
// FallbackDelay specifies the length of time to wait before
// spawning a RFC 6555 Fast Fallback connection. That is, this
// is the amount of time to wait for IPv6 to succeed before
// assuming that IPv6 is misconfigured and falling back to
// IPv4.
//
// If zero, a default delay of 300ms is used.
// A negative value disables Fast Fallback support.
FallbackDelay time.Duration
// KeepAlive specifies the interval between keep-alive
// probes for an active network connection.
// If zero, keep-alive probes are sent with a default value
// (currently 15 seconds), if supported by the protocol and operating
// system. Network protocols or operating systems that do
// not support keep-alives ignore this field.
// If negative, keep-alive probes are disabled.
KeepAlive time.Duration
// Resolver optionally specifies an alternate resolver to use.
Resolver *Resolver
// Cancel is an optional channel whose closure indicates that
// the dial should be canceled. Not all types of dials support
// cancellation.
//
// Deprecated: Use DialContext instead.
Cancel <-chan struct{}
// If Control is not nil, it is called after creating the network
// connection but before actually dialing.
//
// Network and address parameters passed to Control method are not
// necessarily the ones passed to Dial. For example, passing "tcp" to Dial
// will cause the Control function to be called with "tcp4" or "tcp6".
Control func(network, address string, c syscall.RawConn) error
}
net.Dialer包含了创建TCP连接的各种选项：
- Timeout：TCP连接建立的超时时间(也即三次握手的超时时间)，操作系统的超时时间一般为3 minutes
- Deadline：与Timeout作用类似，只不过限制了确定的超时时刻
- LocalAddr：本地地址，TCP四元组的原始IP地址
- DualStack(Deprecated)：enabled RFC 6555 Fast Fallback Feature
- FallbackDelay：IPv6连接建立的等待时间，如果超时，则会切换到IPv4(A negative value disables Fast Fallback support.)
- KeepAlive：设置了活跃连接的TCP keep-alive探针间隔，需要协议层以及操作系统支持(If zero, keep-alive probes are sent with a default value(currently 15 seconds))
- Control：it is called after creating the network connection but before actually dialing ？
接下来我们分析net.Dialer.DialContext，如下：
// Dial connects to the address on the named network.
//
// Known networks are "tcp", "tcp4" (IPv4-only), "tcp6" (IPv6-only),
// "udp", "udp4" (IPv4-only), "udp6" (IPv6-only), "ip", "ip4"
// (IPv4-only), "ip6" (IPv6-only), "unix", "unixgram" and
// "unixpacket".
//
// For TCP and UDP networks, the address has the form "host:port".
// The host must be a literal IP address, or a host name that can be
// resolved to IP addresses.
// The port must be a literal port number or a service name.
// If the host is a literal IPv6 address it must be enclosed in square
// brackets, as in "[2001:db8::1]:80" or "[fe80::1%zone]:80".
// The zone specifies the scope of the literal IPv6 address as defined
// in RFC 4007.
// The functions JoinHostPort and SplitHostPort manipulate a pair of
// host and port in this form.
// When using TCP, and the host resolves to multiple IP addresses,
// Dial will try each IP address in order until one succeeds.
//
// Examples:
// Dial("tcp", "golang.org:http")
// Dial("tcp", "192.0.2.1:http")
// Dial("tcp", "198.51.100.1:80")
// Dial("udp", "[2001:db8::1]:domain")
// Dial("udp", "[fe80::1%lo0]:53")
// Dial("tcp", ":80")
//
// For IP networks, the network must be "ip", "ip4" or "ip6" followed
// by a colon and a literal protocol number or a protocol name, and
// the address has the form "host". The host must be a literal IP
// address or a literal IPv6 address with zone.
// It depends on each operating system how the operating system
// behaves with a non-well known protocol number such as "0" or "255".
//
// Examples:
// Dial("ip4:1", "192.0.2.1")
// Dial("ip6:ipv6-icmp", "2001:db8::1")
// Dial("ip6:58", "fe80::1%lo0")
//
// For TCP, UDP and IP networks, if the host is empty or a literal
// unspecified IP address, as in ":80", "0.0.0.0:80" or "[::]:80" for
// TCP and UDP, "", "0.0.0.0" or "::" for IP, the local system is
// assumed.
//
// For Unix networks, the address must be a file system path.
func Dial(network, address string) (Conn, error) {
var d Dialer
return d.Dial(network, address)
}
...
// DialContext connects to the address on the named network using
// the provided context.
//
// The provided Context must be non-nil. If the context expires before
// the connection is complete, an error is returned. Once successfully
// connected, any expiration of the context will not affect the
// connection.
//
// When using TCP, and the host in the address parameter resolves to multiple
// network addresses, any dial timeout (from d.Timeout or ctx) is spread
// over each consecutive dial, such that each is given an appropriate
// fraction of the time to connect.
// For example, if a host has 4 IP addresses and the timeout is 1 minute,
// the connect to each single address will be given 15 seconds to complete
// before trying the next one.
//
// See func Dial for a description of the network and address
// parameters.
func (d *Dialer) DialContext(ctx context.Context, network, address string) (Conn, error) {
if ctx == nil {
panic("nil context")
}
deadline := d.deadline(ctx, time.Now())
if !deadline.IsZero() {
if d, ok := ctx.Deadline(); !ok || deadline.Before(d) {
subCtx, cancel := context.WithDeadline(ctx, deadline)
defer cancel()
ctx = subCtx
}
}
if oldCancel := d.Cancel; oldCancel != nil {
subCtx, cancel := context.WithCancel(ctx)
defer cancel()
go func() {
select {
case <-oldCancel:
cancel()
case <-subCtx.Done():
}
}()
ctx = subCtx
}
// Shadow the nettrace (if any) during resolve so Connect events don't fire for DNS lookups.
resolveCtx := ctx
if trace, _ := ctx.Value(nettrace.TraceKey{}).(*nettrace.Trace); trace != nil {
shadow := *trace
shadow.ConnectStart = nil
shadow.ConnectDone = nil
resolveCtx = context.WithValue(resolveCtx, nettrace.TraceKey{}, &shadow)
}
addrs, err := d.resolver().resolveAddrList(resolveCtx, "dial", network, address, d.LocalAddr)
if err != nil {
return nil, &OpError{Op: "dial", Net: network, Source: nil, Addr: nil, Err: err}
}
sd := &sysDialer{
Dialer: *d,
network: network,
address: address,
}
var primaries, fallbacks addrList
if d.dualStack() && network == "tcp" {
primaries, fallbacks = addrs.partition(isIPv4)
} else {
primaries = addrs
}
var c Conn
if len(fallbacks) > 0 {
c, err = sd.dialParallel(ctx, primaries, fallbacks)
} else {
c, err = sd.dialSerial(ctx, primaries)
}
if err != nil {
return nil, err
}
if tc, ok := c.(*TCPConn); ok && d.KeepAlive >= 0 {
setKeepAlive(tc.fd, true)
ka := d.KeepAlive
if d.KeepAlive == 0 {
ka = defaultTCPKeepAlive
}
setKeepAlivePeriod(tc.fd, ka)
testHookSetKeepAlive(ka)
}
return c, nil
}
DialContext用于创建指定网络协议(例如tcp，udp)以及指定地址的连接，例如：
// Examples:
// Dial("tcp", "golang.org:http")
// Dial("tcp", "192.0.2.1:http")
// Dial("tcp", "198.51.100.1:80")
// Dial("udp", "[2001:db8::1]:domain")
// Dial("udp", "[fe80::1%lo0]:53")
// Dial("tcp", ":80")
分为三个阶段，如下：
- 1、resolveAddrList
// resolveAddrList resolves addr using hint and returns a list of
// addresses. The result contains at least one address when error is
// nil.
func (r *Resolver) resolveAddrList(ctx context.Context, op, network, addr string, hint Addr) (addrList, error) {
afnet, _, err := parseNetwork(ctx, network, true)
if err != nil {
return nil, err
}
if op == "dial" && addr == "" {
return nil, errMissingAddress
}
switch afnet {
case "unix", "unixgram", "unixpacket":
addr, err := ResolveUnixAddr(afnet, addr)
if err != nil {
return nil, err
}
if op == "dial" && hint != nil && addr.Network() != hint.Network() {
return nil, &AddrError{Err: "mismatched local address type", Addr: hint.String()}
}
return addrList{addr}, nil
}
addrs, err := r.internetAddrList(ctx, afnet, addr)
if err != nil || op != "dial" || hint == nil {
return addrs, err
}
var (
tcp *TCPAddr
udp *UDPAddr
ip *IPAddr
wildcard bool
)
switch hint := hint.(type) {
case *TCPAddr:
tcp = hint
wildcard = tcp.isWildcard()
case *UDPAddr:
udp = hint
wildcard = udp.isWildcard()
case *IPAddr:
ip = hint
wildcard = ip.isWildcard()
}
naddrs := addrs[:0]
for _, addr := range addrs {
if addr.Network() != hint.Network() {
return nil, &AddrError{Err: "mismatched local address type", Addr: hint.String()}
}
switch addr := addr.(type) {
case *TCPAddr:
if !wildcard && !addr.isWildcard() && !addr.IP.matchAddrFamily(tcp.IP) {
continue
}
naddrs = append(naddrs, addr)
case *UDPAddr:
if !wildcard && !addr.isWildcard() && !addr.IP.matchAddrFamily(udp.IP) {
continue
}
naddrs = append(naddrs, addr)
case *IPAddr:
if !wildcard && !addr.isWildcard() && !addr.IP.matchAddrFamily(ip.IP) {
continue
}
naddrs = append(naddrs, addr)
}
}
if len(naddrs) == 0 {
return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: hint.String()}
}
return naddrs, nil
}
// An addrList represents a list of network endpoint addresses.
type addrList []Addr
// Addr represents a network end point address.
//
// The two methods Network and String conventionally return strings
// that can be passed as the arguments to Dial, but the exact form
// and meaning of the strings is up to the implementation.
type Addr interface {
Network() string // name of the network (for example, "tcp", "udp")
String() string // string form of address (for example, "192.0.2.1:25", "[2001:db8::1]:80")
}
根据本地地址网路类型以及地址族分拆目标地址，返回地址列表
- 2、dialSerial
// isIPv4 reports whether addr contains an IPv4 address.
func isIPv4(addr Addr) bool {
switch addr := addr.(type) {
case *TCPAddr:
return addr.IP.To4() != nil
case *UDPAddr:
return addr.IP.To4() != nil
case *IPAddr:
return addr.IP.To4() != nil
}
return false
}
// partition divides an address list into two categories, using a
// strategy function to assign a boolean label to each address.
// The first address, and any with a matching label, are returned as
// primaries, while addresses with the opposite label are returned
// as fallbacks. For non-empty inputs, primaries is guaranteed to be
// non-empty.
func (addrs addrList) partition(strategy func(Addr) bool) (primaries, fallbacks addrList) {
var primaryLabel bool
for i, addr := range addrs {
label := strategy(addr)
if i == 0 || label == primaryLabel {
primaryLabel = label
primaries = append(primaries, addr)
} else {
fallbacks = append(fallbacks, addr)
}
}
return
}
...
sd := &sysDialer{
Dialer: *d,
network: network,
address: address,
}
...
// dialSerial connects to a list of addresses in sequence, returning
// either the first successful connection, or the first error.
func (sd *sysDialer) dialSerial(ctx context.Context, ras addrList) (Conn, error) {
var firstErr error // The error from the first address is most relevant.
for i, ra := range ras {
select {
case <-ctx.Done():
return nil, &OpError{Op: "dial", Net: sd.network, Source: sd.LocalAddr, Addr: ra, Err: mapErr(ctx.Err())}
default:
}
deadline, _ := ctx.Deadline()
partialDeadline, err := partialDeadline(time.Now(), deadline, len(ras)-i)
if err != nil {
// Ran out of time.
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: sd.network, Source: sd.LocalAddr, Addr: ra, Err: err}
}
break
}
dialCtx := ctx
if partialDeadline.Before(deadline) {
var cancel context.CancelFunc
dialCtx, cancel = context.WithDeadline(ctx, partialDeadline)
defer cancel()
}
c, err := sd.dialSingle(dialCtx, ra)
if err == nil {
return c, nil
}
if firstErr == nil {
firstErr = err
}
}
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: sd.network, Source: nil, Addr: nil, Err: errMissingAddress}
}
return nil, firstErr
}
// dialSingle attempts to establish and returns a single connection to
// the destination address.
func (sd *sysDialer) dialSingle(ctx context.Context, ra Addr) (c Conn, err error) {
trace, _ := ctx.Value(nettrace.TraceKey{}).(*nettrace.Trace)
if trace != nil {
raStr := ra.String()
if trace.ConnectStart != nil {
trace.ConnectStart(sd.network, raStr)
}
if trace.ConnectDone != nil {
defer func() { trace.ConnectDone(sd.network, raStr, err) }()
}
}
la := sd.LocalAddr
switch ra := ra.(type) {
case *TCPAddr:
la, _ := la.(*TCPAddr)
c, err = sd.dialTCP(ctx, la, ra)
case *UDPAddr:
la, _ := la.(*UDPAddr)
c, err = sd.dialUDP(ctx, la, ra)
case *IPAddr:
la, _ := la.(*IPAddr)
c, err = sd.dialIP(ctx, la, ra)
case *UnixAddr:
la, _ := la.(*UnixAddr)
c, err = sd.dialUnix(ctx, la, ra)
default:
return nil, &OpError{Op: "dial", Net: sd.network, Source: la, Addr: ra, Err: &AddrError{Err: "unexpected address type", Addr: sd.address}}
}
if err != nil {
return nil, &OpError{Op: "dial", Net: sd.network, Source: la, Addr: ra, Err: err} // c is non-nil interface containing nil pointer
}
return c, nil
}
func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
if testHookDialTCP != nil {
return testHookDialTCP(ctx, sd.network, laddr, raddr)
}
return sd.doDialTCP(ctx, laddr, raddr)
}
// net/tcpsock_posix.go
func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
fd, err := internetSocket(ctx, sd.network, laddr, raddr, syscall.SOCK_STREAM, 0, "dial", sd.Dialer.Control)
// TCP has a rarely used mechanism called a 'simultaneous connection' in
// which Dial("tcp", addr1, addr2) run on the machine at addr1 can
// connect to a simultaneous Dial("tcp", addr2, addr1) run on the machine
// at addr2, without either machine executing Listen. If laddr == nil,
// it means we want the kernel to pick an appropriate originating local
// address. Some Linux kernels cycle blindly through a fixed range of
// local ports, regardless of destination port. If a kernel happens to
// pick local port 50001 as the source for a Dial("tcp", "", "localhost:50001"),
// then the Dial will succeed, having simultaneously connected to itself.
// This can only happen when we are letting the kernel pick a port (laddr == nil)
// and when there is no listener for the destination address.
// It's hard to argue this is anything other than a kernel bug. If we
// see this happen, rather than expose the buggy effect to users, we
// close the fd and try again. If it happens twice more, we relent and
// use the result. See also:
// https://golang.org/issue/2690
// linux - How can you have a TCP connection back to the same port? - Stack Overflow
//
// The opposite can also happen: if we ask the kernel to pick an appropriate
// originating local address, sometimes it picks one that is already in use.
// So if the error is EADDRNOTAVAIL, we have to try again too, just for
// a different reason.
//
// The kernel socket code is no doubt enjoying watching us squirm.
for i := 0; i < 2 && (laddr == nil || laddr.Port == 0) && (selfConnect(fd, err) || spuriousENOTAVAIL(err)); i++ {
if err == nil {
fd.Close()
}
fd, err = internetSocket(ctx, sd.network, laddr, raddr, syscall.SOCK_STREAM, 0, "dial", sd.Dialer.Control)
}
if err != nil {
return nil, err
}
return newTCPConn(fd), nil
}
func internetSocket(ctx context.Context, net string, laddr, raddr sockaddr, sotype, proto int, mode string, ctrlFn func(string, string, syscall.RawConn) error) (fd *netFD, err error) {
if (runtime.GOOS == "aix" || runtime.GOOS == "windows" || runtime.GOOS == "openbsd" || runtime.GOOS == "nacl") && mode == "dial" && raddr.isWildcard() {
raddr = raddr.toLocal(net)
}
family, ipv6only := favoriteAddrFamily(net, laddr, raddr, mode)
return socket(ctx, net, family, sotype, proto, ipv6only, laddr, raddr, ctrlFn)
}
// socket returns a network file descriptor that is ready for
// asynchronous I/O using the network poller.
func socket(ctx context.Context, net string, family, sotype, proto int, ipv6only bool, laddr, raddr sockaddr, ctrlFn func(string, string, syscall.RawConn) error) (fd *netFD, err error) {
s, err := sysSocket(family, sotype, proto)
if err != nil {
return nil, err
}
if err = setDefaultSockopts(s, family, sotype, ipv6only); err != nil {
poll.CloseFunc(s)
return nil, err
}
if fd, err = newFD(s, family, sotype, net); err != nil {
poll.CloseFunc(s)
return nil, err
}
// This function makes a network file descriptor for the
// following applications:
//
// - An endpoint holder that opens a passive stream
// connection, known as a stream listener
//
// - An endpoint holder that opens a destination-unspecific
// datagram connection, known as a datagram listener
//
// - An endpoint holder that opens an active stream or a
// destination-specific datagram connection, known as a
// dialer
//
// - An endpoint holder that opens the other connection, such
// as talking to the protocol stack inside the kernel
//
// For stream and datagram listeners, they will only require
// named sockets, so we can assume that it's just a request
// from stream or datagram listeners when laddr is not nil but
// raddr is nil. Otherwise we assume it's just for dialers or
// the other connection holders.
if laddr != nil && raddr == nil {
switch sotype {
case syscall.SOCK_STREAM, syscall.SOCK_SEQPACKET:
if err := fd.listenStream(laddr, listenerBacklog(), ctrlFn); err != nil {
fd.Close()
return nil, err
}
return fd, nil
case syscall.SOCK_DGRAM:
if err := fd.listenDatagram(laddr, ctrlFn); err != nil {
fd.Close()
return nil, err
}
return fd, nil
}
}
if err := fd.dial(ctx, laddr, raddr, ctrlFn); err != nil {
fd.Close()
return nil, err
}
return fd, nil
}
func newFD(sysfd, family, sotype int, net string) (*netFD, error) {
ret := &netFD{
pfd: poll.FD{
Sysfd: sysfd,
IsStream: sotype == syscall.SOCK_STREAM,
ZeroReadIsEOF: sotype != syscall.SOCK_DGRAM && sotype != syscall.SOCK_RAW,
},
family: family,
sotype: sotype,
net: net,
}
return ret, nil
}
// Network file descriptor.
type netFD struct {
pfd poll.FD
// immutable until Close
family int
sotype int
isConnected bool // handshake completed or use of association with peer
net string
laddr Addr
raddr Addr
}
func newTCPConn(fd *netFD) *TCPConn {
c := &TCPConn{conn{fd}}
setNoDelay(c.fd, true)
return c
}
// TCPConn is an implementation of the Conn interface for TCP network
// connections.
type TCPConn struct {
conn
}
type conn struct {
fd *netFD
}
对resolveAddrList返回的地址依次尝试创建连接，返回第一个创建成功的连接，否则返回第一个错误
- 3、setKeepAlive
创建完连接后，检查该连接是否为TCP连接，如果是TCP连接，则设置KeepAlive时间，如下(net/sockopt_posix.go)：
...
if tc, ok := c.(*TCPConn); ok && d.KeepAlive >= 0 {
setKeepAlive(tc.fd, true)
ka := d.KeepAlive
if d.KeepAlive == 0 {
ka = defaultTCPKeepAlive
}
setKeepAlivePeriod(tc.fd, ka)
testHookSetKeepAlive(ka)
}
...
func setKeepAlive(fd *netFD, keepalive bool) error {
err := fd.pfd.SetsockoptInt(syscall.SOL_SOCKET, syscall.SO_KEEPALIVE, boolint(keepalive))
runtime.KeepAlive(fd)
return wrapSyscallError("setsockopt", err)
}
...
// net/tcpsockopt_darwin.go
func setKeepAlivePeriod(fd *netFD, d time.Duration) error {
// The kernel expects seconds so round to next highest second.
d += (time.Second - time.Nanosecond)
secs := int(d.Seconds())
if err := fd.pfd.SetsockoptInt(syscall.IPPROTO_TCP, sysTCP_KEEPINTVL, secs); err != nil {
return wrapSyscallError("setsockopt", err)
}
err := fd.pfd.SetsockoptInt(syscall.IPPROTO_TCP, syscall.TCP_KEEPALIVE, secs)
runtime.KeepAlive(fd)
return wrapSyscallError("setsockopt", err)
}
// defaultTCPKeepAlive is a default constant value for TCPKeepAlive times
// See golang.org/issue/31510
const (
defaultTCPKeepAlive = 15 * time.Second
)
Transport.IdleConnTimeout与net.Dialer.KeepAlive有什么关系，哪一个是所谓的HTTP keep-alives？？？
回到最开始的http.Client的使用：
// construct encoded endpoint
Url, err := url.Parse(fmt.Sprintf("http://%s:%d", addr, port))
if err != nil {
return err
}
Url.Path += "/index"
endpoint := Url.String()
req, err := http.NewRequest("GET", endpoint, nil)
if err != nil {
return err
}
// use httpClient to send request
rsp, err := client.Do(req)
if err != nil {
return err
}
// close the connection to reuse it
defer rsp.Body.Close()
// check status code
if rsp.StatusCode != http.StatusOK {
return fmt.Errorf("get rsp error: %v", rsp)
}
我们分析http.Client是如何使用http.Transport的：
一、创建http.Request
根据method，url，body创建http.Request：
// NewRequest wraps NewRequestWithContext using the background context.
func NewRequest(method, url string, body io.Reader) (*Request, error) {
return NewRequestWithContext(context.Background(), method, url, body)
}
// NewRequestWithContext returns a new Request given a method, URL, and
// optional body.
//
// If the provided body is also an io.Closer, the returned
// Request.Body is set to body and will be closed by the Client
// methods Do, Post, and PostForm, and Transport.RoundTrip.
//
// NewRequestWithContext returns a Request suitable for use with
// Client.Do or Transport.RoundTrip. To create a request for use with
// testing a Server Handler, either use the NewRequest function in the
// net/http/httptest package, use ReadRequest, or manually update the
// Request fields. For an outgoing client request, the context
// controls the entire lifetime of a request and its response:
// obtaining a connection, sending the request, and reading the
// response headers and body. See the Request type's documentation for
// the difference between inbound and outbound request fields.
//
// If body is of type *bytes.Buffer, *bytes.Reader, or
// *strings.Reader, the returned request's ContentLength is set to its
// exact value (instead of -1), GetBody is populated (so 307 and 308
// redirects can replay the body), and Body is set to NoBody if the
// ContentLength is 0.
func NewRequestWithContext(ctx context.Context, method, url string, body io.Reader) (*Request, error) {
if method == "" {
// We document that "" means "GET" for Request.Method, and people have
// relied on that from NewRequest, so keep that working.
// We still enforce validMethod for non-empty methods.
method = "GET"
}
if !validMethod(method) {
return nil, fmt.Errorf("net/http: invalid method %q", method)
}
if ctx == nil {
return nil, errors.New("net/http: nil Context")
}
u, err := parseURL(url) // Just url.Parse (url is shadowed for godoc).
if err != nil {
return nil, err
}
rc, ok := body.(io.ReadCloser)
if !ok && body != nil {
rc = ioutil.NopCloser(body)
}
// The host's colon:port should be normalized. See Issue 14836.
u.Host = removeEmptyPort(u.Host)
req := &Request{
ctx: ctx,
Method: method,
URL: u,
Proto: "HTTP/1.1",
ProtoMajor: 1,
ProtoMinor: 1,
Header: make(Header),
Body: rc,
Host: u.Host,
}
if body != nil {
switch v := body.(type) {
case *bytes.Buffer:
req.ContentLength = int64(v.Len())
buf := v.Bytes()
req.GetBody = func() (io.ReadCloser, error) {
r := bytes.NewReader(buf)
return ioutil.NopCloser(r), nil
}
case *bytes.Reader:
req.ContentLength = int64(v.Len())
snapshot := *v
req.GetBody = func() (io.ReadCloser, error) {
r := snapshot
return ioutil.NopCloser(&r), nil
}
case *strings.Reader:
req.ContentLength = int64(v.Len())
snapshot := *v
req.GetBody = func() (io.ReadCloser, error) {
r := snapshot
return ioutil.NopCloser(&r), nil
}
default:
// This is where we'd set it to -1 (at least
// if body != NoBody) to mean unknown, but
// that broke people during the Go 1.8 testing
// period. People depend on it being 0 I
// guess. Maybe retry later. See Issue 18117.
}
// For client requests, Request.ContentLength of 0
// means either actually 0, or unknown. The only way
// to explicitly say that the ContentLength is zero is
// to set the Body to nil. But turns out too much code
// depends on NewRequest returning a non-nil Body,
// so we use a well-known ReadCloser variable instead
// and have the http package also treat that sentinel
// variable to mean explicitly zero.
if req.GetBody != nil && req.ContentLength == 0 {
req.Body = NoBody
req.GetBody = func() (io.ReadCloser, error) { return NoBody, nil }
}
}
return req, nil
}
// A Request represents an HTTP request received by a server
// or to be sent by a client.
//
// The field semantics differ slightly between client and server
// usage. In addition to the notes on the fields below, see the
// documentation for Request.Write and RoundTripper.
type Request struct {
// Method specifies the HTTP method (GET, POST, PUT, etc.).
// For client requests, an empty string means GET.
//
// Go's HTTP client does not support sending a request with
// the CONNECT method. See the documentation on Transport for
// details.
Method string
// URL specifies either the URI being requested (for server
// requests) or the URL to access (for client requests).
//
// For server requests, the URL is parsed from the URI
// supplied on the Request-Line as stored in RequestURI. For
// most requests, fields other than Path and RawQuery will be
// empty. (See RFC 7230, Section 5.3)
//
// For client requests, the URL's Host specifies the server to
// connect to, while the Request's Host field optionally
// specifies the Host header value to send in the HTTP
// request.
URL *url.URL
// The protocol version for incoming server requests.
//
// For client requests, these fields are ignored. The HTTP
// client code always uses either HTTP/1.1 or HTTP/2.
// See the docs on Transport for details.
Proto string // "HTTP/1.0"
ProtoMajor int // 1
ProtoMinor int // 0
// Header contains the request header fields either received
// by the server or to be sent by the client.
//
// If a server received a request with header lines,
//
// Host: example.com
// accept-encoding: gzip, deflate
// Accept-Language: en-us
// fOO: Bar
// foo: two
//
// then
//
// Header = map[string][]string{
// "Accept-Encoding": {"gzip, deflate"},
// "Accept-Language": {"en-us"},
// "Foo": {"Bar", "two"},
// }
//
// For incoming requests, the Host header is promoted to the
// Request.Host field and removed from the Header map.
//
// HTTP defines that header names are case-insensitive. The
// request parser implements this by using CanonicalHeaderKey,
// making the first character and any characters following a
// hyphen uppercase and the rest lowercase.
//
// For client requests, certain headers such as Content-Length
// and Connection are automatically written when needed and
// values in Header may be ignored. See the documentation
// for the Request.Write method.
Header Header
// Body is the request's body.
//
// For client requests, a nil body means the request has no
// body, such as a GET request. The HTTP Client's Transport
// is responsible for calling the Close method.
//
// For server requests, the Request Body is always non-nil
// but will return EOF immediately when no body is present.
// The Server will close the request body. The ServeHTTP
// Handler does not need to.
Body io.ReadCloser
// GetBody defines an optional func to return a new copy of
// Body. It is used for client requests when a redirect requires
// reading the body more than once. Use of GetBody still
// requires setting Body.
//
// For server requests, it is unused.
GetBody func() (io.ReadCloser, error)
// ContentLength records the length of the associated content.
// The value -1 indicates that the length is unknown.
// Values >= 0 indicate that the given number of bytes may
// be read from Body.
//
// For client requests, a value of 0 with a non-nil Body is
// also treated as unknown.
ContentLength int64
// TransferEncoding lists the transfer encodings from outermost to
// innermost. An empty list denotes the "identity" encoding.
// TransferEncoding can usually be ignored; chunked encoding is
// automatically added and removed as necessary when sending and
// receiving requests.
TransferEncoding []string
// Close indicates whether to close the connection after
// replying to this request (for servers) or after sending this
// request and reading its response (for clients).
//
// For server requests, the HTTP server handles this automatically
// and this field is not needed by Handlers.
//
// For client requests, setting this field prevents re-use of
// TCP connections between requests to the same hosts, as if
// Transport.DisableKeepAlives were set.
Close bool
// For server requests, Host specifies the host on which the URL
// is sought. Per RFC 7230, section 5.4, this is either the value
// of the "Host" header or the host name given in the URL itself.
// It may be of the form "host:port". For international domain
// names, Host may be in Punycode or Unicode form. Use
// golang.org/x/net/idna to convert it to either format if
// needed.
// To prevent DNS rebinding attacks, server Handlers should
// validate that the Host header has a value for which the
// Handler considers itself authoritative. The included
// ServeMux supports patterns registered to particular host
// names and thus protects its registered Handlers.
//
// For client requests, Host optionally overrides the Host
// header to send. If empty, the Request.Write method uses
// the value of URL.Host. Host may contain an international
// domain name.
Host string
// Form contains the parsed form data, including both the URL
// field's query parameters and the PATCH, POST, or PUT form data.
// This field is only available after ParseForm is called.
// The HTTP client ignores Form and uses Body instead.
Form url.Values
// PostForm contains the parsed form data from PATCH, POST
// or PUT body parameters.
//
// This field is only available after ParseForm is called.
// The HTTP client ignores PostForm and uses Body instead.
PostForm url.Values
// MultipartForm is the parsed multipart form, including file uploads.
// This field is only available after ParseMultipartForm is called.
// The HTTP client ignores MultipartForm and uses Body instead.
MultipartForm *multipart.Form
// Trailer specifies additional headers that are sent after the request
// body.
//
// For server requests, the Trailer map initially contains only the
// trailer keys, with nil values. (The client declares which trailers it
// will later send.) While the handler is reading from Body, it must
// not reference Trailer. After reading from Body returns EOF, Trailer
// can be read again and will contain non-nil values, if they were sent
// by the client.
//
// For client requests, Trailer must be initialized to a map containing
// the trailer keys to later send. The values may be nil or their final
// values. The ContentLength must be 0 or -1, to send a chunked request.
// After the HTTP request is sent the map values can be updated while
// the request body is read. Once the body returns EOF, the caller must
// not mutate Trailer.
//
// Few HTTP clients, servers, or proxies support HTTP trailers.
Trailer Header
// RemoteAddr allows HTTP servers and other software to record
// the network address that sent the request, usually for
// logging. This field is not filled in by ReadRequest and
// has no defined format. The HTTP server in this package
// sets RemoteAddr to an "IP:port" address before invoking a
// handler.
// This field is ignored by the HTTP client.
RemoteAddr string
// RequestURI is the unmodified request-target of the
// Request-Line (RFC 7230, Section 3.1.1) as sent by the client
// to a server. Usually the URL field should be used instead.
// It is an error to set this field in an HTTP client request.
RequestURI string
// TLS allows HTTP servers and other software to record
// information about the TLS connection on which the request
// was received. This field is not filled in by ReadRequest.
// The HTTP server in this package sets the field for
// TLS-enabled connections before invoking a handler;
// otherwise it leaves the field nil.
// This field is ignored by the HTTP client.
TLS *tls.ConnectionState
// Cancel is an optional channel whose closure indicates that the client
// request should be regarded as canceled. Not all implementations of
// RoundTripper may support Cancel.
//
// For server requests, this field is not applicable.
//
// Deprecated: Set the Request's context with NewRequestWithContext
// instead. If a Request's Cancel field and context are both
// set, it is undefined whether Cancel is respected.
Cancel <-chan struct{}
// Response is the redirect response which caused this request
// to be created. This field is only populated during client
// redirects.
Response *Response
// ctx is either the client or server context. It should only
// be modified via copying the whole Request using WithContext.
// It is unexported to prevent people from using Context wrong
// and mutating the contexts held by callers of the same request.
ctx context.Context
}
二、client.Do(req)
使用http.Client发送请求，如下：
// Do sends an HTTP request and returns an HTTP response, following
// policy (such as redirects, cookies, auth) as configured on the
// client.
//
// An error is returned if caused by client policy (such as
// CheckRedirect), or failure to speak HTTP (such as a network
// connectivity problem). A non-2xx status code doesn't cause an
// error.
//
// If the returned error is nil, the Response will contain a non-nil
// Body which the user is expected to close. If the Body is not both
// read to EOF and closed, the Client's underlying RoundTripper
// (typically Transport) may not be able to re-use a persistent TCP
// connection to the server for a subsequent "keep-alive" request.
//
// The request Body, if non-nil, will be closed by the underlying
// Transport, even on errors.
//
// On error, any Response can be ignored. A non-nil Response with a
// non-nil error only occurs when CheckRedirect fails, and even then
// the returned Response.Body is already closed.
//
// Generally Get, Post, or PostForm will be used instead of Do.
//
// If the server replies with a redirect, the Client first uses the
// CheckRedirect function to determine whether the redirect should be
// followed. If permitted, a 301, 302, or 303 redirect causes
// subsequent requests to use HTTP method GET
// (or HEAD if the original request was HEAD), with no body.
// A 307 or 308 redirect preserves the original HTTP method and body,
// provided that the Request.GetBody function is defined.
// The NewRequest function automatically sets GetBody for common
// standard library body types.
//
// Any returned error will be of type *url.Error. The url.Error
// value's Timeout method will report true if request timed out or was
// canceled.
func (c *Client) Do(req *Request) (*Response, error) {
return c.do(req)
}
func (c *Client) do(req *Request) (retres *Response, reterr error) {
if testHookClientDoResult != nil {
defer func() { testHookClientDoResult(retres, reterr) }()
}
if req.URL == nil {
req.closeBody()
return nil, &url.Error{
Op: urlErrorOp(req.Method),
Err: errors.New("http: nil Request.URL"),
}
}
var (
deadline = c.deadline()
reqs []*Request
resp *Response
copyHeaders = c.makeHeadersCopier(req)
reqBodyClosed = false // have we closed the current req.Body?
// Redirect behavior:
redirectMethod string
includeBody bool
)
uerr := func(err error) error {
// the body may have been closed already by c.send()
if !reqBodyClosed {
req.closeBody()
}
var urlStr string
if resp != nil && resp.Request != nil {
urlStr = stripPassword(resp.Request.URL)
} else {
urlStr = stripPassword(req.URL)
}
return &url.Error{
Op: urlErrorOp(reqs[0].Method),
URL: urlStr,
Err: err,
}
}
for {
// For all but the first request, create the next
// request hop and replace req.
if len(reqs) > 0 {
loc := resp.Header.Get("Location")
if loc == "" {
resp.closeBody()
return nil, uerr(fmt.Errorf("%d response missing Location header", resp.StatusCode))
}
u, err := req.URL.Parse(loc)
if err != nil {
resp.closeBody()
return nil, uerr(fmt.Errorf("failed to parse Location header %q: %v", loc, err))
}
host := ""
if req.Host != "" && req.Host != req.URL.Host {
// If the caller specified a custom Host header and the
// redirect location is relative, preserve the Host header
// through the redirect. See issue #22233.
if u, _ := url.Parse(loc); u != nil && !u.IsAbs() {
host = req.Host
}
}
ireq := reqs[0]
req = &Request{
Method: redirectMethod,
Response: resp,
URL: u,
Header: make(Header),
Host: host,
Cancel: ireq.Cancel,
ctx: ireq.ctx,
}
if includeBody && ireq.GetBody != nil {
req.Body, err = ireq.GetBody()
if err != nil {
resp.closeBody()
return nil, uerr(err)
}
req.ContentLength = ireq.ContentLength
}
// Copy original headers before setting the Referer,
// in case the user set Referer on their first request.
// If they really want to override, they can do it in
// their CheckRedirect func.
copyHeaders(req)
// Add the Referer header from the most recent
// request URL to the new one, if it's not https->http:
if ref := refererForURL(reqs[len(reqs)-1].URL, req.URL); ref != "" {
req.Header.Set("Referer", ref)
}
err = c.checkRedirect(req, reqs)
// Sentinel error to let users select the
// previous response, without closing its
// body. See Issue 10069.
if err == ErrUseLastResponse {
return resp, nil
}
// Close the previous response's body. But
// read at least some of the body so if it's
// small the underlying TCP connection will be
// re-used. No need to check for errors: if it
// fails, the Transport won't reuse it anyway.
const maxBodySlurpSize = 2 << 10
if resp.ContentLength == -1 || resp.ContentLength <= maxBodySlurpSize {
io.CopyN(ioutil.Discard, resp.Body, maxBodySlurpSize)
}
resp.Body.Close()
if err != nil {
// Special case for Go 1 compatibility: return both the response
// and an error if the CheckRedirect function failed.
// See https://golang.org/issue/3795
// The resp.Body has already been closed.
ue := uerr(err)
ue.(*url.Error).URL = loc
return resp, ue
}
}
reqs = append(reqs, req)
var err error
var didTimeout func() bool
if resp, didTimeout, err = c.send(req, deadline); err != nil {
// c.send() always closes req.Body
reqBodyClosed = true
if !deadline.IsZero() && didTimeout() {
err = &httpError{
// TODO: early in cycle: s/Client.Timeout exceeded/timeout or context cancellation/
err: err.Error() + " (Client.Timeout exceeded while awaiting headers)",
timeout: true,
}
}
return nil, uerr(err)
}
var shouldRedirect bool
redirectMethod, shouldRedirect, includeBody = redirectBehavior(req.Method, resp, reqs[0])
if !shouldRedirect {
return resp, nil
}
req.closeBody()
}
}
整个http.Client.Do逻辑分为两道，第一道执行send发送请求接收Response，关闭Req.Body；第二层对请求执行重定向等操作(若需要redirect)，并关闭Resp.Body
其中，send执行请求的发送和接收动作，展开如下：
// didTimeout is non-nil only if err != nil.
func (c *Client) send(req *Request, deadline time.Time) (resp *Response, didTimeout func() bool, err error) {
if c.Jar != nil {
for _, cookie := range c.Jar.Cookies(req.URL) {
req.AddCookie(cookie)
}
}
resp, didTimeout, err = send(req, c.transport(), deadline)
if err != nil {
return nil, didTimeout, err
}
if c.Jar != nil {
if rc := resp.Cookies(); len(rc) > 0 {
c.Jar.SetCookies(req.URL, rc)
}
}
return resp, nil, nil
}
// send issues an HTTP request.
// Caller should close resp.Body when done reading from it.
func send(ireq *Request, rt RoundTripper, deadline time.Time) (resp *Response, didTimeout func() bool, err error) {
req := ireq // req is either the original request, or a modified fork
if rt == nil {
req.closeBody()
return nil, alwaysFalse, errors.New("http: no Client.Transport or DefaultTransport")
}
if req.URL == nil {
req.closeBody()
return nil, alwaysFalse, errors.New("http: nil Request.URL")
}
if req.RequestURI != "" {
req.closeBody()
return nil, alwaysFalse, errors.New("http: Request.RequestURI can't be set in client requests.")
}
// forkReq forks req into a shallow clone of ireq the first
// time it's called.
forkReq := func() {
if ireq == req {
req = new(Request)
*req = *ireq // shallow clone
}
}
// Most the callers of send (Get, Post, et al) don't need
// Headers, leaving it uninitialized. We guarantee to the
// Transport that this has been initialized, though.
if req.Header == nil {
forkReq()
req.Header = make(Header)
}
if u := req.URL.User; u != nil && req.Header.Get("Authorization") == "" {
username := u.Username()
password, _ := u.Password()
forkReq()
req.Header = cloneOrMakeHeader(ireq.Header)
req.Header.Set("Authorization", "Basic "+basicAuth(username, password))
}
if !deadline.IsZero() {
forkReq()
}
stopTimer, didTimeout := setRequestCancel(req, rt, deadline)
resp, err = rt.RoundTrip(req)
if err != nil {
stopTimer()
if resp != nil {
log.Printf("RoundTripper returned a response & error; ignoring response")
}
if tlsErr, ok := err.(tls.RecordHeaderError); ok {
// If we get a bad TLS record header, check to see if the
// response looks like HTTP and give a more helpful error.
// See golang.org/issue/11111.
if string(tlsErr.RecordHeader[:]) == "HTTP/" {
err = errors.New("http: server gave HTTP response to HTTPS client")
}
}
return nil, didTimeout, err
}
if !deadline.IsZero() {
resp.Body = &cancelTimerBody{
stop: stopTimer,
rc: resp.Body,
reqDidTimeout: didTimeout,
}
}
return resp, nil, nil
}
func (c *Client) transport() RoundTripper {
if c.Transport != nil {
return c.Transport
}
return DefaultTransport
}
入参为http.Request，http.Transport以及deadline(http.Client.Timeout)。函数处理逻辑具体分为两个步骤，如下：
1.setRequestCancel
设置请求超时时间为http.Client.Timeout：
// setRequestCancel sets the Cancel field of req, if deadline is
// non-zero. The RoundTripper's type is used to determine whether the legacy
// CancelRequest behavior should be used.
//
// As background, there are three ways to cancel a request:
// First was Transport.CancelRequest. (deprecated)
// Second was Request.Cancel (this mechanism).
// Third was Request.Context.
func setRequestCancel(req *Request, rt RoundTripper, deadline time.Time) (stopTimer func(), didTimeout func() bool) {
if deadline.IsZero() {
return nop, alwaysFalse
}
initialReqCancel := req.Cancel // the user's original Request.Cancel, if any
cancel := make(chan struct{})
req.Cancel = cancel
doCancel := func() {
// The newer way (the second way in the func comment):
close(cancel)
// The legacy compatibility way, used only
// for RoundTripper implementations written
// before Go 1.5 or Go 1.6.
type canceler interface {
CancelRequest(*Request)
}
switch v := rt.(type) {
case *Transport, *http2Transport:
// Do nothing. The net/http package's transports
// support the new Request.Cancel channel
case canceler:
v.CancelRequest(req)
}
}
stopTimerCh := make(chan struct{})
var once sync.Once
stopTimer = func() { once.Do(func() { close(stopTimerCh) }) }
timer := time.NewTimer(time.Until(deadline))
var timedOut atomicBool
go func() {
select {
case <-initialReqCancel:
doCancel()
timer.Stop()
case <-timer.C:
timedOut.setTrue()
doCancel()
case <-stopTimerCh:
timer.Stop()
}
}()
return stopTimer, timedOut.isSet
}
// A Request represents an HTTP request received by a server
// or to be sent by a client.
//
// The field semantics differ slightly between client and server
// usage. In addition to the notes on the fields below, see the
// documentation for Request.Write and RoundTripper.
type Request struct {
...
// Cancel is an optional channel whose closure indicates that the client
// request should be regarded as canceled. Not all implementations of
// RoundTripper may support Cancel.
//
// For server requests, this field is not applicable.
//
// Deprecated: Set the Request's context with NewRequestWithContext
// instead. If a Request's Cancel field and context are both
// set, it is undefined whether Cancel is respected.
Cancel <-chan struct{}
// Response is the redirect response which caused this request
// to be created. This field is only populated during client
// redirects.
Response *Response
// ctx is either the client or server context. It should only
// be modified via copying the whole Request using WithContext.
// It is unexported to prevent people from using Context wrong
// and mutating the contexts held by callers of the same request.
ctx context.Context
}
有三种方式取消一个请求，如下：
- First was Transport.CancelRequest. (deprecated)
- Second was Request.Cancel (this mechanism).
- Third was Request.Context.
setRequestCancel执行了前面两种方式
2.resp, err = rt.RoundTrip(req)
在设置了超时timer后，执行具体的请求操作
回到http.Transport(net/http/transport.go)，Transport实现了RoundTripper接口，如下：
client := &http.Client{
Transport: &http.Transport{
Proxy: http.ProxyFromEnvironment,
DialContext: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
DualStack: true,
}).DialContext,
MaxIdleConns: 100,
MaxIdleConnsPerHost: 100,
IdleConnTimeout: 90 * time.Second,
},
}
...
// RoundTrip implements the RoundTripper interface.
//
// For higher-level HTTP client support (such as handling of cookies
// and redirects), see Get, Post, and the Client type.
//
// Like the RoundTripper interface, the error types returned
// by RoundTrip are unspecified.
func (t *Transport) RoundTrip(req *Request) (*Response, error) {
return t.roundTrip(req)
}
// roundTrip implements a RoundTripper over HTTP.
func (t *Transport) roundTrip(req *Request) (*Response, error) {
t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
ctx := req.Context()
trace := httptrace.ContextClientTrace(ctx)
if req.URL == nil {
req.closeBody()
return nil, errors.New("http: nil Request.URL")
}
if req.Header == nil {
req.closeBody()
return nil, errors.New("http: nil Request.Header")
}
scheme := req.URL.Scheme
isHTTP := scheme == "http" || scheme == "https"
if isHTTP {
for k, vv := range req.Header {
if !httpguts.ValidHeaderFieldName(k) {
return nil, fmt.Errorf("net/http: invalid header field name %q", k)
}
for _, v := range vv {
if !httpguts.ValidHeaderFieldValue(v) {
return nil, fmt.Errorf("net/http: invalid header field value %q for key %v", v, k)
}
}
}
}
if t.useRegisteredProtocol(req) {
altProto, _ := t.altProto.Load().(map[string]RoundTripper)
if altRT := altProto[scheme]; altRT != nil {
if resp, err := altRT.RoundTrip(req); err != ErrSkipAltProtocol {
return resp, err
}
}
}
if !isHTTP {
req.closeBody()
return nil, &badStringError{"unsupported protocol scheme", scheme}
}
if req.Method != "" && !validMethod(req.Method) {
return nil, fmt.Errorf("net/http: invalid method %q", req.Method)
}
if req.URL.Host == "" {
req.closeBody()
return nil, errors.New("http: no Host in request URL")
}
for {
select {
case <-ctx.Done():
req.closeBody()
return nil, ctx.Err()
default:
}
// treq gets modified by roundTrip, so we need to recreate for each retry.
treq := &transportRequest{Request: req, trace: trace}
cm, err := t.connectMethodForRequest(treq)
if err != nil {
req.closeBody()
return nil, err
}
// Get the cached or newly-created connection to either the
// host (for http or https), the http proxy, or the http proxy
// pre-CONNECTed to https server. In any case, we'll be ready
// to send it requests.
pconn, err := t.getConn(treq, cm)
if err != nil {
t.setReqCanceler(req, nil)
req.closeBody()
return nil, err
}
var resp *Response
if pconn.alt != nil {
// HTTP/2 path.
t.setReqCanceler(req, nil) // not cancelable with CancelRequest
resp, err = pconn.alt.RoundTrip(req)
} else {
resp, err = pconn.roundTrip(treq)
}
if err == nil {
return resp, nil
}
// Failed. Clean up and determine whether to retry.
_, isH2DialError := pconn.alt.(http2erringRoundTripper)
if http2isNoCachedConnError(err) || isH2DialError {
t.removeIdleConn(pconn)
t.decConnsPerHost(pconn.cacheKey)
}
if !pconn.shouldRetryRequest(req, err) {
// Issue 16465: return underlying net.Conn.Read error from peek,
// as we've historically done.
if e, ok := err.(transportReadFromServerError); ok {
err = e.err
}
return nil, err
}
testHookRoundTripRetried()
// Rewind the body if we're able to.
if req.GetBody != nil {
newReq := *req
var err error
newReq.Body, err = req.GetBody()
if err != nil {
return nil, err
}
req = &newReq
}
}
}
拆分步骤如下：
获取连接(Transport.getConn)
// treq gets modified by roundTrip, so we need to recreate for each retry.
treq := &transportRequest{Request: req, trace: trace}
cm, err := t.connectMethodForRequest(treq)
if err != nil {
req.closeBody()
return nil, err
}
// Get the cached or newly-created connection to either the
// host (for http or https), the http proxy, or the http proxy
// pre-CONNECTed to https server. In any case, we'll be ready
// to send it requests.
pconn, err := t.getConn(treq, cm)
if err != nil {
t.setReqCanceler(req, nil)
req.closeBody()
return nil, err
}
...
// transportRequest is a wrapper around a *Request that adds
// optional extra headers to write and stores any error to return
// from roundTrip.
type transportRequest struct {
*Request // original request, not to be mutated
extra Header // extra headers to write, or nil
trace *httptrace.ClientTrace // optional
mu sync.Mutex // guards err
err error // first setError value for mapRoundTripError to consider
}
func (t *Transport) connectMethodForRequest(treq *transportRequest) (cm connectMethod, err error) {
// TODO: the validPort check is redundant after CL 189258, as url.URL.Port
// only returns valid ports now. golang.org/issue/33600
if port := treq.URL.Port(); !validPort(port) {
return cm, fmt.Errorf("invalid URL port %q", port)
}
cm.targetScheme = treq.URL.Scheme
cm.targetAddr = canonicalAddr(treq.URL)
if t.Proxy != nil {
cm.proxyURL, err = t.Proxy(treq.Request)
if err == nil && cm.proxyURL != nil {
if port := cm.proxyURL.Port(); !validPort(port) {
return cm, fmt.Errorf("invalid proxy URL port %q", port)
}
}
}
cm.onlyH1 = treq.requiresHTTP1()
return cm, err
}
// connectMethod is the map key (in its String form) for keeping persistent
// TCP connections alive for subsequent HTTP requests.
//
// A connect method may be of the following types:
//
// connectMethod.key().String() Description
// ------------------------------ -------------------------
// |http|foo.com http directly to server, no proxy
// |https|foo.com https directly to server, no proxy
// |https,h1|foo.com https directly to server w/o HTTP/2, no proxy
// http://proxy.com|https|foo.com http to proxy, then CONNECT to foo.com
// http://proxy.com|http http to proxy, http to anywhere after that
// socks5://proxy.com|http|foo.com socks5 to proxy, then http to foo.com
// socks5://proxy.com|https|foo.com socks5 to proxy, then https to foo.com
// https://proxy.com|https|foo.com https to proxy, then CONNECT to foo.com
// https://proxy.com|http https to proxy, http to anywhere after that
//
type connectMethod struct {
proxyURL *url.URL // nil for no proxy, else full proxy URL
targetScheme string // "http" or "https"
// If proxyURL specifies an http or https proxy, and targetScheme is http (not https),
// then targetAddr is not included in the connect method key, because the socket can
// be reused for different targetAddr values.
targetAddr string
onlyH1 bool // whether to disable HTTP/2 and force HTTP/1
}
...
// getConn dials and creates a new persistConn to the target as
// specified in the connectMethod. This includes doing a proxy CONNECT
// and/or setting up TLS. If this doesn't return an error, the persistConn
// is ready to write requests to.
func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (pc *persistConn, err error) {
req := treq.Request
trace := treq.trace
ctx := req.Context()
if trace != nil && trace.GetConn != nil {
trace.GetConn(cm.addr())
}
w := &wantConn{
cm: cm,
key: cm.key(),
ctx: ctx,
ready: make(chan struct{}, 1),
beforeDial: testHookPrePendingDial,
afterDial: testHookPostPendingDial,
}
defer func() {
if err != nil {
w.cancel(t, err)
}
}()
// Queue for idle connection.
if delivered := t.queueForIdleConn(w); delivered {
pc := w.pc
// Trace only for HTTP/1.
// HTTP/2 calls trace.GotConn itself.
if pc.alt == nil && trace != nil && trace.GotConn != nil {
trace.GotConn(pc.gotIdleConnTrace(pc.idleAt))
}
// set request canceler to some non-nil function so we
// can detect whether it was cleared between now and when
// we enter roundTrip
t.setReqCanceler(req, func(error) {})
return pc, nil
}
cancelc := make(chan error, 1)
t.setReqCanceler(req, func(err error) { cancelc <- err })
// Queue for permission to dial.
t.queueForDial(w)
// Wait for completion or cancellation.
select {
case <-w.ready:
// Trace success but only for HTTP/1.
// HTTP/2 calls trace.GotConn itself.
if w.pc != nil && w.pc.alt == nil && trace != nil && trace.GotConn != nil {
trace.GotConn(httptrace.GotConnInfo{Conn: w.pc.conn, Reused: w.pc.isReused()})
}
if w.err != nil {
// If the request has been cancelled, that's probably
// what caused w.err; if so, prefer to return the
// cancellation error (see golang.org/issue/16049).
select {
case <-req.Cancel:
return nil, errRequestCanceledConn
case <-req.Context().Done():
return nil, req.Context().Err()
case err := <-cancelc:
if err == errRequestCanceled {
err = errRequestCanceledConn
}
return nil, err
default:
// return below
}
}
return w.pc, w.err
case <-req.Cancel:
return nil, errRequestCanceledConn
case <-req.Context().Done():
return nil, req.Context().Err()
case err := <-cancelc:
if err == errRequestCanceled {
err = errRequestCanceledConn
}
return nil, err
}
}
其中getConn是重点分析的内容。首先调用queueForIdleConn获取空闲连接：
// queueForIdleConn queues w to receive the next idle connection for w.cm.
// As an optimization hint to the caller, queueForIdleConn reports whether
// it successfully delivered an already-idle connection.
func (t *Transport) queueForIdleConn(w *wantConn) (delivered bool) {
if t.DisableKeepAlives {
return false
}
t.idleMu.Lock()
defer t.idleMu.Unlock()
// Stop closing connections that become idle - we might want one.
// (That is, undo the effect of t.CloseIdleConnections.)
t.closeIdle = false
if w == nil {
// Happens in test hook.
return false
}
// Look for most recently-used idle connection.
if list, ok := t.idleConn[w.key]; ok {
stop := false
delivered := false
for len(list) > 0 && !stop {
pconn := list[len(list)-1]
if pconn.isBroken() {
// persistConn.readLoop has marked the connection broken,
// but Transport.removeIdleConn has not yet removed it from the idle list.
// Drop on floor on behalf of Transport.removeIdleConn.
list = list[:len(list)-1]
continue
}
delivered = w.tryDeliver(pconn, nil)
if delivered {
if pconn.alt != nil {
// HTTP/2: multiple clients can share pconn.
// Leave it in the list.
} else {
// HTTP/1: only one client can use pconn.
// Remove it from the list.
t.idleLRU.remove(pconn)
list = list[:len(list)-1]
}
}
stop = true
}
if len(list) > 0 {
t.idleConn[w.key] = list
} else {
delete(t.idleConn, w.key)
}
if stop {
return delivered
}
}
// Register to receive next connection that becomes idle.
if t.idleConnWait == nil {
t.idleConnWait = make(map[connectMethodKey]wantConnQueue)
}
q := t.idleConnWait[w.key]
q.cleanFront()
q.pushBack(w)
t.idleConnWait[w.key] = q
return false
}
// A wantConn records state about a wanted connection
// (that is, an active call to getConn).
// The conn may be gotten by dialing or by finding an idle connection,
// or a cancellation may make the conn no longer wanted.
// These three options are racing against each other and use
// wantConn to coordinate and agree about the winning outcome.
type wantConn struct {
cm connectMethod
key connectMethodKey // cm.key()
ctx context.Context // context for dial
ready chan struct{} // closed when pc, err pair is delivered
// hooks for testing to know when dials are done
// beforeDial is called in the getConn goroutine when the dial is queued.
// afterDial is called when the dial is completed or cancelled.
beforeDial func()
afterDial func()
mu sync.Mutex // protects pc, err, close(ready)
pc *persistConn
err error
}
// tryDeliver attempts to deliver pc, err to w and reports whether it succeeded.
func (w *wantConn) tryDeliver(pc *persistConn, err error) bool {
w.mu.Lock()
defer w.mu.Unlock()
if w.pc != nil || w.err != nil {
return false
}
w.pc = pc
w.err = err
if w.pc == nil && w.err == nil {
panic("net/http: internal error: misuse of tryDeliver")
}
close(w.ready)
return true
}
idleConn(map[connectMethodKey][]*persistConn)表示Transport的空闲连接池。其中connectMethodKey是对url关键字段的分解，代表连接的目标方(代理，协议，目的地址)，而values是persistConn的列表
而persistConn是对连接的一层封装，通常表示keep-alive连接，也可以表示non-keep-alive连接
type Transport struct {
idleMu sync.Mutex
closeIdle bool // user has requested to close all idle conns
idleConn map[connectMethodKey][]*persistConn // most recently used at end
idleConnWait map[connectMethodKey]wantConnQueue // waiting getConns
idleLRU connLRU
...
}
// connectMethodKey is the map key version of connectMethod, with a
// stringified proxy URL (or the empty string) instead of a pointer to
// a URL.
type connectMethodKey struct {
proxy, scheme, addr string
onlyH1 bool
}
// persistConn wraps a connection, usually a persistent one
// (but may be used for non-keep-alive requests as well)
type persistConn struct {
// alt optionally specifies the TLS NextProto RoundTripper.
// This is used for HTTP/2 today and future protocols later.
// If it's non-nil, the rest of the fields are unused.
alt RoundTripper
t *Transport
cacheKey connectMethodKey
conn net.Conn
tlsState *tls.ConnectionState
br *bufio.Reader // from conn
bw *bufio.Writer // to conn
nwrite int64 // bytes written
reqch chan requestAndChan // written by roundTrip; read by readLoop
writech chan writeRequest // written by roundTrip; read by writeLoop
closech chan struct{} // closed when conn closed
isProxy bool
sawEOF bool // whether we've seen EOF from conn; owned by readLoop
readLimit int64 // bytes allowed to be read; owned by readLoop
// writeErrCh passes the request write error (usually nil)
// from the writeLoop goroutine to the readLoop which passes
// it off to the res.Body reader, which then uses it to decide
// whether or not a connection can be reused. Issue 7569.
writeErrCh chan error
writeLoopDone chan struct{} // closed when write loop ends
// Both guarded by Transport.idleMu:
idleAt time.Time // time it last become idle
idleTimer *time.Timer // holding an AfterFunc to close it
mu sync.Mutex // guards following fields
numExpectedResponses int
closed error // set non-nil when conn is closed, before closech is closed
canceledErr error // set non-nil if conn is canceled
broken bool // an error has happened on this connection; marked broken so it's not reused.
reused bool // whether conn has had successful request/response and is being reused.
// mutateHeaderFunc is an optional func to modify extra
// headers on each outbound request before it's written. (the
// original Request given to RoundTrip is not modified)
mutateHeaderFunc func(Header)
}
queueForIdleConn首先尝试从idleConn中获取最近使用的空闲连接(Look for most recently-used idle connection)。如果找到，则从连接列表中删除掉该连接(非HTTP/2情况，因为HTTP/2协议多个请求可以同时共用底层连接)
如果发现没有对应空闲连接，则将wantConn赋值给idleConnWait(waiting getConns)，代表此时多了一个等待获取连接的请求
回到getConn内容。在执行queueForIdleConn获取空闲连接成功后，直接返回该连接；否则执行queueForDial尝试创建连接，等待创建结束并返回连接：
// getConn dials and creates a new persistConn to the target as
// specified in the connectMethod. This includes doing a proxy CONNECT
// and/or setting up TLS. If this doesn't return an error, the persistConn
// is ready to write requests to.
func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (pc *persistConn, err error) {
if delivered := t.queueForIdleConn(w); delivered {
...
}
// Queue for permission to dial.
t.queueForDial(w)
// Wait for completion or cancellation.
select {
case <-w.ready:
// Trace success but only for HTTP/1.
// HTTP/2 calls trace.GotConn itself.
if w.pc != nil && w.pc.alt == nil && trace != nil && trace.GotConn != nil {
trace.GotConn(httptrace.GotConnInfo{Conn: w.pc.conn, Reused: w.pc.isReused()})
}
if w.err != nil {
// If the request has been cancelled, that's probably
// what caused w.err; if so, prefer to return the
// cancellation error (see golang.org/issue/16049).
select {
case <-req.Cancel:
return nil, errRequestCanceledConn
case <-req.Context().Done():
return nil, req.Context().Err()
case err := <-cancelc:
if err == errRequestCanceled {
err = errRequestCanceledConn
}
return nil, err
default:
// return below
}
}
return w.pc, w.err
case <-req.Cancel:
return nil, errRequestCanceledConn
case <-req.Context().Done():
return nil, req.Context().Err()
case err := <-cancelc:
if err == errRequestCanceled {
err = errRequestCanceledConn
}
return nil, err
}
}
// queueForDial queues w to wait for permission to begin dialing.
// Once w receives permission to dial, it will do so in a separate goroutine.
func (t *Transport) queueForDial(w *wantConn) {
w.beforeDial()
if t.MaxConnsPerHost <= 0 {
go t.dialConnFor(w)
return
}
t.connsPerHostMu.Lock()
defer t.connsPerHostMu.Unlock()
if n := t.connsPerHost[w.key]; n < t.MaxConnsPerHost {
if t.connsPerHost == nil {
t.connsPerHost = make(map[connectMethodKey]int)
}
t.connsPerHost[w.key] = n + 1
go t.dialConnFor(w)
return
}
if t.connsPerHostWait == nil {
t.connsPerHostWait = make(map[connectMethodKey]wantConnQueue)
}
q := t.connsPerHostWait[w.key]
q.cleanFront()
q.pushBack(w)
t.connsPerHostWait[w.key] = q
}
// Transport is an implementation of RoundTripper that supports HTTP,
// HTTPS, and HTTP proxies (for either HTTP or HTTPS with CONNECT).
//
// By default, Transport caches connections for future re-use.
// This may leave many open connections when accessing many hosts.
// This behavior can be managed using Transport's CloseIdleConnections method
// and the MaxIdleConnsPerHost and DisableKeepAlives fields.
//
// Transports should be reused instead of created as needed.
// Transports are safe for concurrent use by multiple goroutines.
//
// A Transport is a low-level primitive for making HTTP and HTTPS requests.
// For high-level functionality, such as cookies and redirects, see Client.
//
// Transport uses HTTP/1.1 for HTTP URLs and either HTTP/1.1 or HTTP/2
// for HTTPS URLs, depending on whether the server supports HTTP/2,
// and how the Transport is configured. The DefaultTransport supports HTTP/2.
// To explicitly enable HTTP/2 on a transport, use golang.org/x/net/http2
// and call ConfigureTransport. See the package docs for more about HTTP/2.
//
// Responses with status codes in the 1xx range are either handled
// automatically (100 expect-continue) or ignored. The one
// exception is HTTP status code 101 (Switching Protocols), which is
// considered a terminal status and returned by RoundTrip. To see the
// ignored 1xx responses, use the httptrace trace package's
// ClientTrace.Got1xxResponse.
//
// Transport only retries a request upon encountering a network error
// if the request is idempotent and either has no body or has its
// Request.GetBody defined. HTTP requests are considered idempotent if
// they have HTTP methods GET, HEAD, OPTIONS, or TRACE; or if their
// Header map contains an "Idempotency-Key" or "X-Idempotency-Key"
// entry. If the idempotency key value is an zero-length slice, the
// request is treated as idempotent but the header is not sent on the
// wire.
type Transport struct {
idleMu sync.Mutex
closeIdle bool // user has requested to close all idle conns
idleConn map[connectMethodKey][]*persistConn // most recently used at end
idleConnWait map[connectMethodKey]wantConnQueue // waiting getConns
idleLRU connLRU
reqMu sync.Mutex
reqCanceler map[*Request]func(error)
altMu sync.Mutex // guards changing altProto only
altProto atomic.Value // of nil or map[string]RoundTripper, key is URI scheme
connsPerHostMu sync.Mutex
connsPerHost map[connectMethodKey]int
connsPerHostWait map[connectMethodKey]wantConnQueue // waiting getConns
...
}
// A wantConnQueue is a queue of wantConns.
type wantConnQueue struct {
// This is a queue, not a deque.
// It is split into two stages - head[headPos:] and tail.
// popFront is trivial (headPos++) on the first stage, and
// pushBack is trivial (append) on the second stage.
// If the first stage is empty, popFront can swap the
// first and second stages to remedy the situation.
//
// This two-stage split is analogous to the use of two lists
// in Okasaki's purely functional queue but without the
// overhead of reversing the list when swapping stages.
head []*wantConn
headPos int
tail []*wantConn
}
还记得最开始介绍Transport结构体时有如下参数：
- MaxConnsPerHost：控制某个host的所有连接，包括创建中，正在使用的，以及空闲的连接(including connections in the dialing, active, and idle states)。一旦超过限制，dial会阻塞(Zero means no limit)
- connsPerHost：表示每个host(connectMethodKey)的目前连接个数
- connsPerHostWait：表示每个host(connectMethodKey)等待建立的连接请求
queueForDial的作用是：判断wantConn对应的host目前连接数是否超过Transport.MaxConnsPerHost，如果没有超过，则执行dialConnFor操作为该请求创建连接，同时递增Transport.connsPerHost[wantConn]；否则将wantConn放入connsPerHostWait列表中
接下来看dialConnFor，如下：
// dialConnFor dials on behalf of w and delivers the result to w.
// dialConnFor has received permission to dial w.cm and is counted in t.connCount[w.cm.key()].
// If the dial is cancelled or unsuccessful, dialConnFor decrements t.connCount[w.cm.key()].
func (t *Transport) dialConnFor(w *wantConn) {
defer w.afterDial()
pc, err := t.dialConn(w.ctx, w.cm)
delivered := w.tryDeliver(pc, err)
if err == nil && (!delivered || pc.alt != nil) {
// pconn was not passed to w,
// or it is HTTP/2 and can be shared.
// Add to the idle connection pool.
t.putOrCloseIdleConn(pc)
}
if err != nil {
t.decConnsPerHost(w.key)
}
}
// tryDeliver attempts to deliver pc, err to w and reports whether it succeeded.
func (w *wantConn) tryDeliver(pc *persistConn, err error) bool {
w.mu.Lock()
defer w.mu.Unlock()
if w.pc != nil || w.err != nil {
return false
}
w.pc = pc
w.err = err
if w.pc == nil && w.err == nil {
panic("net/http: internal error: misuse of tryDeliver")
}
close(w.ready)
return true
}
func (t *Transport) dialConn(ctx context.Context, cm connectMethod) (pconn *persistConn, err error) {
pconn = &persistConn{
t: t,
cacheKey: cm.key(),
reqch: make(chan requestAndChan, 1),
writech: make(chan writeRequest, 1),
closech: make(chan struct{}),
writeErrCh: make(chan error, 1),
writeLoopDone: make(chan struct{}),
}
trace := httptrace.ContextClientTrace(ctx)
wrapErr := func(err error) error {
if cm.proxyURL != nil {
// Return a typed error, per Issue 16997
return &net.OpError{Op: "proxyconnect", Net: "tcp", Err: err}
}
return err
}
if cm.scheme() == "https" && t.DialTLS != nil {
var err error
pconn.conn, err = t.DialTLS("tcp", cm.addr())
if err != nil {
return nil, wrapErr(err)
}
if pconn.conn == nil {
return nil, wrapErr(errors.New("net/http: Transport.DialTLS returned (nil, nil)"))
}
if tc, ok := pconn.conn.(*tls.Conn); ok {
// Handshake here, in case DialTLS didn't. TLSNextProto below
// depends on it for knowing the connection state.
if trace != nil && trace.TLSHandshakeStart != nil {
trace.TLSHandshakeStart()
}
if err := tc.Handshake(); err != nil {
go pconn.conn.Close()
if trace != nil && trace.TLSHandshakeDone != nil {
trace.TLSHandshakeDone(tls.ConnectionState{}, err)
}
return nil, err
}
cs := tc.ConnectionState()
if trace != nil && trace.TLSHandshakeDone != nil {
trace.TLSHandshakeDone(cs, nil)
}
pconn.tlsState = &cs
}
} else {
conn, err := t.dial(ctx, "tcp", cm.addr())
if err != nil {
return nil, wrapErr(err)
}
pconn.conn = conn
if cm.scheme() == "https" {
var firstTLSHost string
if firstTLSHost, _, err = net.SplitHostPort(cm.addr()); err != nil {
return nil, wrapErr(err)
}
if err = pconn.addTLS(firstTLSHost, trace); err != nil {
return nil, wrapErr(err)
}
}
}
// Proxy setup.
switch {
case cm.proxyURL == nil:
// Do nothing. Not using a proxy.
case cm.proxyURL.Scheme == "socks5":
conn := pconn.conn
d := socksNewDialer("tcp", conn.RemoteAddr().String())
if u := cm.proxyURL.User; u != nil {
auth := &socksUsernamePassword{
Username: u.Username(),
}
auth.Password, _ = u.Password()
d.AuthMethods = []socksAuthMethod{
socksAuthMethodNotRequired,
socksAuthMethodUsernamePassword,
}
d.Authenticate = auth.Authenticate
}
if _, err := d.DialWithConn(ctx, conn, "tcp", cm.targetAddr); err != nil {
conn.Close()
return nil, err
}
case cm.targetScheme == "http":
pconn.isProxy = true
if pa := cm.proxyAuth(); pa != "" {
pconn.mutateHeaderFunc = func(h Header) {
h.Set("Proxy-Authorization", pa)
}
}
case cm.targetScheme == "https":
conn := pconn.conn
hdr := t.ProxyConnectHeader
if hdr == nil {
hdr = make(Header)
}
connectReq := &Request{
Method: "CONNECT",
URL: &url.URL{Opaque: cm.targetAddr},
Host: cm.targetAddr,
Header: hdr,
}
if pa := cm.proxyAuth(); pa != "" {
connectReq.Header.Set("Proxy-Authorization", pa)
}
connectReq.Write(conn)
// Read response.
// Okay to use and discard buffered reader here, because
// TLS server will not speak until spoken to.
br := bufio.NewReader(conn)
resp, err := ReadResponse(br, connectReq)
if err != nil {
conn.Close()
return nil, err
}
if resp.StatusCode != 200 {
f := strings.SplitN(resp.Status, " ", 2)
conn.Close()
if len(f) < 2 {
return nil, errors.New("unknown status code")
}
return nil, errors.New(f[1])
}
}
if cm.proxyURL != nil && cm.targetScheme == "https" {
if err := pconn.addTLS(cm.tlsHost(), trace); err != nil {
return nil, err
}
}
if s := pconn.tlsState; s != nil && s.NegotiatedProtocolIsMutual && s.NegotiatedProtocol != "" {
if next, ok := t.TLSNextProto[s.NegotiatedProtocol]; ok {
return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: next(cm.targetAddr, pconn.conn.(*tls.Conn))}, nil
}
}
pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())
pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())
go pconn.readLoop()
go pconn.writeLoop()
return pconn, nil
}
// Add TLS to a persistent connection, i.e. negotiate a TLS session. If pconn is already a TLS
// tunnel, this function establishes a nested TLS session inside the encrypted channel.
// The remote endpoint's name may be overridden by TLSClientConfig.ServerName.
func (pconn *persistConn) addTLS(name string, trace *httptrace.ClientTrace) error {
// Initiate TLS and check remote host name against certificate.
cfg := cloneTLSConfig(pconn.t.TLSClientConfig)
if cfg.ServerName == "" {
cfg.ServerName = name
}
if pconn.cacheKey.onlyH1 {
cfg.NextProtos = nil
}
plainConn := pconn.conn
tlsConn := tls.Client(plainConn, cfg)
errc := make(chan error, 2)
var timer *time.Timer // for canceling TLS handshake
if d := pconn.t.TLSHandshakeTimeout; d != 0 {
timer = time.AfterFunc(d, func() {
errc <- tlsHandshakeTimeoutError{}
})
}
go func() {
if trace != nil && trace.TLSHandshakeStart != nil {
trace.TLSHandshakeStart()
}
err := tlsConn.Handshake()
if timer != nil {
timer.Stop()
}
errc <- err
}()
if err := <-errc; err != nil {
plainConn.Close()
if trace != nil && trace.TLSHandshakeDone != nil {
trace.TLSHandshakeDone(tls.ConnectionState{}, err)
}
return err
}
cs := tlsConn.ConnectionState()
if trace != nil && trace.TLSHandshakeDone != nil {
trace.TLSHandshakeDone(cs, nil)
}
pconn.tlsState = &cs
pconn.conn = tlsConn
return nil
}
重点分析dialConn，该函数为connectMethod获取persistConn，步骤如下：
1.判断协议是https还是http，如果是https，则执行TLS握手过程(i.e. negotiate a TLS session)；否则直接执行Transport.dial操作创建TCP连接
var zeroDialer net.Dialer
func (t *Transport) dial(ctx context.Context, network, addr string) (net.Conn, error) {
if t.DialContext != nil {
return t.DialContext(ctx, network, addr)
}
if t.Dial != nil {
c, err := t.Dial(network, addr)
if c == nil && err == nil {
err = errors.New("net/http: Transport.Dial hook returned (nil, nil)")
}
return c, err
}
return zeroDialer.DialContext(ctx, network, addr)
}
这里就是调用前面分析过的net.Dialer.DialContext函数了(前后对接起来了)，不再展开分析
2.执行代理设置
3.设置persistConn的读写buffer
pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())
pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())
go pconn.readLoop()
go pconn.writeLoop()
在分析完getConn之后，回头来分析http.Client.Do的第二个步骤：resp, err = rt.RoundTrip(req)，如下：
// roundTrip implements a RoundTripper over HTTP.
func (t *Transport) roundTrip(req *Request) (*Response, error) {
t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
ctx := req.Context()
trace := httptrace.ContextClientTrace(ctx)
if req.URL == nil {
req.closeBody()
return nil, errors.New("http: nil Request.URL")
}
if req.Header == nil {
req.closeBody()
return nil, errors.New("http: nil Request.Header")
}
scheme := req.URL.Scheme
isHTTP := scheme == "http" || scheme == "https"
if isHTTP {
for k, vv := range req.Header {
if !httpguts.ValidHeaderFieldName(k) {
return nil, fmt.Errorf("net/http: invalid header field name %q", k)
}
for _, v := range vv {
if !httpguts.ValidHeaderFieldValue(v) {
return nil, fmt.Errorf("net/http: invalid header field value %q for key %v", v, k)
}
}
}
}
if t.useRegisteredProtocol(req) {
altProto, _ := t.altProto.Load().(map[string]RoundTripper)
if altRT := altProto[scheme]; altRT != nil {
if resp, err := altRT.RoundTrip(req); err != ErrSkipAltProtocol {
return resp, err
}
}
}
if !isHTTP {
req.closeBody()
return nil, &badStringError{"unsupported protocol scheme", scheme}
}
if req.Method != "" && !validMethod(req.Method) {
return nil, fmt.Errorf("net/http: invalid method %q", req.Method)
}
if req.URL.Host == "" {
req.closeBody()
return nil, errors.New("http: no Host in request URL")
}
for {
select {
case <-ctx.Done():
req.closeBody()
return nil, ctx.Err()
default:
}
// treq gets modified by roundTrip, so we need to recreate for each retry.
treq := &transportRequest{Request: req, trace: trace}
cm, err := t.connectMethodForRequest(treq)
if err != nil {
req.closeBody()
return nil, err
}
// Get the cached or newly-created connection to either the
// host (for http or https), the http proxy, or the http proxy
// pre-CONNECTed to https server. In any case, we'll be ready
// to send it requests.
pconn, err := t.getConn(treq, cm)
if err != nil {
t.setReqCanceler(req, nil)
req.closeBody()
return nil, err
}
var resp *Response
if pconn.alt != nil {
// HTTP/2 path.
t.setReqCanceler(req, nil) // not cancelable with CancelRequest
resp, err = pconn.alt.RoundTrip(req)
} else {
resp, err = pconn.roundTrip(treq)
}
if err == nil {
return resp, nil
}
// Failed. Clean up and determine whether to retry.
_, isH2DialError := pconn.alt.(http2erringRoundTripper)
if http2isNoCachedConnError(err) || isH2DialError {
t.removeIdleConn(pconn)
t.decConnsPerHost(pconn.cacheKey)
}
if !pconn.shouldRetryRequest(req, err) {
// Issue 16465: return underlying net.Conn.Read error from peek,
// as we've historically done.
if e, ok := err.(transportReadFromServerError); ok {
err = e.err
}
return nil, err
}
testHookRoundTripRetried()
// Rewind the body if we're able to.
if req.GetBody != nil {
newReq := *req
var err error
newReq.Body, err = req.GetBody()
if err != nil {
return nil, err
}
req = &newReq
}
}
}
在执行pconn, err := t.getConn(treq, cm)获取连接(新创建的 or 复用空闲连接)后，执行resp, err = pconn.roundTrip(treq)，如下：
func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
...
// Write the request concurrently with waiting for a response,
// in case the server decides to reply before reading our full
// request body.
startBytesWritten := pc.nwrite
writeErrCh := make(chan error, 1)
pc.writech <- writeRequest{req, writeErrCh, continueCh}
resc := make(chan responseAndError)
pc.reqch <- requestAndChan{
req: req.Request,
ch: resc,
addedGzip: requestedGzip,
continueCh: continueCh,
callerGone: gone,
}
var respHeaderTimer <-chan time.Time
cancelChan := req.Request.Cancel
ctxDoneChan := req.Context().Done()
for {
testHookWaitResLoop()
select {
case err := <-writeErrCh:
if debugRoundTrip {
req.logf("writeErrCh resv: %T/%#v", err, err)
}
if err != nil {
pc.close(fmt.Errorf("write error: %v", err))
return nil, pc.mapRoundTripError(req, startBytesWritten, err)
}
if d := pc.t.ResponseHeaderTimeout; d > 0 {
if debugRoundTrip {
req.logf("starting timer for %v", d)
}
timer := time.NewTimer(d)
defer timer.Stop() // prevent leaks
respHeaderTimer = timer.C
}
case <-pc.closech:
if debugRoundTrip {
req.logf("closech recv: %T %#v", pc.closed, pc.closed)
}
return nil, pc.mapRoundTripError(req, startBytesWritten, pc.closed)
case <-respHeaderTimer:
if debugRoundTrip {
req.logf("timeout waiting for response headers.")
}
pc.close(errTimeout)
return nil, errTimeout
case re := <-resc:
if (re.res == nil) == (re.err == nil) {
panic(fmt.Sprintf("internal error: exactly one of res or err should be set; nil=%v", re.res == nil))
}
if debugRoundTrip {
req.logf("resc recv: %p, %T/%#v", re.res, re.err, re.err)
}
if re.err != nil {
return nil, pc.mapRoundTripError(req, startBytesWritten, re.err)
}
return re.res, nil
case <-cancelChan:
pc.t.CancelRequest(req.Request)
cancelChan = nil
case <-ctxDoneChan:
pc.t.cancelRequest(req.Request, req.Context().Err())
cancelChan = nil
ctxDoneChan = nil
}
}
}
这里需要结合前面的pc.readLoop，如下：
func (pc *persistConn) readLoop() {
closeErr := errReadLoopExiting // default value, if not changed below
defer func() {
pc.close(closeErr)
pc.t.removeIdleConn(pc)
}()
tryPutIdleConn := func(trace *httptrace.ClientTrace) bool {
if err := pc.t.tryPutIdleConn(pc); err != nil {
closeErr = err
if trace != nil && trace.PutIdleConn != nil && err != errKeepAlivesDisabled {
trace.PutIdleConn(err)
}
return false
}
if trace != nil && trace.PutIdleConn != nil {
trace.PutIdleConn(nil)
}
return true
}
// eofc is used to block caller goroutines reading from Response.Body
// at EOF until this goroutines has (potentially) added the connection
// back to the idle pool.
eofc := make(chan struct{})
defer close(eofc) // unblock reader on errors
// Read this once, before loop starts. (to avoid races in tests)
testHookMu.Lock()
testHookReadLoopBeforeNextRead := testHookReadLoopBeforeNextRead
testHookMu.Unlock()
alive := true
for alive {
pc.readLimit = pc.maxHeaderResponseSize()
_, err := pc.br.Peek(1)
pc.mu.Lock()
if pc.numExpectedResponses == 0 {
pc.readLoopPeekFailLocked(err)
pc.mu.Unlock()
return
}
pc.mu.Unlock()
rc := <-pc.reqch
trace := httptrace.ContextClientTrace(rc.req.Context())
var resp *Response
if err == nil {
resp, err = pc.readResponse(rc, trace)
} else {
err = transportReadFromServerError{err}
closeErr = err
}
if err != nil {
if pc.readLimit <= 0 {
err = fmt.Errorf("net/http: server response headers exceeded %d bytes; aborted", pc.maxHeaderResponseSize())
}
select {
case rc.ch <- responseAndError{err: err}:
case <-rc.callerGone:
return
}
return
}
pc.readLimit = maxInt64 // effictively no limit for response bodies
pc.mu.Lock()
pc.numExpectedResponses--
pc.mu.Unlock()
bodyWritable := resp.bodyIsWritable()
hasBody := rc.req.Method != "HEAD" && resp.ContentLength != 0
if resp.Close || rc.req.Close || resp.StatusCode <= 199 || bodyWritable {
// Don't do keep-alive on error if either party requested a close
// or we get an unexpected informational (1xx) response.
// StatusCode 100 is already handled above.
alive = false
}
if !hasBody || bodyWritable {
pc.t.setReqCanceler(rc.req, nil)
// Put the idle conn back into the pool before we send the response
// so if they process it quickly and make another request, they'll
// get this same conn. But we use the unbuffered channel 'rc'
// to guarantee that persistConn.roundTrip got out of its select
// potentially waiting for this persistConn to close.
// but after
alive = alive &&
!pc.sawEOF &&
pc.wroteRequest() &&
tryPutIdleConn(trace)
if bodyWritable {
closeErr = errCallerOwnsConn
}
select {
case rc.ch <- responseAndError{res: resp}:
case <-rc.callerGone:
return
}
// Now that they've read from the unbuffered channel, they're safely
// out of the select that also waits on this goroutine to die, so
// we're allowed to exit now if needed (if alive is false)
testHookReadLoopBeforeNextRead()
continue
}
waitForBodyRead := make(chan bool, 2)
body := &bodyEOFSignal{
body: resp.Body,
earlyCloseFn: func() error {
waitForBodyRead <- false
<-eofc // will be closed by deferred call at the end of the function
return nil
},
fn: func(err error) error {
isEOF := err == io.EOF
waitForBodyRead <- isEOF
if isEOF {
<-eofc // see comment above eofc declaration
} else if err != nil {
if cerr := pc.canceled(); cerr != nil {
return cerr
}
}
return err
},
}
resp.Body = body
if rc.addedGzip && strings.EqualFold(resp.Header.Get("Content-Encoding"), "gzip") {
resp.Body = &gzipReader{body: body}
resp.Header.Del("Content-Encoding")
resp.Header.Del("Content-Length")
resp.ContentLength = -1
resp.Uncompressed = true
}
select {
case rc.ch <- responseAndError{res: resp}:
case <-rc.callerGone:
return
}
// Before looping back to the top of this function and peeking on
// the bufio.Reader, wait for the caller goroutine to finish
// reading the response body. (or for cancellation or death)
select {
case bodyEOF := <-waitForBodyRead:
pc.t.setReqCanceler(rc.req, nil) // before pc might return to idle pool
alive = alive &&
bodyEOF &&
!pc.sawEOF &&
pc.wroteRequest() &&
tryPutIdleConn(trace)
if bodyEOF {
eofc <- struct{}{}
}
case <-rc.req.Cancel:
alive = false
pc.t.CancelRequest(rc.req)
case <-rc.req.Context().Done():
alive = false
pc.t.cancelRequest(rc.req, rc.req.Context().Err())
case <-pc.closech:
alive = false
}
testHookReadLoopBeforeNextRead()
}
}
pc.readLoop() => get http response(接收Response) pc.writeLoop() => send http request(发送Request)
注意如下代码段(接收Response)：
rc := <-pc.reqch
trace := httptrace.ContextClientTrace(rc.req.Context())
var resp *Response
if err == nil {
resp, err = pc.readResponse(rc, trace)
} else {
err = transportReadFromServerError{err}
closeErr = err
}
...
// readResponse reads an HTTP response (or two, in the case of "Expect:
// 100-continue") from the server. It returns the final non-100 one.
// trace is optional.
func (pc *persistConn) readResponse(rc requestAndChan, trace *httptrace.ClientTrace) (resp *Response, err error) {
if trace != nil && trace.GotFirstResponseByte != nil {
if peek, err := pc.br.Peek(1); err == nil && len(peek) == 1 {
trace.GotFirstResponseByte()
}
}
num1xx := 0 // number of informational 1xx headers received
const max1xxResponses = 5 // arbitrary bound on number of informational responses
continueCh := rc.continueCh
for {
resp, err = ReadResponse(pc.br, rc.req)
if err != nil {
return
}
resCode := resp.StatusCode
if continueCh != nil {
if resCode == 100 {
if trace != nil && trace.Got100Continue != nil {
trace.Got100Continue()
}
continueCh <- struct{}{}
continueCh = nil
} else if resCode >= 200 {
close(continueCh)
continueCh = nil
}
}
is1xx := 100 <= resCode && resCode <= 199
// treat 101 as a terminal status, see issue 26161
is1xxNonTerminal := is1xx && resCode != StatusSwitchingProtocols
if is1xxNonTerminal {
num1xx++
if num1xx > max1xxResponses {
return nil, errors.New("net/http: too many 1xx informational responses")
}
pc.readLimit = pc.maxHeaderResponseSize() // reset the limit
if trace != nil && trace.Got1xxResponse != nil {
if err := trace.Got1xxResponse(resCode, textproto.MIMEHeader(resp.Header)); err != nil {
return nil, err
}
}
continue
}
break
}
if resp.isProtocolSwitch() {
resp.Body = newReadWriteCloserBody(pc.br, pc.conn)
}
resp.TLS = pc.tlsState
return
}
// ReadResponse reads and returns an HTTP response from r.
// The req parameter optionally specifies the Request that corresponds
// to this Response. If nil, a GET request is assumed.
// Clients must call resp.Body.Close when finished reading resp.Body.
// After that call, clients can inspect resp.Trailer to find key/value
// pairs included in the response trailer.
func ReadResponse(r *bufio.Reader, req *Request) (*Response, error) {
tp := textproto.NewReader(r)
resp := &Response{
Request: req,
}
// Parse the first line of the response.
line, err := tp.ReadLine()
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return nil, err
}
if i := strings.IndexByte(line, ' '); i == -1 {
return nil, &badStringError{"malformed HTTP response", line}
} else {
resp.Proto = line[:i]
resp.Status = strings.TrimLeft(line[i+1:], " ")
}
statusCode := resp.Status
if i := strings.IndexByte(resp.Status, ' '); i != -1 {
statusCode = resp.Status[:i]
}
if len(statusCode) != 3 {
return nil, &badStringError{"malformed HTTP status code", statusCode}
}
resp.StatusCode, err = strconv.Atoi(statusCode)
if err != nil || resp.StatusCode < 0 {
return nil, &badStringError{"malformed HTTP status code", statusCode}
}
var ok bool
if resp.ProtoMajor, resp.ProtoMinor, ok = ParseHTTPVersion(resp.Proto); !ok {
return nil, &badStringError{"malformed HTTP version", resp.Proto}
}
// Parse the response headers.
mimeHeader, err := tp.ReadMIMEHeader()
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return nil, err
}
resp.Header = Header(mimeHeader)
fixPragmaCacheControl(resp.Header)
err = readTransfer(resp, r)
if err != nil {
return nil, err
}
return resp, nil
}
这里可以看到ReadResponse即为读取TCP连接解析HTTP协议，并构建http.Response内容返回
在readLoop成功返回http.Response之后，会将Response塞到pc.reqch.ch管道中(case rc.ch <- responseAndError{res: resp})，如下：文章来源：https://www.toymoban.com/news/detail-669752.html
func (pc *persistConn) readLoop() {
...
alive := true
for alive {
...
rc := <-pc.reqch
trace := httptrace.ContextClientTrace(rc.req.Context())
var resp *Response
if err == nil {
resp, err = pc.readResponse(rc, trace)
} else {
err = transportReadFromServerError{err}
closeErr = err
}
bodyWritable := resp.bodyIsWritable()
hasBody := rc.req.Method != "HEAD" && resp.ContentLength != 0
...
if resp.Close || rc.req.Close || resp.StatusCode <= 199 || bodyWritable {
// Don't do keep-alive on error if either party requested a close
// or we get an unexpected informational (1xx) response.
// StatusCode 100 is already handled above.
alive = false
}
...
resp.Body = body
if rc.addedGzip && strings.EqualFold(resp.Header.Get("Content-Encoding"), "gzip") {
resp.Body = &gzipReader{body: body}
resp.Header.Del("Content-Encoding")
resp.Header.Del("Content-Length")
resp.ContentLength = -1
resp.Uncompressed = true
}
select {
case rc.ch <- responseAndError{res: resp}:
case <-rc.callerGone:
return
}
...
}
}
而pc.roundTrip会读取该channel(case re := <-resc)，并返回http.Response，如下：文章来源地址https://www.toymoban.com/news/detail-669752.html
func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
...
resc := make(chan responseAndError)
pc.reqch <- requestAndChan{
req: req.Request,
ch: resc,
addedGzip: requestedGzip,
continueCh: continueCh,
callerGone: gone,
}
var respHeaderTimer <-chan time.Time
cancelChan := req.Request.Cancel
ctxDoneChan := req.Context().Done()
for {
testHookWaitResLoop()
select {
case re := <-resc:
if (re.res == nil) == (re.err == nil) {
panic(fmt.Sprintf("internal error: exactly one of res or err should be set; nil=%v", re.res == nil))
}
if debugRoundTrip {
req.logf("resc recv: %p, %T/%#v", re.res, re.err, re.err)
}
if re.err != nil {
return nil, pc.mapRoundTripError(req, startBytesWritten, re.err)
}
return re.res, nil
}
}
}
golang http transport结构体关键字段
http.Client
- Timeout：http client请求生命周期超时设置(包括连接建立，发请求，重定向，以及Response body读取等所有阶段)
- RoundTrip(http.Transport实现)
- MaxIdleConns：控制所有hosts的空闲连接最大数目(Zero means no limit.)
- MaxIdleConnsPerHost：控制某个host的空闲连接(keep-alives)最大数目(设置为0，则默认DefaultMaxIdleConnsPerHost=2)
- MaxConnsPerHost：控制某个host的所有连接，包括创建中，正在使用的，以及空闲的连接(including connections in the dialing, active, and idle states)。一旦超过限制，dial会阻塞(Zero means no limit)
- IdleConnTimeout：空闲连接(keep-alives)超时时间
- h2transport：HTTP/2协议对应的transport
- ForceAttemptHTTP2：当Dial, DialTLS, or DialContext func or TLSClientConfig提供时，默认情况下会禁止HTTP/2协议。当使用自定义的这些配置时，需要设置ForceAttemptHTTP2字段开启HTTP2
- DisableKeepAlives：禁止HTTP keep-alives，一个连接只用于一次请求(注意区分TCP keep-alives。HTTP keep-alives用于连接复用；TCP keep-alives用于连接保活)
- idleConn(map[connectMethodKey][]*persistConn)：空闲连接池
- idleConnWait(map[connectMethodKey]wantConnQueue)：等待建立的连接池
- connsPerHost(map[connectMethodKey]int)：表示每个host(connectMethodKey)的目前连接个数
- connsPerHostWait(map[connectMethodKey]wantConnQueue)：表示每个host(connectMethodKey)等待建立的连接请求
- (net.Dialer)DialContext：指定底层TCP连接的创建函数
- Timeout：连接建立的超时时间，操作系统的超时时间一般为3 minutes
- Deadline：与Timeout作用类似，只不过限制了确定的超时时刻
- LocalAddr：本地地址，TCP四元组的原始IP地址
- DualStack(Deprecated)：enabled RFC 6555 Fast Fallback Feature
- FallbackDelay：IPv6连接建立的等待时间，如果超时，则会切换到IPv4(A negative value disables Fast Fallback support.)
- KeepAlive：设置了活跃连接的TCP keep-alive探针间隔，需要协议层以及操作系统支持(If zero, keep-alive probes are sent with a default value(currently 15 seconds))
调用关键流程
- step1 - http.NewRequest(method, url string, body io.Reader) 创建请求
- step2 - http.Client.Do(req *Request) 发送请求&接收应答
整个http.Client.Do逻辑分为两道，第一道执行send发送请求接收Response，关闭Req.Body；第二层对请求执行重定向等操作(若需要redirect)，并关闭Resp.Body
http.Client.Do(req) => send(ireq *Request, rt RoundTripper, deadline time.Time)
-> setRequestCancel(req, rt, deadline) 设置请求超时时间
-> http.Client.RoundTrip(req)
=> http.Client.RoundTrip(req)
-> http.Transport.t.getConn(treq, cm) 获取连接(新创建的 or 复用空闲连接)
-> http.Transport.queueForIdleConn(w *wantConn) 获取空闲连接
-> http.Transport.dialConnFor(w *wantConn) -> http.Transport.dialConn(ctx context.Context, cm connectMethod) 创建新连接
-> http.Transport.dial(ctx context.Context, network, addr string) -> http.Transport.DialContext(net.Dialer.DialContext)
-> http.persistConn.readLoop() read http.Response(读取响应内容，并构建http.Response)
-> http.persistConn.writeLoop() write http.Request(发送请求)
-> http.persistConn.roundTrip(treq) 发送请求，读取Response并返回
- step3 - http.Response.Body.Close() 关闭应答Body
Refs
- duyanghao kubernetes-reading-notes
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