golang 版本：1.12.9
简单的HTTP服务器代码：
package main
import (
"net/http"
)
type TestHandler struct {
str string
}
func (th *TestHandler)ServeHTTP(w http.ResponseWriter, r *http.Request){
w.Write([]byte(string(th.str+",welcome")))
}
func main(){
http.Handle("/", &TestHandler{"Hi,Stranger"})
http.HandleFunc("/test",func(w http.ResponseWriter,r *http.Request){
w.Write([]byte("Hi,Tester"))
})
http.ListenAndServe(":8000",nil)}
在浏览器输入“http://127.0.0.1:8000”得到输出“Hi,Stranger,welcome”；输入“http://127.0.0.1:8000/test”得到输出“Hi,Tester”
handler的注册
handler的相关方法如下：
func NewServeMux() *ServeMux func (mux *ServeMux) Handle(pattern string, handler Handler) //注册handler func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) //注册handler func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) //在mux.m中根据pattern查找handler func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) //handler的具体实现
http使用handler定义请求的路径以及请求的处理。每个handler都必须实现ServeHTTP方法，该方法将请求分发到不同的handler进行处理，每个handler处理一条请求路径。有两种注册handler的方式：http.Handle和http.HandleFunc，两种实现本质上是一致的，前者需要明确写出ServeHTTP方法的实现，后者由内置方法实现(见下文)。
Handler的接口定义如下：
// net/http/server.gotype Handler interface {
ServeHTTP(ResponseWriter, *Request)
}
http.HandleFunc的第二个参数被定义为HandlerFunc，实现了Handler接口。
// net/http/server.gotype HandlerFunc func(ResponseWriter, *Request)
// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
f(w, r)
}
当http.ListenAndServe的第二个参数为nil，则使用http.Handle和http.HandleFunc方法注册的handler，默认保存在http.DefaultServeMux.m中(注册方法为ServeMux.Handle/ServeMux.HandleFunc)。当http server接收到一个request时，会在serverHandler.ServeHTTP中调用DefaultServeMux.ServeHTTP来处理接收到的request，分为两步：
-
- 调用ServeMux.Handler函数，在ServeMux.m中根据pattern遍历查合适的handler
- 调用handler的ServeHTTP方法
serverHandler.ServeHTTP的源码如下：
// net/http/server.go
func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) { // 如果有自注册的handler则使用自注册的，否则使用默认的handler处理请求
handler := sh.srv.Handler
if handler == nil {
handler = DefaultServeMux
}
if req.RequestURI == "*" && req.Method == "OPTIONS" {
handler = globalOptionsHandler{}
}
handler.ServeHTTP(rw, req)
}
DefaultServeMux的结构体定义如下：
var DefaultServeMux = &defaultServeMuxvar defaultServeMux ServeMux
// net/http/server.go
type ServeMux struct {
mu sync.RWMutex
m map[string]muxEntry
es []muxEntry // slice of entries sorted from longest to shortest.
hosts bool // whether any patterns contain hostnames
}
默认的handler的ServeHTTP方法实现如下，主要实现查找handler并处理请求
func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
if r.RequestURI == "*" {
if r.ProtoAtLeast(1, 1) {
w.Header().Set("Connection", "close")
}
w.WriteHeader(StatusBadRequest)
return
} // 根据请求的路径查找注册的handler
h, _ := mux.Handler(r) // 调用注册的handler处理请求,对应上面例子的 // http.HandleFunc("/test",func(w http.ResponseWriter,r *http.Request){w.Write([]byte("Hi,Tester"))})
h.ServeHTTP(w, r)
}
// 本函数根据请求中的路径找到合适的handler或者重定向(请求路径格式不正确)func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
// CONNECT requests are not canonicalized. // 对CONNECT请求的处理,代理场景
if r.Method == "CONNECT" {
// If r.URL.Path is /tree and its handler is not registered,
// the /tree -> /tree/ redirect applies to CONNECT requests
// but the path canonicalization does not. // redirectToPathSlash函数主要用于自动检测是否重定向URL并修改重定向URL路径，当注册的URL路径为/tree/,而请求URL路径为/tree， // redirectToPathSlash函数无法在mux.m中查找注册的handler，则将设请求URL设置为/tree/
if u, ok := mux.redirectToPathSlash(r.URL.Host, r.URL.Path, r.URL); ok {
return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
}
return mux.handler(r.Host, r.URL.Path)
}
// All other requests have any port stripped and path cleaned
// before passing to mux.handler.
host := stripHostPort(r.Host)
path := cleanPath(r.URL.Path)
// 非代理场景重定向的处理，与"CONNECT"逻辑相同
if u, ok := mux.redirectToPathSlash(host, path, r.URL); ok {
return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
}
// 如果请求路径不等于处理后的路径，如请求路径为"//test/",处理后的路径为"/test/",执行重定向并返回URL路径，重定向 // 通过http.redirectHandler.ServeHTTP函数进行处理，如下： /*
< HTTP/1.1 301 Moved Permanently
< Content-Type: text/html; charset=utf-8
< Location: /test/
< Date: Fri, 06 Dec 2019 03:35:59 GMT
< Content-Length: 41
<
<a href="/test/">Moved Permanently</a>.
*/
if path != r.URL.Path {
_, pattern = mux.handler(host, path)
url := *r.URL
url.Path = path
return RedirectHandler(url.String(), StatusMovedPermanently), pattern
}
// 在mux.m和mux.es中根据host/url.path找到对应的handler
return mux.handler(host, r.URL.Path)
}
func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {
Redirect(w, r, rh.url, rh.code)
}
通常使用http.HandleFunc注册handler，使用DefaultServeMux的方法分发处理请求即可。也可以通过http.NewServeMux()创建一个自定义的serverHandler，并实现Serve HTTP方法。
import (
"net/http"
)
type TestHandler struct {
str string
}
func (th *TestHandler)ServeHTTP(w http.ResponseWriter, r *http.Request){
w.Write([]byte(string(th.str+",welcome")))
}
func main(){
serverHandler := http.NewServeMux()
serverHandler.Handle("/", &TestHandler{"Hi,Stranger"})
serverHandler.HandleFunc("/test",func(w http.ResponseWriter,r *http.Request){
w.Write([]byte("Hi,Tester"))
})
http.ListenAndServe(":8000",serverHandler)
}
http.server
调用下面函数进行监听，主要创建监听socket并接收该socket上的连接。通常调用如下接口即可：
func ListenAndServe(addr string, handler Handler) error {
server := &Server{Addr: addr, Handler: handler}
return server.ListenAndServe()
}
一个Server结构体表示一个启用监听端口的真实服务
type Server struct {
Addr string // TCP address to listen on, ":http" if empty
Handler Handler // handler to invoke, http.DefaultServeMux if nil
// TLSConfig optionally provides a TLS configuration for use
// by ServeTLS and ListenAndServeTLS. Note that this value is
// cloned by ServeTLS and ListenAndServeTLS, so it's not
// possible to modify the configuration with methods like
// tls.Config.SetSessionTicketKeys. To use
// SetSessionTicketKeys, use Server.Serve with a TLS Listener
// instead.
TLSConfig *tls.Config
// ReadTimeout is the maximum duration for reading the entire
// request, including the body.
//
// Because ReadTimeout does not let Handlers make per-request
// decisions on each request body's acceptable deadline or
// upload rate, most users will prefer to use
// ReadHeaderTimeout. It is valid to use them both.
ReadTimeout time.Duration
// ReadHeaderTimeout is the amount of time allowed to read
// request headers. The connection's read deadline is reset
// after reading the headers and the Handler can decide what
// is considered too slow for the body. If ReadHeaderTimeout
// is zero, the value of ReadTimeout is used. If both are
// zero, there is no timeout.
ReadHeaderTimeout time.Duration
// WriteTimeout is the maximum duration before timing out
// writes of the response. It is reset whenever a new
// request's header is read. Like ReadTimeout, it does not
// let Handlers make decisions on a per-request basis.
WriteTimeout time.Duration
// IdleTimeout is the maximum amount of time to wait for the
// next request when keep-alives are enabled. If IdleTimeout
// is zero, the value of ReadTimeout is used. If both are
// zero, there is no timeout.
IdleTimeout time.Duration
// MaxHeaderBytes controls the maximum number of bytes the
// server will read parsing the request header's keys and
// values, including the request line. It does not limit the
// size of the request body.
// If zero, DefaultMaxHeaderBytes is used.
MaxHeaderBytes int
// TLSNextProto optionally specifies a function to take over
// ownership of the provided TLS connection when an NPN/ALPN
// protocol upgrade has occurred. The map key is the protocol
// name negotiated. The Handler argument should be used to
// handle HTTP requests and will initialize the Request's TLS
// and RemoteAddr if not already set. The connection is
// automatically closed when the function returns.
// If TLSNextProto is not nil, HTTP/2 support is not enabled
// automatically.
TLSNextProto map[string]func(*Server, *tls.Conn, Handler)
// ConnState specifies an optional callback function that is
// called when a client connection changes state. See the
// ConnState type and associated constants for details.
ConnState func(net.Conn, ConnState)
// ErrorLog specifies an optional logger for errors accepting
// connections, unexpected behavior from handlers, and
// underlying FileSystem errors.
// If nil, logging is done via the log package's standard logger.
ErrorLog *log.Logger
// BaseContext optionally specifies a function that returns
// the base context for incoming requests on this server.
// The provided Listener is the specific Listener that's
// about to start accepting requests.
// If BaseContext is nil, the default is context.Background().
// If non-nil, it must return a non-nil context.
BaseContext func(net.Listener) context.Context
// ConnContext optionally specifies a function that modifies
// the context used for a new connection c. The provided ctx
// is derived from the base context and has a ServerContextKey
// value.
ConnContext func(ctx context.Context, c net.Conn) context.Context
disableKeepAlives int32 // accessed atomically.
inShutdown int32 // accessed atomically (non-zero means we're in Shutdown)
nextProtoOnce sync.Once // guards setupHTTP2_* init
nextProtoErr error // result of http2.ConfigureServer if used
mu sync.Mutex
listeners map[*net.Listener]struct{}
activeConn map[*conn]struct{}
doneChan chan struct{}
onShutdown []func()
}
ListenAndServe在创建监听socket后调用Serve等待连接
func (srv *Server) ListenAndServe() error { // 服务器调用Server.Close或Server.Shutdown关闭连接时会设置shuttingDown为1，表示该服务正在停止，不可提供服务。 // Close会直接关闭底层tcp连接，Shutdown则会调用服务提供的函数Server.onShutdown平滑关闭。推荐使用Shutdown
if srv.shuttingDown() {
return ErrServerClosed
}
addr := srv.Addr
if addr == "" {
addr = ":http"
}
ln, err := net.Listen("tcp", addr)
if err != nil {
return err
}
return srv.Serve(ln)
}
ListenAndServeTLS与ListenAndServe类似，只是入参多了证书参数
func (srv *Server) ListenAndServeTLS(certFile, keyFile string) error {
if srv.shuttingDown() {
return ErrServerClosed
}
addr := srv.Addr
if addr == "" {
addr = ":https"
}
ln, err := net.Listen("tcp", addr)
if err != nil {
return err
}
defer ln.Close()
return srv.ServeTLS(ln, certFile, keyFile)
}
ServeTLS函数中会调用tls.NewListener创建一个tls类型的监听socket，后续会调用tls的Accetp函数接收客户端连接
func (srv *Server) ServeTLS(l net.Listener, certFile, keyFile string) error {
// Setup HTTP/2 before srv.Serve, to initialize srv.TLSConfig
// before we clone it and create the TLS Listener.
if err := srv.setupHTTP2_ServeTLS(); err != nil {
return err
}
config := cloneTLSConfig(srv.TLSConfig)
if !strSliceContains(config.NextProtos, "http/1.1") {
config.NextProtos = append(config.NextProtos, "http/1.1")
}
configHasCert := len(config.Certificates) > 0 || config.GetCertificate != nil
if !configHasCert || certFile != "" || keyFile != "" {
var err error
config.Certificates = make([]tls.Certificate, 1)
config.Certificates[0], err = tls.LoadX509KeyPair(certFile, keyFile)
if err != nil {
return err
}
}
tlsListener := tls.NewListener(l, config)
return srv.Serve(tlsListener)
}
// src/crypto/tls/tls.go// tls的Accept仅仅在处理Server函数是增加了证书相关的参数func (l *listener) Accept() (net.Conn, error) {
c, err := l.Listener.Accept()
if err != nil {
return nil, err
}
return Server(c, l.config), nil
}
Serve主要实现如下。通过Accept与客户端创建连接后，通过newConn函数初始化一个HTTP连接，该连接包含HTTP的描述(监听地址，URL等)和一个TCP连接，然后处理来自客户的HTTP请求。
func (srv *Server) Serve(l net.Listener) error {
...
ctx := context.WithValue(baseCtx, ServerContextKey, srv)
for { // Accept()返回底层TCP的连接
rw, e := l.Accept()
if e != nil {
select {
case <-srv.getDoneChan():
return ErrServerClosed
default:
}
if ne, ok := e.(net.Error); ok && ne.Temporary() { // 处理accept因为网络失败之后的等待时间
if tempDelay == 0 {
tempDelay = 5 * time.Millisecond
} else {
tempDelay *= 2
}
if max := 1 * time.Second; tempDelay > max {
tempDelay = max
}
srv.logf("http: Accept error: %v; retrying in %v", e, tempDelay)
time.Sleep(tempDelay)
continue
}
return e
}
if cc := srv.ConnContext; cc != nil {
ctx = cc(ctx, rw)
if ctx == nil {
panic("ConnContext returned nil")
}
}
tempDelay = 0 //构造HTTP连接
c := srv.newConn(rw)
c.setState(c.rwc, StateNew) // before Serve can return //在另外的goroutine中处理基于该TCP的HTTP请求，本goroutine可以继续accept TCP连接
go c.serve(ctx)
}
}
Accept返回的底层的连接结构如下
type Conn interface {
// Read reads data from the connection.
// Read can be made to time out and return an Error with Timeout() == true
// after a fixed time limit; see SetDeadline and SetReadDeadline.
Read(b []byte) (n int, err error)
// Write writes data to the connection.
// Write can be made to time out and return an Error with Timeout() == true
// after a fixed time limit; see SetDeadline and SetWriteDeadline.
Write(b []byte) (n int, err error)
// Close closes the connection.
// Any blocked Read or Write operations will be unblocked and return errors.
Close() error
// LocalAddr returns the local network address.
LocalAddr() Addr
// RemoteAddr returns the remote network address.
RemoteAddr() Addr
// SetDeadline sets the read and write deadlines associated
// with the connection. It is equivalent to calling both
// SetReadDeadline and SetWriteDeadline.
//
// A deadline is an absolute time after which I/O operations
// fail with a timeout (see type Error) instead of
// blocking. The deadline applies to all future and pending
// I/O, not just the immediately following call to Read or
// Write. After a deadline has been exceeded, the connection
// can be refreshed by setting a deadline in the future.
//
// An idle timeout can be implemented by repeatedly extending
// the deadline after successful Read or Write calls.
//
// A zero value for t means I/O operations will not time out.
//
// Note that if a TCP connection has keep-alive turned on,
// which is the default unless overridden by Dialer.KeepAlive
// or ListenConfig.KeepAlive, then a keep-alive failure may
// also return a timeout error. On Unix systems a keep-alive
// failure on I/O can be detected using
// errors.Is(err, syscall.ETIMEDOUT).
SetDeadline(t time.Time) error
// SetReadDeadline sets the deadline for future Read calls
// and any currently-blocked Read call.
// A zero value for t means Read will not time out.
SetReadDeadline(t time.Time) error
// SetWriteDeadline sets the deadline for future Write calls
// and any currently-blocked Write call.
// Even if write times out, it may return n > 0, indicating that
// some of the data was successfully written.
// A zero value for t means Write will not time out.
SetWriteDeadline(t time.Time) error
}
实现如上接口的有tcpsock的TCPConn以及unixsock的UnixConn，通常使用TCPConn
type TCPConn struct {
conn
}
type UnixConn struct {
conn
}
newConn生成的HTTP结构体如下，它表示一条基于TCP的HTTP连接，封装了3个重要的数据结构：server表示HTTP server的"server"；rwc表示底层连接结构体rwc net.Conn；r用于读取http数据的connReader（从rwc读取数据）。后续的request和response都基于该结构体
type conn struct {
// server is the server on which the connection arrived.
// Immutable; never nil.
server *Server
// cancelCtx cancels the connection-level context.
cancelCtx context.CancelFunc
// rwc is the underlying network connection.
// This is never wrapped by other types and is the value given out
// to CloseNotifier callers. It is usually of type *net.TCPConn or
// *tls.Conn.
rwc net.Conn
// remoteAddr is rwc.RemoteAddr().String(). It is not populated synchronously
// inside the Listener's Accept goroutine, as some implementations block.
// It is populated immediately inside the (*conn).serve goroutine.
// This is the value of a Handler's (*Request).RemoteAddr.
remoteAddr string
// tlsState is the TLS connection state when using TLS.
// nil means not TLS.
tlsState *tls.ConnectionState
// werr is set to the first write error to rwc.
// It is set via checkConnErrorWriter{w}, where bufw writes.
werr error
// r is bufr's read source. It's a wrapper around rwc that provides
// io.LimitedReader-style limiting (while reading request headers)
// and functionality to support CloseNotifier. See *connReader docs.
r *connReader
// bufr reads from r.
bufr *bufio.Reader
// bufw writes to checkConnErrorWriter{c}, which populates werr on error.
bufw *bufio.Writer
// lastMethod is the method of the most recent request
// on this connection, if any.
lastMethod string
curReq atomic.Value // of *response (which has a Request in it)
curState struct{ atomic uint64 } // packed (unixtime<<8|uint8(ConnState))
// mu guards hijackedv
mu sync.Mutex
// hijackedv is whether this connection has been hijacked
// by a Handler with the Hijacker interface.
// It is guarded by mu.
hijackedv bool
}
connReader中的conn就是上面表示http连接的结构体
type connReader struct {
conn *conn
mu sync.Mutex // guards following
hasByte bool
byteBuf [1]byte
cond *sync.Cond
inRead bool
aborted bool // set true before conn.rwc deadline is set to past
remain int64 // bytes remaining
}
在下面的server函数中处理请求并返回响应
func (c *conn) serve(ctx context.Context) {
c.remoteAddr = c.rwc.RemoteAddr().String()
ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
defer func() {
if err := recover(); err != nil && err != ErrAbortHandler {
const size = 64 << 10
buf := make([]byte, size)
buf = buf[:runtime.Stack(buf, false)]
c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
}
if !c.hijacked() {
c.close()
c.setState(c.rwc, StateClosed)
}
}()
// 处理ServeTLS accept的连接
if tlsConn, ok := c.rwc.(*tls.Conn); ok {
if d := c.server.ReadTimeout; d != 0 { // 设置TCP的读超时时间
c.rwc.SetReadDeadline(time.Now().Add(d))
}
if d := c.server.WriteTimeout; d != 0 { // 设置TCP的写超时时间
c.rwc.SetWriteDeadline(time.Now().Add(d))
} // tls协商并判断协商结果
if err := tlsConn.Handshake(); err != nil {
// If the handshake failed due to the client not speaking
// TLS, assume they're speaking plaintext HTTP and write a
// 400 response on the TLS conn's underlying net.Conn.
if re, ok := err.(tls.RecordHeaderError); ok && re.Conn != nil && tlsRecordHeaderLooksLikeHTTP(re.RecordHeader) {
io.WriteString(re.Conn, "HTTP/1.0 400 Bad Request\r\n\r\nClient sent an HTTP request to an HTTPS server.\n")
re.Conn.Close()
return
}
c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), err)
return
}
c.tlsState = new(tls.ConnectionState)
*c.tlsState = tlsConn.ConnectionState() // 用于判断是否使用TLS的NPN扩展协商出非http/1.1和http/1.0的上层协议，如果存在则使用server.TLSNextProto处理请求
if proto := c.tlsState.NegotiatedProtocol; validNPN(proto) {
if fn := c.server.TLSNextProto[proto]; fn != nil {
h := initNPNRequest{ctx, tlsConn, serverHandler{c.server}}
fn(c.server, tlsConn, h)
}
return
}
}
// 下面处理HTTP/1.x的请求
ctx, cancelCtx := context.WithCancel(ctx)
c.cancelCtx = cancelCtx
defer cancelCtx()
// 为c.bufr创建read源，使用sync.pool提高存取效率
c.r = &connReader{conn: c} // read buf长度默认为4096,创建ioReader为c.r的bufio.Reader。用于读取HTTP的request
c.bufr = newBufioReader(c.r) // c.bufw默认长度为4096，4<<10=4096，用于发送response
c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
// 循环处理HTTP请求
for { // 处理请求并返回封装好的响应
w, err := c.readRequest(ctx) // 判断是否有读取过数据,如果读取过数据则设置TCP状态为active
if c.r.remain != c.server.initialReadLimitSize() {
// If we read any bytes off the wire, we're active.
c.setState(c.rwc, StateActive)
} // 处理http请求错误
if err != nil {
const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"
switch {
case err == errTooLarge:
// Their HTTP client may or may not be
// able to read this if we're
// responding to them and hanging up
// while they're still writing their
// request. Undefined behavior.
const publicErr = "431 Request Header Fields Too Large"
fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
c.closeWriteAndWait()
return
// 直接return会断开底层TCP连接(GC？)
case isUnsupportedTEError(err):
// Respond as per RFC 7230 Section 3.3.1 which says,
// A server that receives a request message with a
// transfer coding it does not understand SHOULD
// respond with 501 (Unimplemented).
code := StatusNotImplemented
// We purposefully aren't echoing back the transfer-encoding's value,
// so as to mitigate the risk of cross side scripting by an attacker.
fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s%sUnsupported transfer encoding", code, StatusText(code), errorHeaders)
return
case isCommonNetReadError(err):
return // don't reply
default:
publicErr := "400 Bad Request"
if v, ok := err.(badRequestError); ok {
publicErr = publicErr + ": " + string(v)
}
fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
return
}
}
// Expect 100 Continue support
req := w.req // 如果http首部包含"100-continue"请求
if req.expectsContinue() { // "100-continue"的首部要求http1.1版本以上，且http.body长度不为0
if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
// Wrap the Body reader with one that replies on the connection
req.Body = &expectContinueReader{readCloser: req.Body, resp: w}
} // 非"100-continue"但首部包含"Expect"字段的请求为非法请求
} else if req.Header.get("Expect") != "" {
w.sendExpectationFailed()
return
}
// curReq保存了当前的response，当前代码中主要用于在读失败后调用response中的closeNotifyCh传递信号，此时连接断开
c.curReq.Store(w)
// 判断是否有后续的数据，req.Body在http.readTransfer函数中设置为http.body类型，registerOnHitEOF注册的就是 // 遇到EOF时执行的函数http.body.onHitEOF
if requestBodyRemains(req.Body) {
registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
} else { // 如果没有后续的数据，调用下面函数在新的goroutine中阻塞等待数据的到来，通知finishRequest
w.conn.r.startBackgroundRead()
}
// HTTP cannot have multiple simultaneous active requests.[*]
// Until the server replies to this request, it can't read another,
// so we might as well run the handler in this goroutine.
// [*] Not strictly true: HTTP pipelining. We could let them all process
// in parallel even if their responses need to be serialized.
// But we're not going to implement HTTP pipelining because it
// was never deployed in the wild and the answer is HTTP/2. // 通过请求找到匹配的handler，然后处理请求并发送响应
serverHandler{c.server}.ServeHTTP(w, w.req)
w.cancelCtx()
if c.hijacked() {
return
} // 该函数中会结束HTTP请求，发送response
w.finishRequest() // 判断是否需要重用底层TCP连接，即是否退出本函数的for循环，推出for循环将断开连接
if !w.shouldReuseConnection() { // 不可重用底层连接时,如果请求数据过大或设置提前取消读取数据，则调用closeWriteAndWait平滑关闭TCP连接
if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
c.closeWriteAndWait()
}
return
} // 重用连接，设置底层状态为idle
c.setState(c.rwc, StateIdle)
c.curReq.Store((*response)(nil))
// 如果没有通过SetKeepAlivesEnabled设置HTTP keepalive或底层连接已经通过如Server.Close关闭，则直接退出
if !w.conn.server.doKeepAlives() {
// We're in shutdown mode. We might've replied
// to the user without "Connection: close" and
// they might think they can send another
// request, but such is life with HTTP/1.1.
return
}
if d := c.server.idleTimeout(); d != 0 { // 如果设置了idle状态超时时间，则调用SetReadDeadline设置底层连接deadline，并调用bufr.Peek等待请求
c.rwc.SetReadDeadline(time.Now().Add(d))
if _, err := c.bufr.Peek(4); err != nil {
return
}
}
c.rwc.SetReadDeadline(time.Time{})
}
}
readRequest函数处理http请求
func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
if c.hijacked() {
return nil, ErrHijacked
}
var (
wholeReqDeadline time.Time // or zero if none
hdrDeadline time.Time // or zero if none
)
t0 := time.Now() // 设置读取HTTP的超时时间
if d := c.server.readHeaderTimeout(); d != 0 {
hdrDeadline = t0.Add(d)
} // 设置读取整个HTTP的超时时间
if d := c.server.ReadTimeout; d != 0 {
wholeReqDeadline = t0.Add(d)
} // 通过SetReadDeadline设置TCP读超时时间
c.rwc.SetReadDeadline(hdrDeadline)
if d := c.server.WriteTimeout; d != 0 { // 通过defer设置TCP写超时时间，本函数主要处理读请求，在本函数处理完request之后再设置写超时时间
defer func() {
c.rwc.SetWriteDeadline(time.Now().Add(d))
}()
}
// 设置读取请求的最大字节数，为DefaultMaxHeaderBytes+4096=1052672，用于防止超大报文攻击
c.r.setReadLimit(c.server.initialReadLimitSize()) // 处理老设备的client
if c.lastMethod == "POST" {
// RFC 7230 section 3.5 Message Parsing Robustness tolerance for old buggy clients.
peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
c.bufr.Discard(numLeadingCRorLF(peek))
} // 从bufr读取request，并返回结构体格式的请求
req, err := readRequest(c.bufr, keepHostHeader)
if err != nil { // 如果读取的报文超过限制，则返回错误
if c.r.hitReadLimit() {
return nil, errTooLarge
}
return nil, err
}
// 判断是否是go服务所支持的HTTP/1.x的请求
if !http1ServerSupportsRequest(req) {
return nil, badRequestError("unsupported protocol version")
}
c.lastMethod = req.Method
c.r.setInfiniteReadLimit()
hosts, haveHost := req.Header["Host"]
isH2Upgrade := req.isH2Upgrade() // 判断是否需要Host首部字段
if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade && req.Method != "CONNECT" {
return nil, badRequestError("missing required Host header")
} // 多个Host首部字段
if len(hosts) > 1 {
return nil, badRequestError("too many Host headers")
} // 非法Host首部字段值
if len(hosts) == 1 && !httpguts.ValidHostHeader(hosts[0]) {
return nil, badRequestError("malformed Host header")
} // 判断首部字段值是否有非法字符
for k, vv := range req.Header {
if !httpguts.ValidHeaderFieldName(k) {
return nil, badRequestError("invalid header name")
}
for _, v := range vv {
if !httpguts.ValidHeaderFieldValue(v) {
return nil, badRequestError("invalid header value")
}
}
} // 响应报文中不包含Host字段
delete(req.Header, "Host")
ctx, cancelCtx := context.WithCancel(ctx)
req.ctx = ctx
req.RemoteAddr = c.remoteAddr
req.TLS = c.tlsState
if body, ok := req.Body.(*body); ok {
body.doEarlyClose = true
}
// 判断是否超过请求的最大值
if !hdrDeadline.Equal(wholeReqDeadline) {
c.rwc.SetReadDeadline(wholeReqDeadline)
}
w = &response{
conn: c,
cancelCtx: cancelCtx,
req: req,
reqBody: req.Body,
handlerHeader: make(Header),
contentLength: -1,
closeNotifyCh: make(chan bool, 1),
// We populate these ahead of time so we're not
// reading from req.Header after their Handler starts
// and maybe mutates it (Issue 14940)
wants10KeepAlive: req.wantsHttp10KeepAlive(),
wantsClose: req.wantsClose(),
}
if isH2Upgrade {
w.closeAfterReply = true
} // w.cw.res中保存了response的信息，而response中又保存了底层连接conn，后续将通过w.cw.res.conn写数据
w.cw.res = w // 创建2048字节的写bufio，用于发送response
w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)
return w, nil
}
读取HTTP请求，并将其结构化为http.Request
func readRequest(b *bufio.Reader, deleteHostHeader bool) (req *Request, err error) {
// 封装为textproto.Reader，该结构体实现了读取HTTP的相关方法 tp := newTextprotoReader(b) // 初始化一个Request结构体，该函数后续工作就是填充该变量并返回
req = new(Request)
// First line: GET /index.html HTTP/1.0
var s string // ReadLine会调用<textproto.(*Reader).ReadLine->textproto.(*Reader).readLineSlice->bufio.(*Reader).ReadLine-> // bufio.(*Reader).ReadSlic->bufio.(*Reader).fill->http.(*connReader).Read>读取HTTP的请求并填充b.buf，并返回以"\n"作为 // 分隔符的首行字符串
if s, err = tp.ReadLine(); err != nil {
return nil, err
} // putTextprotoReader函数使用sync.pool来保存textproto.Reader变量，通过重用内存来提升在大量HTTP请求下执行效率。 // 对应函数首部的newTextprotoReader
defer func() {
putTextprotoReader(tp)
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
}()
var ok bool // 解析请求方法，请求URL，请求协议
req.Method, req.RequestURI, req.Proto, ok = parseRequestLine(s)
if !ok {
return nil, &badStringError{"malformed HTTP request", s}
} // 判断方法是否包含非法字符
if !validMethod(req.Method) {
return nil, &badStringError{"invalid method", req.Method}
} // 获取请求路径，如HTTP请求为"http://127.0.0.1:8000/test"时，rawurl为"/test"
rawurl := req.RequestURI // 判断HTTP协议版本有效性，通常为支持HTTP/1.x
if req.ProtoMajor, req.ProtoMinor, ok = ParseHTTPVersion(req.Proto); !ok {
return nil, &badStringError{"malformed HTTP version", req.Proto}
}
// CONNECT requests are used two different ways, and neither uses a full URL:
// The standard use is to tunnel HTTPS through an HTTP proxy.
// It looks like "CONNECT www.google.com:443 HTTP/1.1", and the parameter is
// just the authority section of a URL. This information should go in req.URL.Host.
//
// The net/rpc package also uses CONNECT, but there the parameter is a path
// that starts with a slash. It can be parsed with the regular URL parser,
// and the path will end up in req.URL.Path, where it needs to be in order for
// RPC to work. // 处理代理场景，使用"CONNECT"与代理建立连接时会使用完整的URL(带host)
justAuthority := req.Method == "CONNECT" && !strings.HasPrefix(rawurl, "/")
if justAuthority {
rawurl = "http://" + rawurl
}
if req.URL, err = url.ParseRequestURI(rawurl); err != nil {
return nil, err
}
if justAuthority {
// Strip the bogus "http://" back off.
req.URL.Scheme = ""
}
// 解析request首部的key：value
mimeHeader, err := tp.ReadMIMEHeader()
if err != nil {
return nil, err
}
req.Header = Header(mimeHeader)
// RFC 7230, section 5.3: Must treat
// GET /index.html HTTP/1.1
// Host: www.google.com
// and
// GET http://www.google.com/index.html HTTP/1.1
// Host: doesntmatter
// the same. In the second case, any Host line is ignored.
req.Host = req.URL.Host // 如果是上面注释中的第一种需要从req.Header中获取"Host"字段
if req.Host == "" {
req.Host = req.Header.get("Host")
} // "Host"字段仅存在于request中，在接收到之后需要删除首部的Host字段，更多参见该变量注释
if deleteHostHeader {
delete(req.Header, "Host")
}
//处理"Cache-Control"首部
fixPragmaCacheControl(req.Header)
// 判断是否是长连接，如果是，则保持连接，反之则断开并删除"Connection"首部
req.Close = shouldClose(req.ProtoMajor, req.ProtoMinor, req.Header, false)
// 解析首部字段并填充req内容
err = readTransfer(req, b)
if err != nil {
return nil, err
}
// 当HTTP1.1服务尝试解析HTTP2的消息时使用"PRI"方法
if req.isH2Upgrade() {
// Because it's neither chunked, nor declared:
req.ContentLength = -1
// We want to give handlers a chance to hijack the
// connection, but we need to prevent the Server from
// dealing with the connection further if it's not
// hijacked. Set Close to ensure that:
req.Close = true
}
return req, nil
}
func shouldClose(major, minor int, header Header, removeCloseHeader bool) bool {
// HTTP/1.x以下不支持"connection"指定长连接 if major < 1 {
return true
}
conv := header["Connection"] // 如果首部包含"Connection: close"则断开连接
hasClose := httpguts.HeaderValuesContainsToken(conv, "close") // 使用HTTP/1.0时，如果包含"Connection: close"或不包含"Connection: keep-alive"，则使用短连接； // HTTP/1.1中不指定"Connection"，默认使用长连接
if major == 1 && minor == 0 {
return hasClose || !httpguts.HeaderValuesContainsToken(conv, "keep-alive")
}
// 如果使用非长连接，且需要删除首部中的Connection字段。在经过proxy或gateway时必须移除Connection首部字段
if hasClose && removeCloseHeader {
header.Del("Connection")
}
return hasClose
}
func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
t := &transferReader{RequestMethod: "GET"}
// Unify input
isResponse := false
switch rr := msg.(type) { // 消息为响应时的赋值
case *Response:
t.Header = rr.Header
t.StatusCode = rr.StatusCode
t.ProtoMajor = rr.ProtoMajor
t.ProtoMinor = rr.ProtoMinor // 响应中不需要Connection首部字段，下面函数最后一个参数设置为true，删除该首部字段
t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
isResponse = true
if rr.Request != nil {
t.RequestMethod = rr.Request.Method
} // 消息为请求时的赋值
case *Request:
t.Header = rr.Header
t.RequestMethod = rr.Method
t.ProtoMajor = rr.ProtoMajor
t.ProtoMinor = rr.ProtoMinor
// Transfer semantics for Requests are exactly like those for
// Responses with status code 200, responding to a GET method
t.StatusCode = 200
t.Close = rr.Close
default:
panic("unexpected type")
}
// Default to HTTP/1.1
if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
t.ProtoMajor, t.ProtoMinor = 1, 1
}
// 处理"Transfer-Encoding"首部
err = t.fixTransferEncoding()
if err != nil {
return err
}
// 处理"Content-Length"首部,注意此处返回的是真实的消息载体长度
realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
if err != nil {
return err
} // 如果该消息为响应且对应的请求方法为HEAD，如果响应首部包含Content-Length字段，则将此作为响应的ContentLength的值，表示server // 可以接收到的数据的最大长度，由于该响应没有有效载体，此时不能使用fixLength返回的真实长度0
if isResponse && t.RequestMethod == "HEAD" {
if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
return err
} else {
t.ContentLength = n
}
} else {
t.ContentLength = realLength
}
// 处理Trailer首部字段，主要进行有消息校验
t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
if err != nil {
return err
}
// If there is no Content-Length or chunked Transfer-Encoding on a *Response
// and the status is not 1xx, 204 or 304, then the body is unbounded.
// See RFC 7230, section 3.3. // 含body但不是chunked且不包含length字段的响应称为unbounded(无法衡量长度的消息)消息，根据RFC 7230会被关闭
switch msg.(type) {
case *Response:
if realLength == -1 &&
!chunked(t.TransferEncoding) &&
bodyAllowedForStatus(t.StatusCode) {
// Unbounded body.
t.Close = true
}
}
// Prepare body reader. ContentLength < 0 means chunked encoding
// or close connection when finished, since multipart is not supported yet // 给t.Body赋值
switch { // chunked 场景处理
case chunked(t.TransferEncoding): // 如果请求为HEAD或响应状态码为1xx, 204 or 304，则消息不包含有效载体
if noResponseBodyExpected(t.RequestMethod) || !bodyAllowedForStatus(t.StatusCode) {
t.Body = NoBody
} else { // 下面会创建chunkedReader
t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
}
case realLength == 0:
t.Body = NoBody // 非chunked且包含有效载体(对应Content-Length)，创建limitReader
case realLength > 0:
t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
default:
// realLength < 0, i.e. "Content-Length" not mentioned in header // 此处对于消息有效载体unbounded场景，断开底层连接
if t.Close {
// Close semantics (i.e. HTTP/1.0)
t.Body = &body{src: r, closing: t.Close}
} else {
// Persistent connection (i.e. HTTP/1.1) 好像走不到该分支。。。
t.Body = NoBody
}
}
// 为请求/响应结构体赋值并通过指针返回
switch rr := msg.(type) {
case *Request:
rr.Body = t.Body
rr.ContentLength = t.ContentLength
rr.TransferEncoding = t.TransferEncoding
rr.Close = t.Close
rr.Trailer = t.Trailer
case *Response:
rr.Body = t.Body
rr.ContentLength = t.ContentLength
rr.TransferEncoding = t.TransferEncoding
rr.Close = t.Close
rr.Trailer = t.Trailer
}
return nil
}
// 1.13.3版本的本函数描述有误，下面代码来自最新master分支func (t *transferReader) fixTransferEncoding() error { // 本函数主要处理"Transfer-Encoding"首部，如果不存在，则直接退出
raw, present := t.Header["Transfer-Encoding"]
if !present {
return nil
}
delete(t.Header, "Transfer-Encoding")
// Issue 12785; ignore Transfer-Encoding on HTTP/1.0 requests. // HTTP/1.0不处理此首部
if !t.protoAtLeast(1, 1) {
return nil
}
// "Transfer-Encoding"首部字段使用逗号分割
encodings := strings.Split(raw[0], ",")
te := make([]string, 0, len(encodings))
// When adding new encodings, please maintain the invariant:
// if chunked encoding is present, it must always
// come last and it must be applied only once.
// See RFC 7230 Section 3.3.1 Transfer-Encoding. // 循环处理各个传输编码，目前仅实现了"chunked"
for i, encoding := range encodings {
encoding = strings.ToLower(strings.TrimSpace(encoding))
if encoding == "identity" {
// "identity" should not be mixed with other transfer-encodings/compressions
// because it means "no compression, no transformation".
if len(encodings) != 1 {
return &badStringError{`"identity" when present must be the only transfer encoding`, strings.Join(encodings, ",")}
}
// "identity" is not recorded.
break
}
switch {
case encoding == "chunked":
// "chunked" MUST ALWAYS be the last
// encoding as per the loop invariant.
// That is:
// Invalid: [chunked, gzip]
// Valid: [gzip, chunked]
if i+1 != len(encodings) {
return &badStringError{"chunked must be applied only once, as the last encoding", strings.Join(encodings, ",")}
}
// Supported otherwise.
case isGzipTransferEncoding(encoding):
// Supported
default:
return &unsupportedTEError{fmt.Sprintf("unsupported transfer encoding: %q", encoding)}
}
te = te[0 : len(te)+1]
te[len(te)-1] = encoding
}
if len(te) > 0 {
// RFC 7230 3.3.2 says "A sender MUST NOT send a
// Content-Length header field in any message that
// contains a Transfer-Encoding header field."
//
// but also:
// "If a message is received with both a
// Transfer-Encoding and a Content-Length header
// field, the Transfer-Encoding overrides the
// Content-Length. Such a message might indicate an
// attempt to perform request smuggling (Section 9.5)
// or response splitting (Section 9.4) and ought to be
// handled as an error. A sender MUST remove the
// received Content-Length field prior to forwarding
// such a message downstream."
//
// Reportedly, these appear in the wild. // "Transfer-Encoding"就是为了解决"Content-Length"不存在才出现了，因此当存在"Transfer-Encoding"时无需处理"Content-Length"， // 此处删除"Content-Length"首部，不在fixLength函数中处理
delete(t.Header, "Content-Length")
t.TransferEncoding = te
return nil
}
return nil
}
// 本函数处理Content-Length首部，并返回真实的消息载体长度func fixLength(isResponse bool, status int, requestMethod string, header Header, te []string) (int64, error) {
isRequest := !isResponse
contentLens := header["Content-Length"]
// Hardening against HTTP request smuggling
if len(contentLens) > 1 {
// Per RFC 7230 Section 3.3.2, prevent multiple
// Content-Length headers if they differ in value.
// If there are dups of the value, remove the dups.
// See Issue 16490. // 下面按照RFC 7230的建议进行处理，如果一个Content-Length包含多个不同的value，则认为该消息无效
first := strings.TrimSpace(contentLens[0])
for _, ct := range contentLens[1:] {
if first != strings.TrimSpace(ct) {
return 0, fmt.Errorf("http: message cannot contain multiple Content-Length headers; got %q", contentLens)
}
}
// 如果一个Content-Length包含多个相同的value，则仅保留一个
header.Del("Content-Length")
header.Add("Content-Length", first)
contentLens = header["Content-Length"]
}
// 处理HEAD请求
if noResponseBodyExpected(requestMethod) {
// For HTTP requests, as part of hardening against request
// smuggling (RFC 7230), don't allow a Content-Length header for
// methods which don't permit bodies. As an exception, allow
// exactly one Content-Length header if its value is "0". // 当HEAD请求中的Content-Length为0时允许存在该字段
if isRequest && len(contentLens) > 0 && !(len(contentLens) == 1 && contentLens[0] == "0") {
return 0, fmt.Errorf("http: method cannot contain a Content-Length; got %q", contentLens)
}
return 0, nil
} // 处理状态码为1xx的响应，不包含消息体
if status/100 == 1 {
return 0, nil
} // 处理状态码为204和304的响应，不包含消息体
switch status {
case 204, 304:
return 0, nil
}
// 包含Transfer-Encoding时无法衡量数据长度,以Transfer-Encoding为准，设置返回长度为-1，直接返回
if chunked(te) {
return -1, nil
}
var cl string // 获取Content-Length字段值
if len(contentLens) == 1 {
cl = strings.TrimSpace(contentLens[0])
} // 对Content-Length字段的值进行有效性验证,如果有效则返回该值的整型，无效返回错误
if cl != "" {
n, err := parseContentLength(cl)
if err != nil {
return -1, err
}
return n, nil
} // 数值为空，删除该首部字段
header.Del("Content-Length")
// 请求中没有Content-Length且没有Transfer-Encoding字段的请求被认为没有有效载体
if isRequest {
// RFC 7230 neither explicitly permits nor forbids an
// entity-body on a GET request so we permit one if
// declared, but we default to 0 here (not -1 below)
// if there's no mention of a body.
// Likewise, all other request methods are assumed to have
// no body if neither Transfer-Encoding chunked nor a
// Content-Length are set.
return 0, nil
}
// Body-EOF logic based on other methods (like closing, or chunked coding) // 消息为响应，该场景后续会在readTransfer被close处理
return -1, nil
}
func (cr *connReader) startBackgroundRead() {
cr.lock()
defer cr.unlock() // 表示该连接正在被读取
if cr.inRead {
panic("invalid concurrent Body.Read call")
} // 表示该连接上是否还有数据
if cr.hasByte {
return
}
cr.inRead = true // 设置底层连接deadline为1<<64 -1
cr.conn.rwc.SetReadDeadline(time.Time{}) // 在新的goroutine中等待数据
go cr.backgroundRead()
}
func (cr *connReader) backgroundRead() { // 阻塞等待读取一个字节的数
n, err := cr.conn.rwc.Read(cr.byteBuf[:])
cr.lock() // 如果存在数据则设置cr.hasByte为true,byteBuf容量为1
if n == 1 {
cr.hasByte = true
// We were past the end of the previous request's body already
// (since we wouldn't be in a background read otherwise), so
// this is a pipelined HTTP request. Prior to Go 1.11 we used to
// send on the CloseNotify channel and cancel the context here,
// but the behavior was documented as only "may", and we only
// did that because that's how CloseNotify accidentally behaved
// in very early Go releases prior to context support. Once we
// added context support, people used a Handler's
// Request.Context() and passed it along. Having that context
// cancel on pipelined HTTP requests caused problems.
// Fortunately, almost nothing uses HTTP/1.x pipelining.
// Unfortunately, apt-get does, or sometimes does.
// New Go 1.11 behavior: don't fire CloseNotify or cancel
// contexts on pipelined requests. Shouldn't affect people, but
// fixes cases like Issue 23921. This does mean that a client
// closing their TCP connection after sending a pipelined
// request won't cancel the context, but we'll catch that on any
// write failure (in checkConnErrorWriter.Write).
// If the server never writes, yes, there are still contrived
// server & client behaviors where this fails to ever cancel the
// context, but that's kinda why HTTP/1.x pipelining died
// anyway.
}
if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
// Ignore this error. It's the expected error from
// another goroutine calling abortPendingRead.
} else if err != nil {
cr.handleReadError(err)
}
cr.aborted = false
cr.inRead = false
cr.unlock() // 当有数据时，通知cr.cond.Wait解锁
cr.cond.Broadcast()
}
func (w *response) finishRequest() {
w.handlerDone.setTrue()
// wroteHeader表示是否已经将响应首部写入，没有则写入
if !w.wroteHeader {
w.WriteHeader(StatusOK)
}
// 此处调用w.cw.write(checkConnErrorWriter) -> c.rwc.write发送数据，即调用底层连接的write将buf中的数据发送出去
w.w.Flush() // 将w.w重置并放入sync.pool中，待后续重用
putBufioWriter(w.w) // 主要构造chunked的结束符:"0\r\n"，"\r\n"，通过cw.chunking判断是否是chunked编码
w.cw.close() // 发送bufw缓存的数据
w.conn.bufw.Flush()
// 用于等待处理未读取完的数据，与connReader.backgroundRead中的cr.cond.Broadcast()对应
w.conn.r.abortPendingRead()
// Close the body (regardless of w.closeAfterReply) so we can
// re-use its bufio.Reader later safely.
w.reqBody.Close()
if w.req.MultipartForm != nil {
w.req.MultipartForm.RemoveAll()
}
}
func (w *response) shouldReuseConnection() bool { // 表示是否需要在响应之后关闭底层连接。requestTooLarge，isH2Upgrade或包含首部字段"Connection:close"时置位
if w.closeAfterReply {
// The request or something set while executing the
// handler indicated we shouldn't reuse this
// connection.
return false
}
// 写入数据与"content-length"不匹配,为避免不同步，不重用连接
if w.req.Method != "HEAD" && w.contentLength != -1 && w.bodyAllowed() && w.contentLength != w.written {
// Did not write enough. Avoid getting out of sync.
return false
}
// There was some error writing to the underlying connection
// during the request, so don't re-use this conn. // 底层连接出现错误，不可重用
if w.conn.werr != nil {
return false
}
// 判断是否在读取完数据前执行关闭
if w.closedRequestBodyEarly() {
return false
}
return true
}
// closeWrite flushes any outstanding data and sends a FIN packet (if// client is connected via TCP), signalling that we're done. We then// pause for a bit, hoping the client processes it before any// subsequent RST.//// See https://golang.org/issue/3595func (c *conn) closeWriteAndWait() { // 在关闭写之前将缓冲区中的数据发送出去 c.finalFlush() if tcp, ok := c.rwc.(closeWriter); ok { // 执行tcpsock.go中的TCPConn.CloseWrite，调用SHUT_WR关闭写 tcp.CloseWrite() } time.Sleep(rstAvoidanceDelay)}
func (c *conn) finalFlush() { // 本函数中如果c.bufr或c.bufw不为空，都会重置并重用这部分内存
if c.bufr != nil {
// Steal the bufio.Reader (~4KB worth of memory) and its associated
// reader for a future connection.
putBufioReader(c.bufr)
c.bufr = nil
}
if c.bufw != nil { // 将缓存区中的数据全部通过底层发送出去 // respose写数据调用为c.bufw.wr.Write -> checkConnErrorWriter.write -> c.rwc.write，最终通过底层write发送数据
c.bufw.Flush()
// Steal the bufio.Writer (~4KB worth of memory) and its associated
// writer for a future connection.
putBufioWriter(c.bufw)
c.bufw = nil
}
}
http.transport
NetPoll
参考：
https://golang.org/pkg/net/http/
https://lanre.wtf/blog/2017/07/24/roundtripper-go/
https://lanre.wtf/blog/2017/04/03/http-in-go/
来源：https://www.cnblogs.com/charlieroro/p/11331331.html