该文章是分析golang http-server包的系列文章，本篇是第二篇，核心帮助大家深入http-server包的逻辑。明白http包是如何运转的，如何解析http协议。
我们继续看，直接进入ListenAndServe函数:
func ListenAndServe(addr string, handler Handler) error {
server := &Server{Addr: addr, Handler: handler}
return server.ListenAndServe()
}
可以看到，把addr放到一个Server结构中，并且调用ListenAndServer()。这里面向对象的方法，相当于Java中new一个对象的实例，并且调用该实例的方法。 继续进函数：
func (srv *Server) ListenAndServe() error {
addr := srv.Addr
if addr == "" {
addr = ":http"
}
ln, err := net.Listen("tcp", addr)
if err != nil {
return err
}
return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
}
开了tcp 端口监听，并且返回了个 Serve 函数，把tcp的对象传递进去了。
//2871
func (srv *Server) Serve(l net.Listener) error {
...
var tempDelay time.Duration // how long to sleep on accept failure
ctx := context.WithValue(baseCtx, ServerContextKey, srv)
for {
// Accept()返回底层TCP的连接
rw, err := l.Accept()
if err != nil {
select {
case <-srv.getDoneChan():
return ErrServerClosed
default:
}
if ne, ok := err.(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", err, tempDelay)
time.Sleep(tempDelay)
continue
}
return err
}
connCtx := ctx
if cc := srv.ConnContext; cc != nil {
connCtx = cc(connCtx, rw)
if connCtx == nil {
panic("ConnContext returned nil")
}
}
tempDelay = 0
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(connCtx)
}
}
可以重点关注：
for {
rw, e := l.Accept()
...
c, err := srv.newConn(rw)
...
go c.serve()
}
首先，tcp在监听，然后循环接受请求，建立连接，并且用关键字go开启一个服务并发地处理每一个连接。 继续往下，看serve代码，比较长：
// Serve a new connection.
func (c *conn) serve(ctx context.Context) {
c.remoteAddr = c.rwc.RemoteAddr().String()
ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
// 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; validNextProto(proto) {
if fn := c.server.TLSNextProto[proto]; fn != nil {
h := initALPNRequest{ctx, tlsConn, serverHandler{c.server}}
fn(c.server, tlsConn, h)
}
return
}
}
// HTTP/1.x from here on.
// 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:
const publicErr = "431 Request Header Fields Too Large"
fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
c.closeWriteAndWait()
return
case isUnsupportedTEError(err):
code := StatusNotImplemented
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
// 如果http首部包含"100-continue"请求
req := w.req
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()
}
// 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() {
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{})
}
}
实际上，精简下：
for{
w, err := c.readRequest()
...
serverHandler{c.server}.ServeHTTP(w, w.req)
...
w.finishRequest()
}
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。
下面我们看下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 GET / HTTP/1.1
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
}
看下 shouldClose 方法：
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
}
看下readTransfer方法：
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/3595
func (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
}
}
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