Go HTTP Server

作者收录于 Go

2023-10-31 约 2673 字预计阅读 6 分钟

Go 源码中的一些标记：

//go:linkname syscall_rawSyscall syscall.rawSyscall 是特殊编译器指令。linkname 指令用于将当前包内的一个标识符链接到另一个包的符号。换言之，这允许你跳过导出规则，达到直接调用私有函数/变量的目的。在此例中，它将当前函数命名为 syscall_rawSyscall，并将其链接到 syscall 包的 rawSyscall 函数。这意味着你可以在其他地方使用 syscall_rawSyscall 这个名字来执行 syscall 包中的 rawSyscall 函数。
//go:nosplit 同样是特殊编译器指令，它禁止编译器在该函数的入口插入用于栈分裂（Stack Splitting）的代码。通常情况下，Go 运行时会自动处理栈的生长和收缩，但当函数需要更大的栈空间时，Go 运行时就可能触发所谓的「栈分裂」，在堆上创建一个新的、更大的栈覆盖原来的栈。然而，某些操作（如系统调用）不能在分裂的栈中进行，因此需要使用 //go:nosplit 指令来防止栈分裂发生。

Gin 框架 HTTP Server 分析

Gin 框架中的 HTTP Server 是利用了 Go 标准库的 net/http 包来实现的。一个简单的 Gin 框架的 HTTP 服务代码：

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func main() {
	// Create a new Gin router
	router := gin.Default()

	// Define routes
	router.GET("/", func(c *gin.Context) {
		c.JSON(200, gin.H{
			"message": "Hello, World!",
		})
	})

	// Run the server
	router.Run(":8080")
}

请求流程图：

而 Gin 框架的 router.Run() 代码如下：

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// Run attaches the router to a http.Server and starts listening and serving HTTP requests.
// It is a shortcut for http.ListenAndServe(addr, router)
// Note: this method will block the calling goroutine indefinitely unless an error happens.
func (engine *Engine) Run(addr ...string) (err error) {
	defer func() { debugPrintError(err) }()

	if engine.isUnsafeTrustedProxies() {
		debugPrint("[WARNING] You trusted all proxies, this is NOT safe. We recommend you to set a value.\n" +
			"Please check https://pkg.go.dev/github.com/gin-gonic/gin#readme-don-t-trust-all-proxies for details.")
	}

	address := resolveAddress(addr)
	debugPrint("Listening and serving HTTP on %s\n", address)
	err = http.ListenAndServe(address, engine.Handler())
	return
}

可以看到 Run() 函数中调用了 go 标准库的 net/http 包的 ListenAndServe() 方法。

net/http 包中提供的方法：

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go doc net/http | grep "^func"

func CanonicalHeaderKey(s string) string
func DetectContentType(data []byte) string
func Error(w ResponseWriter, error string, code int)
func Get(url string) (resp *Response, err error)
func Handle(pattern string, handler Handler)
func HandleFunc(pattern string, handler func(ResponseWriter, *Request))
func Head(url string) (resp *Response, err error)
func ListenAndServe(addr string, handler Handler) error
func ListenAndServeTLS(addr, certFile, keyFile string, handler Handler) error
func MaxBytesReader(w ResponseWriter, r io.ReadCloser, n int64) io.ReadCloser
func NewRequest(method, url string, body io.Reader) (*Request, error)
func NewRequestWithContext(ctx context.Context, method, url string, body io.Reader) (*Request, error)
func NotFound(w ResponseWriter, r *Request)
func ParseHTTPVersion(vers string) (major, minor int, ok bool)
func ParseTime(text string) (t time.Time, err error)
func Post(url, contentType string, body io.Reader) (resp *Response, err error)
func PostForm(url string, data url.Values) (resp *Response, err error)
func ProxyFromEnvironment(req *Request) (*url.URL, error)
func ProxyURL(fixedURL *url.URL) func(*Request) (*url.URL, error)
func ReadRequest(b *bufio.Reader) (*Request, error)
func ReadResponse(r *bufio.Reader, req *Request) (*Response, error)
func Redirect(w ResponseWriter, r *Request, url string, code int)
func Serve(l net.Listener, handler Handler) error
func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time, ...)
func ServeFile(w ResponseWriter, r *Request, name string)
func ServeTLS(l net.Listener, handler Handler, certFile, keyFile string) error
func SetCookie(w ResponseWriter, cookie *Cookie)
func StatusText(code int) string

其中包括的 Serve 类方法：

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go doc net/http | grep "^func" | grep "Serve"

func ListenAndServe(addr string, handler Handler) error
func ListenAndServeTLS(addr, certFile, keyFile string, handler Handler) error
func Serve(l net.Listener, handler Handler) error
func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time, ...)
func ServeFile(w ResponseWriter, r *Request, name string)
func ServeTLS(l net.Listener, handler Handler, certFile, keyFile string) error

结构定义：

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go doc net/http | grep "^type" | grep "struct"

type Client struct{ ... }
type Cookie struct{ ... }
type MaxBytesError struct{ ... }
type ProtocolError struct{ ... }
type PushOptions struct{ ... }
type Request struct{ ... }
type Response struct{ ... }
type ResponseController struct{ ... }
type ServeMux struct{ ... }
type Server struct{ ... }
type Transport struct{ ... }

http.ListenAndServe() 方法：创建一个 Server 数据结构，调用 server.ListenAndServe() 方法对外提供服务。

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// ListenAndServe listens on the TCP network address addr and then calls
// Serve with handler to handle requests on incoming connections.
// Accepted connections are configured to enable TCP keep-alives.
//
// The handler is typically nil, in which case the DefaultServeMux is used.
//
// ListenAndServe always returns a non-nil error.
func ListenAndServe(addr string, handler Handler) error {
	server := &Server{Addr: addr, Handler: handler}
	return server.ListenAndServe()
}

server.ListenAndServe() 方法：主要调用 net.Listen() 方法，net.Listen() 方法的第一个参数仅接受 tcp / tcp4 / tcp6 / udp / udp4 / udp6 / unix / unixgram / unixpacket 中的一个，然后调用 Serve() 方法。

net.Listen() 中调用

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// ListenAndServe listens on the TCP network address srv.Addr and then
// calls Serve to handle requests on incoming connections.
// Accepted connections are configured to enable TCP keep-alives.
//
// If srv.Addr is blank, ":http" is used.
//
// ListenAndServe always returns a non-nil error. After Shutdown or Close,
// the returned error is ErrServerClosed.
func (srv *Server) ListenAndServe() error {
	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)
}

srv.Serve() 方法：接受 l net.Listener 上传入的连接，为每个连接创建一个新的服务 Goroutine。服务 Goroutines 读取请求，然后调用 srv.Handler() 来响应它们。

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// Serve accepts incoming connections on the Listener l, creating a
// new service goroutine for each. The service goroutines read requests and
// then call srv.Handler to reply to them.
//
// HTTP/2 support is only enabled if the Listener returns *tls.Conn
// connections and they were configured with "h2" in the TLS
// Config.NextProtos.
//
// Serve always returns a non-nil error and closes l.
// After Shutdown or Close, the returned error is ErrServerClosed.
func (srv *Server) Serve(l net.Listener) error {
	if fn := testHookServerServe; fn != nil {
		fn(srv, l) // call hook with unwrapped listener
	}

	origListener := l
	l = &onceCloseListener{Listener: l}
	defer l.Close()

	if err := srv.setupHTTP2_Serve(); err != nil {
		return err
	}

	if !srv.trackListener(&l, true) {
		return ErrServerClosed
	}
	defer srv.trackListener(&l, false)

	baseCtx := context.Background()
	if srv.BaseContext != nil {
		baseCtx = srv.BaseContext(origListener)
		if baseCtx == nil {
			panic("BaseContext returned a nil context")
		}
	}

	var tempDelay time.Duration // how long to sleep on accept failure

	ctx := context.WithValue(baseCtx, ServerContextKey, srv)
	for {
		rw, err := l.Accept()
		if err != nil {
			if srv.shuttingDown() {
				return ErrServerClosed
			}
			if ne, ok := err.(net.Error); ok && ne.Temporary() {
				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, runHooks) // before Serve can return
		go c.serve(connCtx)
	}
}

c.serve() 方法：判断传入的请求是否需要升级为 HTTPs，接着创建文本的

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// Serve a new connection.
func (c *conn) serve(ctx context.Context) {
	if ra := c.rwc.RemoteAddr(); ra != nil {
		c.remoteAddr = ra.String()
	}
	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
	var inFlightResponse *response
	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 inFlightResponse != nil {
			inFlightResponse.cancelCtx()
		}
		if !c.hijacked() {
			if inFlightResponse != nil {
				inFlightResponse.conn.r.abortPendingRead()
				inFlightResponse.reqBody.Close()
			}
			c.close()
			c.setState(c.rwc, StateClosed, runHooks)
		}
	}()

	if tlsConn, ok := c.rwc.(*tls.Conn); ok {
		tlsTO := c.server.tlsHandshakeTimeout()
		if tlsTO > 0 {
			dl := time.Now().Add(tlsTO)
			c.rwc.SetReadDeadline(dl)
			c.rwc.SetWriteDeadline(dl)
		}
		if err := tlsConn.HandshakeContext(ctx); 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
		}
		// Restore Conn-level deadlines.
		if tlsTO > 0 {
			c.rwc.SetReadDeadline(time.Time{})
			c.rwc.SetWriteDeadline(time.Time{})
		}
		c.tlsState = new(tls.ConnectionState)
		*c.tlsState = tlsConn.ConnectionState()
		if proto := c.tlsState.NegotiatedProtocol; validNextProto(proto) {
			if fn := c.server.TLSNextProto[proto]; fn != nil {
				h := initALPNRequest{ctx, tlsConn, serverHandler{c.server}}
				// Mark freshly created HTTP/2 as active and prevent any server state hooks
				// from being run on these connections. This prevents closeIdleConns from
				// closing such connections. See issue https://golang.org/issue/39776.
				c.setState(c.rwc, StateActive, skipHooks)
				fn(c.server, tlsConn, h)
			}
			return
		}
	}

	// HTTP/1.x from here on.

	ctx, cancelCtx := context.WithCancel(ctx)
	c.cancelCtx = cancelCtx
	defer cancelCtx()

	c.r = &connReader{conn: c}
	c.bufr = newBufioReader(c.r)
	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)

	for {
		w, err := c.readRequest(ctx)
		if c.r.remain != c.server.initialReadLimitSize() {
			// If we read any bytes off the wire, we're active.
			c.setState(c.rwc, StateActive, runHooks)
		}
		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

			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:
				if v, ok := err.(statusError); ok {
					fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s: %s%s%d %s: %s", v.code, StatusText(v.code), v.text, errorHeaders, v.code, StatusText(v.code), v.text)
					return
				}
				publicErr := "400 Bad Request"
				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
				return
			}
		}

		// Expect 100 Continue support
		req := w.req
		if req.expectsContinue() {
			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}
				w.canWriteContinue.Store(true)
			}
		} else if req.Header.get("Expect") != "" {
			w.sendExpectationFailed()
			return
		}

		c.curReq.Store(w)

		if requestBodyRemains(req.Body) {
			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
		} else {
			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.
		inFlightResponse = w
		serverHandler{c.server}.ServeHTTP(w, w.req)
		inFlightResponse = nil
		w.cancelCtx()
		if c.hijacked() {
			return
		}
		w.finishRequest()
		c.rwc.SetWriteDeadline(time.Time{})
		if !w.shouldReuseConnection() {
			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
				c.closeWriteAndWait()
			}
			return
		}
		c.setState(c.rwc, StateIdle, runHooks)
		c.curReq.Store(nil)

		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 {
			c.rwc.SetReadDeadline(time.Now().Add(d))
		} else {
			c.rwc.SetReadDeadline(time.Time{})
		}

		// Wait for the connection to become readable again before trying to
		// read the next request. This prevents a ReadHeaderTimeout or
		// ReadTimeout from starting until the first bytes of the next request
		// have been received.
		if _, err := c.bufr.Peek(4); err != nil {
			return
		}

		c.rwc.SetReadDeadline(time.Time{})
	}
}

目录

Go HTTP Server

Go 源码中的一些标记：

Gin 框架 HTTP Server 分析