【概述】
GO的web服务器的简单helloword 服务器就是使用net/http库的进行编写。需要看一下http.ListenAndServe的工作原理。
package main
import "net/http"
func main() {
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
w.Write([]byte(`hello world`))
})
http.ListenAndServe(":3000", nil)
}
主要包括：
- uri_path跟handler的对应关系是如何初始化的
- 端口接收到请求后，请求是如何处理、以及如何被定义的func处理、响应是如何处理的
HandleFunc的参数
HandleFunc的第二个参数是func(ResponseWriter, *Request)，会赋值给HandlerFunc类型
// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)
// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
f(w, r)
}
映射处理
在src/net/http/server.go中使用HandleFunc进行注册，会将其放入多路复用的结构体ServeMux中。
src/net/http/server.go
// HandleFunc registers the handler function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
mux.Handle(pattern, HandlerFunc(handler))
}
// Handle registers the handler for the given pattern
// in the DefaultServeMux.
// The documentation for ServeMux explains how patterns are matched.
func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
// HandleFunc registers the handler function for the given pattern
// in the DefaultServeMux.
// The documentation for ServeMux explains how patterns are matched.
func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
DefaultServeMux.HandleFunc(pattern, handler)
}
// HandleFunc registers the handler function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
mux.Handle(pattern, HandlerFunc(handler))
}
type Handler interface {
ServeHTTP(ResponseWriter, *Request)
}
func (mux *ServeMux) Handle(pattern string, handler Handler) {
}
// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)
http请求的多路复用结构体ServeMux
// ServeMux is an HTTP request multiplexer.
// It matches the URL of each incoming request against a list of registered
// patterns and calls the handler for the pattern that
// most closely matches the URL.
//
// Patterns name fixed, rooted paths, like "/favicon.ico",
// or rooted subtrees, like "/images/" (note the trailing slash).
// Longer patterns take precedence over shorter ones, so that
// if there are handlers registered for both "/images/"
// and "/images/thumbnails/", the latter handler will be
// called for paths beginning "/images/thumbnails/" and the
// former will receive requests for any other paths in the
// "/images/" subtree.
//
// Note that since a pattern ending in a slash names a rooted subtree,
// the pattern "/" matches all paths not matched by other registered
// patterns, not just the URL with Path == "/".
//
// If a subtree has been registered and a request is received naming the
// subtree root without its trailing slash, ServeMux redirects that
// request to the subtree root (adding the trailing slash). This behavior can
// be overridden with a separate registration for the path without
// the trailing slash. For example, registering "/images/" causes ServeMux
// to redirect a request for "/images" to "/images/", unless "/images" has
// been registered separately.
//
// Patterns may optionally begin with a host name, restricting matches to
// URLs on that host only. Host-specific patterns take precedence over
// general patterns, so that a handler might register for the two patterns
// "/codesearch" and "codesearch.google.com/" without also taking over
// requests for "http://www.google.com/".
//
// ServeMux also takes care of sanitizing the URL request path,
// redirecting any request containing . or .. elements or repeated slashes
// to an equivalent, cleaner URL.
type ServeMux struct {
mu sync.RWMutex
m map[string]muxEntry
hosts bool // whether any patterns contain hostnames
}
对外提供服务
// A Server defines parameters for running an HTTP server.
// The zero value for Server is a valid configuration.
type Server struct {
Addr string // TCP address to listen on, ":http" if empty
Handler Handler // handler to invoke, http.DefaultServeMux if nil
ReadTimeout time.Duration // maximum duration before timing out read of the request
WriteTimeout time.Duration // maximum duration before timing out write of the response
MaxHeaderBytes int // maximum size of request headers, DefaultMaxHeaderBytes if 0
TLSConfig *tls.Config // optional TLS config, used by ListenAndServeTLS
// TLSNextProto optionally specifies a function to take over
// ownership of the provided TLS connection when an NPN
// 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 nil, HTTP/2 support is 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 and unexpected behavior from handlers.
// If nil, logging goes to os.Stderr via the log package's
// standard logger.
ErrorLog *log.Logger
disableKeepAlives int32 // accessed atomically.
nextProtoOnce sync.Once // guards initialization of TLSNextProto in Serve
nextProtoErr error
}
其中ListenAndServe函数的逻辑，其中tcpKeepAliveListener是开启了tcp的keep-alive
// 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.
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)})
}
在Serve中在Accept处于等待，当请求到来时，Accept会从Listener l中接收一个到来的连接并创建一个新的goroutine处理请求。这个goroutine会读取请求，调用Server.Handler来处理他们。
func (srv *Server) Serve(l net.Listener) error {
defer l.Close()
....
for {
rw, e := l.Accept()
if e != nil {
....
return e
}
tempDelay = 0
c := srv.newConn(rw)
c.setState(c.rwc, StateNew) // before Serve can return
go c.serve()
}
}
其中newConn是获得一个新连接
// Create new connection from rwc.
func (srv *Server) newConn(rwc net.Conn) *conn {
c := &conn{
server: srv,
rwc: rwc,
}
if debugServerConnections {
c.rwc = newLoggingConn("server", c.rwc)
}
return c
}
其中conn结构体在net/http/server.go文件中
// A conn represents the server side of an HTTP connection.
type conn struct {
// server is the server on which the connection arrived.
// Immutable; never nil.
server *Server
// 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.
// Users of bufr must hold mu.
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
// mu guards hijackedv, use of bufr, (*response).closeNotifyCh.
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
}
serve方法
// Serve a new connection.
func (c *conn) serve() {
c.remoteAddr = c.rwc.RemoteAddr().String()
defer func() {
... // defer处理
}()
... // tls connection
c.r = &connReader{r: c.rwc}
c.bufr = newBufioReader(c.r)
c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
for {
w, err := c.readRequest() //读取请求
...
if err != nil {
....
return
}
... // Expect 100 Continue support
// 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.
serverHandler{c.server}.ServeHTTP(w, w.req)
... // finish operation
}
}
看一下这里面最核心的 serverHandler{c.server}.ServeHTTP(w, w.rseq)处理逻辑
// serverHandler delegates to either the server's Handler or
// DefaultServeMux and also handles "OPTIONS *" requests.
type serverHandler struct {
srv *Server
}
func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
handler := sh.srv.Handler
if handler == nil {
handler = DefaultServeMux
}
if req.RequestURI == "*" && req.Method == "OPTIONS" {
handler = globalOptionsHandler{}
}
handler.ServeHTTP(rw, req)
}
// ServeHTTP dispatches the request to the handler whose
// pattern most closely matches the request URL.
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
}
h, _ := mux.Handler(r)
h.ServeHTTP(w, r)
}
最后的h,_:=mux.Handler获取的是type HandlerFunc func(ResponseWriter, *Request)，调用ServeHTTP也就是调用了我们注册的
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
w.Write([]byte(`hello world`))
})