golang的http与twirp源码分析

func ListenAndServe(addr string, handler Handler) error {
    server := &Server{Addr: addr, Handler: handler}
    return server.ListenAndServe()
}
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)
}

type Handler interface {
    ServeHTTP(ResponseWriter, *Request)
}

func (srv *Server) Serve(l net.Listener) error {
    .....
    //包装listener
    origListener := l
    l = &onceCloseListener{Listener: l}
    defer l.Close()
    //启动失败直接结束
    if err := srv.setupHTTP2_Serve(); err != nil {
        return err
    }

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

    //绑定上下文等信息
    baseCtx := context.Background()
    if srv.BaseContext != nil {
        baseCtx = srv.BaseContext(origListener)
        if baseCtx == nil {
            panic("BaseContext returned a nil context")
        }
    }
    .....

    ctx := context.WithValue(baseCtx, ServerContextKey, srv)
    for {
        //循环accept请求
        rw, err := l.Accept()
        if err != nil {
            select {
            //如果服务器已经关闭，直接结束
            case <-srv.getDoneChan():
                return ErrServerClosed
            default:
            }
            if ne, ok := err.(net.Error); ok && ne.Temporary() {
            //如果accept失败，等待一个时间周期后continue
            .....
            return err
        }
        connCtx := ctx
        if cc := srv.ConnContext; cc != nil {
            connCtx = cc(connCtx, rw)
            if connCtx == nil {
                panic("ConnContext returned nil")
            }
        }
        tempDelay = 0
        //初始化一个连接对象
        c := srv.newConn(rw)
        //初始化连接状态
        c.setState(c.rwc, StateNew) // before Serve can return
        //开启一个新的goroutine去执行请求
        go c.serve(connCtx)
    }
}

func (c *conn) serve(ctx context.Context) {
    //包装缓存区，上下文信息等
    .....
    for {
        //w是解析request数据得到的一个包装对象，包含请求的详细信息
        w, err := c.readRequest(ctx)
        if c.r.remain != c.server.initialReadLimitSize() {
            //如果这个连接已经被读取过（长连接），更新状态
            c.setState(c.rwc, StateActive)
        }
        if err != nil {
            //如果报文解析出错
            const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"

            switch {
            //根据错误类型，返回不同http status
            case .....
            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
            }
        }

        //进一步解析内容
        req := w.req
        if req.expectsContinue() {
            if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
                req.Body = &expectContinueReader{readCloser: req.Body, resp: w}
            }
        } else if req.Header.get("Expect") != "" {
            w.sendExpectationFailed()
            return
        }
        c.curReq.Store(w)
        //如果body部分的内容还没读取完毕，等待本次io读取完毕后
        //修改管道的io读取为后台读取方式（开启另一个gorountine区完成数据读取）
        if requestBodyRemains(req.Body) {
            registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
        } else {
            w.conn.r.startBackgroundRead()
        }
        //调用ServeHTTP方法处理请求
        serverHandler{c.server}.ServeHTTP(w, w.req)
        w.cancelCtx()
        if c.hijacked() {
            return
        }
        //完成请求
        w.finishRequest()
        if !w.shouldReuseConnection() {
            //如果连接不允许重复使用，结束
            if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
                c.closeWriteAndWait()
            }
            return
        }
        c.setState(c.rwc, StateIdle)
        c.curReq.Store((*response)(nil))
        //如果不是长连接，就结束了
        if !w.conn.server.doKeepAlives() {
            return
        }

        if d := c.server.idleTimeout(); d != 0 {
            //如果设置了超时时间
            c.rwc.SetReadDeadline(time.Now().Add(d))
            if _, err := c.bufr.Peek(4); err != nil {
                //如果连接超时了，结束
                return
            }
        }
        c.rwc.SetReadDeadline(time.Time{})
    }
}

type TwirpServer interface {
    http.Handler
    ServiceDescriptor() ([]byte, int)
    ProtocGenTwirpVersion() string
    PathPrefix() string
}

syntax = "proto3";
package main;

message A{}
message B {
    string result = 1;
}
service Test{
    rpc hello(A) returns(B);
}

const TestPathPrefix = "/twirp/main.Test/"

func (s *testServer) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
    ctx := req.Context()
    ctx = ctxsetters.WithPackageName(ctx, "main")
    ctx = ctxsetters.WithServiceName(ctx, "Test")
    ctx = ctxsetters.WithResponseWriter(ctx, resp)

    var err error
    ctx, err = callRequestReceived(ctx, s.hooks)
    if err != nil {
        s.writeError(ctx, resp, err)
        return
    }

    if req.Method != "POST" {
        msg := fmt.Sprintf("unsupported method %q (only POST is allowed)", req.Method)
        err = badRouteError(msg, req.Method, req.URL.Path)
        s.writeError(ctx, resp, err)
        return
    }

    switch req.URL.Path {
    case "/twirp/main.Test/Hello":
        s.serveHello(ctx, resp, req)
        return
    default:
        msg := fmt.Sprintf("no handler for path %q", req.URL.Path)
        err = badRouteError(msg, req.Method, req.URL.Path)
        s.writeError(ctx, resp, err)
        return
    }
}

/twirp/包名.服务名/方法名

func (s *testServer) serveHello(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
    header := req.Header.Get("Content-Type")
    i := strings.Index(header, ";")
    if i == -1 {
        i = len(header)
    }
    switch strings.TrimSpace(strings.ToLower(header[:i])) {
    case "application/json":
        s.serveHelloJSON(ctx, resp, req)
    case "application/protobuf":
        s.serveHelloProtobuf(ctx, resp, req)
    default:
        msg := fmt.Sprintf("unexpected Content-Type: %q", req.Header.Get("Content-Type"))
        twerr := badRouteError(msg, req.Method, req.URL.Path)
        s.writeError(ctx, resp, twerr)
    }
}

func (s *testServer) serveHelloProtobuf(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
    var err error
    ctx = ctxsetters.WithMethodName(ctx, "Hello")
    //如果在hook里面编写了路由，此处执行
    ctx, err = callRequestRouted(ctx, s.hooks)
    if err != nil {
        s.writeError(ctx, resp, err)
        return
    }
    //读取请求内容
    buf, err := ioutil.ReadAll(req.Body)
    if err != nil {
        s.writeError(ctx, resp, wrapInternal(err, "failed to read request body"))
        return
    }
    reqContent := new(A)
    //Unmarshal请求内容
    if err = proto.Unmarshal(buf, reqContent); err != nil {
        s.writeError(ctx, resp, malformedRequestError("the protobuf request could not be decoded"))
        return
    }

    // Call service method
    //执行对应的服务方法
    var respContent *B
    func() {
        defer ensurePanicResponses(ctx, resp, s.hooks)
        //Test对象就是嵌套在server对象中的真正的服务对象
        respContent, err = s.Test.Hello(ctx, reqContent)
    }()

    if err != nil {
        s.writeError(ctx, resp, err)
        return
    }
    if respContent == nil {
        s.writeError(ctx, resp, twirp.InternalError("received a nil *B and nil error while calling Hello. nil responses are not supported"))
        return
    }
    //执行完服务，执行返回前类型的hooks
    ctx = callResponsePrepared(ctx, s.hooks)
    //将要返回的数据Marshal为字节
    respBytes, err := proto.Marshal(respContent)
    if err != nil {
        s.writeError(ctx, resp, wrapInternal(err, "failed to marshal proto response"))
        return
    }
    //状态码处理等
    ctx = ctxsetters.WithStatusCode(ctx, http.StatusOK)
    resp.Header().Set("Content-Type", "application/protobuf")
    resp.Header().Set("Content-Length", strconv.Itoa(len(respBytes)))
    resp.WriteHeader(http.StatusOK)
    //将数据写回请求客户端
    if n, err := resp.Write(respBytes); err != nil {
        msg := fmt.Sprintf("failed to write response, %d of %d bytes written: %s", n, len(respBytes), err.Error())
        twerr := twirp.NewError(twirp.Unknown, msg)
        callError(ctx, s.hooks, twerr)
    }
    //执行返回后类型的hooks
    callResponseSent(ctx, s.hooks)
}