http client

重要结构

1.Request, 保存http request数据的结构，包括header，body信息
2.Client, 保存Transport，cokie信息
3.Transport，管理一个连接池

client.go

func main() {
    //自定义request
    request, err := http.NewRequest("get", "https://xtz.getblock.io/mainnet/chains", http.NoBody)
    if err != nil {
        fmt.Println(err)
    }
    request.Header.Add("x-api-key", "0ee52bce-e6c2-4e3e-987b-629a3e08")
    request.Header.Add("Content-type", "application/json")

    //自定义transport
    proxyFunc := http.ProxyURL(proxyURL)
    var tlsConfig *tls.Config
    transport := &http.Transport{
        Dial: (&net.Dialer{
            Timeout:   config.GetDuration("rpc.dial_timeout"),
            KeepAlive: config.GetDuration("rpc.keepalive"),
        }).Dial,
        Proxy:                 proxyFunc,
        TLSClientConfig:       tlsConfig,
        IdleConnTimeout:       60,
        ResponseHeaderTimeout: 60,
        ExpectContinueTimeout: 60,
        MaxIdleConns:          5,
        MaxIdleConnsPerHost:   5,
    }
    //自定义client
    client := http.Client{
        Transport: transport,
    }
    response, err := client.Do(request)
    fmt.Println(response)
}

请求的大致流程

1.根据请求条件，构建request对象

2.所有的client请求，都会经过client.do()处理

func (c *Client) do(req *Request) (retres *Response, reterr error) 

2.1 request请求使用client.send()处理

func (c *Client) send(req *Request, deadline time.Time) (resp *Response, didTimeout func() bool, err error)

resp, didTimeout, err = send(req, c.transport(), deadline)//默认传DefaultTransport

3.send函数

func send(ireq *Request, rt RoundTripper, deadline time.Time) (resp *Response, didTimeout func() bool, err error) {
    resp, err = rt.RoundTrip(req) 
}

4.DefaultTransport的RoundTrip方法，实际就是Transport的RoundTrip方法

func (t *Transport) roundTrip(req *Request) (*Response, error) {
    treq := &transportRequest{Request: req, trace: trace} //封装新的request
    cm, err := t.connectMethodForRequest(treq)
    pconn, err := t.getConn(treq, cm) //使用连接池技术，获取连接对象*persistConn，
    resp, err = pconn.roundTrip(treq) //使用连接对象获取response
}

5.使用连接池技术，获取连接对象*persistConn

func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (pc *persistConn, err error) {
    w := &wantConn{ //构建连接对象
        cm:         cm,
        key:        cm.key(),
        ctx:        ctx,
        ready:      make(chan struct{}, 1),
        beforeDial: testHookPrePendingDial,
        afterDial:  testHookPostPendingDial,
    }
    if delivered := t.queueForIdleConn(w); delivered {//从连接池获取符合的连接对象，有就返回
        pc := w.pc        
        return pc, nil
    }    
    t.queueForDial(w)//发起连接

    select {
    case <-w.ready:    //连接准备好，就返回连接对象    
        return w.pc, w.err

}

5.1 Transport.queueForDial发起连接

func (t *Transport) queueForDial(w *wantConn) {
    go t.dialConnFor(w)
}

5.2 发起拨号dialConnFor

func (t *Transport) dialConnFor(w *wantConn) {
    pc, err := t.dialConn(w.ctx, w.cm) //发起拨号，返回连接对象
    delivered := w.tryDeliver(pc, err)
}

5.3 发起拨号

func (t *Transport) dialConn(ctx context.Context, cm connectMethod) (pconn *persistConn, err error) {
    pconn = &persistConn{ //构建连接对象
        t:             t,
        cacheKey:      cm.key(),
        reqch:         make(chan requestAndChan, 1),
        writech:       make(chan writeRequest, 1),
        closech:       make(chan struct{}),
        writeErrCh:    make(chan error, 1),
        writeLoopDone: make(chan struct{}),
    }
    conn, err := t.dial(ctx, "tcp", cm.addr()) //tcp连接，获取到net.conn对象

    pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())//可以从conn读
    pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())//写到conn

    go pconn.readLoop()//开启读协程
    go pconn.writeLoop()//开启写协程
    return pconn, nil
}

5.4读协程,虽然是for循环，但是一次性就把请求的response读完了，如果没有关闭，就会造成协程泄露了

func (pc *persistConn) readLoop() {
    alive := true
    for alive {
        rc := <-pc.reqch //读取request,写入的地方在步骤6

        resp, err = pc.readResponse(rc, trace) //返回response
        //response的body是否可写，服务器code101才可写，所以正常这个是false
        bodyWritable := resp.bodyIsWritable()

        //response.Close设置循环结束，退出协程
        if resp.Close || rc.req.Close || resp.StatusCode <= 199 || bodyWritable {                    alive = false
        }          

        //把response写入通道，在步骤6会读取这个通道
        select {
        case rc.ch <- responseAndError{res: resp}:
        case <-rc.callerGone:
            return
        }
        //循环结束的一些情况
        select {
        case bodyEOF := <-waitForBodyRead: //读完body也会自动结束            
        case <-rc.req.Cancel:
        case <-rc.req.Context().Done():
        case <-pc.closech:
            alive = false
            pc.t.CancelRequest(rc.req)
        }
    }

5.4.1 pc.readResponse 获取response

func (pc *persistConn) readResponse(rc requestAndChan, trace *httptrace.ClientTrace) (resp *Response, err error) {
    for{
        resp, err = ReadResponse(pc.br, rc.req) //获取response
    }
}

5.4.2 ReadResponse读取response

func ReadResponse(r *bufio.Reader, req *Request) (*Response, error) {
    tp := textproto.NewReader(r) //可以处理HTTP, NNTP, SMTP协议的内容，方便读取
    resp := &Response{
        Request: req,
    }    
    line, err := tp.ReadLine()//读取第一行，获取协议，状态码
    resp.Proto = line[:i]
    resp.Status = strings.TrimLeft(line[i+1:], " ")

    mimeHeader, err := tp.ReadMIMEHeader()//读取header头
    resp.Header = Header(mimeHeader)
}

5.5 写协程

func (pc *persistConn) writeLoop() {
    for {
        select {
        case wr := <-pc.writech:
            startBytesWritten := pc.nwrite
            err := wr.req.Request.write(pc.bw, pc.isProxy, wr.req.extra, pc.waitForContinue(wr.continueCh))            
    }
}

6.使用连接对象*persistConn获取response

func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
    var continueCh chan struct{}
    resc := make(chan responseAndError) //response通道

    pc.writech <- writeRequest{req, writeErrCh, continueCh}//written by roundTrip; read by writeLoop   

    pc.reqch <- requestAndChan{ //written by roundTrip; read by readLoop
        req:        req.Request,
        ch:         resc,
        addedGzip:  requestedGzip,
        continueCh: continueCh,
        callerGone: gone,
    }
    for { //监听这些通道
        testHookWaitResLoop()
        select {
        case err := <-writeErrCh:            
        case <-pc.closech:            
        case re := <-resc: //监听 response通道，返回response         
            return re.res, nil
        }
    }
}

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