一次golang fasthttp踩坑经验

func (c *HostClient) doNonNilReqResp(req *Request, resp *Response) (bool, error) {
	if req == nil {
		panic("BUG: req cannot be nil")
	}
	if resp == nil {
		panic("BUG: resp cannot be nil")
	}

	atomic.StoreUint32(&c.lastUseTime, uint32(time.Now().Unix()-startTimeUnix))

	// Free up resources occupied by response before sending the request,
	// so the GC may reclaim these resources (e.g. response body).
	resp.Reset()

	// If we detected a redirect to another schema
	if req.schemaUpdate {
		c.IsTLS = bytes.Equal(req.URI().Scheme(), strHTTPS)
		c.Addr = addMissingPort(string(req.Host()), c.IsTLS)
		c.addrIdx = 0
		c.addrs = nil
		req.schemaUpdate = false
		req.SetConnectionClose()
	}

	cc, err := c.acquireConn()
	if err != nil {
		return false, err
	}
	conn := cc.c

	resp.parseNetConn(conn)

	if c.WriteTimeout > 0 {
		// Set Deadline every time, since golang has fixed the performance issue
		// See https://github.com/golang/go/issues/15133#issuecomment-271571395 for details
		currentTime := time.Now()
		if err = conn.SetWriteDeadline(currentTime.Add(c.WriteTimeout)); err != nil {
			c.closeConn(cc)
			return true, err
		}
	}

	resetConnection := false
	if c.MaxConnDuration > 0 && time.Since(cc.createdTime) > c.MaxConnDuration && !req.ConnectionClose() {
		req.SetConnectionClose()
		resetConnection = true
	}

	userAgentOld := req.Header.UserAgent()
	if len(userAgentOld) == 0 {
		req.Header.userAgent = c.getClientName()
	}
	bw := c.acquireWriter(conn)
	err = req.Write(bw)

	if resetConnection {
		req.Header.ResetConnectionClose()
	}

	if err == nil {
		err = bw.Flush()
	}
	if err != nil {
		c.releaseWriter(bw)
		c.closeConn(cc)
		return true, err
	}
	c.releaseWriter(bw)

	if c.ReadTimeout > 0 {
		// Set Deadline every time, since golang has fixed the performance issue
		// See https://github.com/golang/go/issues/15133#issuecomment-271571395 for details
		currentTime := time.Now()
		if err = conn.SetReadDeadline(currentTime.Add(c.ReadTimeout)); err != nil {
			c.closeConn(cc)
			return true, err
		}
	}

	if !req.Header.IsGet() && req.Header.IsHead() {
		resp.SkipBody = true
	}
	if c.DisableHeaderNamesNormalizing {
		resp.Header.DisableNormalizing()
	}

	br := c.acquireReader(conn)
	if err = resp.ReadLimitBody(br, c.MaxResponseBodySize); err != nil {
		c.releaseReader(br)
		c.closeConn(cc)
		// Don't retry in case of ErrBodyTooLarge since we will just get the same again.
		retry := err != ErrBodyTooLarge
		return retry, err
	}
	c.releaseReader(br)

	if resetConnection || req.ConnectionClose() || resp.ConnectionClose() {
		c.closeConn(cc)
	} else {
		c.releaseConn(cc)
	}

	return false, err
}

func (c *HostClient) acquireConn() (*clientConn, error) {
	var cc *clientConn
	createConn := false
	startCleaner := false

	var n int
	c.connsLock.Lock()
	n = len(c.conns)
	if n == 0 {
		maxConns := c.MaxConns
		if maxConns <= 0 {
			maxConns = DefaultMaxConnsPerHost
		}
		if c.connsCount < maxConns {
			c.connsCount++
			createConn = true
			if !c.connsCleanerRun {
				startCleaner = true
				c.connsCleanerRun = true
			}
		}
	} else {
		n--
		cc = c.conns[n]
		c.conns[n] = nil
		c.conns = c.conns[:n]
	}
	c.connsLock.Unlock()

	if cc != nil {
		return cc, nil
	}
	if !createConn {
		return nil, ErrNoFreeConns
	}

	if startCleaner {
		go c.connsCleaner()
	}

	conn, err := c.dialHostHard()
	if err != nil {
		c.decConnsCount()
		return nil, err
	}
	cc = acquireClientConn(conn)

	return cc, nil
}

func clientDoDeadline(req *Request, resp *Response, deadline time.Time, c clientDoer) error {
	timeout := -time.Since(deadline)
	if timeout <= 0 {
		return ErrTimeout
	}

	var ch chan error
	chv := errorChPool.Get()
	if chv == nil {
		chv = make(chan error, 1)
	}
	ch = chv.(chan error)

	// Make req and resp copies, since on timeout they no longer
	// may be accessed.
	reqCopy := AcquireRequest()
	req.copyToSkipBody(reqCopy)
	swapRequestBody(req, reqCopy)
	respCopy := AcquireResponse()
	if resp != nil {
		// Not calling resp.copyToSkipBody(respCopy) here to avoid
		// unexpected messing with headers
		respCopy.SkipBody = resp.SkipBody
	}

	// Note that the request continues execution on ErrTimeout until
	// client-specific ReadTimeout exceeds. This helps limiting load
	// on slow hosts by MaxConns* concurrent requests.
	//
	// Without this 'hack' the load on slow host could exceed MaxConns*
	// concurrent requests, since timed out requests on client side
	// usually continue execution on the host.

	var mu sync.Mutex
	var timedout bool
        //这个goroutine是用来处理连接以及发送请求的
	go func() {
		errDo := c.Do(reqCopy, respCopy)
		mu.Lock()
		{
			if !timedout {
				if resp != nil {
					respCopy.copyToSkipBody(resp)
					swapResponseBody(resp, respCopy)
				}
				swapRequestBody(reqCopy, req)
				ch <- errDo
			}
		}
		mu.Unlock()

		ReleaseResponse(respCopy)
		ReleaseRequest(reqCopy)
	}()
        //这块内容是用来处理超时的
	tc := AcquireTimer(timeout)
	var err error
	select {
	case err = <-ch:
	case <-tc.C:
		mu.Lock()
		{
			timedout = true
			err = ErrTimeout
		}
		mu.Unlock()
	}
	ReleaseTimer(tc)

	select {
	case <-ch:
	default:
	}
	errorChPool.Put(chv)

	return err
}

// DoTimeout performs the given request and waits for response during
// the given timeout duration.
//
// Request must contain at least non-zero RequestURI with full url (including
// scheme and host) or non-zero Host header + RequestURI.
//
// The function doesn't follow redirects. Use Get* for following redirects.
//
// Response is ignored if resp is nil.
//
// ErrTimeout is returned if the response wasn't returned during
// the given timeout.
//
// ErrNoFreeConns is returned if all HostClient.MaxConns connections
// to the host are busy.
//
// It is recommended obtaining req and resp via AcquireRequest
// and AcquireResponse in performance-critical code.
//
// Warning: DoTimeout does not terminate the request itself. The request will
// continue in the background and the response will be discarded.
// If requests take too long and the connection pool gets filled up please
// try setting a ReadTimeout.
func (c *HostClient) DoTimeout(req *Request, resp *Response, timeout time.Duration) error {
	return clientDoTimeout(req, resp, timeout, c)
}