代码版本:go1.20.2
咱们晓得在用go的http client时不须要咱们被动敞开Request Body,上面你Client.Do的源码应用阐明:
//src/net/http/client.go//...// 这里说了底层的Transport会被动敞开request Body// The request Body, if non-nil, will be closed by the underlying// Transport, even on errors.//// ...func (c *Client) Do(req *Request) (*Response, error) { return c.do(req)}咱们在我的项目中须要用到这个个性，就是须要client被动帮忙咱们敞开request.Body，然而咱们发现协程泄露，最初定位到可能是因为request.Body没有被被动敞开导致.难懂是官网的形容有问题吗？最初咱们在github issue中看到了有人提出request.Body在特定状况下不会被关掉的场景, 最初官网也进行了修复.
咱们先来看下这个issue(https://github.com/golang/go/issues/49621):
他还写了演示示例(https://play.golang.com/p/lku8lEgiPu6)
重点次要是这上图中说的在writeLoop()里,可能pc.writech和pc.closech都有内容，然而执行到了<-pc.closech导致Request.Body没有被close
咱们先来看下writeLoop()源码,重点看下中文正文:
//src/net/http/transport.gofunc (pc *persistConn) writeLoop() { defer close(pc.writeLoopDone) for { select { case wr := <-pc.writech: startBytesWritten := pc.nwrite // 这外面会去敞开Request.Body,具体细节就不去看了 err := wr.req.Request.write(pc.bw, pc.isProxy, wr.req.extra, pc.waitForContinue(wr.continueCh)) if bre, ok := err.(requestBodyReadError); ok { //... } if err == nil { err = pc.bw.Flush() } if err != nil { if pc.nwrite == startBytesWritten { err = nothingWrittenError{err} } } pc.writeErrCh <- err // to the body reader, which might recycle us wr.ch <- err // to the roundTrip function if err != nil { pc.close(err) return } case <-pc.closech: //间接退出 return } }}咱们能够看到如果失常申请下须要进入到case wr := <-pc.writech才会对request进行操作，才会在外面close request.Body.如果case wr := <-pc.writech和case <-pc.closech都满足，然而进入到了case <-pc.closech就会导致request.Body不会被敞开。那么这种状况在什么时候会产生了呢？
//src/net/http/transport.gofunc (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) { // ... // Write the request concurrently with waiting for a response, // in case the server decides to reply before reading our full // request body. startBytesWritten := pc.nwrite writeErrCh := make(chan error, 1) // 这里写入pc.writech pc.writech <- writeRequest{req, writeErrCh, continueCh} //...}下面的roundTrip()写入了pc.writech，然而pc.closech是在其余协程写入的
//src/net/http/transport.go// close closes the underlying TCP connection and closes// the pc.closech channel.//// The provided err is only for testing and debugging; in normal// circumstances it should never be seen by users.func (pc *persistConn) close(err error) { pc.mu.Lock() defer pc.mu.Unlock() pc.closeLocked(err)}func (pc *persistConn) closeLocked(err error) { if err == nil { panic("nil error") } pc.broken = true if pc.closed == nil { pc.closed = err pc.t.decConnsPerHost(pc.cacheKey) // Close HTTP/1 (pc.alt == nil) connection. // HTTP/2 closes its connection itself. if pc.alt == nil { if err != errCallerOwnsConn { pc.conn.Close() } close(pc.closech) // 这里唤醒pc.closech } } pc.mutateHeaderFunc = nil}咱们能够看到pc.closech次要是在persistConn close()的时候唤醒.所以大抵逻辑就是申请到了一条连贯persistConn而后在Read/Write的时候疾速失败，因为这两个在不同的协程导致pc.writech和pc.closech同时满足条件。go官网修复了这个bug(https://go-review.googlesource.com/c/go/+/461675)，咱们来看下怎么修复的：
https://go-review.googlesource.com/c/go/+/461675/4/src/net/ht...
看下面批改局部就是在(t *Transport) roundTrip(req *Request)外面再去尝试敞开request.Body.咱们再看下这次pr的测试用例，很清晰:
https://go-review.googlesource.com/c/go/+/461675/4/src/net/ht...
上面把重要局部解释下:
// https://go.dev/issue/49621func TestConnClosedBeforeRequestIsWritten(t *testing.T) { run(t, testConnClosedBeforeRequestIsWritten, testNotParallel, []testMode{http1Mode})}func testConnClosedBeforeRequestIsWritten(t *testing.T, mode testMode) { ts := newClientServerTest(t, mode, HandlerFunc(func(w ResponseWriter, r *Request) {}), func(tr *Transport) { tr.DialContext = func(_ context.Context, network, addr string) (net.Conn, error) { // Connection会疾速返回谬误 return &funcConn{ // 这里本人定义一个conn，不论是Read还是Write都会即刻返回谬误 read: func([]byte) (int, error) { return 0, errors.New("error") }, write: func([]byte) (int, error) { return 0, errors.New("error") }, }, nil } }, ).ts // 这里设置了一个hook就是在进入RoundTrip前劳动一下给足够的工夫让closech被close SetEnterRoundTripHook(func() { time.Sleep(1 * time.Millisecond) }) defer SetEnterRoundTripHook(nil) var closes int _, err := ts.Client().Post(ts.URL, "text/plain", countCloseReader{&closes, strings.NewReader("hello")}) if err == nil { t.Fatalf("expected request to fail, but it did not") } // 这里的closes应该等于1 if closes != 1 { t.Errorf("after RoundTrip, request body was closed %v times; want 1", closes) }}目前这个bug fix曾经合入了master,然而什么时候公布到正式版本未知
总结
不要太置信官网的操作，官网也是可能有bug的，要大胆猜疑并去摸索。
相干链接
- bug fix: https://go-review.googlesource.com/c/go/+/461675
- issue: https://github.com/golang/go/issues/49621