Method probeRequestBody

transfer.go:179–219

probeRequestBody reads a byte from t.Body to see whether it's empty (returns io.EOF right away). But because we've had problems with this blocking users in the past (issue 17480) when the body is a pipe (perhaps waiting on the response headers before the pipe is fed data), we need to be careful and

()

// In other words, this delay will not normally affect anybody, and there
// are workarounds if it does.
func (t *transferWriter) probeRequestBody() {
	t.ByteReadCh = make(chan readResult, 1)
	go func(body io.Reader) {
		var buf [1]byte
		var rres readResult
		rres.n, rres.err = body.Read(buf[:])
		if rres.n == 1 {
			rres.b = buf[0]
		}
		t.ByteReadCh <- rres
		close(t.ByteReadCh)
	}(t.Body)
	timer := time.NewTimer(200 * time.Millisecond)
	select {
	case rres := <-t.ByteReadCh:
		timer.Stop()
		if rres.n == 0 && rres.err == io.EOF {
			// It was empty.
			t.Body = nil
			t.ContentLength = 0
		} else if rres.n == 1 {
			if rres.err != nil {
				t.Body = io.MultiReader(&byteReader{b: rres.b}, errorReader{rres.err})
			} else {
				t.Body = io.MultiReader(&byteReader{b: rres.b}, t.Body)
			}
		} else if rres.err != nil {
			t.Body = errorReader{rres.err}
		}
	case <-timer.C:
		// Too slow. Don't wait. Read it later, and keep
		// assuming that this is ContentLength == -1
		// (unknown), which means we'll send a
		// "Transfer-Encoding: chunked" header.
		t.Body = io.MultiReader(finishAsyncByteRead{t}, t.Body)
		// Request that Request.Write flush the headers to the
		// network before writing the body, since our body may not
		// become readable until it's seen the response headers.
		t.FlushHeaders = true
	}
}

func noResponseBodyExpected(requestMethod string) bool {
	return requestMethod == "HEAD"