Response not returned when server forcefully closes connection

[ArminBTVS]

When using fasthttp.HostClient to send a request, a response is ignored if the remote side forcefully closes the connection (via RST flag) right after sending a response.

Instead of returning the error message: "An existing connection was forcibly closed by the remote host", I would expect the response to be read and a nil error to be returned from client.Do(req, resp).

According to the HTTP spec 8.2.2 the client SHOULD monitor the network connection for an error status while it is transmitting the request. In case of fasthttp the response is not read after writing failed due to a closed connection.

[erikdubbelboer]

I see you made some changes here: ArminBTVS@76a66e1
If those changes are working I'm willing to accept a pull request.

Also curious, do you know how net/http handles this?

[ArminBTVS]

@erikdubbelboer so I am still evaluating my fix a bit before I open a PR. For now it looks fine. I am not sure how exactly go solves this issue, but if you look at the unit test I wrote and replace the fasthttp client with the golang client it passes:

func TestRstConnResponseWhileSending(t *testing.T) {
	const expectedStatus = http.StatusTeapot
	const payload = "payload"

	srv, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err.Error())
	}

	go func() {
		conn, err := srv.Accept()
		if err != nil {
			t.Errorf(err.Error())
		}

		// Read at least one byte of the header
		// Otherwise we would have an unsolicited response
		ioutil.ReadAll(io.LimitReader(conn, 1))

		// Respond
		conn.Write([]byte("HTTP/1.1 418 Teapot\r\n\r\n"))

		// Forcefully close connection
		err = conn.(*net.TCPConn).SetLinger(0)
		if err != nil {
			t.Errorf(err.Error())
		}
		conn.Close()
	}()

	svrUrl := "http://" + srv.Addr().String()

	httpResp, err := http.Post(svrUrl, "application/json", strings.NewReader(payload))
	if err != nil {
		t.Fatal(err.Error())
	}
	if expectedStatus != httpResp.StatusCode {
		t.Fatalf("Expected %d status code, but got %d", expectedStatus, httpResp.StatusCode)
	}
}