Fix http transport client blocking recv (#2744)

* reproduce blocking recv

* fix blocking recv call on httpTransportClient

* prevent race condition

* refactoring

transport/http_client.go

@@ -111,9 +111,17 @@ func (h *httpTransportClient) Recv(msg *Message) (err error) {
 	var req *http.Request
 
 	if !h.dialOpts.Stream {
-		rc, ok := <-h.req
+
+		var rc *http.Request
+		var ok bool
+
+		h.Lock()
+		select {
+		case rc, ok = <-h.req:
+		default:
+		}
+
 		if !ok {
-			h.Lock()
 			if len(h.reqList) == 0 {
 				h.Unlock()
 				return io.EOF
@@ -121,8 +129,8 @@ func (h *httpTransportClient) Recv(msg *Message) (err error) {
 
 			rc = h.reqList[0]
 			h.reqList = h.reqList[1:]
-			h.Unlock()
 		}
+		h.Unlock()
 
 		req = rc
 	}

transport/http_client_test.go

@@ -0,0 +1,77 @@
+package transport
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/pkg/errors"
+)
+
+func TestHttpTransportClient(t *testing.T) {
+	// arrange
+	l, c, err := echoHttpTransportClient("127.0.0.1:")
+	if err != nil {
+		t.Error(err)
+	}
+	defer l.Close()
+	defer c.Close()
+
+	// act + assert
+	N := cap(c.req)
+	// Send N+1 messages to overflow the buffered channel and place the extra message in the internal buffer
+	for i := 0; i < N+1; i++ {
+		body := fmt.Sprintf("msg-%d", i)
+		if err := c.Send(&Message{Body: []byte(body)}); err != nil {
+			t.Errorf("Unexpected send err: %v", err)
+		}
+	}
+
+	// consume all requests from the buffered channel
+	for i := 0; i < N; i++ {
+		msg := Message{}
+		if err := c.Recv(&msg); err != nil {
+			t.Errorf("Unexpected recv err: %v", err)
+		}
+	}
+
+	if len(c.reqList) != 1 {
+		t.Error("Unexpected reqList")
+	}
+
+	msg := Message{}
+	if err := c.Recv(&msg); err != nil {
+		t.Errorf("Unexpected recv err: %v", err)
+	}
+	want := fmt.Sprintf("msg-%d", N)
+	got := string(msg.Body)
+	if want != got {
+		t.Errorf("Unexpected message: got %q, want %q", got, want)
+	}
+}
+
+func echoHttpTransportClient(addr string) (*httpTransportListener, *httpTransportClient, error) {
+	tr := NewHTTPTransport()
+	l, err := tr.Listen(addr)
+	if err != nil {
+		return nil, nil, errors.Errorf("Unexpected listen err: %v", err)
+	}
+	c, err := tr.Dial(l.Addr())
+	if err != nil {
+		return nil, nil, errors.Errorf("Unexpected dial err: %v", err)
+	}
+	go l.Accept(echoHandler)
+	return l.(*httpTransportListener), c.(*httpTransportClient), nil
+}
+
+func echoHandler(sock Socket) {
+	defer sock.Close()
+	for {
+		var msg Message
+		if err := sock.Recv(&msg); err != nil {
+			return
+		}
+		if err := sock.Send(&msg); err != nil {
+			return
+		}
+	}
+}