Support adding headers to before calloption header (#3038)

Co-authored-by: Ibrahim Barghouthi <ibrahim.barghouthi@cenomi.com>

transport/http/calloption.go

@@ -17,9 +17,10 @@ type CallOption interface {
 }
 
 type callInfo struct {
-	contentType  string
-	operation    string
-	pathTemplate string
+	contentType   string
+	operation     string
+	pathTemplate  string
+	headerCarrier *http.Header
 }
 
 // EmptyCallOption does not alter the Call configuration.
@@ -102,6 +103,11 @@ type HeaderCallOption struct {
 	header *http.Header
 }
 
+func (o HeaderCallOption) before(c *callInfo) error {
+	c.headerCarrier = o.header
+	return nil
+}
+
 func (o HeaderCallOption) after(_ *callInfo, cs *csAttempt) {
 	if cs.res != nil && cs.res.Header != nil {
 		*o.header = cs.res.Header

transport/http/calloption_test.go

@@ -86,6 +86,19 @@ func TestHeader(t *testing.T) {
 	}
 }
 
+func TestHeaderCallOption_before(t *testing.T) {
+	h := http.Header{"A": []string{"123"}}
+	c := &callInfo{}
+	o := Header(&h)
+	err := o.before(c)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(&h, c.headerCarrier) {
+		t.Errorf("want: %v,got: %v", &h, o.(HeaderCallOption).header)
+	}
+}
+
 func TestHeaderCallOption_after(t *testing.T) {
 	h := http.Header{"A": []string{"123"}}
 	c := &callInfo{}

transport/http/client.go

@@ -231,6 +231,10 @@ func (client *Client) Invoke(ctx context.Context, method, path string, args inte
 	if err != nil {
 		return err
 	}
+	if c.headerCarrier != nil {
+		req.Header = *c.headerCarrier
+	}
+
 	if contentType != "" {
 		req.Header.Set("Content-Type", c.contentType)
 	}