Copy metadata

metadata/metadata.go

@@ -12,6 +12,14 @@ type metaKey struct{}
 // from Transport headers.
 type Metadata map[string]string
 
+func Copy(md Metadata) Metadata {
+	cmd := make(Metadata)
+	for k, v := range md {
+		cmd[k] = v
+	}
+	return cmd
+}
+
 func FromContext(ctx context.Context) (Metadata, bool) {
 	md, ok := ctx.Value(metaKey{}).(Metadata)
 	return md, ok

metadata/metadata_test.go

@@ -5,6 +5,21 @@ import (
 	"testing"
 )
 
+func TestMetadataCopy(t *testing.T) {
+	md := Metadata{
+		"foo": "bar",
+		"bar": "baz",
+	}
+
+	cp := Copy(md)
+
+	for k, v := range md {
+		if cv := cp[k]; cv != v {
+			t.Fatalf("Got %s:%s for %s:%s", k, cv, k, v)
+		}
+	}
+}
+
 func TestMetadataContext(t *testing.T) {
 	md := Metadata{
 		"foo": "bar",

wrapper.go

@@ -13,15 +13,11 @@ type clientWrapper struct {
 }
 
 func (c *clientWrapper) setHeaders(ctx context.Context) context.Context {
-	md := make(metadata.Metadata)
-
-	if mda, ok := metadata.FromContext(ctx); ok {
-		// make copy of metadata
-		for k, v := range mda {
-			md[k] = v
-		}
-	}
+	// copy metadata
+	mda, _ := metadata.FromContext(ctx)
+	md := metadata.Copy(mda)
 
+	// set headers
 	for k, v := range c.headers {
 		if _, ok := md[k]; !ok {
 			md[k] = v