adding PatchContext - this will create new context with original + patch metadata

metadata/metadata.go

@@ -28,3 +28,17 @@ func FromContext(ctx context.Context) (Metadata, bool) {
 func NewContext(ctx context.Context, md Metadata) context.Context {
 	return context.WithValue(ctx, metaKey{}, md)
 }
+
+// PatchContext : will add/replace source metadata fields with given patch metadata fields
+func PatchContext(ctx context.Context, patchMd Metadata) context.Context {
+	md, _ := ctx.Value(metaKey{}).(Metadata)
+	cmd := make(Metadata)
+	for k, v := range md {
+		cmd[k] = v
+	}
+	for k, v := range patchMd {
+		cmd[k] = v
+	}
+	return context.WithValue(ctx, metaKey{}, cmd)
+
+}

metadata/metadata_test.go

@@ -40,3 +40,28 @@ func TestMetadataContext(t *testing.T) {
 		t.Errorf("Expected metadata length 1 got %d", i)
 	}
 }
+func TestPatchContext(t *testing.T) {
+
+	original := Metadata{
+		"foo": "bar",
+	}
+
+	patch := Metadata{
+		"sumo": "demo",
+	}
+	ctx := NewContext(context.TODO(), original)
+
+	patchedCtx := PatchContext(ctx, patch)
+
+	patchedMd, ok := FromContext(patchedCtx)
+	if !ok {
+		t.Errorf("Unexpected error retrieving metadata, got %t", ok)
+	}
+
+	if patchedMd["sumo"] != patch["sumo"] {
+		t.Errorf("Expected key: %s val: %s, got key: %s val: %s", "sumo", patch["sumo"], "sumo", patchedMd["sumo"])
+	}
+	if patchedMd["foo"] != original["foo"] {
+		t.Errorf("Expected key: %s val: %s, got key: %s val: %s", "foo", original["foo"], "foo", patchedMd["foo"])
+	}
+}