metadata: add exclude to Copy func

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

metadata/metadata.go

@@ -67,11 +67,12 @@ func (md Metadata) Del(keys ...string) {
 }
 
 // Copy makes a copy of the metadata
-func Copy(md Metadata) Metadata {
+func Copy(md Metadata, exclude ...string) Metadata {
 	nmd := make(Metadata, len(md))
 	for k, v := range md {
 		nmd[k] = v
 	}
+	nmd.Del(exclude...)
 	return nmd
 }
 

metadata/metadata_test.go

@@ -189,3 +189,14 @@ func TestMetadataContext(t *testing.T) {
 		t.Errorf("Expected metadata length 1 got %d", i)
 	}
 }
+
+func TestCopy(t *testing.T) {
+	md := New(2)
+	md.Set("key1", "val1", "key2", "val2")
+	nmd := Copy(md, "key2")
+	if len(nmd) != 1 {
+		t.Fatal("Copy exclude not works")
+	} else if nmd["Key1"][0] != "val1" {
+		t.Fatal("Copy exclude not works")
+	}
+}