GODRIVER-2655 Optimize ObjectIDFromHex a bit. (#1125)

Author: isopov

bson/primitive/objectid.go

@@ -82,14 +82,12 @@ func ObjectIDFromHex(s string) (ObjectID, error) {
 		return NilObjectID, ErrInvalidHex
 	}
 
-	b, err := hex.DecodeString(s)
+	var oid [12]byte
+	_, err := hex.Decode(oid[:], []byte(s))
 	if err != nil {
 		return NilObjectID, err
 	}
 
-	var oid [12]byte
-	copy(oid[:], b)
-
 	return oid, nil
 }
 

bson/primitive/objectid_test.go

@@ -35,6 +35,13 @@ func BenchmarkHex(b *testing.B) {
 	}
 }
 
+func BenchmarkObjectIDFromHex(b *testing.B) {
+	id := NewObjectID().Hex()
+	for i := 0; i < b.N; i++ {
+		_, _ = ObjectIDFromHex(id)
+	}
+}
+
 func TestFromHex_RoundTrip(t *testing.T) {
 	before := NewObjectID()
 	after, err := ObjectIDFromHex(before.Hex())