WIP

bson/marshal.go

@@ -73,22 +73,32 @@ func MarshalValue(val interface{}) (bsontype.Type, []byte, error) {
 	return MarshalValueWithRegistry(DefaultRegistry, val)
 }
 
-// MarshalValueAppend will append the BSON encoding of val to dst. If dst is not large enough to hold the BSON encoding
-// of val, dst will be grown.
-//
-// Deprecated: Appending individual BSON elements to an existing slice will not be supported in Go
-// Driver 2.0.
-func MarshalValueAppend(dst []byte, val interface{}) (bsontype.Type, []byte, error) {
-	return MarshalValueAppendWithRegistry(DefaultRegistry, dst, val)
-}
-
 // MarshalValueWithRegistry returns the BSON encoding of val using Registry r.
 //
 // Deprecated: Using a custom registry to marshal individual BSON values will not be supported in Go
 // Driver 2.0.
 func MarshalValueWithRegistry(r *bsoncodec.Registry, val interface{}) (bsontype.Type, []byte, error) {
-	dst := make([]byte, 0)
-	return MarshalValueAppendWithRegistry(r, dst, val)
+	sw := new(bsonrw.SliceWriter)
+	*sw = make([]byte, 0)
+	vwFlusher := bvwPool.GetAtModeElement(sw)
+
+	// get an Encoder and encode the value
+	enc := encPool.Get().(*Encoder)
+	defer encPool.Put(enc)
+	enc.Reset(vwFlusher)
+	enc.ec = bsoncodec.EncodeContext{Registry: r}
+	if err := enc.Encode(val); err != nil {
+		return 0, nil, err
+	}
+
+	// flush the bytes written because we cannot guarantee that a full document has been written
+	// after the flush, *sw will be in the format
+	// [value type, 0 (null byte to indicate end of empty element name), value bytes..]
+	if err := vwFlusher.Flush(); err != nil {
+		return 0, nil, err
+	}
+	buffer := *sw
+	return bsontype.Type(buffer[0]), buffer[2:], nil
 }
 
 // MarshalValueWithContext returns the BSON encoding of val using EncodeContext ec.