proto: implement Merge
Change-Id: Ibb579bf5ad8548359dfd9805fd3022bcd53a6379
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/183679
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/proto/merge.go b/proto/merge.go
new file mode 100644
index 0000000..7cea77d
--- /dev/null
+++ b/proto/merge.go
@@ -0,0 +1,78 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package proto
+
+import "google.golang.org/protobuf/reflect/protoreflect"
+
+// Merge merges src into dst, which must be messages with the same descriptor.
+//
+// Populated scalar fields in src are copied to dst, while populated
+// singular messages in src are merged into dst by recursively calling Merge.
+// The elements of every list field in src is appended to the corresponded
+// list fields in dst. The entries of every map field in src is copied into
+// the corresponding map field in dst, possibly replacing existing entries.
+// The unknown fields of src are appended to the unknown fields of dst.
+func Merge(dst, src Message) {
+ mergeMessage(dst.ProtoReflect(), src.ProtoReflect())
+}
+
+func mergeMessage(dst, src protoreflect.Message) {
+ if dst.Descriptor() != src.Descriptor() {
+ panic("descriptor mismatch")
+ }
+
+ src.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
+ switch {
+ case fd.IsList():
+ mergeList(dst.Mutable(fd).List(), v.List(), fd)
+ case fd.IsMap():
+ mergeMap(dst.Mutable(fd).Map(), v.Map(), fd.MapValue())
+ case fd.Message() != nil:
+ mergeMessage(dst.Mutable(fd).Message(), v.Message())
+ case fd.Kind() == protoreflect.BytesKind:
+ dst.Set(fd, cloneBytes(v))
+ default:
+ dst.Set(fd, v)
+ }
+ return true
+ })
+
+ dst.SetUnknown(append(dst.GetUnknown(), src.GetUnknown()...))
+}
+
+func mergeList(dst, src protoreflect.List, fd protoreflect.FieldDescriptor) {
+ for i := 0; i < src.Len(); i++ {
+ switch v := src.Get(i); {
+ case fd.Message() != nil:
+ m := dst.NewMessage()
+ mergeMessage(m, v.Message())
+ dst.Append(protoreflect.ValueOf(m))
+ case fd.Kind() == protoreflect.BytesKind:
+ dst.Append(cloneBytes(v))
+ default:
+ dst.Append(v)
+ }
+ }
+}
+
+func mergeMap(dst, src protoreflect.Map, fd protoreflect.FieldDescriptor) {
+ src.Range(func(k protoreflect.MapKey, v protoreflect.Value) bool {
+ switch {
+ case fd.Message() != nil:
+ m := dst.NewMessage()
+ mergeMessage(m, v.Message())
+ dst.Set(k, protoreflect.ValueOf(m)) // may replace existing entry
+ case fd.Kind() == protoreflect.BytesKind:
+ dst.Set(k, cloneBytes(v))
+ default:
+ dst.Set(k, v)
+ }
+ return true
+ })
+}
+
+func cloneBytes(v protoreflect.Value) protoreflect.Value {
+ return protoreflect.ValueOf(append([]byte{}, v.Bytes()...))
+}