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merge.go (4485B)

      1 // Copyright 2019 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 package proto
      6 
      7 import (
      8 	"fmt"
      9 
     10 	"google.golang.org/protobuf/reflect/protoreflect"
     11 	"google.golang.org/protobuf/runtime/protoiface"
     12 )
     13 
     14 // Merge merges src into dst, which must be a message with the same descriptor.
     15 //
     16 // Populated scalar fields in src are copied to dst, while populated
     17 // singular messages in src are merged into dst by recursively calling Merge.
     18 // The elements of every list field in src is appended to the corresponded
     19 // list fields in dst. The entries of every map field in src is copied into
     20 // the corresponding map field in dst, possibly replacing existing entries.
     21 // The unknown fields of src are appended to the unknown fields of dst.
     22 //
     23 // It is semantically equivalent to unmarshaling the encoded form of src
     24 // into dst with the UnmarshalOptions.Merge option specified.
     25 func Merge(dst, src Message) {
     26 	// TODO: Should nil src be treated as semantically equivalent to a
     27 	// untyped, read-only, empty message? What about a nil dst?
     28 
     29 	dstMsg, srcMsg := dst.ProtoReflect(), src.ProtoReflect()
     30 	if dstMsg.Descriptor() != srcMsg.Descriptor() {
     31 		if got, want := dstMsg.Descriptor().FullName(), srcMsg.Descriptor().FullName(); got != want {
     32 			panic(fmt.Sprintf("descriptor mismatch: %v != %v", got, want))
     33 		}
     34 		panic("descriptor mismatch")
     35 	}
     36 	mergeOptions{}.mergeMessage(dstMsg, srcMsg)
     37 }
     38 
     39 // Clone returns a deep copy of m.
     40 // If the top-level message is invalid, it returns an invalid message as well.
     41 func Clone(m Message) Message {
     42 	// NOTE: Most usages of Clone assume the following properties:
     43 	//	t := reflect.TypeOf(m)
     44 	//	t == reflect.TypeOf(m.ProtoReflect().New().Interface())
     45 	//	t == reflect.TypeOf(m.ProtoReflect().Type().Zero().Interface())
     46 	//
     47 	// Embedding protobuf messages breaks this since the parent type will have
     48 	// a forwarded ProtoReflect method, but the Interface method will return
     49 	// the underlying embedded message type.
     50 	if m == nil {
     51 		return nil
     52 	}
     53 	src := m.ProtoReflect()
     54 	if !src.IsValid() {
     55 		return src.Type().Zero().Interface()
     56 	}
     57 	dst := src.New()
     58 	mergeOptions{}.mergeMessage(dst, src)
     59 	return dst.Interface()
     60 }
     61 
     62 // mergeOptions provides a namespace for merge functions, and can be
     63 // exported in the future if we add user-visible merge options.
     64 type mergeOptions struct{}
     65 
     66 func (o mergeOptions) mergeMessage(dst, src protoreflect.Message) {
     67 	methods := protoMethods(dst)
     68 	if methods != nil && methods.Merge != nil {
     69 		in := protoiface.MergeInput{
     70 			Destination: dst,
     71 			Source:      src,
     72 		}
     73 		out := methods.Merge(in)
     74 		if out.Flags&protoiface.MergeComplete != 0 {
     75 			return
     76 		}
     77 	}
     78 
     79 	if !dst.IsValid() {
     80 		panic(fmt.Sprintf("cannot merge into invalid %v message", dst.Descriptor().FullName()))
     81 	}
     82 
     83 	src.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
     84 		switch {
     85 		case fd.IsList():
     86 			o.mergeList(dst.Mutable(fd).List(), v.List(), fd)
     87 		case fd.IsMap():
     88 			o.mergeMap(dst.Mutable(fd).Map(), v.Map(), fd.MapValue())
     89 		case fd.Message() != nil:
     90 			o.mergeMessage(dst.Mutable(fd).Message(), v.Message())
     91 		case fd.Kind() == protoreflect.BytesKind:
     92 			dst.Set(fd, o.cloneBytes(v))
     93 		default:
     94 			dst.Set(fd, v)
     95 		}
     96 		return true
     97 	})
     98 
     99 	if len(src.GetUnknown()) > 0 {
    100 		dst.SetUnknown(append(dst.GetUnknown(), src.GetUnknown()...))
    101 	}
    102 }
    103 
    104 func (o mergeOptions) mergeList(dst, src protoreflect.List, fd protoreflect.FieldDescriptor) {
    105 	// Merge semantics appends to the end of the existing list.
    106 	for i, n := 0, src.Len(); i < n; i++ {
    107 		switch v := src.Get(i); {
    108 		case fd.Message() != nil:
    109 			dstv := dst.NewElement()
    110 			o.mergeMessage(dstv.Message(), v.Message())
    111 			dst.Append(dstv)
    112 		case fd.Kind() == protoreflect.BytesKind:
    113 			dst.Append(o.cloneBytes(v))
    114 		default:
    115 			dst.Append(v)
    116 		}
    117 	}
    118 }
    119 
    120 func (o mergeOptions) mergeMap(dst, src protoreflect.Map, fd protoreflect.FieldDescriptor) {
    121 	// Merge semantics replaces, rather than merges into existing entries.
    122 	src.Range(func(k protoreflect.MapKey, v protoreflect.Value) bool {
    123 		switch {
    124 		case fd.Message() != nil:
    125 			dstv := dst.NewValue()
    126 			o.mergeMessage(dstv.Message(), v.Message())
    127 			dst.Set(k, dstv)
    128 		case fd.Kind() == protoreflect.BytesKind:
    129 			dst.Set(k, o.cloneBytes(v))
    130 		default:
    131 			dst.Set(k, v)
    132 		}
    133 		return true
    134 	})
    135 }
    136 
    137 func (o mergeOptions) cloneBytes(v protoreflect.Value) protoreflect.Value {
    138 	return protoreflect.ValueOfBytes(append([]byte{}, v.Bytes()...))
    139 }