source: code/trunk/vendor/google.golang.org/protobuf/proto/merge.go@ 822

// 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 (
        "fmt"

        "google.golang.org/protobuf/reflect/protoreflect"
        "google.golang.org/protobuf/runtime/protoiface"
)

// Merge merges src into dst, which must be a message 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.
//
// It is semantically equivalent to unmarshaling the encoded form of src
// into dst with the UnmarshalOptions.Merge option specified.
func Merge(dst, src Message) {
        // TODO: Should nil src be treated as semantically equivalent to a
        // untyped, read-only, empty message? What about a nil dst?

        dstMsg, srcMsg := dst.ProtoReflect(), src.ProtoReflect()
        if dstMsg.Descriptor() != srcMsg.Descriptor() {
                if got, want := dstMsg.Descriptor().FullName(), srcMsg.Descriptor().FullName(); got != want {
                        panic(fmt.Sprintf("descriptor mismatch: %v != %v", got, want))
                }
                panic("descriptor mismatch")
        }
        mergeOptions{}.mergeMessage(dstMsg, srcMsg)
}

// Clone returns a deep copy of m.
// If the top-level message is invalid, it returns an invalid message as well.
func Clone(m Message) Message {
        // NOTE: Most usages of Clone assume the following properties:
        //      t := reflect.TypeOf(m)
        //      t == reflect.TypeOf(m.ProtoReflect().New().Interface())
        //      t == reflect.TypeOf(m.ProtoReflect().Type().Zero().Interface())
        //
        // Embedding protobuf messages breaks this since the parent type will have
        // a forwarded ProtoReflect method, but the Interface method will return
        // the underlying embedded message type.
        if m == nil {
                return nil
        }
        src := m.ProtoReflect()
        if !src.IsValid() {
                return src.Type().Zero().Interface()
        }
        dst := src.New()
        mergeOptions{}.mergeMessage(dst, src)
        return dst.Interface()
}

// mergeOptions provides a namespace for merge functions, and can be
// exported in the future if we add user-visible merge options.
type mergeOptions struct{}

func (o mergeOptions) mergeMessage(dst, src protoreflect.Message) {
        methods := protoMethods(dst)
        if methods != nil && methods.Merge != nil {
                in := protoiface.MergeInput{
                        Destination: dst,
                        Source:      src,
                }
                out := methods.Merge(in)
                if out.Flags&protoiface.MergeComplete != 0 {
                        return
                }
        }

        if !dst.IsValid() {
                panic(fmt.Sprintf("cannot merge into invalid %v message", dst.Descriptor().FullName()))
        }

        src.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
                switch {
                case fd.IsList():
                        o.mergeList(dst.Mutable(fd).List(), v.List(), fd)
                case fd.IsMap():
                        o.mergeMap(dst.Mutable(fd).Map(), v.Map(), fd.MapValue())
                case fd.Message() != nil:
                        o.mergeMessage(dst.Mutable(fd).Message(), v.Message())
                case fd.Kind() == protoreflect.BytesKind:
                        dst.Set(fd, o.cloneBytes(v))
                default:
                        dst.Set(fd, v)
                }
                return true
        })

        if len(src.GetUnknown()) > 0 {
                dst.SetUnknown(append(dst.GetUnknown(), src.GetUnknown()...))
        }
}

func (o mergeOptions) mergeList(dst, src protoreflect.List, fd protoreflect.FieldDescriptor) {
        // Merge semantics appends to the end of the existing list.
        for i, n := 0, src.Len(); i < n; i++ {
                switch v := src.Get(i); {
                case fd.Message() != nil:
                        dstv := dst.NewElement()
                        o.mergeMessage(dstv.Message(), v.Message())
                        dst.Append(dstv)
                case fd.Kind() == protoreflect.BytesKind:
                        dst.Append(o.cloneBytes(v))
                default:
                        dst.Append(v)
                }
        }
}

func (o mergeOptions) mergeMap(dst, src protoreflect.Map, fd protoreflect.FieldDescriptor) {
        // Merge semantics replaces, rather than merges into existing entries.
        src.Range(func(k protoreflect.MapKey, v protoreflect.Value) bool {
                switch {
                case fd.Message() != nil:
                        dstv := dst.NewValue()
                        o.mergeMessage(dstv.Message(), v.Message())
                        dst.Set(k, dstv)
                case fd.Kind() == protoreflect.BytesKind:
                        dst.Set(k, o.cloneBytes(v))
                default:
                        dst.Set(k, v)
                }
                return true
        })
}

func (o mergeOptions) cloneBytes(v protoreflect.Value) protoreflect.Value {
        return protoreflect.ValueOfBytes(append([]byte{}, v.Bytes()...))
}