text: // Go support for Protocol Buffers - Google's data interchange format
  //
  // Copyright 2011 The Go Authors.  All rights reserved.
  // https://github.com/golang/protobuf
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  // Protocol buffer deep copy and merge.
  // TODO: RawMessage.
  
  package proto
  
  import (
  	"fmt"
  	"log"
  	"reflect"
  	"strings"
  )
  
  // Clone returns a deep copy of a protocol buffer.
  func Clone(src Message) Message {
  	in := reflect.ValueOf(src)
  	if in.IsNil() {
  		return src
  	}
  	out := reflect.New(in.Type().Elem())
  	dst := out.Interface().(Message)
  	Merge(dst, src)
  	return dst
  }
  
  // Merger is the interface representing objects that can merge messages of the same type.
  type Merger interface {
  	// Merge merges src into this message.
  	// Required and optional fields that are set in src will be set to that value in dst.
  	// Elements of repeated fields will be appended.
  	//
  	// Merge may panic if called with a different argument type than the receiver.
  	Merge(src Message)
  }
  
  // generatedMerger is the custom merge method that generated protos will have.
  // We must add this method since a generate Merge method will conflict with
  // many existing protos that have a Merge data field already defined.
  type generatedMerger interface {
  	XXX_Merge(src Message)
  }
  
  // Merge merges src into dst.
  // Required and optional fields that are set in src will be set to that value in dst.
  // Elements of repeated fields will be appended.
  // Merge panics if src and dst are not the same type, or if dst is nil.
  func Merge(dst, src Message) {
  	if m, ok := dst.(Merger); ok {
  		m.Merge(src)
  		return
  	}
  
  	in := reflect.ValueOf(src)
  	out := reflect.ValueOf(dst)
  	if out.IsNil() {
  		panic("proto: nil destination")
  	}
  	if in.Type() != out.Type() {
  		panic(fmt.Sprintf("proto.Merge(%T, %T) type mismatch", dst, src))
  	}
  	if in.IsNil() {
  		return // Merge from nil src is a noop
  	}
  	if m, ok := dst.(generatedMerger); ok {
  		m.XXX_Merge(src)
  		return
  	}
  	mergeStruct(out.Elem(), in.Elem())
  }
  
  func mergeStruct(out, in reflect.Value) {
  	sprop := GetProperties(in.Type())
  	for i := 0; i < in.NumField(); i++ {
  		f := in.Type().Field(i)
  		if strings.HasPrefix(f.Name, "XXX_") {
  			continue
  		}
  		mergeAny(out.Field(i), in.Field(i), false, sprop.Prop[i])
  	}
  
  	if emIn, err := extendable(in.Addr().Interface()); err == nil {
  		emOut, _ := extendable(out.Addr().Interface())
  		mIn, muIn := emIn.extensionsRead()
  		if mIn != nil {
  			mOut := emOut.extensionsWrite()
  			muIn.Lock()
  			mergeExtension(mOut, mIn)
  			muIn.Unlock()
  		}
  	}
  
  	uf := in.FieldByName("XXX_unrecognized")
  	if !uf.IsValid() {
  		return
  	}
  	uin := uf.Bytes()
  	if len(uin) > 0 {
  		out.FieldByName("XXX_unrecognized").SetBytes(append([]byte(nil), uin...))
  	}
  }
  
  // mergeAny performs a merge between two values of the same type.
  // viaPtr indicates whether the values were indirected through a pointer (implying proto2).
  // prop is set if this is a struct field (it may be nil).
  func mergeAny(out, in reflect.Value, viaPtr bool, prop *Properties) {
  	if in.Type() == protoMessageType {
  		if !in.IsNil() {
  			if out.IsNil() {
  				out.Set(reflect.ValueOf(Clone(in.Interface().(Message))))
  			} else {
  				Merge(out.Interface().(Message), in.Interface().(Message))
  			}
  		}
  		return
  	}
  	switch in.Kind() {
  	case reflect.Bool, reflect.Float32, reflect.Float64, reflect.Int32, reflect.Int64,
  		reflect.String, reflect.Uint32, reflect.Uint64:
  		if !viaPtr && isProto3Zero(in) {
  			return
  		}
  		out.Set(in)
  	case reflect.Interface:
  		// Probably a oneof field; copy non-nil values.
  		if in.IsNil() {
  			return
  		}
  		// Allocate destination if it is not set, or set to a different type.
  		// Otherwise we will merge as normal.
  		if out.IsNil() || out.Elem().Type() != in.Elem().Type() {
  			out.Set(reflect.New(in.Elem().Elem().Type())) // interface -> *T -> T -> new(T)
  		}
  		mergeAny(out.Elem(), in.Elem(), false, nil)
  	case reflect.Map:
  		if in.Len() == 0 {
  			return
  		}
  		if out.IsNil() {
  			out.Set(reflect.MakeMap(in.Type()))
  		}
  		// For maps with value types of *T or []byte we need to deep copy each value.
  		elemKind := in.Type().Elem().Kind()
  		for _, key := range in.MapKeys() {
  			var val reflect.Value
  			switch elemKind {
  			case reflect.Ptr:
  				val = reflect.New(in.Type().Elem().Elem())
  				mergeAny(val, in.MapIndex(key), false, nil)
  			case reflect.Slice:
  				val = in.MapIndex(key)
  				val = reflect.ValueOf(append([]byte{}, val.Bytes()...))
  			default:
  				val = in.MapIndex(key)
  			}
  			out.SetMapIndex(key, val)
  		}
  	case reflect.Ptr:
  		if in.IsNil() {
  			return
  		}
  		if out.IsNil() {
  			out.Set(reflect.New(in.Elem().Type()))
  		}
  		mergeAny(out.Elem(), in.Elem(), true, nil)
  	case reflect.Slice:
  		if in.IsNil() {
  			return
  		}
  		if in.Type().Elem().Kind() == reflect.Uint8 {
  			// []byte is a scalar bytes field, not a repeated field.
  
  			// Edge case: if this is in a proto3 message, a zero length
  			// bytes field is considered the zero value, and should not
  			// be merged.
  			if prop != nil && prop.proto3 && in.Len() == 0 {
  				return
  			}
  
  			// Make a deep copy.
  			// Append to []byte{} instead of []byte(nil) so that we never end up
  			// with a nil result.
  			out.SetBytes(append([]byte{}, in.Bytes()...))
  			return
  		}
  		n := in.Len()
  		if out.IsNil() {
  			out.Set(reflect.MakeSlice(in.Type(), 0, n))
  		}
  		switch in.Type().Elem().Kind() {
  		case reflect.Bool, reflect.Float32, reflect.Float64, reflect.Int32, reflect.Int64,
  			reflect.String, reflect.Uint32, reflect.Uint64:
  			out.Set(reflect.AppendSlice(out, in))
  		default:
  			for i := 0; i < n; i++ {
  				x := reflect.Indirect(reflect.New(in.Type().Elem()))
  				mergeAny(x, in.Index(i), false, nil)
  				out.Set(reflect.Append(out, x))
  			}
  		}
  	case reflect.Struct:
  		mergeStruct(out, in)
  	default:
  		// unknown type, so not a protocol buffer
  		log.Printf("proto: don't know how to copy %v", in)
  	}
  }
  
  func mergeExtension(out, in map[int32]Extension) {
  	for extNum, eIn := range in {
  		eOut := Extension{desc: eIn.desc}
  		if eIn.value != nil {
  			v := reflect.New(reflect.TypeOf(eIn.value)).Elem()
  			mergeAny(v, reflect.ValueOf(eIn.value), false, nil)
  			eOut.value = v.Interface()
  		}
  		if eIn.enc != nil {
  			eOut.enc = make([]byte, len(eIn.enc))
  			copy(eOut.enc, eIn.enc)
  		}
  
  		out[extNum] = eOut
  	}
  }
  