text: // Go support for Protocol Buffers - Google's data interchange format
  //
  // Copyright 2017 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.
  
  package proto
  
  import (
  	"fmt"
  	"reflect"
  	"strings"
  	"sync"
  	"sync/atomic"
  )
  
  type generatedDiscarder interface {
  	XXX_DiscardUnknown()
  }
  
  // DiscardUnknown recursively discards all unknown fields from this message
  // and all embedded messages.
  //
  // When unmarshaling a message with unrecognized fields, the tags and values
  // of such fields are preserved in the Message. This allows a later call to
  // marshal to be able to produce a message that continues to have those
  // unrecognized fields. To avoid this, DiscardUnknown is used to
  // explicitly clear the unknown fields after unmarshaling.
  //
  // For proto2 messages, the unknown fields of message extensions are only
  // discarded from messages that have been accessed via GetExtension.
  func DiscardUnknown(m Message) {
  	if m, ok := m.(generatedDiscarder); ok {
  		m.XXX_DiscardUnknown()
  		return
  	}
  	// TODO: Dynamically populate a InternalMessageInfo for legacy messages,
  	// but the master branch has no implementation for InternalMessageInfo,
  	// so it would be more work to replicate that approach.
  	discardLegacy(m)
  }
  
  // DiscardUnknown recursively discards all unknown fields.
  func (a *InternalMessageInfo) DiscardUnknown(m Message) {
  	di := atomicLoadDiscardInfo(&a.discard)
  	if di == nil {
  		di = getDiscardInfo(reflect.TypeOf(m).Elem())
  		atomicStoreDiscardInfo(&a.discard, di)
  	}
  	di.discard(toPointer(&m))
  }
  
  type discardInfo struct {
  	typ reflect.Type
  
  	initialized int32 // 0: only typ is valid, 1: everything is valid
  	lock        sync.Mutex
  
  	fields       []discardFieldInfo
  	unrecognized field
  }
  
  type discardFieldInfo struct {
  	field   field // Offset of field, guaranteed to be valid
  	discard func(src pointer)
  }
  
  var (
  	discardInfoMap  = map[reflect.Type]*discardInfo{}
  	discardInfoLock sync.Mutex
  )
  
  func getDiscardInfo(t reflect.Type) *discardInfo {
  	discardInfoLock.Lock()
  	defer discardInfoLock.Unlock()
  	di := discardInfoMap[t]
  	if di == nil {
  		di = &discardInfo{typ: t}
  		discardInfoMap[t] = di
  	}
  	return di
  }
  
  func (di *discardInfo) discard(src pointer) {
  	if src.isNil() {
  		return // Nothing to do.
  	}
  
  	if atomic.LoadInt32(&di.initialized) == 0 {
  		di.computeDiscardInfo()
  	}
  
  	for _, fi := range di.fields {
  		sfp := src.offset(fi.field)
  		fi.discard(sfp)
  	}
  
  	// For proto2 messages, only discard unknown fields in message extensions
  	// that have been accessed via GetExtension.
  	if em, err := extendable(src.asPointerTo(di.typ).Interface()); err == nil {
  		// Ignore lock since DiscardUnknown is not concurrency safe.
  		emm, _ := em.extensionsRead()
  		for _, mx := range emm {
  			if m, ok := mx.value.(Message); ok {
  				DiscardUnknown(m)
  			}
  		}
  	}
  
  	if di.unrecognized.IsValid() {
  		*src.offset(di.unrecognized).toBytes() = nil
  	}
  }
  
  func (di *discardInfo) computeDiscardInfo() {
  	di.lock.Lock()
  	defer di.lock.Unlock()
  	if di.initialized != 0 {
  		return
  	}
  	t := di.typ
  	n := t.NumField()
  
  	for i := 0; i < n; i++ {
  		f := t.Field(i)
  		if strings.HasPrefix(f.Name, "XXX_") {
  			continue
  		}
  
  		dfi := discardFieldInfo{field: toField(&f)}
  		tf := f.Type
  
  		// Unwrap tf to get its most basic type.
  		var isPointer, isSlice bool
  		if tf.Kind() == reflect.Slice && tf.Elem().Kind() != reflect.Uint8 {
  			isSlice = true
  			tf = tf.Elem()
  		}
  		if tf.Kind() == reflect.Ptr {
  			isPointer = true
  			tf = tf.Elem()
  		}
  		if isPointer && isSlice && tf.Kind() != reflect.Struct {
  			panic(fmt.Sprintf("%v.%s cannot be a slice of pointers to primitive types", t, f.Name))
  		}
  
  		switch tf.Kind() {
  		case reflect.Struct:
  			switch {
  			case !isPointer:
  				panic(fmt.Sprintf("%v.%s cannot be a direct struct value", t, f.Name))
  			case isSlice: // E.g., []*pb.T
  				di := getDiscardInfo(tf)
  				dfi.discard = func(src pointer) {
  					sps := src.getPointerSlice()
  					for _, sp := range sps {
  						if !sp.isNil() {
  							di.discard(sp)
  						}
  					}
  				}
  			default: // E.g., *pb.T
  				di := getDiscardInfo(tf)
  				dfi.discard = func(src pointer) {
  					sp := src.getPointer()
  					if !sp.isNil() {
  						di.discard(sp)
  					}
  				}
  			}
  		case reflect.Map:
  			switch {
  			case isPointer || isSlice:
  				panic(fmt.Sprintf("%v.%s cannot be a pointer to a map or a slice of map values", t, f.Name))
  			default: // E.g., map[K]V
  				if tf.Elem().Kind() == reflect.Ptr { // Proto struct (e.g., *T)
  					dfi.discard = func(src pointer) {
  						sm := src.asPointerTo(tf).Elem()
  						if sm.Len() == 0 {
  							return
  						}
  						for _, key := range sm.MapKeys() {
  							val := sm.MapIndex(key)
  							DiscardUnknown(val.Interface().(Message))
  						}
  					}
  				} else {
  					dfi.discard = func(pointer) {} // Noop
  				}
  			}
  		case reflect.Interface:
  			// Must be oneof field.
  			switch {
  			case isPointer || isSlice:
  				panic(fmt.Sprintf("%v.%s cannot be a pointer to a interface or a slice of interface values", t, f.Name))
  			default: // E.g., interface{}
  				// TODO: Make this faster?
  				dfi.discard = func(src pointer) {
  					su := src.asPointerTo(tf).Elem()
  					if !su.IsNil() {
  						sv := su.Elem().Elem().Field(0)
  						if sv.Kind() == reflect.Ptr && sv.IsNil() {
  							return
  						}
  						switch sv.Type().Kind() {
  						case reflect.Ptr: // Proto struct (e.g., *T)
  							DiscardUnknown(sv.Interface().(Message))
  						}
  					}
  				}
  			}
  		default:
  			continue
  		}
  		di.fields = append(di.fields, dfi)
  	}
  
  	di.unrecognized = invalidField
  	if f, ok := t.FieldByName("XXX_unrecognized"); ok {
  		if f.Type != reflect.TypeOf([]byte{}) {
  			panic("expected XXX_unrecognized to be of type []byte")
  		}
  		di.unrecognized = toField(&f)
  	}
  
  	atomic.StoreInt32(&di.initialized, 1)
  }
  
  func discardLegacy(m Message) {
  	v := reflect.ValueOf(m)
  	if v.Kind() != reflect.Ptr || v.IsNil() {
  		return
  	}
  	v = v.Elem()
  	if v.Kind() != reflect.Struct {
  		return
  	}
  	t := v.Type()
  
  	for i := 0; i < v.NumField(); i++ {
  		f := t.Field(i)
  		if strings.HasPrefix(f.Name, "XXX_") {
  			continue
  		}
  		vf := v.Field(i)
  		tf := f.Type
  
  		// Unwrap tf to get its most basic type.
  		var isPointer, isSlice bool
  		if tf.Kind() == reflect.Slice && tf.Elem().Kind() != reflect.Uint8 {
  			isSlice = true
  			tf = tf.Elem()
  		}
  		if tf.Kind() == reflect.Ptr {
  			isPointer = true
  			tf = tf.Elem()
  		}
  		if isPointer && isSlice && tf.Kind() != reflect.Struct {
  			panic(fmt.Sprintf("%T.%s cannot be a slice of pointers to primitive types", m, f.Name))
  		}
  
  		switch tf.Kind() {
  		case reflect.Struct:
  			switch {
  			case !isPointer:
  				panic(fmt.Sprintf("%T.%s cannot be a direct struct value", m, f.Name))
  			case isSlice: // E.g., []*pb.T
  				for j := 0; j < vf.Len(); j++ {
  					discardLegacy(vf.Index(j).Interface().(Message))
  				}
  			default: // E.g., *pb.T
  				discardLegacy(vf.Interface().(Message))
  			}
  		case reflect.Map:
  			switch {
  			case isPointer || isSlice:
  				panic(fmt.Sprintf("%T.%s cannot be a pointer to a map or a slice of map values", m, f.Name))
  			default: // E.g., map[K]V
  				tv := vf.Type().Elem()
  				if tv.Kind() == reflect.Ptr && tv.Implements(protoMessageType) { // Proto struct (e.g., *T)
  					for _, key := range vf.MapKeys() {
  						val := vf.MapIndex(key)
  						discardLegacy(val.Interface().(Message))
  					}
  				}
  			}
  		case reflect.Interface:
  			// Must be oneof field.
  			switch {
  			case isPointer || isSlice:
  				panic(fmt.Sprintf("%T.%s cannot be a pointer to a interface or a slice of interface values", m, f.Name))
  			default: // E.g., test_proto.isCommunique_Union interface
  				if !vf.IsNil() && f.Tag.Get("protobuf_oneof") != "" {
  					vf = vf.Elem() // E.g., *test_proto.Communique_Msg
  					if !vf.IsNil() {
  						vf = vf.Elem()   // E.g., test_proto.Communique_Msg
  						vf = vf.Field(0) // E.g., Proto struct (e.g., *T) or primitive value
  						if vf.Kind() == reflect.Ptr {
  							discardLegacy(vf.Interface().(Message))
  						}
  					}
  				}
  			}
  		}
  	}
  
  	if vf := v.FieldByName("XXX_unrecognized"); vf.IsValid() {
  		if vf.Type() != reflect.TypeOf([]byte{}) {
  			panic("expected XXX_unrecognized to be of type []byte")
  		}
  		vf.Set(reflect.ValueOf([]byte(nil)))
  	}
  
  	// For proto2 messages, only discard unknown fields in message extensions
  	// that have been accessed via GetExtension.
  	if em, err := extendable(m); err == nil {
  		// Ignore lock since discardLegacy is not concurrency safe.
  		emm, _ := em.extensionsRead()
  		for _, mx := range emm {
  			if m, ok := mx.value.(Message); ok {
  				discardLegacy(m)
  			}
  		}
  	}
  }
  