internal/impl/codec_extension.go

// 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 impl

import (
	"sync"
	"sync/atomic"

	"google.golang.org/protobuf/internal/encoding/wire"
	"google.golang.org/protobuf/internal/errors"
	pref "google.golang.org/protobuf/reflect/protoreflect"
)

type extensionFieldInfo struct {
	wiretag             uint64
	tagsize             int
	unmarshalNeedsValue bool
	funcs               valueCoderFuncs
	validation          validationInfo
}

var legacyExtensionFieldInfoCache sync.Map // map[protoreflect.ExtensionType]*extensionFieldInfo

func getExtensionFieldInfo(xt pref.ExtensionType) *extensionFieldInfo {
	if xi, ok := xt.(*ExtensionInfo); ok {
		xi.lazyInit()
		return xi.info
	}
	return legacyLoadExtensionFieldInfo(xt)
}

// legacyLoadExtensionFieldInfo dynamically loads a *ExtensionInfo for xt.
func legacyLoadExtensionFieldInfo(xt pref.ExtensionType) *extensionFieldInfo {
	if xi, ok := legacyExtensionFieldInfoCache.Load(xt); ok {
		return xi.(*extensionFieldInfo)
	}
	e := makeExtensionFieldInfo(xt.TypeDescriptor())
	if e, ok := legacyMessageTypeCache.LoadOrStore(xt, e); ok {
		return e.(*extensionFieldInfo)
	}
	return e
}

func makeExtensionFieldInfo(xd pref.ExtensionDescriptor) *extensionFieldInfo {
	var wiretag uint64
	if !xd.IsPacked() {
		wiretag = wire.EncodeTag(xd.Number(), wireTypes[xd.Kind()])
	} else {
		wiretag = wire.EncodeTag(xd.Number(), wire.BytesType)
	}
	e := &extensionFieldInfo{
		wiretag: wiretag,
		tagsize: wire.SizeVarint(wiretag),
		funcs:   encoderFuncsForValue(xd),
	}
	// Does the unmarshal function need a value passed to it?
	// This is true for composite types, where we pass in a message, list, or map to fill in,
	// and for enums, where we pass in a prototype value to specify the concrete enum type.
	switch xd.Kind() {
	case pref.MessageKind, pref.GroupKind, pref.EnumKind:
		e.unmarshalNeedsValue = true
	default:
		if xd.Cardinality() == pref.Repeated {
			e.unmarshalNeedsValue = true
		}
	}
	return e
}

type lazyExtensionValue struct {
	atomicOnce uint32 // atomically set if value is valid
	mu         sync.Mutex
	xi         *extensionFieldInfo
	value      pref.Value
	b          []byte
	fn         func() pref.Value
}

type ExtensionField struct {
	typ pref.ExtensionType

	// value is either the value of GetValue,
	// or a *lazyExtensionValue that then returns the value of GetValue.
	value pref.Value
	lazy  *lazyExtensionValue
}

func (f *ExtensionField) appendLazyBytes(xt pref.ExtensionType, xi *extensionFieldInfo, num wire.Number, wtyp wire.Type, b []byte) {
	if f.lazy == nil {
		f.lazy = &lazyExtensionValue{xi: xi}
	}
	f.typ = xt
	f.lazy.xi = xi
	f.lazy.b = wire.AppendTag(f.lazy.b, num, wtyp)
	f.lazy.b = append(f.lazy.b, b...)
}

func (f *ExtensionField) canLazy(xt pref.ExtensionType) bool {
	if f.typ == nil {
		return true
	}
	if f.typ == xt && f.lazy != nil && atomic.LoadUint32(&f.lazy.atomicOnce) == 0 {
		return true
	}
	return false
}

func (f *ExtensionField) lazyInit() {
	f.lazy.mu.Lock()
	defer f.lazy.mu.Unlock()
	if f.lazy.xi != nil {
		b := f.lazy.b
		val := f.typ.New()
		for len(b) > 0 {
			var tag uint64
			if b[0] < 0x80 {
				tag = uint64(b[0])
				b = b[1:]
			} else if len(b) >= 2 && b[1] < 128 {
				tag = uint64(b[0]&0x7f) + uint64(b[1])<<7
				b = b[2:]
			} else {
				var n int
				tag, n = wire.ConsumeVarint(b)
				if n < 0 {
					panic(errors.New("bad tag in lazy extension decoding"))
				}
				b = b[n:]
			}
			num := wire.Number(tag >> 3)
			wtyp := wire.Type(tag & 7)
			var out unmarshalOutput
			var err error
			val, out, err = f.lazy.xi.funcs.unmarshal(b, val, num, wtyp, unmarshalOptions{}) // TODO: options
			if err != nil {
				panic(errors.New("decode failure in lazy extension decoding: %v", err))
			}
			b = b[out.n:]
		}
		f.lazy.value = val
	} else {
		f.lazy.value = f.lazy.fn()
	}
	f.lazy.xi = nil
	f.lazy.fn = nil
	f.lazy.b = nil
	atomic.StoreUint32(&f.lazy.atomicOnce, 1)
}

// Set sets the type and value of the extension field.
// This must not be called concurrently.
func (f *ExtensionField) Set(t pref.ExtensionType, v pref.Value) {
	f.typ = t
	f.value = v
	f.lazy = nil
}

// SetLazy sets the type and a value that is to be lazily evaluated upon first use.
// This must not be called concurrently.
func (f *ExtensionField) SetLazy(t pref.ExtensionType, fn func() pref.Value) {
	f.typ = t
	f.lazy = &lazyExtensionValue{fn: fn}
}

// Value returns the value of the extension field.
// This may be called concurrently.
func (f *ExtensionField) Value() pref.Value {
	if f.lazy != nil {
		if atomic.LoadUint32(&f.lazy.atomicOnce) == 0 {
			f.lazyInit()
		}
		return f.lazy.value
	}
	return f.value
}

// Type returns the type of the extension field.
// This may be called concurrently.
func (f ExtensionField) Type() pref.ExtensionType {
	return f.typ
}

// IsSet returns whether the extension field is set.
// This may be called concurrently.
func (f ExtensionField) IsSet() bool {
	return f.typ != nil
}

// Deprecated: Do not use.
func (f ExtensionField) HasType() bool {
	return f.typ != nil
}

// Deprecated: Do not use.
func (f ExtensionField) GetType() pref.ExtensionType {
	return f.typ
}

// Deprecated: Do not use.
func (f *ExtensionField) SetType(t pref.ExtensionType) {
	f.typ = t
}

// Deprecated: Do not use.
func (f ExtensionField) HasValue() bool {
	return f.value.IsValid() || f.lazy != nil
}

// Deprecated: Do not use.
func (f ExtensionField) GetValue() interface{} {
	return f.typ.InterfaceOf(f.Value())
}

// Deprecated: Do not use.
func (f *ExtensionField) SetEagerValue(ival interface{}) {
	f.value = f.typ.ValueOf(ival)
}

// Deprecated: Do not use.
func (f *ExtensionField) SetLazyValue(fn func() interface{}) {
	f.SetLazy(f.typ, func() pref.Value {
		return f.typ.ValueOf(fn())
	})
}