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// Copyright 2009 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.
//go:generate go run encgen.go -output enc_helpers.go
package gob
import (
"encoding"
"encoding/binary"
"math"
"math/bits"
"reflect"
"sync"
)
const uint64Size = 8
type encHelper func(state *encoderState, v reflect.Value) bool
// encoderState is the global execution state of an instance of the encoder.
// Field numbers are delta encoded and always increase. The field
// number is initialized to -1 so 0 comes out as delta(1). A delta of
// 0 terminates the structure.
type encoderState struct {
enc *Encoder
b *encBuffer
sendZero bool // encoding an array element or map key/value pair; send zero values
fieldnum int // the last field number written.
buf [1 + uint64Size]byte // buffer used by the encoder; here to avoid allocation.
next *encoderState // for free list
}
// encBuffer is an extremely simple, fast implementation of a write-only byte buffer.
// It never returns a non-nil error, but Write returns an error value so it matches io.Writer.
type encBuffer struct {
data []byte
scratch [64]byte
}
var encBufferPool = sync.Pool{
New: func() any {
e := new(encBuffer)
e.data = e.scratch[0:0]
return e
},
}
func (e *encBuffer) writeByte(c byte) {
e.data = append(e.data, c)
}
func (e *encBuffer) Write(p []byte) (int, error) {
e.data = append(e.data, p...)
return len(p), nil
}
func (e *encBuffer) WriteString(s string) {
e.data = append(e.data, s...)
}
func (e *encBuffer) Len() int {
return len(e.data)
}
func (e *encBuffer) Bytes() []byte {
return e.data
}
func (e *encBuffer) Reset() {
if len(e.data) >= tooBig {
e.data = e.scratch[0:0]
} else {
e.data = e.data[0:0]
}
}
func (enc *Encoder) newEncoderState(b *encBuffer) *encoderState {
e := enc.freeList
if e == nil {
e = new(encoderState)
e.enc = enc
} else {
enc.freeList = e.next
}
e.sendZero = false
e.fieldnum = 0
e.b = b
if len(b.data) == 0 {
b.data = b.scratch[0:0]
}
return e
}
func (enc *Encoder) freeEncoderState(e *encoderState) {
e.next = enc.freeList
enc.freeList = e
}
// Unsigned integers have a two-state encoding. If the number is less
// than 128 (0 through 0x7F), its value is written directly.
// Otherwise the value is written in big-endian byte order preceded
// by the byte length, negated.
// encodeUint writes an encoded unsigned integer to state.b.
func (state *encoderState) encodeUint(x uint64) {
if x <= 0x7F {
state.b.writeByte(uint8(x))
return
}
binary.BigEndian.PutUint64(state.buf[1:], x)
bc := bits.LeadingZeros64(x) >> 3 // 8 - bytelen(x)
state.buf[bc] = uint8(bc - uint64Size) // and then we subtract 8 to get -bytelen(x)
state.b.Write(state.buf[bc : uint64Size+1])
}
// encodeInt writes an encoded signed integer to state.w.
// The low bit of the encoding says whether to bit complement the (other bits of the)
// uint to recover the int.
func (state *encoderState) encodeInt(i int64) {
var x uint64
if i < 0 {
x = uint64(^i<<1) | 1
} else {
x = uint64(i << 1)
}
state.encodeUint(x)
}
// encOp is the signature of an encoding operator for a given type.
type encOp func(i *encInstr, state *encoderState, v reflect.Value)
// The 'instructions' of the encoding machine
type encInstr struct {
op encOp
field int // field number in input
index []int // struct index
indir int // how many pointer indirections to reach the value in the struct
}
// update emits a field number and updates the state to record its value for delta encoding.
// If the instruction pointer is nil, it does nothing
func (state *encoderState) update(instr *encInstr) {
if instr != nil {
state.encodeUint(uint64(instr.field - state.fieldnum))
state.fieldnum = instr.field
}
}
// Each encoder for a composite is responsible for handling any
// indirections associated with the elements of the data structure.
// If any pointer so reached is nil, no bytes are written. If the
// data item is zero, no bytes are written. Single values - ints,
// strings etc. - are indirected before calling their encoders.
// Otherwise, the output (for a scalar) is the field number, as an
// encoded integer, followed by the field data in its appropriate
// format.
// encIndirect dereferences pv indir times and returns the result.
func encIndirect(pv reflect.Value, indir int) reflect.Value {
for ; indir > 0; indir-- {
if pv.IsNil() {
break
}
pv = pv.Elem()
}
return pv
}
// encBool encodes the bool referenced by v as an unsigned 0 or 1.
func encBool(i *encInstr, state *encoderState, v reflect.Value) {
b := v.Bool()
if b || state.sendZero {
state.update(i)
if b {
state.encodeUint(1)
} else {
state.encodeUint(0)
}
}
}
// encInt encodes the signed integer (int int8 int16 int32 int64) referenced by v.
func encInt(i *encInstr, state *encoderState, v reflect.Value) {
value := v.Int()
if value != 0 || state.sendZero {
state.update(i)
state.encodeInt(value)
}
}
// encUint encodes the unsigned integer (uint uint8 uint16 uint32 uint64 uintptr) referenced by v.
func encUint(i *encInstr, state *encoderState, v reflect.Value) {
value := v.Uint()
if value != 0 || state.sendZero {
state.update(i)
state.encodeUint(value)
}
}
// floatBits returns a uint64 holding the bits of a floating-point number.
// Floating-point numbers are transmitted as uint64s holding the bits
// of the underlying representation. They are sent byte-reversed, with
// the exponent end coming out first, so integer floating point numbers
// (for example) transmit more compactly. This routine does the
// swizzling.
func floatBits(f float64) uint64 {
u := math.Float64bits(f)
return bits.ReverseBytes64(u)
}
// encFloat encodes the floating point value (float32 float64) referenced by v.
func encFloat(i *encInstr, state *encoderState, v reflect.Value) {
f := v.Float()
if f != 0 || state.sendZero {
bits := floatBits(f)
state.update(i)
state.encodeUint(bits)
}
}
// encComplex encodes the complex value (complex64 complex128) referenced by v.
// Complex numbers are just a pair of floating-point numbers, real part first.
func encComplex(i *encInstr, state *encoderState, v reflect.Value) {
c := v.Complex()
if c != 0+0i || state.sendZero {
rpart := floatBits(real(c))
ipart := floatBits(imag(c))
state.update(i)
state.encodeUint(rpart)
state.encodeUint(ipart)
}
}
// encUint8Array encodes the byte array referenced by v.
// Byte arrays are encoded as an unsigned count followed by the raw bytes.
func encUint8Array(i *encInstr, state *encoderState, v reflect.Value) {
b := v.Bytes()
if len(b) > 0 || state.sendZero {
state.update(i)
state.encodeUint(uint64(len(b)))
state.b.Write(b)
}
}
// encString encodes the string referenced by v.
// Strings are encoded as an unsigned count followed by the raw bytes.
func encString(i *encInstr, state *encoderState, v reflect.Value) {
s := v.String()
if len(s) > 0 || state.sendZero {
state.update(i)
state.encodeUint(uint64(len(s)))
state.b.WriteString(s)
}
}
// encStructTerminator encodes the end of an encoded struct
// as delta field number of 0.
func encStructTerminator(i *encInstr, state *encoderState, v reflect.Value) {
state.encodeUint(0)
}
// Execution engine
// encEngine an array of instructions indexed by field number of the encoding
// data, typically a struct. It is executed top to bottom, walking the struct.
type encEngine struct {
instr []encInstr
}
const singletonField = 0
// valid reports whether the value is valid and a non-nil pointer.
// (Slices, maps, and chans take care of themselves.)
func valid(v reflect.Value) bool {
switch v.Kind() {
case reflect.Invalid:
return false
case reflect.Pointer:
return !v.IsNil()
}
return true
}
// encodeSingle encodes a single top-level non-struct value.
func (enc *Encoder) encodeSingle(b *encBuffer, engine *encEngine, value reflect.Value) {
state := enc.newEncoderState(b)
defer enc.freeEncoderState(state)
state.fieldnum = singletonField
// There is no surrounding struct to frame the transmission, so we must
// generate data even if the item is zero. To do this, set sendZero.
state.sendZero = true
instr := &engine.instr[singletonField]
if instr.indir > 0 {
value = encIndirect(value, instr.indir)
}
if valid(value) {
instr.op(instr, state, value)
}
}
// encodeStruct encodes a single struct value.
func (enc *Encoder) encodeStruct(b *encBuffer, engine *encEngine, value reflect.Value) {
if !valid(value) {
return
}
state := enc.newEncoderState(b)
defer enc.freeEncoderState(state)
state.fieldnum = -1
for i := 0; i < len(engine.instr); i++ {
instr := &engine.instr[i]
if i >= value.NumField() {
// encStructTerminator
instr.op(instr, state, reflect.Value{})
break
}
field := value.FieldByIndex(instr.index)
if instr.indir > 0 {
field = encIndirect(field, instr.indir)
// TODO: Is field guaranteed valid? If so we could avoid this check.
if !valid(field) {
continue
}
}
instr.op(instr, state, field)
}
}
// encodeArray encodes an array.
func (enc *Encoder) encodeArray(b *encBuffer, value reflect.Value, op encOp, elemIndir int, length int, helper encHelper) {
state := enc.newEncoderState(b)
defer enc.freeEncoderState(state)
state.fieldnum = -1
state.sendZero = true
state.encodeUint(uint64(length))
if helper != nil && helper(state, value) {
return
}
for i := 0; i < length; i++ {
elem := value.Index(i)
if elemIndir > 0 {
elem = encIndirect(elem, elemIndir)
// TODO: Is elem guaranteed valid? If so we could avoid this check.
if !valid(elem) {
errorf("encodeArray: nil element")
}
}
op(nil, state, elem)
}
}
// encodeReflectValue is a helper for maps. It encodes the value v.
func encodeReflectValue(state *encoderState, v reflect.Value, op encOp, indir int) {
for i := 0; i < indir && v.IsValid(); i++ {
v = reflect.Indirect(v)
}
if !v.IsValid() {
errorf("encodeReflectValue: nil element")
}
op(nil, state, v)
}
// encodeMap encodes a map as unsigned count followed by key:value pairs.
func (enc *Encoder) encodeMap(b *encBuffer, mv reflect.Value, keyOp, elemOp encOp, keyIndir, elemIndir int) {
state := enc.newEncoderState(b)
state.fieldnum = -1
state.sendZero = true
state.encodeUint(uint64(mv.Len()))
mi := mv.MapRange()
for mi.Next() {
encodeReflectValue(state, mi.Key(), keyOp, keyIndir)
encodeReflectValue(state, mi.Value(), elemOp, elemIndir)
}
enc.freeEncoderState(state)
}
// encodeInterface encodes the interface value iv.
// To send an interface, we send a string identifying the concrete type, followed
// by the type identifier (which might require defining that type right now), followed
// by the concrete value. A nil value gets sent as the empty string for the name,
// followed by no value.
func (enc *Encoder) encodeInterface(b *encBuffer, iv reflect.Value) {
// Gobs can encode nil interface values but not typed interface
// values holding nil pointers, since nil pointers point to no value.
elem := iv.Elem()
if elem.Kind() == reflect.Pointer && elem.IsNil() {
errorf("gob: cannot encode nil pointer of type %s inside interface", iv.Elem().Type())
}
state := enc.newEncoderState(b)
state.fieldnum = -1
state.sendZero = true
if iv.IsNil() {
state.encodeUint(0)
return
}
ut := userType(iv.Elem().Type())
namei, ok := concreteTypeToName.Load(ut.base)
if !ok {
errorf("type not registered for interface: %s", ut.base)
}
name := namei.(string)
// Send the name.
state.encodeUint(uint64(len(name)))
state.b.WriteString(name)
// Define the type id if necessary.
enc.sendTypeDescriptor(enc.writer(), state, ut)
// Send the type id.
enc.sendTypeId(state, ut)
// Encode the value into a new buffer. Any nested type definitions
// should be written to b, before the encoded value.
enc.pushWriter(b)
data := encBufferPool.Get().(*encBuffer)
data.Write(spaceForLength)
enc.encode(data, elem, ut)
if enc.err != nil {
error_(enc.err)
}
enc.popWriter()
enc.writeMessage(b, data)
data.Reset()
encBufferPool.Put(data)
if enc.err != nil {
error_(enc.err)
}
enc.freeEncoderState(state)
}
// isZero reports whether the value is the zero of its type.
func isZero(val reflect.Value) bool {
switch val.Kind() {
case reflect.Array:
for i := 0; i < val.Len(); i++ {
if !isZero(val.Index(i)) {
return false
}
}
return true
case reflect.Map, reflect.Slice, reflect.String:
return val.Len() == 0
case reflect.Bool:
return !val.Bool()
case reflect.Complex64, reflect.Complex128:
return val.Complex() == 0
case reflect.Chan, reflect.Func, reflect.Interface, reflect.Pointer:
return val.IsNil()
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return val.Int() == 0
case reflect.Float32, reflect.Float64:
return val.Float() == 0
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return val.Uint() == 0
case reflect.Struct:
for i := 0; i < val.NumField(); i++ {
if !isZero(val.Field(i)) {
return false
}
}
return true
}
panic("unknown type in isZero " + val.Type().String())
}
// encGobEncoder encodes a value that implements the GobEncoder interface.
// The data is sent as a byte array.
func (enc *Encoder) encodeGobEncoder(b *encBuffer, ut *userTypeInfo, v reflect.Value) {
// TODO: should we catch panics from the called method?
var data []byte
var err error
// We know it's one of these.
switch ut.externalEnc {
case xGob:
data, err = v.Interface().(GobEncoder).GobEncode()
case xBinary:
data, err = v.Interface().(encoding.BinaryMarshaler).MarshalBinary()
case xText:
data, err = v.Interface().(encoding.TextMarshaler).MarshalText()
}
if err != nil {
error_(err)
}
state := enc.newEncoderState(b)
state.fieldnum = -1
state.encodeUint(uint64(len(data)))
state.b.Write(data)
enc.freeEncoderState(state)
}
var encOpTable = [...]encOp{
reflect.Bool: encBool,
reflect.Int: encInt,
reflect.Int8: encInt,
reflect.Int16: encInt,
reflect.Int32: encInt,
reflect.Int64: encInt,
reflect.Uint: encUint,
reflect.Uint8: encUint,
reflect.Uint16: encUint,
reflect.Uint32: encUint,
reflect.Uint64: encUint,
reflect.Uintptr: encUint,
reflect.Float32: encFloat,
reflect.Float64: encFloat,
reflect.Complex64: encComplex,
reflect.Complex128: encComplex,
reflect.String: encString,
}
// encOpFor returns (a pointer to) the encoding op for the base type under rt and
// the indirection count to reach it.
func encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp, building map[*typeInfo]bool) (*encOp, int) {
ut := userType(rt)
// If the type implements GobEncoder, we handle it without further processing.
if ut.externalEnc != 0 {
return gobEncodeOpFor(ut)
}
// If this type is already in progress, it's a recursive type (e.g. map[string]*T).
// Return the pointer to the op we're already building.
if opPtr := inProgress[rt]; opPtr != nil {
return opPtr, ut.indir
}
typ := ut.base
indir := ut.indir
k := typ.Kind()
var op encOp
if int(k) < len(encOpTable) {
op = encOpTable[k]
}
if op == nil {
inProgress[rt] = &op
// Special cases
switch t := typ; t.Kind() {
case reflect.Slice:
if t.Elem().Kind() == reflect.Uint8 {
op = encUint8Array
break
}
// Slices have a header; we decode it to find the underlying array.
elemOp, elemIndir := encOpFor(t.Elem(), inProgress, building)
helper := encSliceHelper[t.Elem().Kind()]
op = func(i *encInstr, state *encoderState, slice reflect.Value) {
if !state.sendZero && slice.Len() == 0 {
return
}
state.update(i)
state.enc.encodeArray(state.b, slice, *elemOp, elemIndir, slice.Len(), helper)
}
case reflect.Array:
// True arrays have size in the type.
elemOp, elemIndir := encOpFor(t.Elem(), inProgress, building)
helper := encArrayHelper[t.Elem().Kind()]
op = func(i *encInstr, state *encoderState, array reflect.Value) {
state.update(i)
state.enc.encodeArray(state.b, array, *elemOp, elemIndir, array.Len(), helper)
}
case reflect.Map:
keyOp, keyIndir := encOpFor(t.Key(), inProgress, building)
elemOp, elemIndir := encOpFor(t.Elem(), inProgress, building)
op = func(i *encInstr, state *encoderState, mv reflect.Value) {
// We send zero-length (but non-nil) maps because the
// receiver might want to use the map. (Maps don't use append.)
if !state.sendZero && mv.IsNil() {
return
}
state.update(i)
state.enc.encodeMap(state.b, mv, *keyOp, *elemOp, keyIndir, elemIndir)
}
case reflect.Struct:
// Generate a closure that calls out to the engine for the nested type.
getEncEngine(userType(typ), building)
info := mustGetTypeInfo(typ)
op = func(i *encInstr, state *encoderState, sv reflect.Value) {
state.update(i)
// indirect through info to delay evaluation for recursive structs
enc := info.encoder.Load().(*encEngine)
state.enc.encodeStruct(state.b, enc, sv)
}
case reflect.Interface:
op = func(i *encInstr, state *encoderState, iv reflect.Value) {
if !state.sendZero && (!iv.IsValid() || iv.IsNil()) {
return
}
state.update(i)
state.enc.encodeInterface(state.b, iv)
}
}
}
if op == nil {
errorf("can't happen: encode type %s", rt)
}
return &op, indir
}
// gobEncodeOpFor returns the op for a type that is known to implement GobEncoder.
func gobEncodeOpFor(ut *userTypeInfo) (*encOp, int) {
rt := ut.user
if ut.encIndir == -1 {
rt = reflect.PointerTo(rt)
} else if ut.encIndir > 0 {
for i := int8(0); i < ut.encIndir; i++ {
rt = rt.Elem()
}
}
var op encOp
op = func(i *encInstr, state *encoderState, v reflect.Value) {
if ut.encIndir == -1 {
// Need to climb up one level to turn value into pointer.
if !v.CanAddr() {
errorf("unaddressable value of type %s", rt)
}
v = v.Addr()
}
if !state.sendZero && isZero(v) {
return
}
state.update(i)
state.enc.encodeGobEncoder(state.b, ut, v)
}
return &op, int(ut.encIndir) // encIndir: op will get called with p == address of receiver.
}
// compileEnc returns the engine to compile the type.
func compileEnc(ut *userTypeInfo, building map[*typeInfo]bool) *encEngine {
srt := ut.base
engine := new(encEngine)
seen := make(map[reflect.Type]*encOp)
rt := ut.base
if ut.externalEnc != 0 {
rt = ut.user
}
if ut.externalEnc == 0 && srt.Kind() == reflect.Struct {
for fieldNum, wireFieldNum := 0, 0; fieldNum < srt.NumField(); fieldNum++ {
f := srt.Field(fieldNum)
if !isSent(&f) {
continue
}
op, indir := encOpFor(f.Type, seen, building)
engine.instr = append(engine.instr, encInstr{*op, wireFieldNum, f.Index, indir})
wireFieldNum++
}
if srt.NumField() > 0 && len(engine.instr) == 0 {
errorf("type %s has no exported fields", rt)
}
engine.instr = append(engine.instr, encInstr{encStructTerminator, 0, nil, 0})
} else {
engine.instr = make([]encInstr, 1)
op, indir := encOpFor(rt, seen, building)
engine.instr[0] = encInstr{*op, singletonField, nil, indir}
}
return engine
}
// getEncEngine returns the engine to compile the type.
func getEncEngine(ut *userTypeInfo, building map[*typeInfo]bool) *encEngine {
info, err := getTypeInfo(ut)
if err != nil {
error_(err)
}
enc, ok := info.encoder.Load().(*encEngine)
if !ok {
enc = buildEncEngine(info, ut, building)
}
return enc
}
func buildEncEngine(info *typeInfo, ut *userTypeInfo, building map[*typeInfo]bool) *encEngine {
// Check for recursive types.
if building != nil && building[info] {
return nil
}
info.encInit.Lock()
defer info.encInit.Unlock()
enc, ok := info.encoder.Load().(*encEngine)
if !ok {
if building == nil {
building = make(map[*typeInfo]bool)
}
building[info] = true
enc = compileEnc(ut, building)
info.encoder.Store(enc)
}
return enc
}
func (enc *Encoder) encode(b *encBuffer, value reflect.Value, ut *userTypeInfo) {
defer catchError(&enc.err)
engine := getEncEngine(ut, nil)
indir := ut.indir
if ut.externalEnc != 0 {
indir = int(ut.encIndir)
}
for i := 0; i < indir; i++ {
value = reflect.Indirect(value)
}
if ut.externalEnc == 0 && value.Type().Kind() == reflect.Struct {
enc.encodeStruct(b, engine, value)
} else {
enc.encodeSingle(b, engine, value)
}
}