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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.
package gob
import (
"bytes"
"io"
"math"
"os"
"reflect"
"unsafe"
)
const uint64Size = unsafe.Sizeof(uint64(0))
// 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 *bytes.Buffer
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.
}
func newEncoderState(enc *Encoder, b *bytes.Buffer) *encoderState {
return &encoderState{enc: enc, b: b}
}
// 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 encodeUint(state *encoderState, x uint64) {
if x <= 0x7F {
err := state.b.WriteByte(uint8(x))
if err != nil {
error(err)
}
return
}
var n, m int
m = uint64Size
for n = 1; x > 0; n++ {
state.buf[m] = uint8(x & 0xFF)
x >>= 8
m--
}
state.buf[m] = uint8(-(n - 1))
n, err := state.b.Write(state.buf[m : uint64Size+1])
if err != nil {
error(err)
}
}
// 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 encodeInt(state *encoderState, i int64) {
var x uint64
if i < 0 {
x = uint64(^i<<1) | 1
} else {
x = uint64(i << 1)
}
encodeUint(state, uint64(x))
}
type encOp func(i *encInstr, state *encoderState, p unsafe.Pointer)
// The 'instructions' of the encoding machine
type encInstr struct {
op encOp
field int // field number
indir int // how many pointer indirections to reach the value in the struct
offset uintptr // offset in the structure of the field to encode
}
// Emit a field number and update the state to record its value for delta encoding.
// If the instruction pointer is nil, do nothing
func (state *encoderState) update(instr *encInstr) {
if instr != nil {
encodeUint(state, uint64(instr.field-state.fieldnum))
state.fieldnum = instr.field
}
}
// Each encoder is responsible for handling any indirections associated
// with the data structure. If any pointer so reached is nil, no bytes are written.
// If the data item is zero, no bytes are written.
// Otherwise, the output (for a scalar) is the field number, as an encoded integer,
// followed by the field data in its appropriate format.
func encIndirect(p unsafe.Pointer, indir int) unsafe.Pointer {
for ; indir > 0; indir-- {
p = *(*unsafe.Pointer)(p)
if p == nil {
return unsafe.Pointer(nil)
}
}
return p
}
func encBool(i *encInstr, state *encoderState, p unsafe.Pointer) {
b := *(*bool)(p)
if b || state.sendZero {
state.update(i)
if b {
encodeUint(state, 1)
} else {
encodeUint(state, 0)
}
}
}
func encInt(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeInt(state, v)
}
}
func encUint(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeUint(state, v)
}
}
func encInt8(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int8)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeInt(state, v)
}
}
func encUint8(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint8)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeUint(state, v)
}
}
func encInt16(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int16)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeInt(state, v)
}
}
func encUint16(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint16)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeUint(state, v)
}
}
func encInt32(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int32)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeInt(state, v)
}
}
func encUint32(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint32)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeUint(state, v)
}
}
func encInt64(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := *(*int64)(p)
if v != 0 || state.sendZero {
state.update(i)
encodeInt(state, v)
}
}
func encUint64(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := *(*uint64)(p)
if v != 0 || state.sendZero {
state.update(i)
encodeUint(state, v)
}
}
func encUintptr(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uintptr)(p))
if v != 0 || state.sendZero {
state.update(i)
encodeUint(state, v)
}
}
// 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)
var v uint64
for i := 0; i < 8; i++ {
v <<= 8
v |= u & 0xFF
u >>= 8
}
return v
}
func encFloat(i *encInstr, state *encoderState, p unsafe.Pointer) {
f := *(*float)(p)
if f != 0 || state.sendZero {
v := floatBits(float64(f))
state.update(i)
encodeUint(state, v)
}
}
func encFloat32(i *encInstr, state *encoderState, p unsafe.Pointer) {
f := *(*float32)(p)
if f != 0 || state.sendZero {
v := floatBits(float64(f))
state.update(i)
encodeUint(state, v)
}
}
func encFloat64(i *encInstr, state *encoderState, p unsafe.Pointer) {
f := *(*float64)(p)
if f != 0 || state.sendZero {
state.update(i)
v := floatBits(f)
encodeUint(state, v)
}
}
// Complex numbers are just a pair of floating-point numbers, real part first.
func encComplex(i *encInstr, state *encoderState, p unsafe.Pointer) {
c := *(*complex)(p)
if c != 0+0i || state.sendZero {
rpart := floatBits(float64(real(c)))
ipart := floatBits(float64(imag(c)))
state.update(i)
encodeUint(state, rpart)
encodeUint(state, ipart)
}
}
func encComplex64(i *encInstr, state *encoderState, p unsafe.Pointer) {
c := *(*complex64)(p)
if c != 0+0i || state.sendZero {
rpart := floatBits(float64(real(c)))
ipart := floatBits(float64(imag(c)))
state.update(i)
encodeUint(state, rpart)
encodeUint(state, ipart)
}
}
func encComplex128(i *encInstr, state *encoderState, p unsafe.Pointer) {
c := *(*complex128)(p)
if c != 0+0i || state.sendZero {
rpart := floatBits(real(c))
ipart := floatBits(imag(c))
state.update(i)
encodeUint(state, rpart)
encodeUint(state, ipart)
}
}
// Byte arrays are encoded as an unsigned count followed by the raw bytes.
func encUint8Array(i *encInstr, state *encoderState, p unsafe.Pointer) {
b := *(*[]byte)(p)
if len(b) > 0 || state.sendZero {
state.update(i)
encodeUint(state, uint64(len(b)))
state.b.Write(b)
}
}
// Strings are encoded as an unsigned count followed by the raw bytes.
func encString(i *encInstr, state *encoderState, p unsafe.Pointer) {
s := *(*string)(p)
if len(s) > 0 || state.sendZero {
state.update(i)
encodeUint(state, uint64(len(s)))
io.WriteString(state.b, s)
}
}
// The end of a struct is marked by a delta field number of 0.
func encStructTerminator(i *encInstr, state *encoderState, p unsafe.Pointer) {
encodeUint(state, 0)
}
// Execution engine
// The encoder engine is 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
func (enc *Encoder) encodeSingle(b *bytes.Buffer, engine *encEngine, basep uintptr) {
state := newEncoderState(enc, b)
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]
p := unsafe.Pointer(basep) // offset will be zero
if instr.indir > 0 {
if p = encIndirect(p, instr.indir); p == nil {
return
}
}
instr.op(instr, state, p)
}
func (enc *Encoder) encodeStruct(b *bytes.Buffer, engine *encEngine, basep uintptr) {
state := newEncoderState(enc, b)
state.fieldnum = -1
for i := 0; i < len(engine.instr); i++ {
instr := &engine.instr[i]
p := unsafe.Pointer(basep + instr.offset)
if instr.indir > 0 {
if p = encIndirect(p, instr.indir); p == nil {
continue
}
}
instr.op(instr, state, p)
}
}
func (enc *Encoder) encodeArray(b *bytes.Buffer, p uintptr, op encOp, elemWid uintptr, elemIndir int, length int) {
state := newEncoderState(enc, b)
state.fieldnum = -1
state.sendZero = true
encodeUint(state, uint64(length))
for i := 0; i < length; i++ {
elemp := p
up := unsafe.Pointer(elemp)
if elemIndir > 0 {
if up = encIndirect(up, elemIndir); up == nil {
errorf("gob: encodeArray: nil element")
}
elemp = uintptr(up)
}
op(nil, state, unsafe.Pointer(elemp))
p += uintptr(elemWid)
}
}
func encodeReflectValue(state *encoderState, v reflect.Value, op encOp, indir int) {
for i := 0; i < indir && v != nil; i++ {
v = reflect.Indirect(v)
}
if v == nil {
errorf("gob: encodeReflectValue: nil element")
}
op(nil, state, unsafe.Pointer(v.Addr()))
}
func (enc *Encoder) encodeMap(b *bytes.Buffer, mv *reflect.MapValue, keyOp, elemOp encOp, keyIndir, elemIndir int) {
state := newEncoderState(enc, b)
state.fieldnum = -1
state.sendZero = true
keys := mv.Keys()
encodeUint(state, uint64(len(keys)))
for _, key := range keys {
encodeReflectValue(state, key, keyOp, keyIndir)
encodeReflectValue(state, mv.Elem(key), elemOp, elemIndir)
}
}
// 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 *bytes.Buffer, iv *reflect.InterfaceValue) {
state := newEncoderState(enc, b)
state.fieldnum = -1
state.sendZero = true
if iv.IsNil() {
encodeUint(state, 0)
return
}
typ, _ := indirect(iv.Elem().Type())
name, ok := concreteTypeToName[typ]
if !ok {
errorf("gob: type not registered for interface: %s", typ)
}
// Send the name.
encodeUint(state, uint64(len(name)))
_, err := io.WriteString(state.b, name)
if err != nil {
error(err)
}
// Send (and maybe first define) the type id.
enc.sendTypeDescriptor(typ)
// Encode the value into a new buffer.
data := new(bytes.Buffer)
err = enc.encode(data, iv.Elem())
if err != nil {
error(err)
}
encodeUint(state, uint64(data.Len()))
_, err = state.b.Write(data.Bytes())
if err != nil {
error(err)
}
}
var encOpMap = []encOp{
reflect.Bool: encBool,
reflect.Int: encInt,
reflect.Int8: encInt8,
reflect.Int16: encInt16,
reflect.Int32: encInt32,
reflect.Int64: encInt64,
reflect.Uint: encUint,
reflect.Uint8: encUint8,
reflect.Uint16: encUint16,
reflect.Uint32: encUint32,
reflect.Uint64: encUint64,
reflect.Uintptr: encUintptr,
reflect.Float: encFloat,
reflect.Float32: encFloat32,
reflect.Float64: encFloat64,
reflect.Complex: encComplex,
reflect.Complex64: encComplex64,
reflect.Complex128: encComplex128,
reflect.String: encString,
}
// Return the encoding op for the base type under rt and
// the indirection count to reach it.
func (enc *Encoder) encOpFor(rt reflect.Type) (encOp, int) {
typ, indir := indirect(rt)
var op encOp
k := typ.Kind()
if int(k) < len(encOpMap) {
op = encOpMap[k]
}
if op == nil {
// Special cases
switch t := typ.(type) {
case *reflect.SliceType:
if t.Elem().Kind() == reflect.Uint8 {
op = encUint8Array
break
}
// Slices have a header; we decode it to find the underlying array.
elemOp, indir := enc.encOpFor(t.Elem())
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
slice := (*reflect.SliceHeader)(p)
if !state.sendZero && slice.Len == 0 {
return
}
state.update(i)
state.enc.encodeArray(state.b, slice.Data, elemOp, t.Elem().Size(), indir, int(slice.Len))
}
case *reflect.ArrayType:
// True arrays have size in the type.
elemOp, indir := enc.encOpFor(t.Elem())
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
state.update(i)
state.enc.encodeArray(state.b, uintptr(p), elemOp, t.Elem().Size(), indir, t.Len())
}
case *reflect.MapType:
keyOp, keyIndir := enc.encOpFor(t.Key())
elemOp, elemIndir := enc.encOpFor(t.Elem())
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
// Maps cannot be accessed by moving addresses around the way
// that slices etc. can. We must recover a full reflection value for
// the iteration.
v := reflect.NewValue(unsafe.Unreflect(t, unsafe.Pointer((p))))
mv := reflect.Indirect(v).(*reflect.MapValue)
if !state.sendZero && mv.Len() == 0 {
return
}
state.update(i)
state.enc.encodeMap(state.b, mv, keyOp, elemOp, keyIndir, elemIndir)
}
case *reflect.StructType:
// Generate a closure that calls out to the engine for the nested type.
enc.getEncEngine(typ)
info := mustGetTypeInfo(typ)
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
state.update(i)
// indirect through info to delay evaluation for recursive structs
state.enc.encodeStruct(state.b, info.encoder, uintptr(p))
}
case *reflect.InterfaceType:
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
// Interfaces transmit the name and contents of the concrete
// value they contain.
v := reflect.NewValue(unsafe.Unreflect(t, unsafe.Pointer((p))))
iv := reflect.Indirect(v).(*reflect.InterfaceValue)
if !state.sendZero && (iv == nil || iv.IsNil()) {
return
}
state.update(i)
state.enc.encodeInterface(state.b, iv)
}
}
}
if op == nil {
errorf("gob enc: can't happen: encode type %s", rt.String())
}
return op, indir
}
// The local Type was compiled from the actual value, so we know it's compatible.
func (enc *Encoder) compileEnc(rt reflect.Type) *encEngine {
srt, isStruct := rt.(*reflect.StructType)
engine := new(encEngine)
if isStruct {
engine.instr = make([]encInstr, srt.NumField()+1) // +1 for terminator
for fieldnum := 0; fieldnum < srt.NumField(); fieldnum++ {
f := srt.Field(fieldnum)
op, indir := enc.encOpFor(f.Type)
engine.instr[fieldnum] = encInstr{op, fieldnum, indir, uintptr(f.Offset)}
}
engine.instr[srt.NumField()] = encInstr{encStructTerminator, 0, 0, 0}
} else {
engine.instr = make([]encInstr, 1)
op, indir := enc.encOpFor(rt)
engine.instr[0] = encInstr{op, singletonField, indir, 0} // offset is zero
}
return engine
}
// typeLock must be held (or we're in initialization and guaranteed single-threaded).
// The reflection type must have all its indirections processed out.
func (enc *Encoder) getEncEngine(rt reflect.Type) *encEngine {
info, err1 := getTypeInfo(rt)
if err1 != nil {
error(err1)
}
if info.encoder == nil {
// mark this engine as underway before compiling to handle recursive types.
info.encoder = new(encEngine)
info.encoder = enc.compileEnc(rt)
}
return info.encoder
}
// Put this in a function so we can hold the lock only while compiling, not when encoding.
func (enc *Encoder) lockAndGetEncEngine(rt reflect.Type) *encEngine {
typeLock.Lock()
defer typeLock.Unlock()
return enc.getEncEngine(rt)
}
func (enc *Encoder) encode(b *bytes.Buffer, value reflect.Value) (err os.Error) {
defer catchError(&err)
// Dereference down to the underlying object.
rt, indir := indirect(value.Type())
for i := 0; i < indir; i++ {
value = reflect.Indirect(value)
}
engine := enc.lockAndGetEncEngine(rt)
if value.Type().Kind() == reflect.Struct {
enc.encodeStruct(b, engine, value.Addr())
} else {
enc.encodeSingle(b, engine, value.Addr())
}
return nil
}