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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"
"math"
"reflect"
"unsafe"
)
const uint64Size = int(unsafe.Sizeof(uint64(0)))
// 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 *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.
next *encoderState // for free list
}
func (enc *Encoder) newEncoderState(b *bytes.Buffer) *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
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 {
err := state.b.WriteByte(uint8(x))
if err != nil {
error_(err)
}
return
}
i := uint64Size
for x > 0 {
state.buf[i] = uint8(x)
x >>= 8
i--
}
state.buf[i] = uint8(i - uint64Size) // = loop count, negated
_, err := state.b.Write(state.buf[i : 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 (state *encoderState) encodeInt(i int64) {
var x uint64
if i < 0 {
x = uint64(^i<<1) | 1
} else {
x = uint64(i << 1)
}
state.encodeUint(uint64(x))
}
// encOp is the signature of an encoding operator for a given type.
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
}
// 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 p indir times and returns the result.
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
}
// encBool encodes the bool with address p as an unsigned 0 or 1.
func encBool(i *encInstr, state *encoderState, p unsafe.Pointer) {
b := *(*bool)(p)
if b || state.sendZero {
state.update(i)
if b {
state.encodeUint(1)
} else {
state.encodeUint(0)
}
}
}
// encInt encodes the int with address p.
func encInt(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeInt(v)
}
}
// encUint encodes the uint with address p.
func encUint(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeUint(v)
}
}
// encInt8 encodes the int8 with address p.
func encInt8(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int8)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeInt(v)
}
}
// encUint8 encodes the uint8 with address p.
func encUint8(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint8)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeUint(v)
}
}
// encInt16 encodes the int16 with address p.
func encInt16(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int16)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeInt(v)
}
}
// encUint16 encodes the uint16 with address p.
func encUint16(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint16)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeUint(v)
}
}
// encInt32 encodes the int32 with address p.
func encInt32(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int32)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeInt(v)
}
}
// encUint encodes the uint32 with address p.
func encUint32(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint32)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeUint(v)
}
}
// encInt64 encodes the int64 with address p.
func encInt64(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := *(*int64)(p)
if v != 0 || state.sendZero {
state.update(i)
state.encodeInt(v)
}
}
// encInt64 encodes the uint64 with address p.
func encUint64(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := *(*uint64)(p)
if v != 0 || state.sendZero {
state.update(i)
state.encodeUint(v)
}
}
// encUintptr encodes the uintptr with address p.
func encUintptr(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uintptr)(p))
if v != 0 || state.sendZero {
state.update(i)
state.encodeUint(v)
}
}
// 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)
var v uint64
for i := 0; i < 8; i++ {
v <<= 8
v |= u & 0xFF
u >>= 8
}
return v
}
// encFloat32 encodes the float32 with address p.
func encFloat32(i *encInstr, state *encoderState, p unsafe.Pointer) {
f := *(*float32)(p)
if f != 0 || state.sendZero {
v := floatBits(float64(f))
state.update(i)
state.encodeUint(v)
}
}
// encFloat64 encodes the float64 with address p.
func encFloat64(i *encInstr, state *encoderState, p unsafe.Pointer) {
f := *(*float64)(p)
if f != 0 || state.sendZero {
state.update(i)
v := floatBits(f)
state.encodeUint(v)
}
}
// encComplex64 encodes the complex64 with address p.
// Complex numbers are just a pair of floating-point numbers, real part first.
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)
state.encodeUint(rpart)
state.encodeUint(ipart)
}
}
// encComplex128 encodes the complex128 with address p.
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)
state.encodeUint(rpart)
state.encodeUint(ipart)
}
}
// encUint8Array encodes the byte slice whose header has address p.
// 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)
state.encodeUint(uint64(len(b)))
state.b.Write(b)
}
}
// encString encodes the string whose header has address p.
// 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)
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, p unsafe.Pointer) {
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
// encodeSingle encodes a single top-level non-struct value.
func (enc *Encoder) encodeSingle(b *bytes.Buffer, engine *encEngine, basep uintptr) {
state := enc.newEncoderState(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)
enc.freeEncoderState(state)
}
// encodeStruct encodes a single struct value.
func (enc *Encoder) encodeStruct(b *bytes.Buffer, engine *encEngine, basep uintptr) {
state := enc.newEncoderState(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)
}
enc.freeEncoderState(state)
}
// encodeArray encodes the array whose 0th element is at p.
func (enc *Encoder) encodeArray(b *bytes.Buffer, p uintptr, op encOp, elemWid uintptr, elemIndir int, length int) {
state := enc.newEncoderState(b)
state.fieldnum = -1
state.sendZero = true
state.encodeUint(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("encodeArray: nil element")
}
elemp = uintptr(up)
}
op(nil, state, unsafe.Pointer(elemp))
p += uintptr(elemWid)
}
enc.freeEncoderState(state)
}
// 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, unsafe.Pointer(unsafeAddr(v)))
}
// encodeMap encodes a map as unsigned count followed by key:value pairs.
// Because map internals are not exposed, we must use reflection rather than
// addresses.
func (enc *Encoder) encodeMap(b *bytes.Buffer, mv reflect.Value, keyOp, elemOp encOp, keyIndir, elemIndir int) {
state := enc.newEncoderState(b)
state.fieldnum = -1
state.sendZero = true
keys := mv.MapKeys()
state.encodeUint(uint64(len(keys)))
for _, key := range keys {
encodeReflectValue(state, key, keyOp, keyIndir)
encodeReflectValue(state, mv.MapIndex(key), 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 *bytes.Buffer, iv reflect.Value) {
state := enc.newEncoderState(b)
state.fieldnum = -1
state.sendZero = true
if iv.IsNil() {
state.encodeUint(0)
return
}
ut := userType(iv.Elem().Type())
name, ok := concreteTypeToName[ut.base]
if !ok {
errorf("type not registered for interface: %s", ut.base)
}
// Send the name.
state.encodeUint(uint64(len(name)))
_, err := state.b.WriteString(name)
if err != nil {
error_(err)
}
// 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 := new(bytes.Buffer)
data.Write(spaceForLength)
enc.encode(data, iv.Elem(), ut)
if enc.err != nil {
error_(enc.err)
}
enc.popWriter()
enc.writeMessage(b, data)
if enc.err != nil {
error_(err)
}
enc.freeEncoderState(state)
}
// isZero returns 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.Ptr:
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 *bytes.Buffer, v reflect.Value) {
// TODO: should we catch panics from the called method?
// We know it's a GobEncoder, so just call the method directly.
data, err := v.Interface().(GobEncoder).GobEncode()
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: 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.Float32: encFloat32,
reflect.Float64: encFloat64,
reflect.Complex64: encComplex64,
reflect.Complex128: encComplex128,
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 (enc *Encoder) encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp) (*encOp, int) {
ut := userType(rt)
// If the type implements GobEncoder, we handle it without further processing.
if ut.isGobEncoder {
return enc.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, indir := enc.encOpFor(t.Elem(), inProgress)
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.Array:
// True arrays have size in the type.
elemOp, indir := enc.encOpFor(t.Elem(), inProgress)
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.Map:
keyOp, keyIndir := enc.encOpFor(t.Key(), inProgress)
elemOp, elemIndir := enc.encOpFor(t.Elem(), inProgress)
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.NewAt(t, unsafe.Pointer(p)).Elem()
mv := reflect.Indirect(v)
// 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.
enc.getEncEngine(userType(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.Interface:
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
// Interfaces transmit the name and contents of the concrete
// value they contain.
v := reflect.NewAt(t, unsafe.Pointer(p)).Elem()
iv := reflect.Indirect(v)
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 (enc *Encoder) gobEncodeOpFor(ut *userTypeInfo) (*encOp, int) {
rt := ut.user
if ut.encIndir == -1 {
rt = reflect.PtrTo(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, p unsafe.Pointer) {
var v reflect.Value
if ut.encIndir == -1 {
// Need to climb up one level to turn value into pointer.
v = reflect.NewAt(rt, unsafe.Pointer(&p)).Elem()
} else {
v = reflect.NewAt(rt, p).Elem()
}
if !state.sendZero && isZero(v) {
return
}
state.update(i)
state.enc.encodeGobEncoder(state.b, 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 (enc *Encoder) compileEnc(ut *userTypeInfo) *encEngine {
srt := ut.base
engine := new(encEngine)
seen := make(map[reflect.Type]*encOp)
rt := ut.base
if ut.isGobEncoder {
rt = ut.user
}
if !ut.isGobEncoder &&
srt.Kind() == reflect.Struct {
for fieldNum, wireFieldNum := 0, 0; fieldNum < srt.NumField(); fieldNum++ {
f := srt.Field(fieldNum)
if !isExported(f.Name) {
continue
}
op, indir := enc.encOpFor(f.Type, seen)
engine.instr = append(engine.instr, encInstr{*op, wireFieldNum, indir, uintptr(f.Offset)})
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, 0, 0})
} else {
engine.instr = make([]encInstr, 1)
op, indir := enc.encOpFor(rt, seen)
engine.instr[0] = encInstr{*op, singletonField, indir, 0} // offset is zero
}
return engine
}
// getEncEngine returns the engine to compile the type.
// typeLock must be held (or we're in initialization and guaranteed single-threaded).
func (enc *Encoder) getEncEngine(ut *userTypeInfo) *encEngine {
info, err1 := getTypeInfo(ut)
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(ut)
}
return info.encoder
}
// lockAndGetEncEngine is a function that locks and compiles.
// This lets us hold the lock only while compiling, not when encoding.
func (enc *Encoder) lockAndGetEncEngine(ut *userTypeInfo) *encEngine {
typeLock.Lock()
defer typeLock.Unlock()
return enc.getEncEngine(ut)
}
func (enc *Encoder) encode(b *bytes.Buffer, value reflect.Value, ut *userTypeInfo) {
defer catchError(&enc.err)
engine := enc.lockAndGetEncEngine(ut)
indir := ut.indir
if ut.isGobEncoder {
indir = int(ut.encIndir)
}
for i := 0; i < indir; i++ {
value = reflect.Indirect(value)
}
if !ut.isGobEncoder && value.Type().Kind() == reflect.Struct {
enc.encodeStruct(b, engine, unsafeAddr(value))
} else {
enc.encodeSingle(b, engine, unsafeAddr(value))
}
}