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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 {
b *bytes.Buffer;
err os.Error; // error encountered during encoding;
fieldnum int; // the last field number written.
buf [1 + uint64Size]byte; // buffer used by the encoder; here to avoid allocation.
}
// 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. Sets state.err.
// If state.err is already non-nil, it does nothing.
func encodeUint(state *encoderState, x uint64) {
if state.err != nil {
return
}
if x <= 0x7F {
state.err = state.b.WriteByte(uint8(x));
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, state.err = state.b.Write(state.buf[m : 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.
// Sets state.err. If state.err is already non-nil, it does nothing.
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.update(i);
encodeUint(state, 1);
}
}
func encInt(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int)(p));
if v != 0 {
state.update(i);
encodeInt(state, v);
}
}
func encUint(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint)(p));
if v != 0 {
state.update(i);
encodeUint(state, v);
}
}
func encInt8(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int8)(p));
if v != 0 {
state.update(i);
encodeInt(state, v);
}
}
func encUint8(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint8)(p));
if v != 0 {
state.update(i);
encodeUint(state, v);
}
}
func encInt16(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int16)(p));
if v != 0 {
state.update(i);
encodeInt(state, v);
}
}
func encUint16(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint16)(p));
if v != 0 {
state.update(i);
encodeUint(state, v);
}
}
func encInt32(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := int64(*(*int32)(p));
if v != 0 {
state.update(i);
encodeInt(state, v);
}
}
func encUint32(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uint32)(p));
if v != 0 {
state.update(i);
encodeUint(state, v);
}
}
func encInt64(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := *(*int64)(p);
if v != 0 {
state.update(i);
encodeInt(state, v);
}
}
func encUint64(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := *(*uint64)(p);
if v != 0 {
state.update(i);
encodeUint(state, v);
}
}
func encUintptr(i *encInstr, state *encoderState, p unsafe.Pointer) {
v := uint64(*(*uintptr)(p));
if v != 0 {
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(*(*float)(p));
if f != 0 {
v := floatBits(float64(f));
state.update(i);
encodeUint(state, v);
}
}
func encFloat32(i *encInstr, state *encoderState, p unsafe.Pointer) {
f := float32(*(*float32)(p));
if f != 0 {
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.update(i);
v := floatBits(f);
encodeUint(state, v);
}
}
// 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.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.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;
}
func encodeStruct(engine *encEngine, b *bytes.Buffer, basep uintptr) os.Error {
state := new(encoderState);
state.b = 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);
if state.err != nil {
break
}
}
return state.err;
}
func encodeArray(b *bytes.Buffer, p uintptr, op encOp, elemWid uintptr, length int, elemIndir int) os.Error {
state := new(encoderState);
state.b = b;
state.fieldnum = -1;
encodeUint(state, uint64(length));
for i := 0; i < length && state.err == nil; i++ {
elemp := p;
up := unsafe.Pointer(elemp);
if elemIndir > 0 {
if up = encIndirect(up, elemIndir); up == nil {
state.err = os.ErrorString("gob: encodeArray: nil element");
break;
}
elemp = uintptr(up);
}
op(nil, state, unsafe.Pointer(elemp));
p += uintptr(elemWid);
}
return state.err;
}
var encOpMap = map[reflect.Type]encOp{
valueKind(false): encBool,
valueKind(int(0)): encInt,
valueKind(int8(0)): encInt8,
valueKind(int16(0)): encInt16,
valueKind(int32(0)): encInt32,
valueKind(int64(0)): encInt64,
valueKind(uint(0)): encUint,
valueKind(uint8(0)): encUint8,
valueKind(uint16(0)): encUint16,
valueKind(uint32(0)): encUint32,
valueKind(uint64(0)): encUint64,
valueKind(uintptr(0)): encUintptr,
valueKind(float(0)): encFloat,
valueKind(float32(0)): encFloat32,
valueKind(float64(0)): encFloat64,
valueKind("x"): encString,
}
// Return the encoding op for the base type under rt and
// the indirection count to reach it.
func encOpFor(rt reflect.Type) (encOp, int, os.Error) {
typ, indir := indirect(rt);
op, ok := encOpMap[reflect.Typeof(typ)];
if !ok {
typ, _ := indirect(rt);
// Special cases
switch t := typ.(type) {
case *reflect.SliceType:
if _, ok := t.Elem().(*reflect.Uint8Type); ok {
op = encUint8Array;
break;
}
// Slices have a header; we decode it to find the underlying array.
elemOp, indir, err := encOpFor(t.Elem());
if err != nil {
return nil, 0, err
}
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
slice := (*reflect.SliceHeader)(p);
if slice.Len == 0 {
return
}
state.update(i);
state.err = encodeArray(state.b, slice.Data, elemOp, t.Elem().Size(), int(slice.Len), indir);
};
case *reflect.ArrayType:
// True arrays have size in the type.
elemOp, indir, err := encOpFor(t.Elem());
if err != nil {
return nil, 0, err
}
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
state.update(i);
state.err = encodeArray(state.b, uintptr(p), elemOp, t.Elem().Size(), t.Len(), indir);
};
case *reflect.StructType:
// Generate a closure that calls out to the engine for the nested type.
_, err := getEncEngine(typ);
if err != nil {
return nil, 0, err
}
info := getTypeInfoNoError(typ);
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
state.update(i);
// indirect through info to delay evaluation for recursive structs
state.err = encodeStruct(info.encoder, state.b, uintptr(p));
};
}
}
if op == nil {
return op, indir, os.ErrorString("gob enc: can't happen: encode type" + rt.String())
}
return op, indir, nil;
}
// The local Type was compiled from the actual value, so we know it's compatible.
func compileEnc(rt reflect.Type) (*encEngine, os.Error) {
srt, ok := rt.(*reflect.StructType);
if !ok {
panicln("can't happen: non-struct")
}
engine := new(encEngine);
engine.instr = make([]encInstr, srt.NumField()+1); // +1 for terminator
for fieldnum := 0; fieldnum < srt.NumField(); fieldnum++ {
f := srt.Field(fieldnum);
op, indir, err := encOpFor(f.Type);
if err != nil {
return nil, err
}
engine.instr[fieldnum] = encInstr{op, fieldnum, indir, uintptr(f.Offset)};
}
engine.instr[srt.NumField()] = encInstr{encStructTerminator, 0, 0, 0};
return engine, nil;
}
// typeLock must be held (or we're in initialization and guaranteed single-threaded).
// The reflection type must have all its indirections processed out.
func getEncEngine(rt reflect.Type) (*encEngine, os.Error) {
info, err := getTypeInfo(rt);
if err != nil {
return nil, err
}
if info.encoder == nil {
// mark this engine as underway before compiling to handle recursive types.
info.encoder = new(encEngine);
info.encoder, err = compileEnc(rt);
}
return info.encoder, err;
}
func encode(b *bytes.Buffer, e interface{}) os.Error {
// Dereference down to the underlying object.
rt, indir := indirect(reflect.Typeof(e));
v := reflect.NewValue(e);
for i := 0; i < indir; i++ {
v = reflect.Indirect(v)
}
if _, ok := v.(*reflect.StructValue); !ok {
return os.ErrorString("gob: encode can't handle " + v.Type().String())
}
typeLock.Lock();
engine, err := getEncEngine(rt);
typeLock.Unlock();
if err != nil {
return err
}
return encodeStruct(engine, b, v.Addr());
}