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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
// TODO(rsc): When garbage collector changes, revisit
// the allocations in this file that use unsafe.Pointer.
import (
"bytes"
"io"
"math"
"os"
"reflect"
"unsafe"
)
var (
errBadUint = os.NewError("gob: encoded unsigned integer out of range")
errBadType = os.NewError("gob: unknown type id or corrupted data")
errRange = os.NewError("gob: bad data: field numbers out of bounds")
)
// decoderState is the execution state of an instance of the decoder. A new state
// is created for nested objects.
type decoderState struct {
dec *Decoder
// The buffer is stored with an extra indirection because it may be replaced
// if we load a type during decode (when reading an interface value).
b *bytes.Buffer
fieldnum int // the last field number read.
buf []byte
next *decoderState // for free list
}
// We pass the bytes.Buffer separately for easier testing of the infrastructure
// without requiring a full Decoder.
func (dec *Decoder) newDecoderState(buf *bytes.Buffer) *decoderState {
d := dec.freeList
if d == nil {
d = new(decoderState)
d.dec = dec
d.buf = make([]byte, uint64Size)
} else {
dec.freeList = d.next
}
d.b = buf
return d
}
func (dec *Decoder) freeDecoderState(d *decoderState) {
d.next = dec.freeList
dec.freeList = d
}
func overflow(name string) os.Error {
return os.NewError(`value for "` + name + `" out of range`)
}
// decodeUintReader reads an encoded unsigned integer from an io.Reader.
// Used only by the Decoder to read the message length.
func decodeUintReader(r io.Reader, buf []byte) (x uint64, width int, err os.Error) {
width = 1
_, err = r.Read(buf[0:width])
if err != nil {
return
}
b := buf[0]
if b <= 0x7f {
return uint64(b), width, nil
}
n := -int(int8(b))
if n > uint64Size {
err = errBadUint
return
}
width, err = io.ReadFull(r, buf[0:n])
if err != nil {
if err == os.EOF {
err = io.ErrUnexpectedEOF
}
return
}
// Could check that the high byte is zero but it's not worth it.
for _, b := range buf[0:width] {
x = x<<8 | uint64(b)
}
width++ // +1 for length byte
return
}
// decodeUint reads an encoded unsigned integer from state.r.
// Does not check for overflow.
func (state *decoderState) decodeUint() (x uint64) {
b, err := state.b.ReadByte()
if err != nil {
error(err)
}
if b <= 0x7f {
return uint64(b)
}
n := -int(int8(b))
if n > uint64Size {
error(errBadUint)
}
width, err := state.b.Read(state.buf[0:n])
if err != nil {
error(err)
}
// Don't need to check error; it's safe to loop regardless.
// Could check that the high byte is zero but it's not worth it.
for _, b := range state.buf[0:width] {
x = x<<8 | uint64(b)
}
return x
}
// decodeInt reads an encoded signed integer from state.r.
// Does not check for overflow.
func (state *decoderState) decodeInt() int64 {
x := state.decodeUint()
if x&1 != 0 {
return ^int64(x >> 1)
}
return int64(x >> 1)
}
// decOp is the signature of a decoding operator for a given type.
type decOp func(i *decInstr, state *decoderState, p unsafe.Pointer)
// The 'instructions' of the decoding machine
type decInstr struct {
op decOp
field int // field number of the wire type
indir int // how many pointer indirections to reach the value in the struct
offset uintptr // offset in the structure of the field to encode
ovfl os.Error // error message for overflow/underflow (for arrays, of the elements)
}
// Since the encoder writes no zeros, if we arrive at a decoder we have
// a value to extract and store. The field number has already been read
// (it's how we knew to call this decoder).
// Each decoder is responsible for handling any indirections associated
// with the data structure. If any pointer so reached is nil, allocation must
// be done.
// Walk the pointer hierarchy, allocating if we find a nil. Stop one before the end.
func decIndirect(p unsafe.Pointer, indir int) unsafe.Pointer {
for ; indir > 1; indir-- {
if *(*unsafe.Pointer)(p) == nil {
// Allocation required
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(unsafe.Pointer))
}
p = *(*unsafe.Pointer)(p)
}
return p
}
// ignoreUint discards a uint value with no destination.
func ignoreUint(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.decodeUint()
}
// ignoreTwoUints discards a uint value with no destination. It's used to skip
// complex values.
func ignoreTwoUints(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.decodeUint()
state.decodeUint()
}
// decBool decodes a uint and stores it as a boolean through p.
func decBool(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(bool))
}
p = *(*unsafe.Pointer)(p)
}
*(*bool)(p) = state.decodeUint() != 0
}
// decInt8 decodes an integer and stores it as an int8 through p.
func decInt8(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(int8))
}
p = *(*unsafe.Pointer)(p)
}
v := state.decodeInt()
if v < math.MinInt8 || math.MaxInt8 < v {
error(i.ovfl)
} else {
*(*int8)(p) = int8(v)
}
}
// decUint8 decodes an unsigned integer and stores it as a uint8 through p.
func decUint8(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(uint8))
}
p = *(*unsafe.Pointer)(p)
}
v := state.decodeUint()
if math.MaxUint8 < v {
error(i.ovfl)
} else {
*(*uint8)(p) = uint8(v)
}
}
// decInt16 decodes an integer and stores it as an int16 through p.
func decInt16(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(int16))
}
p = *(*unsafe.Pointer)(p)
}
v := state.decodeInt()
if v < math.MinInt16 || math.MaxInt16 < v {
error(i.ovfl)
} else {
*(*int16)(p) = int16(v)
}
}
// decUint16 decodes an unsigned integer and stores it as a uint16 through p.
func decUint16(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(uint16))
}
p = *(*unsafe.Pointer)(p)
}
v := state.decodeUint()
if math.MaxUint16 < v {
error(i.ovfl)
} else {
*(*uint16)(p) = uint16(v)
}
}
// decInt32 decodes an integer and stores it as an int32 through p.
func decInt32(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(int32))
}
p = *(*unsafe.Pointer)(p)
}
v := state.decodeInt()
if v < math.MinInt32 || math.MaxInt32 < v {
error(i.ovfl)
} else {
*(*int32)(p) = int32(v)
}
}
// decUint32 decodes an unsigned integer and stores it as a uint32 through p.
func decUint32(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(uint32))
}
p = *(*unsafe.Pointer)(p)
}
v := state.decodeUint()
if math.MaxUint32 < v {
error(i.ovfl)
} else {
*(*uint32)(p) = uint32(v)
}
}
// decInt64 decodes an integer and stores it as an int64 through p.
func decInt64(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(int64))
}
p = *(*unsafe.Pointer)(p)
}
*(*int64)(p) = int64(state.decodeInt())
}
// decUint64 decodes an unsigned integer and stores it as a uint64 through p.
func decUint64(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(uint64))
}
p = *(*unsafe.Pointer)(p)
}
*(*uint64)(p) = uint64(state.decodeUint())
}
// 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
// unswizzling.
func floatFromBits(u uint64) float64 {
var v uint64
for i := 0; i < 8; i++ {
v <<= 8
v |= u & 0xFF
u >>= 8
}
return math.Float64frombits(v)
}
// storeFloat32 decodes an unsigned integer, treats it as a 32-bit floating-point
// number, and stores it through p. It's a helper function for float32 and complex64.
func storeFloat32(i *decInstr, state *decoderState, p unsafe.Pointer) {
v := floatFromBits(state.decodeUint())
av := v
if av < 0 {
av = -av
}
// +Inf is OK in both 32- and 64-bit floats. Underflow is always OK.
if math.MaxFloat32 < av && av <= math.MaxFloat64 {
error(i.ovfl)
} else {
*(*float32)(p) = float32(v)
}
}
// decFloat32 decodes an unsigned integer, treats it as a 32-bit floating-point
// number, and stores it through p.
func decFloat32(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(float32))
}
p = *(*unsafe.Pointer)(p)
}
storeFloat32(i, state, p)
}
// decFloat64 decodes an unsigned integer, treats it as a 64-bit floating-point
// number, and stores it through p.
func decFloat64(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(float64))
}
p = *(*unsafe.Pointer)(p)
}
*(*float64)(p) = floatFromBits(uint64(state.decodeUint()))
}
// decComplex64 decodes a pair of unsigned integers, treats them as a
// pair of floating point numbers, and stores them as a complex64 through p.
// The real part comes first.
func decComplex64(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(complex64))
}
p = *(*unsafe.Pointer)(p)
}
storeFloat32(i, state, p)
storeFloat32(i, state, unsafe.Pointer(uintptr(p)+unsafe.Sizeof(float32(0))))
}
// decComplex128 decodes a pair of unsigned integers, treats them as a
// pair of floating point numbers, and stores them as a complex128 through p.
// The real part comes first.
func decComplex128(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(complex128))
}
p = *(*unsafe.Pointer)(p)
}
real := floatFromBits(uint64(state.decodeUint()))
imag := floatFromBits(uint64(state.decodeUint()))
*(*complex128)(p) = complex(real, imag)
}
// decUint8Slice decodes a byte slice and stores through p a slice header
// describing the data.
// uint8 slices are encoded as an unsigned count followed by the raw bytes.
func decUint8Slice(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new([]uint8))
}
p = *(*unsafe.Pointer)(p)
}
n := int(state.decodeUint())
if n < 0 {
errorf("negative length decoding []byte")
}
slice := (*[]uint8)(p)
if cap(*slice) < n {
*slice = make([]uint8, n)
} else {
*slice = (*slice)[0:n]
}
if _, err := state.b.Read(*slice); err != nil {
errorf("error decoding []byte: %s", err)
}
}
// decString decodes byte array and stores through p a string header
// describing the data.
// Strings are encoded as an unsigned count followed by the raw bytes.
func decString(i *decInstr, state *decoderState, p unsafe.Pointer) {
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.Pointer(new(string))
}
p = *(*unsafe.Pointer)(p)
}
b := make([]byte, state.decodeUint())
state.b.Read(b)
// It would be a shame to do the obvious thing here,
// *(*string)(p) = string(b)
// because we've already allocated the storage and this would
// allocate again and copy. So we do this ugly hack, which is even
// even more unsafe than it looks as it depends the memory
// representation of a string matching the beginning of the memory
// representation of a byte slice (a byte slice is longer).
*(*string)(p) = *(*string)(unsafe.Pointer(&b))
}
// ignoreUint8Array skips over the data for a byte slice value with no destination.
func ignoreUint8Array(i *decInstr, state *decoderState, p unsafe.Pointer) {
b := make([]byte, state.decodeUint())
state.b.Read(b)
}
// Execution engine
// The encoder engine is an array of instructions indexed by field number of the incoming
// decoder. It is executed with random access according to field number.
type decEngine struct {
instr []decInstr
numInstr int // the number of active instructions
}
// allocate makes sure storage is available for an object of underlying type rtyp
// that is indir levels of indirection through p.
func allocate(rtyp reflect.Type, p uintptr, indir int) uintptr {
if indir == 0 {
return p
}
up := unsafe.Pointer(p)
if indir > 1 {
up = decIndirect(up, indir)
}
if *(*unsafe.Pointer)(up) == nil {
// Allocate object.
*(*unsafe.Pointer)(up) = unsafe.New(rtyp)
}
return *(*uintptr)(up)
}
// decodeSingle decodes a top-level value that is not a struct and stores it through p.
// Such values are preceded by a zero, making them have the memory layout of a
// struct field (although with an illegal field number).
func (dec *Decoder) decodeSingle(engine *decEngine, ut *userTypeInfo, basep uintptr) (err os.Error) {
state := dec.newDecoderState(&dec.buf)
state.fieldnum = singletonField
delta := int(state.decodeUint())
if delta != 0 {
errorf("decode: corrupted data: non-zero delta for singleton")
}
instr := &engine.instr[singletonField]
if instr.indir != ut.indir {
return os.NewError("gob: internal error: inconsistent indirection")
}
ptr := unsafe.Pointer(basep) // offset will be zero
if instr.indir > 1 {
ptr = decIndirect(ptr, instr.indir)
}
instr.op(instr, state, ptr)
dec.freeDecoderState(state)
return nil
}
// decodeSingle decodes a top-level struct and stores it through p.
// Indir is for the value, not the type. At the time of the call it may
// differ from ut.indir, which was computed when the engine was built.
// This state cannot arise for decodeSingle, which is called directly
// from the user's value, not from the innards of an engine.
func (dec *Decoder) decodeStruct(engine *decEngine, ut *userTypeInfo, p uintptr, indir int) {
p = allocate(ut.base, p, indir)
state := dec.newDecoderState(&dec.buf)
state.fieldnum = -1
basep := p
for state.b.Len() > 0 {
delta := int(state.decodeUint())
if delta < 0 {
errorf("decode: corrupted data: negative delta")
}
if delta == 0 { // struct terminator is zero delta fieldnum
break
}
fieldnum := state.fieldnum + delta
if fieldnum >= len(engine.instr) {
error(errRange)
break
}
instr := &engine.instr[fieldnum]
p := unsafe.Pointer(basep + instr.offset)
if instr.indir > 1 {
p = decIndirect(p, instr.indir)
}
instr.op(instr, state, p)
state.fieldnum = fieldnum
}
dec.freeDecoderState(state)
}
// ignoreStruct discards the data for a struct with no destination.
func (dec *Decoder) ignoreStruct(engine *decEngine) {
state := dec.newDecoderState(&dec.buf)
state.fieldnum = -1
for state.b.Len() > 0 {
delta := int(state.decodeUint())
if delta < 0 {
errorf("ignore decode: corrupted data: negative delta")
}
if delta == 0 { // struct terminator is zero delta fieldnum
break
}
fieldnum := state.fieldnum + delta
if fieldnum >= len(engine.instr) {
error(errRange)
}
instr := &engine.instr[fieldnum]
instr.op(instr, state, unsafe.Pointer(nil))
state.fieldnum = fieldnum
}
dec.freeDecoderState(state)
}
// ignoreSingle discards the data for a top-level non-struct value with no
// destination. It's used when calling Decode with a nil value.
func (dec *Decoder) ignoreSingle(engine *decEngine) {
state := dec.newDecoderState(&dec.buf)
state.fieldnum = singletonField
delta := int(state.decodeUint())
if delta != 0 {
errorf("decode: corrupted data: non-zero delta for singleton")
}
instr := &engine.instr[singletonField]
instr.op(instr, state, unsafe.Pointer(nil))
dec.freeDecoderState(state)
}
// decodeArrayHelper does the work for decoding arrays and slices.
func (dec *Decoder) decodeArrayHelper(state *decoderState, p uintptr, elemOp decOp, elemWid uintptr, length, elemIndir int, ovfl os.Error) {
instr := &decInstr{elemOp, 0, elemIndir, 0, ovfl}
for i := 0; i < length; i++ {
up := unsafe.Pointer(p)
if elemIndir > 1 {
up = decIndirect(up, elemIndir)
}
elemOp(instr, state, up)
p += uintptr(elemWid)
}
}
// decodeArray decodes an array and stores it through p, that is, p points to the zeroth element.
// The length is an unsigned integer preceding the elements. Even though the length is redundant
// (it's part of the type), it's a useful check and is included in the encoding.
func (dec *Decoder) decodeArray(atyp reflect.Type, state *decoderState, p uintptr, elemOp decOp, elemWid uintptr, length, indir, elemIndir int, ovfl os.Error) {
if indir > 0 {
p = allocate(atyp, p, 1) // All but the last level has been allocated by dec.Indirect
}
if n := state.decodeUint(); n != uint64(length) {
errorf("length mismatch in decodeArray")
}
dec.decodeArrayHelper(state, p, elemOp, elemWid, length, elemIndir, ovfl)
}
// decodeIntoValue is a helper for map decoding. Since maps are decoded using reflection,
// unlike the other items we can't use a pointer directly.
func decodeIntoValue(state *decoderState, op decOp, indir int, v reflect.Value, ovfl os.Error) reflect.Value {
instr := &decInstr{op, 0, indir, 0, ovfl}
up := unsafe.Pointer(unsafeAddr(v))
if indir > 1 {
up = decIndirect(up, indir)
}
op(instr, state, up)
return v
}
// decodeMap decodes a map and stores its header through p.
// Maps are encoded as a length followed by key:value pairs.
// Because the internals of maps are not visible to us, we must
// use reflection rather than pointer magic.
func (dec *Decoder) decodeMap(mtyp reflect.Type, state *decoderState, p uintptr, keyOp, elemOp decOp, indir, keyIndir, elemIndir int, ovfl os.Error) {
if indir > 0 {
p = allocate(mtyp, p, 1) // All but the last level has been allocated by dec.Indirect
}
up := unsafe.Pointer(p)
if *(*unsafe.Pointer)(up) == nil { // maps are represented as a pointer in the runtime
// Allocate map.
*(*unsafe.Pointer)(up) = unsafe.Pointer(reflect.MakeMap(mtyp).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.ValueOf(unsafe.Unreflect(mtyp, unsafe.Pointer(p)))
n := int(state.decodeUint())
for i := 0; i < n; i++ {
key := decodeIntoValue(state, keyOp, keyIndir, allocValue(mtyp.Key()), ovfl)
elem := decodeIntoValue(state, elemOp, elemIndir, allocValue(mtyp.Elem()), ovfl)
v.SetMapIndex(key, elem)
}
}
// ignoreArrayHelper does the work for discarding arrays and slices.
func (dec *Decoder) ignoreArrayHelper(state *decoderState, elemOp decOp, length int) {
instr := &decInstr{elemOp, 0, 0, 0, os.NewError("no error")}
for i := 0; i < length; i++ {
elemOp(instr, state, nil)
}
}
// ignoreArray discards the data for an array value with no destination.
func (dec *Decoder) ignoreArray(state *decoderState, elemOp decOp, length int) {
if n := state.decodeUint(); n != uint64(length) {
errorf("length mismatch in ignoreArray")
}
dec.ignoreArrayHelper(state, elemOp, length)
}
// ignoreMap discards the data for a map value with no destination.
func (dec *Decoder) ignoreMap(state *decoderState, keyOp, elemOp decOp) {
n := int(state.decodeUint())
keyInstr := &decInstr{keyOp, 0, 0, 0, os.NewError("no error")}
elemInstr := &decInstr{elemOp, 0, 0, 0, os.NewError("no error")}
for i := 0; i < n; i++ {
keyOp(keyInstr, state, nil)
elemOp(elemInstr, state, nil)
}
}
// decodeSlice decodes a slice and stores the slice header through p.
// Slices are encoded as an unsigned length followed by the elements.
func (dec *Decoder) decodeSlice(atyp reflect.Type, state *decoderState, p uintptr, elemOp decOp, elemWid uintptr, indir, elemIndir int, ovfl os.Error) {
n := int(uintptr(state.decodeUint()))
if indir > 0 {
up := unsafe.Pointer(p)
if *(*unsafe.Pointer)(up) == nil {
// Allocate the slice header.
*(*unsafe.Pointer)(up) = unsafe.Pointer(new([]unsafe.Pointer))
}
p = *(*uintptr)(up)
}
// Allocate storage for the slice elements, that is, the underlying array,
// if the existing slice does not have the capacity.
// Always write a header at p.
hdrp := (*reflect.SliceHeader)(unsafe.Pointer(p))
if hdrp.Cap < n {
hdrp.Data = uintptr(unsafe.NewArray(atyp.Elem(), n))
hdrp.Cap = n
}
hdrp.Len = n
dec.decodeArrayHelper(state, hdrp.Data, elemOp, elemWid, n, elemIndir, ovfl)
}
// ignoreSlice skips over the data for a slice value with no destination.
func (dec *Decoder) ignoreSlice(state *decoderState, elemOp decOp) {
dec.ignoreArrayHelper(state, elemOp, int(state.decodeUint()))
}
// setInterfaceValue sets an interface value to a concrete value,
// but first it checks that the assignment will succeed.
func setInterfaceValue(ivalue reflect.Value, value reflect.Value) {
if !value.Type().AssignableTo(ivalue.Type()) {
errorf("cannot assign value of type %s to %s", value.Type(), ivalue.Type())
}
ivalue.Set(value)
}
// decodeInterface decodes an interface value and stores it through p.
// Interfaces are encoded as the name of a concrete type followed by a value.
// If the name is empty, the value is nil and no value is sent.
func (dec *Decoder) decodeInterface(ityp reflect.Type, state *decoderState, p uintptr, indir int) {
// Create a writable interface reflect.Value. We need one even for the nil case.
ivalue := allocValue(ityp)
// Read the name of the concrete type.
b := make([]byte, state.decodeUint())
state.b.Read(b)
name := string(b)
if name == "" {
// Copy the representation of the nil interface value to the target.
// This is horribly unsafe and special.
*(*[2]uintptr)(unsafe.Pointer(p)) = ivalue.InterfaceData()
return
}
// The concrete type must be registered.
typ, ok := nameToConcreteType[name]
if !ok {
errorf("name not registered for interface: %q", name)
}
// Read the type id of the concrete value.
concreteId := dec.decodeTypeSequence(true)
if concreteId < 0 {
error(dec.err)
}
// Byte count of value is next; we don't care what it is (it's there
// in case we want to ignore the value by skipping it completely).
state.decodeUint()
// Read the concrete value.
value := allocValue(typ)
dec.decodeValue(concreteId, value)
if dec.err != nil {
error(dec.err)
}
// Allocate the destination interface value.
if indir > 0 {
p = allocate(ityp, p, 1) // All but the last level has been allocated by dec.Indirect
}
// Assign the concrete value to the interface.
// Tread carefully; it might not satisfy the interface.
setInterfaceValue(ivalue, value)
// Copy the representation of the interface value to the target.
// This is horribly unsafe and special.
*(*[2]uintptr)(unsafe.Pointer(p)) = ivalue.InterfaceData()
}
// ignoreInterface discards the data for an interface value with no destination.
func (dec *Decoder) ignoreInterface(state *decoderState) {
// Read the name of the concrete type.
b := make([]byte, state.decodeUint())
_, err := state.b.Read(b)
if err != nil {
error(err)
}
id := dec.decodeTypeSequence(true)
if id < 0 {
error(dec.err)
}
// At this point, the decoder buffer contains a delimited value. Just toss it.
state.b.Next(int(state.decodeUint()))
}
// decodeGobDecoder decodes something implementing the GobDecoder interface.
// The data is encoded as a byte slice.
func (dec *Decoder) decodeGobDecoder(state *decoderState, v reflect.Value) {
// Read the bytes for the value.
b := make([]byte, state.decodeUint())
_, err := state.b.Read(b)
if err != nil {
error(err)
}
// We know it's a GobDecoder, so just call the method directly.
err = v.Interface().(GobDecoder).GobDecode(b)
if err != nil {
error(err)
}
}
// ignoreGobDecoder discards the data for a GobDecoder value with no destination.
func (dec *Decoder) ignoreGobDecoder(state *decoderState) {
// Read the bytes for the value.
b := make([]byte, state.decodeUint())
_, err := state.b.Read(b)
if err != nil {
error(err)
}
}
// Index by Go types.
var decOpTable = [...]decOp{
reflect.Bool: decBool,
reflect.Int8: decInt8,
reflect.Int16: decInt16,
reflect.Int32: decInt32,
reflect.Int64: decInt64,
reflect.Uint8: decUint8,
reflect.Uint16: decUint16,
reflect.Uint32: decUint32,
reflect.Uint64: decUint64,
reflect.Float32: decFloat32,
reflect.Float64: decFloat64,
reflect.Complex64: decComplex64,
reflect.Complex128: decComplex128,
reflect.String: decString,
}
// Indexed by gob types. tComplex will be added during type.init().
var decIgnoreOpMap = map[typeId]decOp{
tBool: ignoreUint,
tInt: ignoreUint,
tUint: ignoreUint,
tFloat: ignoreUint,
tBytes: ignoreUint8Array,
tString: ignoreUint8Array,
tComplex: ignoreTwoUints,
}
// decOpFor returns the decoding op for the base type under rt and
// the indirection count to reach it.
func (dec *Decoder) decOpFor(wireId typeId, rt reflect.Type, name string, inProgress map[reflect.Type]*decOp) (*decOp, int) {
ut := userType(rt)
// If the type implements GobEncoder, we handle it without further processing.
if ut.isGobDecoder {
return dec.gobDecodeOpFor(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
var op decOp
k := typ.Kind()
if int(k) < len(decOpTable) {
op = decOpTable[k]
}
if op == nil {
inProgress[rt] = &op
// Special cases
switch t := typ; t.Kind() {
case reflect.Array:
name = "element of " + name
elemId := dec.wireType[wireId].ArrayT.Elem
elemOp, elemIndir := dec.decOpFor(elemId, t.Elem(), name, inProgress)
ovfl := overflow(name)
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.decodeArray(t, state, uintptr(p), *elemOp, t.Elem().Size(), t.Len(), i.indir, elemIndir, ovfl)
}
case reflect.Map:
name = "element of " + name
keyId := dec.wireType[wireId].MapT.Key
elemId := dec.wireType[wireId].MapT.Elem
keyOp, keyIndir := dec.decOpFor(keyId, t.Key(), name, inProgress)
elemOp, elemIndir := dec.decOpFor(elemId, t.Elem(), name, inProgress)
ovfl := overflow(name)
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
up := unsafe.Pointer(p)
state.dec.decodeMap(t, state, uintptr(up), *keyOp, *elemOp, i.indir, keyIndir, elemIndir, ovfl)
}
case reflect.Slice:
name = "element of " + name
if t.Elem().Kind() == reflect.Uint8 {
op = decUint8Slice
break
}
var elemId typeId
if tt, ok := builtinIdToType[wireId]; ok {
elemId = tt.(*sliceType).Elem
} else {
elemId = dec.wireType[wireId].SliceT.Elem
}
elemOp, elemIndir := dec.decOpFor(elemId, t.Elem(), name, inProgress)
ovfl := overflow(name)
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.decodeSlice(t, state, uintptr(p), *elemOp, t.Elem().Size(), i.indir, elemIndir, ovfl)
}
case reflect.Struct:
// Generate a closure that calls out to the engine for the nested type.
enginePtr, err := dec.getDecEnginePtr(wireId, userType(typ))
if err != nil {
error(err)
}
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
// indirect through enginePtr to delay evaluation for recursive structs.
dec.decodeStruct(*enginePtr, userType(typ), uintptr(p), i.indir)
}
case reflect.Interface:
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.decodeInterface(t, state, uintptr(p), i.indir)
}
}
}
if op == nil {
errorf("decode can't handle type %s", rt)
}
return &op, indir
}
// decIgnoreOpFor returns the decoding op for a field that has no destination.
func (dec *Decoder) decIgnoreOpFor(wireId typeId) decOp {
op, ok := decIgnoreOpMap[wireId]
if !ok {
if wireId == tInterface {
// Special case because it's a method: the ignored item might
// define types and we need to record their state in the decoder.
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.ignoreInterface(state)
}
return op
}
// Special cases
wire := dec.wireType[wireId]
switch {
case wire == nil:
errorf("bad data: undefined type %s", wireId.string())
case wire.ArrayT != nil:
elemId := wire.ArrayT.Elem
elemOp := dec.decIgnoreOpFor(elemId)
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.ignoreArray(state, elemOp, wire.ArrayT.Len)
}
case wire.MapT != nil:
keyId := dec.wireType[wireId].MapT.Key
elemId := dec.wireType[wireId].MapT.Elem
keyOp := dec.decIgnoreOpFor(keyId)
elemOp := dec.decIgnoreOpFor(elemId)
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.ignoreMap(state, keyOp, elemOp)
}
case wire.SliceT != nil:
elemId := wire.SliceT.Elem
elemOp := dec.decIgnoreOpFor(elemId)
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.ignoreSlice(state, elemOp)
}
case wire.StructT != nil:
// Generate a closure that calls out to the engine for the nested type.
enginePtr, err := dec.getIgnoreEnginePtr(wireId)
if err != nil {
error(err)
}
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
// indirect through enginePtr to delay evaluation for recursive structs
state.dec.ignoreStruct(*enginePtr)
}
case wire.GobEncoderT != nil:
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
state.dec.ignoreGobDecoder(state)
}
}
}
if op == nil {
errorf("bad data: ignore can't handle type %s", wireId.string())
}
return op
}
// gobDecodeOpFor returns the op for a type that is known to implement
// GobDecoder.
func (dec *Decoder) gobDecodeOpFor(ut *userTypeInfo) (*decOp, int) {
rcvrType := ut.user
if ut.decIndir == -1 {
rcvrType = reflect.PtrTo(rcvrType)
} else if ut.decIndir > 0 {
for i := int8(0); i < ut.decIndir; i++ {
rcvrType = rcvrType.Elem()
}
}
var op decOp
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
// Caller has gotten us to within one indirection of our value.
if i.indir > 0 {
if *(*unsafe.Pointer)(p) == nil {
*(*unsafe.Pointer)(p) = unsafe.New(ut.base)
}
}
// Now p is a pointer to the base type. Do we need to climb out to
// get to the receiver type?
var v reflect.Value
if ut.decIndir == -1 {
v = reflect.ValueOf(unsafe.Unreflect(rcvrType, unsafe.Pointer(&p)))
} else {
v = reflect.ValueOf(unsafe.Unreflect(rcvrType, p))
}
state.dec.decodeGobDecoder(state, v)
}
return &op, int(ut.indir)
}
// compatibleType asks: Are these two gob Types compatible?
// Answers the question for basic types, arrays, maps and slices, plus
// GobEncoder/Decoder pairs.
// Structs are considered ok; fields will be checked later.
func (dec *Decoder) compatibleType(fr reflect.Type, fw typeId, inProgress map[reflect.Type]typeId) bool {
if rhs, ok := inProgress[fr]; ok {
return rhs == fw
}
inProgress[fr] = fw
ut := userType(fr)
wire, ok := dec.wireType[fw]
// If fr is a GobDecoder, the wire type must be GobEncoder.
// And if fr is not a GobDecoder, the wire type must not be either.
if ut.isGobDecoder != (ok && wire.GobEncoderT != nil) { // the parentheses look odd but are correct.
return false
}
if ut.isGobDecoder { // This test trumps all others.
return true
}
switch t := ut.base; t.Kind() {
default:
// chan, etc: cannot handle.
return false
case reflect.Bool:
return fw == tBool
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return fw == tInt
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return fw == tUint
case reflect.Float32, reflect.Float64:
return fw == tFloat
case reflect.Complex64, reflect.Complex128:
return fw == tComplex
case reflect.String:
return fw == tString
case reflect.Interface:
return fw == tInterface
case reflect.Array:
if !ok || wire.ArrayT == nil {
return false
}
array := wire.ArrayT
return t.Len() == array.Len && dec.compatibleType(t.Elem(), array.Elem, inProgress)
case reflect.Map:
if !ok || wire.MapT == nil {
return false
}
MapType := wire.MapT
return dec.compatibleType(t.Key(), MapType.Key, inProgress) && dec.compatibleType(t.Elem(), MapType.Elem, inProgress)
case reflect.Slice:
// Is it an array of bytes?
if t.Elem().Kind() == reflect.Uint8 {
return fw == tBytes
}
// Extract and compare element types.
var sw *sliceType
if tt, ok := builtinIdToType[fw]; ok {
sw = tt.(*sliceType)
} else {
sw = dec.wireType[fw].SliceT
}
elem := userType(t.Elem()).base
return sw != nil && dec.compatibleType(elem, sw.Elem, inProgress)
case reflect.Struct:
return true
}
return true
}
// typeString returns a human-readable description of the type identified by remoteId.
func (dec *Decoder) typeString(remoteId typeId) string {
if t := idToType[remoteId]; t != nil {
// globally known type.
return t.string()
}
return dec.wireType[remoteId].string()
}
// compileSingle compiles the decoder engine for a non-struct top-level value, including
// GobDecoders.
func (dec *Decoder) compileSingle(remoteId typeId, ut *userTypeInfo) (engine *decEngine, err os.Error) {
rt := ut.user
engine = new(decEngine)
engine.instr = make([]decInstr, 1) // one item
name := rt.String() // best we can do
if !dec.compatibleType(rt, remoteId, make(map[reflect.Type]typeId)) {
return nil, os.NewError("gob: wrong type received for local value " + name + ": " + dec.typeString(remoteId))
}
op, indir := dec.decOpFor(remoteId, rt, name, make(map[reflect.Type]*decOp))
ovfl := os.NewError(`value for "` + name + `" out of range`)
engine.instr[singletonField] = decInstr{*op, singletonField, indir, 0, ovfl}
engine.numInstr = 1
return
}
// compileIgnoreSingle compiles the decoder engine for a non-struct top-level value that will be discarded.
func (dec *Decoder) compileIgnoreSingle(remoteId typeId) (engine *decEngine, err os.Error) {
engine = new(decEngine)
engine.instr = make([]decInstr, 1) // one item
op := dec.decIgnoreOpFor(remoteId)
ovfl := overflow(dec.typeString(remoteId))
engine.instr[0] = decInstr{op, 0, 0, 0, ovfl}
engine.numInstr = 1
return
}
// compileDec compiles the decoder engine for a value. If the value is not a struct,
// it calls out to compileSingle.
func (dec *Decoder) compileDec(remoteId typeId, ut *userTypeInfo) (engine *decEngine, err os.Error) {
rt := ut.base
srt := rt
if srt.Kind() != reflect.Struct ||
ut.isGobDecoder {
return dec.compileSingle(remoteId, ut)
}
var wireStruct *structType
// Builtin types can come from global pool; the rest must be defined by the decoder.
// Also we know we're decoding a struct now, so the client must have sent one.
if t, ok := builtinIdToType[remoteId]; ok {
wireStruct, _ = t.(*structType)
} else {
wire := dec.wireType[remoteId]
if wire == nil {
error(errBadType)
}
wireStruct = wire.StructT
}
if wireStruct == nil {
errorf("type mismatch in decoder: want struct type %s; got non-struct", rt)
}
engine = new(decEngine)
engine.instr = make([]decInstr, len(wireStruct.Field))
seen := make(map[reflect.Type]*decOp)
// Loop over the fields of the wire type.
for fieldnum := 0; fieldnum < len(wireStruct.Field); fieldnum++ {
wireField := wireStruct.Field[fieldnum]
if wireField.Name == "" {
errorf("empty name for remote field of type %s", wireStruct.Name)
}
ovfl := overflow(wireField.Name)
// Find the field of the local type with the same name.
localField, present := srt.FieldByName(wireField.Name)
// TODO(r): anonymous names
if !present || !isExported(wireField.Name) {
op := dec.decIgnoreOpFor(wireField.Id)
engine.instr[fieldnum] = decInstr{op, fieldnum, 0, 0, ovfl}
continue
}
if !dec.compatibleType(localField.Type, wireField.Id, make(map[reflect.Type]typeId)) {
errorf("wrong type (%s) for received field %s.%s", localField.Type, wireStruct.Name, wireField.Name)
}
op, indir := dec.decOpFor(wireField.Id, localField.Type, localField.Name, seen)
engine.instr[fieldnum] = decInstr{*op, fieldnum, indir, uintptr(localField.Offset), ovfl}
engine.numInstr++
}
return
}
// getDecEnginePtr returns the engine for the specified type.
func (dec *Decoder) getDecEnginePtr(remoteId typeId, ut *userTypeInfo) (enginePtr **decEngine, err os.Error) {
rt := ut.base
decoderMap, ok := dec.decoderCache[rt]
if !ok {
decoderMap = make(map[typeId]**decEngine)
dec.decoderCache[rt] = decoderMap
}
if enginePtr, ok = decoderMap[remoteId]; !ok {
// To handle recursive types, mark this engine as underway before compiling.
enginePtr = new(*decEngine)
decoderMap[remoteId] = enginePtr
*enginePtr, err = dec.compileDec(remoteId, ut)
if err != nil {
delete(decoderMap, remoteId)
}
}
return
}
// emptyStruct is the type we compile into when ignoring a struct value.
type emptyStruct struct{}
var emptyStructType = reflect.TypeOf(emptyStruct{})
// getDecEnginePtr returns the engine for the specified type when the value is to be discarded.
func (dec *Decoder) getIgnoreEnginePtr(wireId typeId) (enginePtr **decEngine, err os.Error) {
var ok bool
if enginePtr, ok = dec.ignorerCache[wireId]; !ok {
// To handle recursive types, mark this engine as underway before compiling.
enginePtr = new(*decEngine)
dec.ignorerCache[wireId] = enginePtr
wire := dec.wireType[wireId]
if wire != nil && wire.StructT != nil {
*enginePtr, err = dec.compileDec(wireId, userType(emptyStructType))
} else {
*enginePtr, err = dec.compileIgnoreSingle(wireId)
}
if err != nil {
delete(dec.ignorerCache, wireId)
}
}
return
}
// decodeValue decodes the data stream representing a value and stores it in val.
func (dec *Decoder) decodeValue(wireId typeId, val reflect.Value) {
defer catchError(&dec.err)
// If the value is nil, it means we should just ignore this item.
if !val.IsValid() {
dec.decodeIgnoredValue(wireId)
return
}
// Dereference down to the underlying type.
ut := userType(val.Type())
base := ut.base
var enginePtr **decEngine
enginePtr, dec.err = dec.getDecEnginePtr(wireId, ut)
if dec.err != nil {
return
}
engine := *enginePtr
if st := base; st.Kind() == reflect.Struct && !ut.isGobDecoder {
if engine.numInstr == 0 && st.NumField() > 0 && len(dec.wireType[wireId].StructT.Field) > 0 {
name := base.Name()
errorf("type mismatch: no fields matched compiling decoder for %s", name)
}
dec.decodeStruct(engine, ut, uintptr(unsafeAddr(val)), ut.indir)
} else {
dec.decodeSingle(engine, ut, uintptr(unsafeAddr(val)))
}
}
// decodeIgnoredValue decodes the data stream representing a value of the specified type and discards it.
func (dec *Decoder) decodeIgnoredValue(wireId typeId) {
var enginePtr **decEngine
enginePtr, dec.err = dec.getIgnoreEnginePtr(wireId)
if dec.err != nil {
return
}
wire := dec.wireType[wireId]
if wire != nil && wire.StructT != nil {
dec.ignoreStruct(*enginePtr)
} else {
dec.ignoreSingle(*enginePtr)
}
}
func init() {
var iop, uop decOp
switch reflect.TypeOf(int(0)).Bits() {
case 32:
iop = decInt32
uop = decUint32
case 64:
iop = decInt64
uop = decUint64
default:
panic("gob: unknown size of int/uint")
}
decOpTable[reflect.Int] = iop
decOpTable[reflect.Uint] = uop
// Finally uintptr
switch reflect.TypeOf(uintptr(0)).Bits() {
case 32:
uop = decUint32
case 64:
uop = decUint64
default:
panic("gob: unknown size of uintptr")
}
decOpTable[reflect.Uintptr] = uop
}
// Gob assumes it can call UnsafeAddr on any Value
// in order to get a pointer it can copy data from.
// Values that have just been created and do not point
// into existing structs or slices cannot be addressed,
// so simulate it by returning a pointer to a copy.
// Each call allocates once.
func unsafeAddr(v reflect.Value) uintptr {
if v.CanAddr() {
return v.UnsafeAddr()
}
x := reflect.New(v.Type()).Elem()
x.Set(v)
return x.UnsafeAddr()
}
// Gob depends on being able to take the address
// of zeroed Values it creates, so use this wrapper instead
// of the standard reflect.Zero.
// Each call allocates once.
func allocValue(t reflect.Type) reflect.Value {
return reflect.New(t).Elem()
}