mirror of
https://github.com/autc04/Retro68.git
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219 lines
6.5 KiB
Go
219 lines
6.5 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package gob
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import (
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"bufio"
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"errors"
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"io"
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"reflect"
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"sync"
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)
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// tooBig provides a sanity check for sizes; used in several places.
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// Upper limit of 1GB, allowing room to grow a little without overflow.
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// TODO: make this adjustable?
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const tooBig = 1 << 30
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// A Decoder manages the receipt of type and data information read from the
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// remote side of a connection.
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type Decoder struct {
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mutex sync.Mutex // each item must be received atomically
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r io.Reader // source of the data
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buf decBuffer // buffer for more efficient i/o from r
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wireType map[typeId]*wireType // map from remote ID to local description
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decoderCache map[reflect.Type]map[typeId]**decEngine // cache of compiled engines
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ignorerCache map[typeId]**decEngine // ditto for ignored objects
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freeList *decoderState // list of free decoderStates; avoids reallocation
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countBuf []byte // used for decoding integers while parsing messages
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err error
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}
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// NewDecoder returns a new decoder that reads from the io.Reader.
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// If r does not also implement io.ByteReader, it will be wrapped in a
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// bufio.Reader.
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func NewDecoder(r io.Reader) *Decoder {
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dec := new(Decoder)
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// We use the ability to read bytes as a plausible surrogate for buffering.
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if _, ok := r.(io.ByteReader); !ok {
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r = bufio.NewReader(r)
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}
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dec.r = r
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dec.wireType = make(map[typeId]*wireType)
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dec.decoderCache = make(map[reflect.Type]map[typeId]**decEngine)
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dec.ignorerCache = make(map[typeId]**decEngine)
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dec.countBuf = make([]byte, 9) // counts may be uint64s (unlikely!), require 9 bytes
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return dec
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}
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// recvType loads the definition of a type.
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func (dec *Decoder) recvType(id typeId) {
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// Have we already seen this type? That's an error
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if id < firstUserId || dec.wireType[id] != nil {
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dec.err = errors.New("gob: duplicate type received")
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return
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}
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// Type:
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wire := new(wireType)
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dec.decodeValue(tWireType, reflect.ValueOf(wire))
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if dec.err != nil {
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return
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}
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// Remember we've seen this type.
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dec.wireType[id] = wire
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}
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var errBadCount = errors.New("invalid message length")
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// recvMessage reads the next count-delimited item from the input. It is the converse
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// of Encoder.writeMessage. It returns false on EOF or other error reading the message.
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func (dec *Decoder) recvMessage() bool {
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// Read a count.
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nbytes, _, err := decodeUintReader(dec.r, dec.countBuf)
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if err != nil {
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dec.err = err
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return false
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}
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if nbytes >= tooBig {
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dec.err = errBadCount
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return false
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}
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dec.readMessage(int(nbytes))
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return dec.err == nil
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}
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// readMessage reads the next nbytes bytes from the input.
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func (dec *Decoder) readMessage(nbytes int) {
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if dec.buf.Len() != 0 {
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// The buffer should always be empty now.
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panic("non-empty decoder buffer")
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}
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// Read the data
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dec.buf.Size(nbytes)
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_, dec.err = io.ReadFull(dec.r, dec.buf.Bytes())
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if dec.err != nil {
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if dec.err == io.EOF {
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dec.err = io.ErrUnexpectedEOF
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}
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}
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}
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// toInt turns an encoded uint64 into an int, according to the marshaling rules.
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func toInt(x uint64) int64 {
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i := int64(x >> 1)
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if x&1 != 0 {
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i = ^i
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}
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return i
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}
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func (dec *Decoder) nextInt() int64 {
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n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
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if err != nil {
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dec.err = err
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}
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return toInt(n)
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}
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func (dec *Decoder) nextUint() uint64 {
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n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
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if err != nil {
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dec.err = err
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}
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return n
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}
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// decodeTypeSequence parses:
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// TypeSequence
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// (TypeDefinition DelimitedTypeDefinition*)?
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// and returns the type id of the next value. It returns -1 at
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// EOF. Upon return, the remainder of dec.buf is the value to be
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// decoded. If this is an interface value, it can be ignored by
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// resetting that buffer.
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func (dec *Decoder) decodeTypeSequence(isInterface bool) typeId {
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for dec.err == nil {
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if dec.buf.Len() == 0 {
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if !dec.recvMessage() {
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break
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}
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}
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// Receive a type id.
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id := typeId(dec.nextInt())
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if id >= 0 {
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// Value follows.
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return id
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}
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// Type definition for (-id) follows.
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dec.recvType(-id)
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// When decoding an interface, after a type there may be a
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// DelimitedValue still in the buffer. Skip its count.
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// (Alternatively, the buffer is empty and the byte count
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// will be absorbed by recvMessage.)
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if dec.buf.Len() > 0 {
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if !isInterface {
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dec.err = errors.New("extra data in buffer")
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break
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}
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dec.nextUint()
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}
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}
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return -1
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}
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// Decode reads the next value from the input stream and stores
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// it in the data represented by the empty interface value.
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// If e is nil, the value will be discarded. Otherwise,
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// the value underlying e must be a pointer to the
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// correct type for the next data item received.
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// If the input is at EOF, Decode returns io.EOF and
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// does not modify e.
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func (dec *Decoder) Decode(e interface{}) error {
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if e == nil {
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return dec.DecodeValue(reflect.Value{})
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}
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value := reflect.ValueOf(e)
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// If e represents a value as opposed to a pointer, the answer won't
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// get back to the caller. Make sure it's a pointer.
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if value.Type().Kind() != reflect.Ptr {
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dec.err = errors.New("gob: attempt to decode into a non-pointer")
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return dec.err
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}
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return dec.DecodeValue(value)
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}
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// DecodeValue reads the next value from the input stream.
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// If v is the zero reflect.Value (v.Kind() == Invalid), DecodeValue discards the value.
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// Otherwise, it stores the value into v. In that case, v must represent
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// a non-nil pointer to data or be an assignable reflect.Value (v.CanSet())
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// If the input is at EOF, DecodeValue returns io.EOF and
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// does not modify v.
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func (dec *Decoder) DecodeValue(v reflect.Value) error {
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if v.IsValid() {
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if v.Kind() == reflect.Ptr && !v.IsNil() {
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// That's okay, we'll store through the pointer.
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} else if !v.CanSet() {
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return errors.New("gob: DecodeValue of unassignable value")
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}
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}
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// Make sure we're single-threaded through here.
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dec.mutex.Lock()
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defer dec.mutex.Unlock()
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dec.buf.Reset() // In case data lingers from previous invocation.
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dec.err = nil
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id := dec.decodeTypeSequence(false)
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if dec.err == nil {
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dec.decodeValue(id, v)
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}
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return dec.err
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}
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// If debug.go is compiled into the program , debugFunc prints a human-readable
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// representation of the gob data read from r by calling that file's Debug function.
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// Otherwise it is nil.
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var debugFunc func(io.Reader)
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