1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
16 // A Decoder manages the receipt of type and data information read from the
17 // remote side of a connection.
19 mutex sync.Mutex // each item must be received atomically
20 r io.Reader // source of the data
21 buf bytes.Buffer // buffer for more efficient i/o from r
22 wireType map[typeId]*wireType // map from remote ID to local description
23 decoderCache map[reflect.Type]map[typeId]**decEngine // cache of compiled engines
24 ignorerCache map[typeId]**decEngine // ditto for ignored objects
25 freeList *decoderState // list of free decoderStates; avoids reallocation
26 countBuf []byte // used for decoding integers while parsing messages
27 tmp []byte // temporary storage for i/o; saves reallocating
31 // NewDecoder returns a new decoder that reads from the io.Reader.
32 // If r does not also implement io.ByteReader, it will be wrapped in a
34 func NewDecoder(r io.Reader) *Decoder {
36 // We use the ability to read bytes as a plausible surrogate for buffering.
37 if _, ok := r.(io.ByteReader); !ok {
38 r = bufio.NewReader(r)
41 dec.wireType = make(map[typeId]*wireType)
42 dec.decoderCache = make(map[reflect.Type]map[typeId]**decEngine)
43 dec.ignorerCache = make(map[typeId]**decEngine)
44 dec.countBuf = make([]byte, 9) // counts may be uint64s (unlikely!), require 9 bytes
49 // recvType loads the definition of a type.
50 func (dec *Decoder) recvType(id typeId) {
51 // Have we already seen this type? That's an error
52 if id < firstUserId || dec.wireType[id] != nil {
53 dec.err = os.NewError("gob: duplicate type received")
59 dec.decodeValue(tWireType, reflect.ValueOf(wire))
63 // Remember we've seen this type.
64 dec.wireType[id] = wire
67 var errBadCount = os.NewError("invalid message length")
69 // recvMessage reads the next count-delimited item from the input. It is the converse
70 // of Encoder.writeMessage. It returns false on EOF or other error reading the message.
71 func (dec *Decoder) recvMessage() bool {
73 nbytes, _, err := decodeUintReader(dec.r, dec.countBuf)
82 dec.readMessage(int(nbytes))
86 // readMessage reads the next nbytes bytes from the input.
87 func (dec *Decoder) readMessage(nbytes int) {
88 // Allocate the buffer.
89 if cap(dec.tmp) < nbytes {
90 dec.tmp = make([]byte, nbytes+100) // room to grow
92 dec.tmp = dec.tmp[:nbytes]
95 _, dec.err = io.ReadFull(dec.r, dec.tmp)
97 if dec.err == os.EOF {
98 dec.err = io.ErrUnexpectedEOF
102 dec.buf.Write(dec.tmp)
105 // toInt turns an encoded uint64 into an int, according to the marshaling rules.
106 func toInt(x uint64) int64 {
114 func (dec *Decoder) nextInt() int64 {
115 n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
122 func (dec *Decoder) nextUint() uint64 {
123 n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
130 // decodeTypeSequence parses:
132 // (TypeDefinition DelimitedTypeDefinition*)?
133 // and returns the type id of the next value. It returns -1 at
134 // EOF. Upon return, the remainder of dec.buf is the value to be
135 // decoded. If this is an interface value, it can be ignored by
136 // simply resetting that buffer.
137 func (dec *Decoder) decodeTypeSequence(isInterface bool) typeId {
139 if dec.buf.Len() == 0 {
140 if !dec.recvMessage() {
144 // Receive a type id.
145 id := typeId(dec.nextInt())
150 // Type definition for (-id) follows.
152 // When decoding an interface, after a type there may be a
153 // DelimitedValue still in the buffer. Skip its count.
154 // (Alternatively, the buffer is empty and the byte count
155 // will be absorbed by recvMessage.)
156 if dec.buf.Len() > 0 {
158 dec.err = os.NewError("extra data in buffer")
167 // Decode reads the next value from the connection and stores
168 // it in the data represented by the empty interface value.
169 // If e is nil, the value will be discarded. Otherwise,
170 // the value underlying e must be a pointer to the
171 // correct type for the next data item received.
172 func (dec *Decoder) Decode(e interface{}) os.Error {
174 return dec.DecodeValue(reflect.Value{})
176 value := reflect.ValueOf(e)
177 // If e represents a value as opposed to a pointer, the answer won't
178 // get back to the caller. Make sure it's a pointer.
179 if value.Type().Kind() != reflect.Ptr {
180 dec.err = os.NewError("gob: attempt to decode into a non-pointer")
183 return dec.DecodeValue(value)
186 // DecodeValue reads the next value from the connection.
187 // If v is the zero reflect.Value (v.Kind() == Invalid), DecodeValue discards the value.
188 // Otherwise, it stores the value into v. In that case, v must represent
189 // a non-nil pointer to data or be an assignable reflect.Value (v.CanSet())
190 func (dec *Decoder) DecodeValue(v reflect.Value) os.Error {
192 if v.Kind() == reflect.Ptr && !v.IsNil() {
193 // That's okay, we'll store through the pointer.
194 } else if !v.CanSet() {
195 return os.NewError("gob: DecodeValue of unassignable value")
198 // Make sure we're single-threaded through here.
200 defer dec.mutex.Unlock()
202 dec.buf.Reset() // In case data lingers from previous invocation.
204 id := dec.decodeTypeSequence(false)
206 dec.decodeValue(id, v)
211 // If debug.go is compiled into the program , debugFunc prints a human-readable
212 // representation of the gob data read from r by calling that file's Debug function.
213 // Otherwise it is nil.
214 var debugFunc func(io.Reader)