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 func NewDecoder(r io.Reader) *Decoder {
34 dec.r = bufio.NewReader(r)
35 dec.wireType = make(map[typeId]*wireType)
36 dec.decoderCache = make(map[reflect.Type]map[typeId]**decEngine)
37 dec.ignorerCache = make(map[typeId]**decEngine)
38 dec.countBuf = make([]byte, 9) // counts may be uint64s (unlikely!), require 9 bytes
43 // recvType loads the definition of a type.
44 func (dec *Decoder) recvType(id typeId) {
45 // Have we already seen this type? That's an error
46 if id < firstUserId || dec.wireType[id] != nil {
47 dec.err = os.NewError("gob: duplicate type received")
53 dec.decodeValue(tWireType, reflect.ValueOf(wire))
57 // Remember we've seen this type.
58 dec.wireType[id] = wire
61 // recvMessage reads the next count-delimited item from the input. It is the converse
62 // of Encoder.writeMessage. It returns false on EOF or other error reading the message.
63 func (dec *Decoder) recvMessage() bool {
65 nbytes, _, err := decodeUintReader(dec.r, dec.countBuf)
70 dec.readMessage(int(nbytes))
74 // readMessage reads the next nbytes bytes from the input.
75 func (dec *Decoder) readMessage(nbytes int) {
76 // Allocate the buffer.
77 if cap(dec.tmp) < nbytes {
78 dec.tmp = make([]byte, nbytes+100) // room to grow
80 dec.tmp = dec.tmp[:nbytes]
83 _, dec.err = io.ReadFull(dec.r, dec.tmp)
85 if dec.err == os.EOF {
86 dec.err = io.ErrUnexpectedEOF
90 dec.buf.Write(dec.tmp)
93 // toInt turns an encoded uint64 into an int, according to the marshaling rules.
94 func toInt(x uint64) int64 {
102 func (dec *Decoder) nextInt() int64 {
103 n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
110 func (dec *Decoder) nextUint() uint64 {
111 n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
118 // decodeTypeSequence parses:
120 // (TypeDefinition DelimitedTypeDefinition*)?
121 // and returns the type id of the next value. It returns -1 at
122 // EOF. Upon return, the remainder of dec.buf is the value to be
123 // decoded. If this is an interface value, it can be ignored by
124 // simply resetting that buffer.
125 func (dec *Decoder) decodeTypeSequence(isInterface bool) typeId {
127 if dec.buf.Len() == 0 {
128 if !dec.recvMessage() {
132 // Receive a type id.
133 id := typeId(dec.nextInt())
138 // Type definition for (-id) follows.
140 // When decoding an interface, after a type there may be a
141 // DelimitedValue still in the buffer. Skip its count.
142 // (Alternatively, the buffer is empty and the byte count
143 // will be absorbed by recvMessage.)
144 if dec.buf.Len() > 0 {
146 dec.err = os.NewError("extra data in buffer")
155 // Decode reads the next value from the connection and stores
156 // it in the data represented by the empty interface value.
157 // If e is nil, the value will be discarded. Otherwise,
158 // the value underlying e must be a pointer to the
159 // correct type for the next data item received.
160 func (dec *Decoder) Decode(e interface{}) os.Error {
162 return dec.DecodeValue(reflect.Value{})
164 value := reflect.ValueOf(e)
165 // If e represents a value as opposed to a pointer, the answer won't
166 // get back to the caller. Make sure it's a pointer.
167 if value.Type().Kind() != reflect.Ptr {
168 dec.err = os.NewError("gob: attempt to decode into a non-pointer")
171 return dec.DecodeValue(value)
174 // DecodeValue reads the next value from the connection.
175 // If v is the zero reflect.Value (v.Kind() == Invalid), DecodeValue discards the value.
176 // Otherwise, it stores the value into v. In that case, v must represent
177 // a non-nil pointer to data or be an assignable reflect.Value (v.CanSet())
178 func (dec *Decoder) DecodeValue(v reflect.Value) os.Error {
180 if v.Kind() == reflect.Ptr && !v.IsNil() {
181 // That's okay, we'll store through the pointer.
182 } else if !v.CanSet() {
183 return os.NewError("gob: DecodeValue of unassignable value")
186 // Make sure we're single-threaded through here.
188 defer dec.mutex.Unlock()
190 dec.buf.Reset() // In case data lingers from previous invocation.
192 id := dec.decodeTypeSequence(false)
194 dec.decodeValue(id, v)
199 // If debug.go is compiled into the program , debugFunc prints a human-readable
200 // representation of the gob data read from r by calling that file's Debug function.
201 // Otherwise it is nil.
202 var debugFunc func(io.Reader)