1 files changed, 237 insertions, 0 deletions
diff --git a/src/encoding/gob/decoder.go b/src/encoding/gob/decoder.go
new file mode 100644
index 000000000..3a769ec12
--- /dev/null
+++ b/src/encoding/gob/decoder.go
@@ -0,0 +1,237 @@
+// 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 (
+	"bufio"
+	"bytes"
+	"errors"
+	"io"
+	"reflect"
+	"sync"
+)
+
+// A Decoder manages the receipt of type and data information read from the
+// remote side of a connection.
+type Decoder struct {
+	mutex        sync.Mutex                              // each item must be received atomically
+	r            io.Reader                               // source of the data
+	buf          bytes.Buffer                            // buffer for more efficient i/o from r
+	wireType     map[typeId]*wireType                    // map from remote ID to local description
+	decoderCache map[reflect.Type]map[typeId]**decEngine // cache of compiled engines
+	ignorerCache map[typeId]**decEngine                  // ditto for ignored objects
+	freeList     *decoderState                           // list of free decoderStates; avoids reallocation
+	countBuf     []byte                                  // used for decoding integers while parsing messages
+	tmp          []byte                                  // temporary storage for i/o; saves reallocating
+	err          error
+}
+
+// NewDecoder returns a new decoder that reads from the io.Reader.
+// If r does not also implement io.ByteReader, it will be wrapped in a
+// bufio.Reader.
+func NewDecoder(r io.Reader) *Decoder {
+	dec := new(Decoder)
+	// We use the ability to read bytes as a plausible surrogate for buffering.
+	if _, ok := r.(io.ByteReader); !ok {
+		r = bufio.NewReader(r)
+	}
+	dec.r = r
+	dec.wireType = make(map[typeId]*wireType)
+	dec.decoderCache = make(map[reflect.Type]map[typeId]**decEngine)
+	dec.ignorerCache = make(map[typeId]**decEngine)
+	dec.countBuf = make([]byte, 9) // counts may be uint64s (unlikely!), require 9 bytes
+
+	return dec
+}
+
+// recvType loads the definition of a type.
+func (dec *Decoder) recvType(id typeId) {
+	// Have we already seen this type?  That's an error
+	if id < firstUserId || dec.wireType[id] != nil {
+		dec.err = errors.New("gob: duplicate type received")
+		return
+	}
+
+	// Type:
+	wire := new(wireType)
+	dec.decodeValue(tWireType, reflect.ValueOf(wire))
+	if dec.err != nil {
+		return
+	}
+	// Remember we've seen this type.
+	dec.wireType[id] = wire
+}
+
+var errBadCount = errors.New("invalid message length")
+
+// recvMessage reads the next count-delimited item from the input. It is the converse
+// of Encoder.writeMessage. It returns false on EOF or other error reading the message.
+func (dec *Decoder) recvMessage() bool {
+	// Read a count.
+	nbytes, _, err := decodeUintReader(dec.r, dec.countBuf)
+	if err != nil {
+		dec.err = err
+		return false
+	}
+	// Upper limit of 1GB, allowing room to grow a little without overflow.
+	// TODO: We might want more control over this limit.
+	if nbytes >= 1<<30 {
+		dec.err = errBadCount
+		return false
+	}
+	dec.readMessage(int(nbytes))
+	return dec.err == nil
+}
+
+// readMessage reads the next nbytes bytes from the input.
+func (dec *Decoder) readMessage(nbytes int) {
+	// Allocate the dec.tmp buffer, up to 10KB.
+	const maxBuf = 10 * 1024
+	nTmp := nbytes
+	if nTmp > maxBuf {
+		nTmp = maxBuf
+	}
+	if cap(dec.tmp) < nTmp {
+		nAlloc := nTmp + 100 // A little extra for growth.
+		if nAlloc > maxBuf {
+			nAlloc = maxBuf
+		}
+		dec.tmp = make([]byte, nAlloc)
+	}
+	dec.tmp = dec.tmp[:nTmp]
+
+	// Read the data
+	dec.buf.Grow(nbytes)
+	for nbytes > 0 {
+		if nbytes < nTmp {
+			dec.tmp = dec.tmp[:nbytes]
+		}
+		var nRead int
+		nRead, dec.err = io.ReadFull(dec.r, dec.tmp)
+		if dec.err != nil {
+			if dec.err == io.EOF {
+				dec.err = io.ErrUnexpectedEOF
+			}
+			return
+		}
+		dec.buf.Write(dec.tmp)
+		nbytes -= nRead
+	}
+}
+
+// toInt turns an encoded uint64 into an int, according to the marshaling rules.
+func toInt(x uint64) int64 {
+	i := int64(x >> 1)
+	if x&1 != 0 {
+		i = ^i
+	}
+	return i
+}
+
+func (dec *Decoder) nextInt() int64 {
+	n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
+	if err != nil {
+		dec.err = err
+	}
+	return toInt(n)
+}
+
+func (dec *Decoder) nextUint() uint64 {
+	n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
+	if err != nil {
+		dec.err = err
+	}
+	return n
+}
+
+// decodeTypeSequence parses:
+// TypeSequence
+//	(TypeDefinition DelimitedTypeDefinition*)?
+// and returns the type id of the next value.  It returns -1 at
+// EOF.  Upon return, the remainder of dec.buf is the value to be
+// decoded.  If this is an interface value, it can be ignored by
+// resetting that buffer.
+func (dec *Decoder) decodeTypeSequence(isInterface bool) typeId {
+	for dec.err == nil {
+		if dec.buf.Len() == 0 {
+			if !dec.recvMessage() {
+				break
+			}
+		}
+		// Receive a type id.
+		id := typeId(dec.nextInt())
+		if id >= 0 {
+			// Value follows.
+			return id
+		}
+		// Type definition for (-id) follows.
+		dec.recvType(-id)
+		// When decoding an interface, after a type there may be a
+		// DelimitedValue still in the buffer.  Skip its count.
+		// (Alternatively, the buffer is empty and the byte count
+		// will be absorbed by recvMessage.)
+		if dec.buf.Len() > 0 {
+			if !isInterface {
+				dec.err = errors.New("extra data in buffer")
+				break
+			}
+			dec.nextUint()
+		}
+	}
+	return -1
+}
+
+// Decode reads the next value from the input stream and stores
+// it in the data represented by the empty interface value.
+// If e is nil, the value will be discarded. Otherwise,
+// the value underlying e must be a pointer to the
+// correct type for the next data item received.
+// If the input is at EOF, Decode returns io.EOF and
+// does not modify e.
+func (dec *Decoder) Decode(e interface{}) error {
+	if e == nil {
+		return dec.DecodeValue(reflect.Value{})
+	}
+	value := reflect.ValueOf(e)
+	// If e represents a value as opposed to a pointer, the answer won't
+	// get back to the caller.  Make sure it's a pointer.
+	if value.Type().Kind() != reflect.Ptr {
+		dec.err = errors.New("gob: attempt to decode into a non-pointer")
+		return dec.err
+	}
+	return dec.DecodeValue(value)
+}
+
+// DecodeValue reads the next value from the input stream.
+// If v is the zero reflect.Value (v.Kind() == Invalid), DecodeValue discards the value.
+// Otherwise, it stores the value into v.  In that case, v must represent
+// a non-nil pointer to data or be an assignable reflect.Value (v.CanSet())
+// If the input is at EOF, DecodeValue returns io.EOF and
+// does not modify e.
+func (dec *Decoder) DecodeValue(v reflect.Value) error {
+	if v.IsValid() {
+		if v.Kind() == reflect.Ptr && !v.IsNil() {
+			// That's okay, we'll store through the pointer.
+		} else if !v.CanSet() {
+			return errors.New("gob: DecodeValue of unassignable value")
+		}
+	}
+	// Make sure we're single-threaded through here.
+	dec.mutex.Lock()
+	defer dec.mutex.Unlock()
+
+	dec.buf.Reset() // In case data lingers from previous invocation.
+	dec.err = nil
+	id := dec.decodeTypeSequence(false)
+	if dec.err == nil {
+		dec.decodeValue(id, v)
+	}
+	return dec.err
+}
+
+// If debug.go is compiled into the program , debugFunc prints a human-readable
+// representation of the gob data read from r by calling that file's Debug function.
+// Otherwise it is nil.
+var debugFunc func(io.Reader)