first cut at gob decoder.

R=rsc
DELTA=184  (181 added, 1 deleted, 2 changed)
OCL=31474
CL=31486

1 files changed, 85 insertions, 0 deletions

diff --git a/src/pkg/gob/decoder.go b/src/pkg/gob/decoder.go
new file mode 100644
index 000000000..4941a788b
--- /dev/null
+++ b/src/pkg/gob/decoder.go
@@ -0,0 +1,85 @@
+// 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 (
+	"gob";
+	"io";
+	"os";
+	"reflect";
+	"sync";
+)
+
+type Decoder struct {
+	sync.Mutex;	// each item must be received atomically
+	seen	map[TypeId] *wireType;	// which types we've already seen described
+	state	*DecState;	// so we can encode integers, strings directly
+}
+
+func NewDecoder(r io.Reader) *Decoder {
+	dec := new(Decoder);
+	dec.seen = make(map[TypeId] *wireType);
+	dec.state = new(DecState);
+	dec.state.r = r;	// the rest isn't important; all we need is buffer and reader
+
+	return dec;
+}
+
+func (dec *Decoder) recvType(id TypeId) {
+	// Have we already seen this type?  That's an error
+	if wt_, alreadySeen := dec.seen[id]; alreadySeen {
+		dec.state.err = os.ErrorString("gob: duplicate type received");
+		return
+	}
+
+	// Type:
+	wire := new(wireType);
+	Decode(dec.state.r, wire);
+	// Remember we've seen this type.
+	dec.seen[id] = wire;
+}
+
+// The value underlying e must be the correct type for the next
+// value to be received for this decoder.
+func (dec *Decoder) Decode(e interface{}) os.Error {
+	rt, indir := indirect(reflect.Typeof(e));
+
+	// Make sure we're single-threaded through here.
+	dec.Lock();
+	defer dec.Unlock();
+
+	var id TypeId;
+	for dec.state.err == nil {
+		// Receive a type id.
+		id = TypeId(DecodeInt(dec.state));
+
+		// If the id is positive, we have a value.  0 is the error state
+		if id >= 0 {
+			break;
+		}
+
+		// The id is negative; a type descriptor follows.
+		dec.recvType(-id);
+	}
+	if dec.state.err != nil {
+		return dec.state.err
+	}
+
+	info := getTypeInfo(rt);
+
+	// Check type compatibility.
+	// TODO(r): need to make the decoder work correctly if the wire type is compatible
+	// but not equal to the local type (e.g, extra fields).
+	if info.wire.name != dec.seen[id].name {
+		dec.state.err = os.ErrorString("gob decode: incorrect type for wire value");
+		return dec.state.err
+	}
+
+	// Receive a value.
+	Decode(dec.state.r, e);
+
+	// Release and return.
+	return dec.state.err
+}