1 files changed, 28 insertions, 2 deletions
diff --git a/src/pkg/gob/encode.go b/src/pkg/gob/encode.go
index 941e26052..317014efd 100644
--- a/src/pkg/gob/encode.go
+++ b/src/pkg/gob/encode.go
@@ -62,7 +62,7 @@ func (state *encoderState) encodeUint(x uint64) {
 	var n, m int
 	m = uint64Size
 	for n = 1; x > 0; n++ {
-		state.buf[m] = uint8(x & 0xFF)
+		state.buf[m] = uint8(x)
 		x >>= 8
 		m--
 	}
@@ -466,6 +466,27 @@ func (enc *Encoder) encodeInterface(b *bytes.Buffer, iv reflect.Value) {
 	enc.freeEncoderState(state)
 }
 
+// isZero returns whether the value is the zero of its type.
+func isZero(val reflect.Value) bool {
+	switch val.Kind() {
+	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
+		return val.Len() == 0
+	case reflect.Bool:
+		return !val.Bool()
+	case reflect.Complex64, reflect.Complex128:
+		return val.Complex() == 0
+	case reflect.Chan, reflect.Func, reflect.Ptr:
+		return val.IsNil()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return val.Int() == 0
+	case reflect.Float32, reflect.Float64:
+		return val.Float() == 0
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return val.Uint() == 0
+	}
+	panic("unknown type in isZero " + val.Type().String())
+}
+
 // encGobEncoder encodes a value that implements the GobEncoder interface.
 // The data is sent as a byte array.
 func (enc *Encoder) encodeGobEncoder(b *bytes.Buffer, v reflect.Value) {
@@ -557,7 +578,9 @@ func (enc *Encoder) encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp
 				// the iteration.
 				v := reflect.ValueOf(unsafe.Unreflect(t, unsafe.Pointer(p)))
 				mv := reflect.Indirect(v)
-				if !state.sendZero && mv.Len() == 0 {
+				// We send zero-length (but non-nil) maps because the
+				// receiver might want to use the map.  (Maps don't use append.)
+				if !state.sendZero && mv.IsNil() {
 					return
 				}
 				state.update(i)
@@ -612,6 +635,9 @@ func (enc *Encoder) gobEncodeOpFor(ut *userTypeInfo) (*encOp, int) {
 		} else {
 			v = reflect.ValueOf(unsafe.Unreflect(rt, p))
 		}
+		if !state.sendZero && isZero(v) {
+			return
+		}
 		state.update(i)
 		state.enc.encodeGobEncoder(state.b, v)
 	}