gob: allow transmission of things other than structs at the top level.

also fix a bug handling nil maps: before, would needlessly send empty map

R=rsc
CC=golang-dev
https://golang.org/cl/1739043

src/pkg/gob/codec_test.go

@@ -1039,7 +1039,7 @@ func TestInvalidField(t *testing.T) {
 type Indirect struct {
 	a ***[3]int
 	s ***[]int
-	m ***map[string]int
+	m ****map[string]int
 }
 
 type Direct struct {
@@ -1059,10 +1059,11 @@ func TestIndirectSliceMapArray(t *testing.T) {
 	*i.s = new(*[]int)
 	**i.s = new([]int)
 	***i.s = []int{4, 5, 6}
-	i.m = new(**map[string]int)
-	*i.m = new(*map[string]int)
-	**i.m = new(map[string]int)
-	***i.m = map[string]int{"one": 1, "two": 2, "three": 3}
+	i.m = new(***map[string]int)
+	*i.m = new(**map[string]int)
+	**i.m = new(*map[string]int)
+	***i.m = new(map[string]int)
+	****i.m = map[string]int{"one": 1, "two": 2, "three": 3}
 	b := new(bytes.Buffer)
 	NewEncoder(b).Encode(i)
 	dec := NewDecoder(b)
@@ -1093,12 +1094,12 @@ func TestIndirectSliceMapArray(t *testing.T) {
 		t.Error("error: ", err)
 	}
 	if len(***i.a) != 3 || (***i.a)[0] != 11 || (***i.a)[1] != 22 || (***i.a)[2] != 33 {
-		t.Errorf("indirect to direct: ***i.a is %v not %v", ***i.a, d.a)
+		t.Errorf("direct to indirect: ***i.a is %v not %v", ***i.a, d.a)
 	}
 	if len(***i.s) != 3 || (***i.s)[0] != 44 || (***i.s)[1] != 55 || (***i.s)[2] != 66 {
-		t.Errorf("indirect to direct: ***i.s is %v not %v", ***i.s, ***i.s)
+		t.Errorf("direct to indirect: ***i.s is %v not %v", ***i.s, ***i.s)
 	}
-	if len(***i.m) != 3 || (***i.m)["four"] != 4 || (***i.m)["five"] != 5 || (***i.m)["six"] != 6 {
-		t.Errorf("indirect to direct: ***i.m is %v not %v", ***i.m, d.m)
+	if len(****i.m) != 3 || (****i.m)["four"] != 4 || (****i.m)["five"] != 5 || (****i.m)["six"] != 6 {
+		t.Errorf("direct to indirect: ****i.m is %v not %v", ****i.m, d.m)
 	}
 }

src/pkg/gob/decode.go

@@ -13,15 +13,13 @@ import (
 	"math"
 	"os"
 	"reflect"
-	"runtime"
 	"unsafe"
 )
 
 var (
-	errBadUint   = os.ErrorString("gob: encoded unsigned integer out of range")
-	errBadType   = os.ErrorString("gob: unknown type id or corrupted data")
-	errRange     = os.ErrorString("gob: internal error: field numbers out of bounds")
-	errNotStruct = os.ErrorString("gob: TODO: can only handle structs")
+	errBadUint = os.ErrorString("gob: encoded unsigned integer out of range")
+	errBadType = os.ErrorString("gob: unknown type id or corrupted data")
+	errRange   = os.ErrorString("gob: internal error: field numbers out of bounds")
 )
 
 // The global execution state of an instance of the decoder.
@@ -389,18 +387,44 @@ type decEngine struct {
 	numInstr int // the number of active instructions
 }
 
-func decodeStruct(engine *decEngine, rtyp *reflect.StructType, b *bytes.Buffer, p uintptr, indir int) os.Error {
-	if indir > 0 {
-		up := unsafe.Pointer(p)
-		if indir > 1 {
-			up = decIndirect(up, indir)
-		}
-		if *(*unsafe.Pointer)(up) == nil {
-			// Allocate object.
-			*(*unsafe.Pointer)(up) = unsafe.New((*runtime.StructType)(unsafe.Pointer(rtyp)))
-		}
-		p = *(*uintptr)(up)
+// allocate makes sure storage is available for an object of underlying type rtyp
+// that is indir levels of indirection through p.
+func allocate(rtyp reflect.Type, p uintptr, indir int) uintptr {
+	if indir == 0 {
+		return p
+	}
+	up := unsafe.Pointer(p)
+	if indir > 1 {
+		up = decIndirect(up, indir)
 	}
+	if *(*unsafe.Pointer)(up) == nil {
+		// Allocate object.
+		*(*unsafe.Pointer)(up) = unsafe.New(rtyp)
+	}
+	return *(*uintptr)(up)
+}
+
+func decodeSingle(engine *decEngine, rtyp reflect.Type, b *bytes.Buffer, p uintptr, indir int) os.Error {
+	p = allocate(rtyp, p, indir)
+	state := newDecodeState(b)
+	state.fieldnum = singletonField
+	basep := p
+	delta := int(decodeUint(state))
+	if delta != 0 {
+		state.err = os.ErrorString("gob decode: corrupted data: non-zero delta for singleton")
+		return state.err
+	}
+	instr := &engine.instr[singletonField]
+	ptr := unsafe.Pointer(basep) // offset will be zero
+	if instr.indir > 1 {
+		ptr = decIndirect(ptr, instr.indir)
+	}
+	instr.op(instr, state, ptr)
+	return state.err
+}
+
+func decodeStruct(engine *decEngine, rtyp *reflect.StructType, b *bytes.Buffer, p uintptr, indir int) os.Error {
+	p = allocate(rtyp, p, indir)
 	state := newDecodeState(b)
 	state.fieldnum = -1
 	basep := p
@@ -468,12 +492,7 @@ func decodeArrayHelper(state *decodeState, p uintptr, elemOp decOp, elemWid uint
 
 func decodeArray(atyp *reflect.ArrayType, state *decodeState, p uintptr, elemOp decOp, elemWid uintptr, length, indir, elemIndir int, ovfl os.ErrorString) os.Error {
 	if indir > 0 {
-		up := unsafe.Pointer(p)
-		if *(*unsafe.Pointer)(up) == nil {
-			// Allocate object.
-			*(*unsafe.Pointer)(up) = unsafe.New(atyp)
-		}
-		p = *(*uintptr)(up)
+		p = allocate(atyp, p, 1) // All but the last level has been allocated by dec.Indirect
 	}
 	if n := decodeUint(state); n != uint64(length) {
 		return os.ErrorString("gob: length mismatch in decodeArray")
@@ -493,12 +512,7 @@ func decodeIntoValue(state *decodeState, op decOp, indir int, v reflect.Value, o
 
 func decodeMap(mtyp *reflect.MapType, state *decodeState, p uintptr, keyOp, elemOp decOp, indir, keyIndir, elemIndir int, ovfl os.ErrorString) os.Error {
 	if indir > 0 {
-		up := unsafe.Pointer(p)
-		if *(*unsafe.Pointer)(up) == nil {
-			// Allocate object.
-			*(*unsafe.Pointer)(up) = unsafe.New(mtyp)
-		}
-		p = *(*uintptr)(up)
+		p = allocate(mtyp, p, 1) // All but the last level has been allocated by dec.Indirect
 	}
 	up := unsafe.Pointer(p)
 	if *(*unsafe.Pointer)(up) == nil { // maps are represented as a pointer in the runtime
@@ -806,18 +820,34 @@ func (dec *Decoder) compatibleType(fr reflect.Type, fw typeId) bool {
 	return true
 }
 
+func (dec *Decoder) compileSingle(remoteId typeId, rt reflect.Type) (engine *decEngine, err os.Error) {
+	engine = new(decEngine)
+	engine.instr = make([]decInstr, 1) // one item
+	name := rt.String()                // best we can do
+	if !dec.compatibleType(rt, remoteId) {
+		return nil, os.ErrorString("gob: wrong type received for local value " + name)
+	}
+	op, indir, err := dec.decOpFor(remoteId, rt, name)
+	if err != nil {
+		return nil, err
+	}
+	ovfl := os.ErrorString(`value for "` + name + `" out of range`)
+	engine.instr[singletonField] = decInstr{op, singletonField, indir, 0, ovfl}
+	engine.numInstr = 1
+	return
+}
+
 func (dec *Decoder) compileDec(remoteId typeId, rt reflect.Type) (engine *decEngine, err os.Error) {
-	srt, ok1 := rt.(*reflect.StructType)
+	srt, ok := rt.(*reflect.StructType)
+	if !ok {
+		return dec.compileSingle(remoteId, rt)
+	}
 	var wireStruct *structType
 	// Builtin types can come from global pool; the rest must be defined by the decoder
 	if t, ok := builtinIdToType[remoteId]; ok {
 		wireStruct = t.(*structType)
 	} else {
-		w, ok2 := dec.wireType[remoteId]
-		if !ok1 || !ok2 {
-			return nil, errNotStruct
-		}
-		wireStruct = w.structT
+		wireStruct = dec.wireType[remoteId].structT
 	}
 	engine = new(decEngine)
 	engine.instr = make([]decInstr, len(wireStruct.field))
@@ -891,20 +921,19 @@ func (dec *Decoder) getIgnoreEnginePtr(wireId typeId) (enginePtr **decEngine, er
 func (dec *Decoder) decode(wireId typeId, e interface{}) os.Error {
 	// Dereference down to the underlying struct type.
 	rt, indir := indirect(reflect.Typeof(e))
-	st, ok := rt.(*reflect.StructType)
-	if !ok {
-		return os.ErrorString("gob: decode can't handle " + rt.String())
-	}
 	enginePtr, err := dec.getDecEnginePtr(wireId, rt)
 	if err != nil {
 		return err
 	}
 	engine := *enginePtr
-	if engine.numInstr == 0 && st.NumField() > 0 && len(dec.wireType[wireId].structT.field) > 0 {
-		name := rt.Name()
-		return os.ErrorString("gob: type mismatch: no fields matched compiling decoder for " + name)
+	if st, ok := rt.(*reflect.StructType); ok {
+		if engine.numInstr == 0 && st.NumField() > 0 && len(dec.wireType[wireId].structT.field) > 0 {
+			name := rt.Name()
+			return os.ErrorString("gob: type mismatch: no fields matched compiling decoder for " + name)
+		}
+		return decodeStruct(engine, st, dec.state.b, uintptr(reflect.NewValue(e).Addr()), indir)
 	}
-	return decodeStruct(engine, st, dec.state.b, uintptr(reflect.NewValue(e).Addr()), indir)
+	return decodeSingle(engine, rt, dec.state.b, uintptr(reflect.NewValue(e).Addr()), indir)
 }
 
 func init() {

src/pkg/gob/decoder.go

@@ -108,8 +108,9 @@ func (dec *Decoder) Decode(e interface{}) os.Error {
 		}
 
 		// No, it's a value.
-		// Make sure the type has been defined already.
-		if dec.wireType[id] == nil {
+		// Make sure the type has been defined already or is a builtin type (for
+		// top-level singleton values).
+		if dec.wireType[id] == nil && builtinIdToType[id] == nil {
 			dec.state.err = errBadType
 			break
 		}

src/pkg/gob/encoder.go

@@ -68,7 +68,7 @@ func (enc *Encoder) send() {
 	}
 }
 
-func (enc *Encoder) sendType(origt reflect.Type) {
+func (enc *Encoder) sendType(origt reflect.Type) (sent bool) {
 	// Drill down to the base type.
 	rt, _ := indirect(origt)
 
@@ -147,11 +147,6 @@ func (enc *Encoder) Encode(e interface{}) os.Error {
 
 	enc.state.err = nil
 	rt, _ := indirect(reflect.Typeof(e))
-	// Must be a struct
-	if _, ok := rt.(*reflect.StructType); !ok {
-		enc.badType(rt)
-		return enc.state.err
-	}
 
 	// Sanity check only: encoder should never come in with data present.
 	if enc.state.b.Len() > 0 || enc.countState.b.Len() > 0 {
@@ -163,10 +158,23 @@ func (enc *Encoder) Encode(e interface{}) os.Error {
 	// First, have we already sent this type?
 	if _, alreadySent := enc.sent[rt]; !alreadySent {
 		// No, so send it.
-		enc.sendType(rt)
+		sent := enc.sendType(rt)
 		if enc.state.err != nil {
 			return enc.state.err
 		}
+		// If the type info has still not been transmitted, it means we have
+		// a singleton basic type (int, []byte etc.) at top level.  We don't
+		// need to send the type info but we do need to update enc.sent.
+		if !sent {
+			typeLock.Lock()
+			info, err := getTypeInfo(rt)
+			typeLock.Unlock()
+			if err != nil {
+				enc.setError(err)
+				return err
+			}
+			enc.sent[rt] = info.id
+		}
 	}
 
 	// Identify the type of this top-level value.

src/pkg/gob/encoder_test.go

@@ -131,17 +131,10 @@ func TestBadData(t *testing.T) {
 	corruptDataCheck("\x03now is the time for all good men", errBadType, t)
 }
 
-// Types not supported by the Encoder (only structs work at the top level).
-// Basic types work implicitly.
+// Types not supported by the Encoder.
 var unsupportedValues = []interface{}{
-	3,
-	"hi",
-	7.2,
-	[]int{1, 2, 3},
-	[3]int{1, 2, 3},
 	make(chan int),
 	func(a int) bool { return true },
-	make(map[string]int),
 	new(interface{}),
 }
 
@@ -275,3 +268,59 @@ func TestDefaultsInArray(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+var testInt int
+var testFloat32 float32
+var testString string
+var testSlice []string
+var testMap map[string]int
+
+type SingleTest struct {
+	in  interface{}
+	out interface{}
+	err string
+}
+
+var singleTests = []SingleTest{
+	SingleTest{17, &testInt, ""},
+	SingleTest{float32(17.5), &testFloat32, ""},
+	SingleTest{"bike shed", &testString, ""},
+	SingleTest{[]string{"bike", "shed", "paint", "color"}, &testSlice, ""},
+	SingleTest{map[string]int{"seven": 7, "twelve": 12}, &testMap, ""},
+
+	// Decode errors
+	SingleTest{172, &testFloat32, "wrong type"},
+}
+
+func TestSingletons(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	dec := NewDecoder(b)
+	for _, test := range singleTests {
+		b.Reset()
+		err := enc.Encode(test.in)
+		if err != nil {
+			t.Errorf("error encoding %v: %s", test.in, err)
+			continue
+		}
+		err = dec.Decode(test.out)
+		switch {
+		case err != nil && test.err == "":
+			t.Errorf("error decoding %v: %s", test.in, err)
+			continue
+		case err == nil && test.err != "":
+			t.Errorf("expected error decoding %v: %s", test.in, test.err)
+			continue
+		case err != nil && test.err != "":
+			if strings.Index(err.String(), test.err) < 0 {
+				t.Errorf("wrong error decoding %v: wanted %s, got %v", test.in, test.err, err)
+			}
+			continue
+		}
+		// Get rid of the pointer in the rhs
+		val := reflect.NewValue(test.out).(*reflect.PtrValue).Elem().Interface()
+		if !reflect.DeepEqual(test.in, val) {
+			t.Errorf("decoding int: expected %v got %v", test.in, val)
+		}
+	}
+}