encoding/json: handle misspelled JSON literals in ,string

Fixes #15146.

Change-Id: I229611b9cc995a1391681c492c4d742195c787ea
Reviewed-on: https://go-review.googlesource.com/30943
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/encoding/json/decode.go

@@ -851,13 +851,25 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 
 	switch c := item[0]; c {
 	case 'n': // null
+		// The main parser checks that only true and false can reach here,
+		// but if this was a quoted string input, it could be anything.
+		if fromQuoted && string(item) != "null" {
+			d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
+			break
+		}
 		switch v.Kind() {
 		case reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
 			v.Set(reflect.Zero(v.Type()))
 			// otherwise, ignore null for primitives/string
 		}
 	case 't', 'f': // true, false
-		value := c == 't'
+		value := item[0] == 't'
+		// The main parser checks that only true and false can reach here,
+		// but if this was a quoted string input, it could be anything.
+		if fromQuoted && string(item) != "true" && string(item) != "false" {
+			d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
+			break
+		}
 		switch v.Kind() {
 		default:
 			if fromQuoted {

src/encoding/json/decode_test.go

@@ -379,6 +379,10 @@ type unmarshalTest struct {
 	golden    bool
 }
 
+type B struct {
+	B bool `json:",string"`
+}
+
 var unmarshalTests = []unmarshalTest{
 	// basic types
 	{in: `true`, ptr: new(bool), out: true},
@@ -778,6 +782,16 @@ var unmarshalTests = []unmarshalTest{
 			Offset: 30,
 		},
 	},
+
+	// issue 15146.
+	// invalid inputs in wrongStringTests below.
+	{in: `{"B":"true"}`, ptr: new(B), out: B{true}, golden: true},
+	{in: `{"B":"false"}`, ptr: new(B), out: B{false}, golden: true},
+	{in: `{"B": "maybe"}`, ptr: new(B), err: errors.New(`json: invalid use of ,string struct tag, trying to unmarshal "maybe" into bool`)},
+	{in: `{"B": "tru"}`, ptr: new(B), err: errors.New(`json: invalid use of ,string struct tag, trying to unmarshal "tru" into bool`)},
+	{in: `{"B": "False"}`, ptr: new(B), err: errors.New(`json: invalid use of ,string struct tag, trying to unmarshal "False" into bool`)},
+	{in: `{"B": "null"}`, ptr: new(B), out: B{false}},
+	{in: `{"B": "nul"}`, ptr: new(B), err: errors.New(`json: invalid use of ,string struct tag, trying to unmarshal "nul" into bool`)},
 }
 
 func TestMarshal(t *testing.T) {