encoding/json: fix scanner byte offset on scanEnd

itchyny · mvdan · commit 7450960a1300 · 2019-09-02T11:00:29.000Z
scanEnd is delayed one byte so we decrement the scanner bytes count by 1 to ensure that this value is correct in the next call of Decode. Fixes golang#32399 Change-Id: I8c8698e7f95bbcf0373aceaa05319819eae9d86f GitHub-Last-Rev: 0ac25d8 GitHub-Pull-Request: golang#32598 Reviewed-on: https://go-review.googlesource.com/c/go/+/182117 Reviewed-by: Daniel Martí <mvdan@mvdan.cc> Run-TryBot: Daniel Martí <mvdan@mvdan.cc> TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
@@ -2345,6 +2345,41 @@ func TestUnmarshalEmbeddedUnexported(t *testing.T) {
 	}
 }
 
+func TestUnmarshalErrorAfterMultipleJSON(t *testing.T) {
+	tests := []struct {
+		in  string
+		err error
+	}{{
+		in:  `1 false null :`,
+		err: &SyntaxError{"invalid character ':' looking for beginning of value", 14},
+	}, {
+		in:  `1 [] [,]`,
+		err: &SyntaxError{"invalid character ',' looking for beginning of value", 7},
+	}, {
+		in:  `1 [] [true:]`,
+		err: &SyntaxError{"invalid character ':' after array element", 11},
+	}, {
+		in:  `1  {}    {"x"=}`,
+		err: &SyntaxError{"invalid character '=' after object key", 14},
+	}, {
+		in:  `falsetruenul#`,
+		err: &SyntaxError{"invalid character '#' in literal null (expecting 'l')", 13},
+	}}
+	for i, tt := range tests {
+		dec := NewDecoder(strings.NewReader(tt.in))
+		var err error
+		for {
+			var v interface{}
+			if err = dec.Decode(&v); err != nil {
+				break
+			}
+		}
+		if !reflect.DeepEqual(err, tt.err) {
+			t.Errorf("#%d: got %#v, want %#v", i, err, tt.err)
+		}
+	}
+}
+
 type unmarshalPanic struct{}
 
 func (unmarshalPanic) UnmarshalJSON([]byte) error { panic(0xdead) }
diff --git a/src/encoding/json/stream.go b/src/encoding/json/stream.go
@@ -102,6 +102,10 @@ Input:
 			dec.scan.bytes++
 			switch dec.scan.step(&dec.scan, c) {
 			case scanEnd:
+				// scanEnd is delayed one byte so we decrement
+				// the scanner bytes count by 1 to ensure that
+				// this value is correct in the next call of Decode.
+				dec.scan.bytes--
 				break Input
 			case scanEndObject, scanEndArray:
 				// scanEnd is delayed one byte.
