Add UnmarshalFirst

bench_test.go

@@ -211,6 +211,54 @@ func BenchmarkUnmarshal(b *testing.B) {
 	}
 }
 
+func BenchmarkUnmarshalFirst(b *testing.B) {
+	// Random trailing data
+	trailingData := hexDecode("4a6b0f4718c73f391091ea1c")
+	for _, bm := range decodeBenchmarks {
+		for _, t := range bm.decodeToTypes {
+			name := "CBOR " + bm.name + " to Go " + t.String()
+			if t.Kind() == reflect.Struct {
+				name = "CBOR " + bm.name + " to Go " + t.Kind().String()
+			}
+			data := make([]byte, 0, len(bm.cborData)+len(trailingData))
+			data = append(data, bm.cborData...)
+			data = append(data, trailingData...)
+			b.Run(name, func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					vPtr := reflect.New(t).Interface()
+					if _, err := UnmarshalFirst(data, vPtr); err != nil {
+						b.Fatal("UnmarshalFirst:", err)
+					}
+				}
+			})
+		}
+	}
+}
+
+func BenchmarkUnmarshalFirstViaDecoder(b *testing.B) {
+	// Random trailing data
+	trailingData := hexDecode("4a6b0f4718c73f391091ea1c")
+	for _, bm := range decodeBenchmarks {
+		for _, t := range bm.decodeToTypes {
+			name := "CBOR " + bm.name + " to Go " + t.String()
+			if t.Kind() == reflect.Struct {
+				name = "CBOR " + bm.name + " to Go " + t.Kind().String()
+			}
+			data := make([]byte, 0, len(bm.cborData)+len(trailingData))
+			data = append(data, bm.cborData...)
+			data = append(data, trailingData...)
+			b.Run(name, func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					vPtr := reflect.New(t).Interface()
+					if err := NewDecoder(bytes.NewReader(data)).Decode(vPtr); err != nil {
+						b.Fatal("UnmarshalDecoder:", err)
+					}
+				}
+			})
+		}
+	}
+}
+
 func BenchmarkDecode(b *testing.B) {
 	for _, bm := range decodeBenchmarks {
 		for _, t := range bm.decodeToTypes {

decode.go

@@ -95,10 +95,25 @@ import (
 //
 // Unmarshal supports CBOR tag 55799 (self-describe CBOR), tag 0 and 1 (time),
 // and tag 2 and 3 (bignum).
+//
+// Unmarshal returns ExtraneousDataError error (without decoding into v)
+// if there are any remaining bytes following the first valid CBOR data item.
+// See UnmarshalFirst, if you want to unmarshal only the first
+// CBOR data item without ExtraneousDataError caused by remaining bytes.
 func Unmarshal(data []byte, v interface{}) error {
 	return defaultDecMode.Unmarshal(data, v)
 }
 
+// UnmarshalFirst parses the first CBOR data item into the value pointed to by v
+// using default decoding options.  Any remaining bytes are returned in rest.
+//
+// If v is nil, not a pointer, or a nil pointer, UnmarshalFirst returns an error.
+//
+// See the documentation for Unmarshal for details.
+func UnmarshalFirst(data []byte, v interface{}) (rest []byte, err error) {
+	return defaultDecMode.UnmarshalFirst(data, v)
+}
+
 // Valid checks whether data is a well-formed encoded CBOR data item and
 // that it complies with default restrictions such as MaxNestedLevels,
 // MaxArrayElements, MaxMapPairs, etc.
@@ -604,6 +619,35 @@ func (dm *decMode) Unmarshal(data []byte, v interface{}) error {
 	return d.value(v)
 }
 
+// UnmarshalFirst parses the first CBOR data item into the value pointed to by v
+// using dm decoding mode.  Any remaining bytes are returned in rest.
+//
+// If v is nil, not a pointer, or a nil pointer, UnmarshalFirst returns an error.
+//
+// See the documentation for Unmarshal for details.
+func (dm *decMode) UnmarshalFirst(data []byte, v interface{}) (rest []byte, err error) {
+	d := decoder{data: data, dm: dm}
+
+	// check well-formedness.
+	off := d.off             // Save offset before data validation
+	err = d.wellformed(true) // allow extra data after well-formed data item
+	d.off = off              // Restore offset
+
+	// If it is well-formed, parse the value. This is structured like this to allow
+	// better test coverage
+	if err == nil {
+		err = d.value(v)
+	}
+
+	// If either wellformed or value returned an error, do not return rest bytes
+	if err != nil {
+		return nil, err
+	}
+
+	// Return the rest of the data slice (which might be len 0)
+	return d.data[d.off:], nil
+}
+
 // Valid checks whether data is a well-formed encoded CBOR data item and
 // that it complies with configurable restrictions such as MaxNestedLevels,
 // MaxArrayElements, MaxMapPairs, etc.

decode_test.go

@@ -5981,3 +5981,60 @@ func TestUnmarshalToDefaultMapType(t *testing.T) {
 		})
 	}
 }
+
+func TestUnmarshalFirstNoTrailing(t *testing.T) {
+	for _, tc := range unmarshalTests {
+		var v interface{}
+		if rest, err := UnmarshalFirst(tc.cborData, &v); err != nil {
+			t.Errorf("UnmarshalFirst(0x%x) returned error %v", tc.cborData, err)
+		} else {
+			if len(rest) != 0 {
+				t.Errorf("UnmarshalFirst(0x%x) returned rest %x (want [])", tc.cborData, rest)
+			}
+			// Check the value as well, although this is covered by other tests
+			if tm, ok := tc.emptyInterfaceValue.(time.Time); ok {
+				if vt, ok := v.(time.Time); !ok || !tm.Equal(vt) {
+					t.Errorf("UnmarshalFirst(0x%x) = %v (%T), want %v (%T)", tc.cborData, v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+				}
+			} else if !reflect.DeepEqual(v, tc.emptyInterfaceValue) {
+				t.Errorf("UnmarshalFirst(0x%x) = %v (%T), want %v (%T)", tc.cborData, v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+			}
+		}
+	}
+}
+
+func TestUnmarshalfirstTrailing(t *testing.T) {
+	// Random trailing data
+	trailingData := hexDecode("4a6b0f4718c73f391091ea1c")
+	for _, tc := range unmarshalTests {
+		data := make([]byte, 0, len(tc.cborData)+len(trailingData))
+		data = append(data, tc.cborData...)
+		data = append(data, trailingData...)
+		var v interface{}
+		if rest, err := UnmarshalFirst(data, &v); err != nil {
+			t.Errorf("UnmarshalFirst(0x%x) returned error %v", data, err)
+		} else {
+			if !bytes.Equal(trailingData, rest) {
+				t.Errorf("UnmarshalFirst(0x%x) returned rest %x (want %x)", data, rest, trailingData)
+			}
+			// Check the value as well, although this is covered by other tests
+			if tm, ok := tc.emptyInterfaceValue.(time.Time); ok {
+				if vt, ok := v.(time.Time); !ok || !tm.Equal(vt) {
+					t.Errorf("UnmarshalFirst(0x%x) = %v (%T), want %v (%T)", data, v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+				}
+			} else if !reflect.DeepEqual(v, tc.emptyInterfaceValue) {
+				t.Errorf("UnmarshalFirst(0x%x) = %v (%T), want %v (%T)", data, v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+			}
+		}
+	}
+}
+
+func TestUnmarshalFirstInvalidItem(t *testing.T) {
+	// UnmarshalFirst should not return "rest" if the item was not well-formed
+	invalidCBOR := hexDecode("83FF20030102")
+	var v interface{}
+	rest, err := UnmarshalFirst(invalidCBOR, &v)
+	if rest != nil {
+		t.Errorf("UnmarshalFirst(0x%x) = (%x, %v), want (nil, err)", invalidCBOR, rest, err)
+	}
+}