Merge pull request #308 from fxamacker/fxamacker/decode-registered-cb…

…or-tag-to-registered-type

Add support for decoding registered CBOR tag to interface type

README.md

@@ -373,6 +373,7 @@ See [Options](#options) section for details about each setting.
 * Decoder always checks for invalid UTF-8 string errors.
 * Decoder always decodes in-place to slices, maps, and structs.
 * Decoder tries case-sensitive first and falls back to case-insensitive field name match when decoding to structs. 
+* Decoder supports decoding registered CBOR tag data to interface types. 
 * Both encoder and decoder support indefinite length CBOR data (["streaming"](https://tools.ietf.org/html/rfc7049#section-2.2)).
 * Both encoder and decoder correctly handles nil slice, map, pointer, and interface values.
 
@@ -454,6 +455,7 @@ If any of these limitations prevent you from using this library, please open an
 * CBOR `Undefined` (0xf7) value decodes to Go's `nil` value.  CBOR `Null` (0xf6) more closely matches Go's `nil`.
 * CBOR map keys with data types not supported by Go for map keys are ignored and an error is returned after continuing to decode remaining items.  
 * When using io.Reader interface to read very large or indefinite length CBOR data, Go's `io.LimitReader` should be used to limit size.
+* When decoding registered CBOR tag data to interface type, decoder creates a pointer to registered Go type matching CBOR tag number.  Requiring a pointer for this is a Go limitation. 
 
 <hr>
 

decode.go

@@ -553,9 +553,34 @@ const (
 // and does not perform bounds checking.
 func (d *decoder) parseToValue(v reflect.Value, tInfo *typeInfo) error { //nolint:gocyclo
 
-	if tInfo.spclType == specialTypeIface && !v.IsNil() {
-		v = v.Elem()
-		tInfo = getTypeInfo(v.Type())
+	if tInfo.spclType == specialTypeIface {
+		if !v.IsNil() {
+			// Use value type
+			v = v.Elem()
+			tInfo = getTypeInfo(v.Type())
+		} else {
+			// Create and use registered type if CBOR data is registered tag
+			if d.dm.tags != nil && d.nextCBORType() == cborTypeTag {
+
+				off := d.off
+				var tagNums []uint64
+				for d.nextCBORType() == cborTypeTag {
+					_, _, tagNum := d.getHead()
+					tagNums = append(tagNums, tagNum)
+				}
+				d.off = off
+
+				registeredType := d.dm.tags.getTypeFromTagNum(tagNums)
+				if registeredType != nil {
+					if registeredType.Implements(tInfo.nonPtrType) ||
+						reflect.PtrTo(registeredType).Implements(tInfo.nonPtrType) {
+						v.Set(reflect.New(registeredType))
+						v = v.Elem()
+						tInfo = getTypeInfo(registeredType)
+					}
+				}
+			}
+		}
 	}
 
 	// Create new value for the pointer v to point to if CBOR value is not nil/undefined.

decode_test.go

@@ -5401,6 +5401,96 @@ func TestUnmarshalTaggedDataToInterface(t *testing.T) {
 	}
 }
 
+type B interface {
+	Foo()
+}
+
+type C struct {
+	Field int
+}
+
+func (c *C) Foo() {}
+
+type D struct {
+	Field string
+}
+
+func (d *D) Foo() {}
+
+type A1 struct {
+	Field B
+}
+
+type A2 struct {
+	Fields []B
+}
+
+func TestUnmarshalRegisteredTagToInterface(t *testing.T) {
+	var err error
+	tags := NewTagSet()
+	err = tags.Add(TagOptions{EncTag: EncTagRequired, DecTag: DecTagRequired}, reflect.TypeOf(C{}), 279)
+	if err != nil {
+		t.Error(err)
+	}
+	err = tags.Add(TagOptions{EncTag: EncTagRequired, DecTag: DecTagRequired}, reflect.TypeOf(D{}), 280)
+	if err != nil {
+		t.Error(err)
+	}
+
+	encMode, _ := PreferredUnsortedEncOptions().EncModeWithTags(tags)
+	decMode, _ := DecOptions{}.DecModeWithTags(tags)
+
+	v1 := A1{Field: &C{Field: 5}}
+	data1, err := encMode.Marshal(v1)
+	if err != nil {
+		t.Fatalf("Marshal(%+v) returned error %v", v1, err)
+	}
+
+	v2 := A2{Fields: []B{&C{Field: 5}, &D{Field: "a"}}}
+	data2, err := encMode.Marshal(v2)
+	if err != nil {
+		t.Fatalf("Marshal(%+v) returned error %v", v2, err)
+	}
+
+	testCases := []struct {
+		name           string
+		data           []byte
+		unmarshalToObj interface{}
+		wantValue      interface{}
+	}{
+		{
+			name:           "interface type",
+			data:           data1,
+			unmarshalToObj: &A1{},
+			wantValue:      &v1,
+		},
+		{
+			name:           "concrete type",
+			data:           data1,
+			unmarshalToObj: &A1{Field: &C{}},
+			wantValue:      &v1,
+		},
+		{
+			name:           "slice of interface type",
+			data:           data2,
+			unmarshalToObj: &A2{},
+			wantValue:      &v2,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err = decMode.Unmarshal(tc.data, tc.unmarshalToObj)
+			if err != nil {
+				t.Errorf("Unmarshal(0x%x) returned error %v", tc.data, err)
+			}
+			if !reflect.DeepEqual(tc.unmarshalToObj, tc.wantValue) {
+				t.Errorf("Unmarshal(0x%x) = %v, want %v", tc.data, tc.unmarshalToObj, tc.wantValue)
+			}
+		})
+	}
+}
+
 func TestDecModeInvalidDefaultMapType(t *testing.T) {
 	testCases := []struct {
 		name         string