Add support for embedded CBOR in EDN decoder

edn.go

@@ -231,6 +231,9 @@
 	case '\'':
 		s.convertBytes()
 
+	case '<':
+		s.convertEmbeddedCBOR()
+
 	// text string
 	case '"':
 		s.convertString()
@@ -779,6 +782,67 @@
 	s.writeByte(0xff)
 }
 
+func (s *ednDecState) convertEmbeddedCBOR() {
+	if !bytes.HasPrefix(s.data[s.off:], []byte("<<")) {
+		s.err = newSemanticError("cbor: invalid embedded CBOR")
+		return
+	}
+
+	// skip "<<"
+	s.off += len("<<")
+	t := &ednDecState{data: s.data, off: s.off}
+	first := true
+	for {
+		t.skipWhitespace()
+		if t.err != nil {
+			s.err = t.err
+			return
+		}
+		ch, err := t.peekByte()
+		if err != nil {
+			s.err = err
+			return
+		}
+		if ch == '>' {
+			// end of array
+			t.off++
+			break
+		}
+		if !first {
+			if ch == ',' {
+				t.off++
+			} else {
+				s.err = newSemanticError("cbor: expected comma")
+				return
+			}
+		}
+		first = false
+
+		// next element
+		t.decode()
+		if t.err != nil {
+			s.err = t.err
+			return
+		}
+	}
+	s.off = t.off
+	ch, err := s.peekByte()
+	if err != nil {
+		s.err = err
+		return
+	}
+	if ch != '>' {
+		s.err = newSemanticError("cbor: expected '>'")
+		return
+	}
+	s.off++
+
+	ind := s.decodeEncodingIndicator()
+	s.writeUint(majorTypeBytes, ind, uint64(t.buf.Len()))
+	t.buf.WriteTo(&s.buf)
+
+}
+
 func (s *ednDecState) convertArray() {
 	ch, err := s.peekByte()
 	if err != nil {

edn_test.go

@@ -123,6 +123,24 @@ func TestDecodeEDN(t *testing.T) {
 			out: RawMessage{0x5f, 0xff},
 		},
 
+		// from RFC 8610 Appendix G.3.
+		{
+			in:  "<<1>>",
+			out: RawMessage{0x41, 0x01},
+		},
+		{
+			in:  "<<1, 2>>",
+			out: RawMessage{0x42, 0x01, 0x02},
+		},
+		{
+			in:  `<<"foo", null>>`,
+			out: RawMessage{0x45, 0x63, 0x66, 0x6f, 0x6f, 0xf6},
+		},
+		{
+			in:  `<<>>`,
+			out: RawMessage{0x40},
+		},
+
 		// from RFC 8610 Appendix G.1. and G.6.
 		{
 			in:  "h'48656c6c6f20776f726c64'",