add support for concatenated text messages with UDH

README.md

@@ -2,7 +2,7 @@
 
 The tetra-pei library allows to communicate with a TETRA radio terminal through its peripheral equipment interface (PEI), with the main focus on simple radio control and the handling of SDS messages. This implementation is solely based on the relevant ETSI specifications:
 
-* ETSI TS 100 392-2 V2.9.2 (2020-06): Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 2: Air Interface (AI)
+* ETSI TS 100 392-2 V3.9.2 (2020-06): Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 2: Air Interface (AI)
 * ETSI EN 300 392-5 V2.7.1 (2020-04): Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D) and Direct Mode Operation (DMO); Part 5: Peripheral Equipment Interface (PEI)
 
 ## Restrictions

sds/sds.go

@@ -122,6 +122,11 @@ func (p ProtocolIdentifier) Encode(bytes []byte, bits int) ([]byte, int) {
 	return append(bytes, byte(p)), bits + 8
 }
 
+// Length of this protocol identifier in bytes.
+func (p ProtocolIdentifier) Length() int {
+	return 1
+}
+
 // All protocol identifiers relevant for SDS handling, according to [AI] table 29.21
 const (
 	SimpleTextMessaging            ProtocolIdentifier = 0x02
@@ -381,6 +386,72 @@ func NewTextMessageTransfer(messageReference MessageReference, immediate bool, d
 	}
 }
 
+// NewConcatenatedMessageTransfer returns a set of SDS_TRANSFER PDUs for that make up the given text using concatenated text messages with a UDH.
+func NewConcatenatedMessageTransfer(messageReference MessageReference, deliveryReport DeliveryReportRequest, encoding TextEncoding, maxPDUBits int, text string) []SDSTransfer {
+	blueprint := SDSTransfer{
+		protocol:              UserDataHeaderMessaging,
+		MessageReference:      messageReference,
+		DeliveryReportRequest: deliveryReport,
+		UserData: ConcatenatedTextSDU{
+			TextSDU: TextSDU{
+				TextHeader: TextHeader{
+					Encoding: encoding,
+				},
+				Text: "",
+			},
+			UserDataHeader: ConcatenatedTextUDH{
+				ElementID:        ConcatenatedTextMessageWithShortReference,
+				MessageReference: uint16(messageReference),
+				TotalNumber:      0,
+				SequenceNumber:   0,
+			},
+		},
+	}
+	blueprintBits := blueprint.Length() * 8
+
+	textParts := SplitToMaxBits(encoding, maxPDUBits-blueprintBits, text)
+
+	if len(textParts) == 1 {
+		return []SDSTransfer{{
+			protocol:              TextMessaging,
+			MessageReference:      messageReference,
+			DeliveryReportRequest: deliveryReport,
+			UserData: TextSDU{
+				TextHeader: TextHeader{
+					Encoding: encoding,
+				},
+				Text: text,
+			},
+		}}
+	}
+
+	result := make([]SDSTransfer, len(textParts))
+	for i, textPart := range textParts {
+		result[i] = SDSTransfer{
+			protocol:                        UserDataHeaderMessaging,
+			ServiceSelectionShortFormReport: true,
+			MessageReference:                messageReference + MessageReference(i),
+			DeliveryReportRequest:           deliveryReport,
+			UserData: ConcatenatedTextSDU{
+				TextSDU: TextSDU{
+					TextHeader: TextHeader{
+						Encoding: encoding,
+					},
+					Text: textPart,
+				},
+				UserDataHeader: ConcatenatedTextUDH{
+					ElementID:        ConcatenatedTextMessageWithShortReference,
+					MessageReference: uint16(messageReference),
+					TotalNumber:      byte(len(textParts)),
+					SequenceNumber:   byte(i + 1),
+				},
+			},
+		}
+	}
+
+	return result
+}
+
 // SDSTransfer represents the SDS-TRANSFER PDU contents as defined in [AI] 29.4.2.4
 type SDSTransfer struct {
 	protocol                        ProtocolIdentifier
@@ -410,12 +481,27 @@ func (m SDSTransfer) Encode(bytes []byte, bits int) ([]byte, int) {
 	case TextSDU:
 		bytes, bits = sdu.Encode(bytes, bits)
 	case ConcatenatedTextSDU:
-		// bytes, bits = sdu.Encode(bytes, bits)
+		bytes, bits = sdu.Encode(bytes, bits)
 	}
 
 	return bytes, bits
 }
 
+// Length of this SDS-TRANSFER in bytes.
+func (m SDSTransfer) Length() int {
+	var result int
+	result += m.protocol.Length()
+	result++ // byte1
+	result++ // message reference
+	switch sdu := m.UserData.(type) {
+	case TextSDU:
+		result += sdu.Length()
+	case ConcatenatedTextSDU:
+		result += sdu.Length()
+	}
+	return result
+}
+
 // ReceivedReportRequested indicates if for this SDS-TRANSFER PDU a delivery report is requested for receipt
 func (m SDSTransfer) ReceivedReportRequested() bool {
 	return m.DeliveryReportRequest == MessageReceivedReportRequested ||
@@ -857,7 +943,7 @@ func ParseConcatenatedTextSDU(bytes []byte) (ConcatenatedTextSDU, error) {
 		00: Message Type[4], Delivery Report Request[2], Service Selection/Short form report[1], Store/forward control[1]
 		C9: Message Reference[8] (0xC9) <-- This one is incremented for each part of the concatenated message
 		<no store forward control information>
-		8D: Timestamp Used[1] (yes), Text Encoding Scheme[7] (ISO8859-15/Latin 0 ???)
+		8D: Timestamp Used[1] (yes), Text Encoding Scheme[7] (ISO8859-15/Latin 0)
 		04 5A 8F: Timestamp[24]
 		05: User Data Header length[8] (5)
 		00: UDH Information Element ID[8] (0)
@@ -901,6 +987,15 @@ type ConcatenatedTextSDU struct {
 	UserDataHeader ConcatenatedTextUDH
 }
 
+// Encode this concatenated text SDU
+func (t ConcatenatedTextSDU) Encode(bytes []byte, bits int) ([]byte, int) {
+	bytes, bits = t.TextHeader.Encode(bytes, bits)
+	bytes, bits = t.UserDataHeader.Encode(bytes, bits)
+	bytes, bits = AppendEncodedPayloadText(bytes, bits, t.Text, t.TextHeader.Encoding)
+
+	return bytes, bits
+}
+
 // Length returns the length of this encoded concatenated text SDU in bytes.
 func (t ConcatenatedTextSDU) Length() int {
 	return t.TextSDU.Length() + t.UserDataHeader.Length()
@@ -949,9 +1044,45 @@ type ConcatenatedTextUDH struct {
 	SequenceNumber   byte
 }
 
+// Encode this concatenated text UDH
+func (h ConcatenatedTextUDH) Encode(bytes []byte, bits int) ([]byte, int) {
+	headerLengthIndex := len(bytes)
+	bytes = append(bytes, 0)
+	bits += 8
+
+	bytes = append(bytes, byte(h.ElementID))
+	bits += 8
+
+	elementLengthIndex := len(bytes)
+	bytes = append(bytes, 0)
+	bits += 8
+
+	bytes = append(bytes, byte(h.MessageReference))
+	bits += 8
+	if h.ElementID == ConcatenatedTextMessageWithLongReference {
+		bytes = append(bytes, byte(h.MessageReference>>8))
+		bits += 8
+	}
+
+	bytes = append(bytes, h.TotalNumber)
+	bits += 8
+	bytes = append(bytes, h.SequenceNumber)
+	bits += 8
+
+	bytes[headerLengthIndex] = byte(len(bytes) - headerLengthIndex - 1)
+	bytes[elementLengthIndex] = byte(len(bytes) - elementLengthIndex - 1)
+
+	return bytes, bits
+}
+
 // Length returns the length of this header in bytes.
 func (h ConcatenatedTextUDH) Length() int {
-	return int(h.HeaderLength) + 1 // the HeaderLength byte itself
+	result := 6
+	if h.ElementID == ConcatenatedTextMessageWithLongReference {
+		result++
+	}
+
+	return result
 }
 
 // UDHInformationElementID enum according to [AI] 29.5.9.4.1

sds/sds_test.go

@@ -9,6 +9,7 @@ import (
 )
 
 func TestParseMessage(t *testing.T) {
+	expectedTimestamp := time.Date(time.Now().Year(), time.April, 11, 10, 15, 0, 0, time.Local)
 	tt := []struct {
 		desc      string
 		header    string
@@ -143,7 +144,7 @@ func TestParseMessage(t *testing.T) {
 					UserData: TextSDU{
 						TextHeader: TextHeader{
 							Encoding:  ISO8859_1,
-							Timestamp: time.Date(2021, time.April, 11, 10, 15, 0, 0, time.Local),
+							Timestamp: expectedTimestamp,
 						},
 						Text: "testmessage",
 					},
@@ -163,7 +164,7 @@ func TestParseMessage(t *testing.T) {
 						TextSDU: TextSDU{
 							TextHeader: TextHeader{
 								Encoding:  ISO8859_1,
-								Timestamp: time.Date(2021, time.April, 11, 10, 15, 0, 0, time.Local),
+								Timestamp: expectedTimestamp,
 							},
 							Text: "testmessage",
 						},
@@ -192,7 +193,7 @@ func TestParseMessage(t *testing.T) {
 						TextSDU: TextSDU{
 							TextHeader: TextHeader{
 								Encoding:  ISO8859_1,
-								Timestamp: time.Date(2021, time.April, 11, 10, 15, 0, 0, time.Local),
+								Timestamp: expectedTimestamp,
 							},
 							Text: "testmessage",
 						},
@@ -446,6 +447,7 @@ func TestParseHeader(t *testing.T) {
 }
 
 func TestEncode(t *testing.T) {
+	expectedTimestamp := time.Date(time.Now().Year(), time.April, 11, 8, 15, 0, 0, time.UTC)
 	tt := []struct {
 		desc          string
 		values        []Encoder
@@ -484,13 +486,13 @@ func TestEncode(t *testing.T) {
 					UserData: TextSDU{
 						TextHeader: TextHeader{
 							Encoding:  ISO8859_1,
-							Timestamp: time.Date(2021, time.April, 11, 10, 15, 0, 0, time.UTC),
+							Timestamp: expectedTimestamp,
 						},
 						Text: "testmessage",
 					},
 				},
 			},
-			expectedBytes: []byte{0x82, 0x06, 0xC9, 0x81, 0x44, 0x5A, 0x8F, 0x74, 0x65, 0x73, 0x74, 0x6D, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65},
+			expectedBytes: []byte{0x82, 0x06, 0xC9, 0x81, 0x44, 0x5A, 0x0F, 0x74, 0x65, 0x73, 0x74, 0x6D, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65},
 			expectedBits:  144,
 		},
 		{
@@ -505,6 +507,34 @@ func TestEncode(t *testing.T) {
 			expectedBytes: []byte{0x02, 0x01, 0x74, 0x65, 0x73, 0x74, 0x6D, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65},
 			expectedBits:  104,
 		},
+		{
+			desc: "SDS-TRANSFER concatenated text message with UDH",
+			values: []Encoder{
+				SDSTransfer{
+					protocol:         UserDataHeaderMessaging,
+					MessageReference: 0xC9,
+					UserData: ConcatenatedTextSDU{
+						TextSDU: TextSDU{
+							TextHeader: TextHeader{
+								Encoding:  ISO8859_1,
+								Timestamp: expectedTimestamp,
+							},
+							Text: "testmessage",
+						},
+						UserDataHeader: ConcatenatedTextUDH{
+							HeaderLength:     5,
+							ElementID:        0,
+							ElementLength:    3,
+							MessageReference: 0xC9,
+							TotalNumber:      2,
+							SequenceNumber:   1,
+						},
+					},
+				},
+			},
+			expectedBytes: []byte{0x8A, 0x02, 0xC9, 0x81, 0x44, 0x5A, 0x0F, 0x05, 0x00, 0x03, 0xC9, 0x02, 0x01, 0x74, 0x65, 0x73, 0x74, 0x6D, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65},
+			expectedBits:  192,
+		},
 	}
 	for _, tc := range tt {
 		t.Run(tc.desc, func(t *testing.T) {

sds/text.go

@@ -124,6 +124,40 @@ func TextBytesToBits(encoding TextEncoding, length int) int {
 	}
 }
 
+// BitsToTextBytes returns the number of bytes of a text that fit into the given number of bits using the given encoding
+func BitsToTextBytes(encoding TextEncoding, bits int) int {
+	switch encoding {
+	case Packed7Bit:
+		return bits / 7
+	default:
+		return bits / 8
+	}
+}
+
+// SplitToMaxBits splits the given text into parts that do not exceed the given maximum number of bits using the given encoding
+func SplitToMaxBits(encoding TextEncoding, maxPDUBits int, text string) []string {
+	if text == "" {
+		return []string{}
+	}
+
+	maxPartLength := BitsToTextBytes(encoding, maxPDUBits)
+	maxPartsCount := len(text)/maxPartLength + 1
+	result := make([]string, 0, maxPartsCount)
+
+	remainingText := text
+	for len(remainingText) > maxPartLength {
+		part := remainingText[0:maxPartLength]
+		remainingText = remainingText[maxPartLength:]
+		if part != "" {
+			result = append(result, part)
+		}
+	}
+	if len(remainingText) > 0 {
+		result = append(result, remainingText)
+	}
+	return result
+}
+
 // ParseTextHeader in text messages and concatenated text messages.
 func ParseTextHeader(bytes []byte) (TextHeader, error) {
 	if len(bytes) < 1 {

sds/text_test.go

@@ -6,6 +6,116 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestBitsToTextBytes(t *testing.T) {
+	tt := []struct {
+		desc          string
+		encoding      TextEncoding
+		bits          int
+		expectedBytes int
+	}{
+		{
+			desc:          "7bit, 0",
+			encoding:      Packed7Bit,
+			bits:          0,
+			expectedBytes: 0,
+		},
+		{
+			desc:          "8bit, 0",
+			encoding:      ISO8859_1,
+			bits:          0,
+			expectedBytes: 0,
+		},
+		{
+			desc:          "7bit, 1",
+			encoding:      Packed7Bit,
+			bits:          1,
+			expectedBytes: 0,
+		},
+		{
+			desc:          "8bit, 1",
+			encoding:      ISO8859_1,
+			bits:          1,
+			expectedBytes: 0,
+		},
+		{
+			desc:          "7bit, 8",
+			encoding:      Packed7Bit,
+			bits:          8,
+			expectedBytes: 1,
+		},
+		{
+			desc:          "7bit, 14",
+			encoding:      Packed7Bit,
+			bits:          14,
+			expectedBytes: 2,
+		},
+		{
+			desc:          "8bit, 14",
+			encoding:      ISO8859_1,
+			bits:          14,
+			expectedBytes: 1,
+		},
+		{
+			desc:          "7bit, 56",
+			encoding:      Packed7Bit,
+			bits:          56,
+			expectedBytes: 8,
+		},
+		{
+			desc:          "8bit, 56",
+			encoding:      ISO8859_1,
+			bits:          56,
+			expectedBytes: 7,
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.desc, func(t *testing.T) {
+			actualBytes := BitsToTextBytes(tc.encoding, tc.bits)
+			assert.Equal(t, tc.expectedBytes, actualBytes)
+		})
+	}
+}
+
+func TestSplitToMaxBits(t *testing.T) {
+	tt := []struct {
+		encoding      TextEncoding
+		maxPDUBits    int
+		text          string
+		expectedParts []string
+	}{
+		{
+			encoding:      Packed7Bit,
+			maxPDUBits:    56,
+			text:          "7-bit, 056",
+			expectedParts: []string{"7-bit, 0", "56"},
+		},
+		{
+			encoding:      ISO8859_1,
+			maxPDUBits:    56,
+			text:          "8-bit, 056",
+			expectedParts: []string{"8-bit, ", "056"},
+		},
+		{
+			encoding:      Packed7Bit,
+			maxPDUBits:    128,
+			text:          "7-bit, 128",
+			expectedParts: []string{"7-bit, 128"},
+		},
+		{
+			encoding:      ISO8859_1,
+			maxPDUBits:    128,
+			text:          "8-bit, 128",
+			expectedParts: []string{"8-bit, 128"},
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.text, func(t *testing.T) {
+			actualParts := SplitToMaxBits(tc.encoding, tc.maxPDUBits, tc.text)
+			assert.Equal(t, tc.expectedParts, actualParts)
+		})
+	}
+}
+
 func TestSplitLeadingOPTA(t *testing.T) {
 	tt := []struct {
 		desc         string