RTCP Google Transport Congestion Feedback

(WIP)

src/packets/RTCP/FeedbackPacket.ts

@@ -33,7 +33,11 @@ export enum RtpFeedbackMessageType
 	/**
 	 * Explicit Congestion Notification (ECN).
 	 */
-	ECN = 8
+	ECN = 8,
+	/**
+	 * Google Transport-wide Congestion Control.
+	 */
+	TCC = 15
 }
 
 /**
@@ -109,6 +113,11 @@ function messageTypeToString(
 			return 'Explicit Congestion Notification (ECN)';
 		}
 
+		case RtpFeedbackMessageType.TCC:
+		{
+			return 'Google Transport-wide Congestion Control';
+		}
+
 		case PsFeedbackMessageType.PLI:
 		{
 			return 'Picture Loss Indication';

src/packets/RTCP/TccPacket.ts

@@ -0,0 +1,228 @@
+import { RtcpPacketType } from './RtcpPacket';
+import {
+	FeedbackPacket,
+	RtpFeedbackMessageType,
+	FeedbackPacketDump,
+	FIXED_HEADER_LENGTH
+} from './FeedbackPacket';
+
+const TCC_MIN_PACKET_LENGTH = FIXED_HEADER_LENGTH + 8;
+const MAX_MISSING_PACKETS = (1 << 13) - 1;
+const MAX_PACKET_STATUS_COUNT = (1 << 16) - 1;
+const MAX_PACKET_DELTA = 0x7FFF;
+
+/**
+ * RTCP TCC packet info dump.
+ *
+ * @category RTCP
+ */
+export type TccPacketDump = FeedbackPacketDump &
+{
+	baseSequenceNumber: number;
+	packetStatusCount: number;
+	referenceTime: number;
+	feedbackPacketCount: number;
+	packetChunks: number[];
+	recvDeltas: number[];
+};
+
+/**
+ * RTCP TCC packet (RTCP Transport Layer Feedback).
+ *
+ * ```text
+ *  0                   1                   2                   3
+ *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |V=2|P|  FMT=15 |    PT=205     |           length              |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                     SSRC of packet sender                     |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                      SSRC of media source                     |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |      base sequence number     |      packet status count      |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                 reference time                | fb pkt. count |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |          packet chunk         |         packet chunk          |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * .                                                               .
+ * .                                                               .
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |         packet chunk          |  recv delta   |  recv delta   |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * .                                                               .
+ * .                                                               .
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |           recv delta          |  recv delta   | zero padding  |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * ```
+ *
+ * @category RTCP
+ *
+ * @see
+ * - [draft-holmer-rmcat-transport-wide-cc-extensions-01 section 3.1](https://datatracker.ietf.org/doc/html/draft-holmer-rmcat-transport-wide-cc-extensions-01#section-3.1)
+ */
+export class TccPacket extends FeedbackPacket
+{
+	#items: { pid: number; bitmask: number }[] = [];
+
+	/**
+	 * @param view - If given it will be parsed. Otherwise an empty RTCP TCC
+	 *   packet will be created.
+	 *
+	 * @throws
+	 * - If given `view` does not contain a valid RTCP TCC packet.
+	 */
+	constructor(view?: DataView)
+	{
+		super(RtcpPacketType.RTPFB, RtpFeedbackMessageType.TCC, view);
+
+		if (!this.view)
+		{
+			this.view = new DataView(new ArrayBuffer(FIXED_HEADER_LENGTH));
+
+			// Write version, packet type and feedback message type.
+			this.writeFixedHeader();
+
+			return;
+		}
+
+		// Position relative to the DataView byte offset.
+		let pos = 0;
+
+		// Move to items.
+		pos += FIXED_HEADER_LENGTH;
+
+		while (pos < this.view.byteLength - this.padding)
+		{
+			const pid = this.view.getUint16(pos);
+
+			pos += 2;
+
+			const bitmask = this.view.getUint16(pos);
+
+			pos += 2;
+
+			this.#items.push({ pid, bitmask });
+		}
+
+		pos += this.padding;
+
+		// Ensure that view length and parsed length match.
+		if (pos !== this.view.byteLength)
+		{
+			throw new RangeError(
+				`parsed length (${pos} bytes) does not match view length (${this.view.byteLength} bytes)`
+			);
+		}
+	}
+
+	/**
+	 * Dump RTCP TCC packet info.
+	 */
+	dump(): TccPacketDump
+	{
+		return {
+			...super.dump(),
+			baseSequenceNumber  : this.getBaseSequenceNumber();
+			packetStatusCount   : this.getPacketStatusCount();
+			referenceTime       : this.getReferenceTime();
+			feedbackPacketCount : this.getFeedbackPacketCount();
+		};
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	getByteLength(): number
+	{
+		if (!this.needsSerialization())
+		{
+			return this.view.byteLength;
+		}
+
+		const packetLength =
+			FIXED_HEADER_LENGTH +
+			(this.#items.length * 4) +
+			this.padding;
+
+		return packetLength;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	serialize(buffer?: ArrayBuffer, byteOffset?: number): void
+	{
+		const view = this.serializeBase(buffer, byteOffset);
+
+		// Position relative to the DataView byte offset.
+		let pos = 0;
+
+		// Move to items.
+		pos += FIXED_HEADER_LENGTH;
+
+		// Write items.
+		for (const { pid, bitmask } of this.#items)
+		{
+			view.setUint16(pos, pid);
+
+			pos += 2;
+
+			view.setUint16(pos, bitmask);
+
+			pos += 2;
+		}
+
+		pos += this.padding;
+
+		// Assert that current position is equal than new buffer length.
+		if (pos !== view.byteLength)
+		{
+			throw new RangeError(
+				`filled length (${pos} bytes) is different than the available buffer size (${view.byteLength} bytes)`
+			);
+		}
+
+		// Update DataView.
+		this.view = view;
+
+		this.setSerializationNeeded(false);
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	clone(
+		buffer?: ArrayBuffer,
+		byteOffset?: number,
+		serializationBuffer?: ArrayBuffer,
+		serializationByteOffset?: number
+	): TccPacket
+	{
+		const view = this.cloneInternal(
+			buffer,
+			byteOffset,
+			serializationBuffer,
+			serializationByteOffset
+		);
+
+		return new TccPacket(view);
+	}
+
+	/**
+	 * Get base sequence number.
+	 */
+	getBaseSequenceNumber(): number
+	{
+		return this.view.getUint16(12);
+	}
+
+	/**
+	 * Get packet status count.
+	 */
+	getPacketStatusCount(): number
+	{
+		return this.view.getUint16(14);
+	}
+}