erlang_quic Features

Core Protocol (RFC 9000)

Connection Management

• [x] Connection establishment with TLS 1.3 handshake
• [x] Connection close (immediate and draining states)
• [x] Idle timeout enforcement (configurable via idle_timeout option)
• [x] Version negotiation
• [x] Retry packets for address validation

• [x] Latency spin bit (RFC 9000 §17.4) with spin_bit => true | false

• [x] NEW_TOKEN frame dispatch (server rejects peer-received tokens per §8.1.3); client caches received tokens keyed by {Host, Port} and reuses them in the Initial of the next connect to the same endpoint
• [x] Stateless reset (RFC 9000 §10.3): listener emits resets for orphan packets; per-connection NEW_CONNECTION_ID tokens share the listener's HMAC secret so they match orphan-path tokens
• [x] Server-side address validation (RFC 9000 §8.1): opt in with address_validation => always on quic:start_server/3. Listener emits a Retry packet with an HMAC-signed retry token when a client Initial arrives without one; subsequent Initials carrying a valid token skip retry and spawn a connection that echoes retry_source_connection_id. Server issues a NEW_TOKEN after handshake so the next reconnect skips retry entirely

Streams

• [x] Bidirectional streams (client and server initiated)
• [x] Unidirectional streams
• [x] Stream prioritization (RFC 9218) with 8 urgency levels
• [x] Incremental delivery flag support
• [x] RESET_STREAM_AT extension (draft-ietf-quic-reliable-stream-reset-07)

Flow Control

• [x] Connection-level flow control (MAX_DATA)
• [x] Stream-level flow control (MAX_STREAM_DATA)
• [x] MAX_STREAMS limits (bidirectional and unidirectional)

Packet Handling

• [x] Initial, Handshake, and 1-RTT packet types
• [x] Short header (1-RTT) packets
• [x] Packet number encoding (1-4 bytes)
• [x] Packet number reconstruction per RFC 9000 Appendix A
• [x] Coalesced packets
• [x] Frame coalescing (ACK + small stream data in single packet)

Connection Migration (RFC 9000 Section 9)

• [x] PATH_CHALLENGE / PATH_RESPONSE validation
• [x] Active connection migration (quic:migrate/1, quic:migrate/2)
• [x] Preferred address handling (RFC 9000 Section 9.6)
• [x] Server-side address change detection (NAT rebinding and active migration)
• [x] Congestion control reset on path change (RFC 9002 Section 9.4)
• [x] CID rotation on migration for path unlinkability (RFC 9000 Section 9.5)
• [x] disable_active_migration transport parameter support
• [x] Path validation timeout with retry (3 * PTO, up to 3 attempts)

Connection ID Management

• [x] Multiple connection IDs
• [x] NEW_CONNECTION_ID frames
• [x] RETIRE_CONNECTION_ID frames
• [x] Active connection ID limit

Loss Detection & Congestion Control (RFC 9002)

Loss Detection

• [x] Packet loss detection
• [x] Probe timeout (PTO)
• [x] RTT measurement (smoothed RTT, RTT variance)

Congestion Control

• [x] Pluggable congestion control behavior
• [x] NewReno (default, RFC 9002)
• [x] CUBIC (RFC 9438)
• [x] BBR (Bottleneck Bandwidth and RTT)
• [x] HyStart++ slow start (RFC 9406) for all algorithms
• [x] Slow start with improved exit detection
• [x] Congestion avoidance
• [x] Recovery on packet loss
• [x] Persistent congestion detection (resets cwnd after PTO * 3)
• [x] ECN support (ECN-CE triggers congestion response)
• [x] Packet pacing (RFC 9002 Section 7.7) to prevent bursts
• [x] RTT-based flow control auto-tuning

Path MTU Discovery (RFC 8899 - DPLPMTUD)

• [x] Binary search probing for optimal MTU
• [x] Integration with peer's max_udp_payload_size transport parameter
• [x] Black hole detection and recovery
• [x] Automatic MTU reset on connection migration
• [x] Periodic re-probing for MTU increases
• [x] Congestion control integration (updates cwnd-related parameters)

TLS 1.3 Integration (RFC 9001)

Handshake

• [x] Full TLS 1.3 handshake
• [x] ALPN negotiation
• [x] Transport parameters exchange
• [x] Certificate verification

Encryption

• [x] AES-128-GCM cipher suite
• [x] AES-256-GCM cipher suite
• [x] ChaCha20-Poly1305 cipher suite
• [x] Header protection
• [x] Key derivation (HKDF)

Key Management

• [x] Initial secrets derivation
• [x] Handshake secrets
• [x] Application secrets
• [x] Key updates (RFC 9001 Section 6)

Session Resumption

• [x] Session tickets (NewSessionTicket)
• [x] PSK-based resumption
• [x] 0-RTT early data

QUIC Version 2 (RFC 9369)

• [x] Version 2 (0x6b3343cf) support
• [x] Updated initial salt
• [x] Updated retry integrity tag key

QUIC-LB Load Balancer Support (RFC 9312)

• [x] Server ID encoding in Connection IDs for LB routing
• [x] Config rotation bits for LB coordination
• [x] Variable CID length support (1-20 bytes)
• [x] Three encoding algorithms:
  • Plaintext: Server ID visible in CID (no encryption)
  • Stream Cipher: AES-128-CTR encryption
  • Block Cipher: Feistel network for variable lengths
• [x] LB-aware CID generation in listener and connection

Reliable Stream Reset (draft-ietf-quic-reliable-stream-reset-07)

RESET_STREAM_AT allows resetting a stream while ensuring data up to a specified offset is reliably delivered. Required for WebTransport where stream headers must be received even if the stream is immediately reset.

Features

• [x] Frame type 0x24 (RESET_STREAM_AT) encode/decode
• [x] Transport parameter negotiation (0x17f7586d2cb571)
• [x] Reliable delivery guarantee up to ReliableSize
• [x] Retransmission filtering (data beyond ReliableSize not retransmitted)
• [x] Validation: ReliableSize cannot exceed FinalSize
• [x] Validation: ReliableSize cannot be increased after initial reset
• [x] Validation: ErrorCode cannot change after initial reset

Usage

%% Enable in connection options (both client and server)
Opts = #{reset_stream_at => true, alpn => [<<"webtransport">>]},
{ok, Conn} = quic:connect(Host, Port, Opts, self()),

%% Send stream header (e.g., WebTransport session ID)
{ok, StreamId} = quic:open_stream(Conn),
ok = quic:send_data(Conn, StreamId, Header, false),

%% Reset stream but ensure header is delivered
ok = quic:reset_stream_at(Conn, StreamId, ErrorCode, byte_size(Header)).

API

Connection

• quic:connect/3,4 - Connect to server
• quic:close/1,2,3 - Close connection (with optional app error code)
• quic:peername/1 - Get peer address
• quic:sockname/1 - Get local address
• quic:peercert/1 - Get peer certificate
• quic:migrate/1,2 - Trigger connection migration (with optional timeout)

Datagrams (RFC 9221)

• quic:send_datagram/2 - Send unreliable datagram
• quic:datagram_max_size/1 - Get max datagram size (0 if unsupported)
• quic:datagram_stats/1 - Delivered / dropped / sent counters (backpressure)

HTTP Datagrams (RFC 9297)

• quic_h3:send_datagram/3 - Send an HTTP datagram bound to a request stream
• quic_h3:h3_datagrams_enabled/1 - Whether both sides negotiated support
• quic_h3:max_datagram_size/2 - Max payload per datagram for a given stream
• Owner event: {quic_h3, Conn, {datagram, StreamId, Payload}}
• Set h3_datagram_enabled => true on connect/3 / start_server/3 to enable. CONNECT-UDP (RFC 9298) builds on this in a separate library.

HTTP/3 Extension Streams

• quic_h3:open_bidi_stream/1,2 - Open a client-initiated bidi stream; with a non-negative SignalType varint the stream is pre-claimed and inbound bytes route as {stream_type_data, bidi, ...} owner messages instead of HTTP/3 request frames (e.g. WebTransport's 0x41)
• stream_type_handler option on start_server/3 claims peer-initiated uni / bidi streams whose first varint matches a caller-supplied filter
• Owner events: {stream_type_open, Direction, StreamId, VarintType}, {stream_type_data, Direction, StreamId, Data, Fin}, {stream_type_closed, Direction, StreamId}, {stream_type_reset, Direction, StreamId, ErrorCode}, {stream_type_stop_sending, Direction, StreamId, ErrorCode}
• Per-connection owner override via connection_handler callback on start_server/3 for hosting many sessions on one listener

Streams

• quic:open_stream/1 - Open bidirectional stream
• quic:open_unidirectional_stream/1 - Open unidirectional stream
• quic:send/3,4 - Send data on stream
• quic:close_stream/2,3 - Close stream
• quic:reset_stream/3 - Reset stream with error code
• quic:reset_stream_at/4 - Reset stream with reliable delivery up to specified size
• quic:set_stream_priority/4 - Set stream priority (urgency, incremental)
• quic:get_stream_priority/2 - Get stream priority

Server / Multi-Pool Server Management

• quic:start_server/3 - Start named server pool
• quic:stop_server/1 - Stop named server
• quic:get_server_info/1 - Get server information
• quic:get_server_port/1 - Get server listening port
• quic:get_server_connections/1 - Get server connection PIDs
• quic:which_servers/0 - List all running servers

Load Balancer (RFC 9312)

• quic_lb:new_config/1 - Create LB configuration from options map
• quic_lb:new_cid_config/1 - Create CID generation configuration
• quic_lb:generate_cid/1 - Generate CID with encoded server_id
• quic_lb:decode_server_id/2 - Extract server_id from CID
• quic_lb:is_lb_routable/1 - Check if CID has valid LB routing bits
• quic_lb:get_config_rotation/1 - Get config rotation bits from CID
• quic_lb:expected_cid_len/1 - Calculate expected CID length from config

Options

• idle_timeout - Connection idle timeout in milliseconds (0 to disable)
• max_data - Connection-level flow control limit
• max_stream_data - Stream-level flow control limit
• max_datagram_frame_size - Max datagram size to accept (0 = disabled, default: 0)
• datagram_recv_queue_len - Bounded receive queue for inbound datagrams (default: infinity; drops oldest on overflow, tracked via datagram_stats/1)
• reset_stream_at - Enable RESET_STREAM_AT extension (default: false)
• alpn - ALPN protocols list
• verify - Certificate verification mode
• preferred_ipv4 - Server preferred IPv4 address
• preferred_ipv6 - Server preferred IPv6 address
• pool_size - Number of listener processes for server pools (default: 1)
• connection_handler - Callback for handling new connections
• lb_config - QUIC-LB configuration map for load balancer routing
• keep_alive_interval - Keep-alive PING interval (disabled, auto, or milliseconds)
• pmtu_enabled - Enable Path MTU Discovery (default: true)
• pmtu_max_mtu - Maximum MTU to probe (default: 1500)
• recbuf - UDP receive buffer size in bytes (default: 7MB)
• sndbuf - UDP send buffer size in bytes (default: 7MB)
• server_send_batching - Per-connection send batching on the server (default: true). On Linux + socket_backend => socket with UDP_SEGMENT, outgoing packets are coalesced into GSO super-datagrams via sendmsg cmsg; neutral on macOS / gen_udp. Set to false to fall back to direct gen_udp:send/4

PMTU Discovery

• quic:get_mtu/1 - Get current effective MTU for a connection

Erlang Distribution (quic_dist)

QUIC-based Erlang distribution protocol implementation.

Features

• [x] Full distribution protocol over QUIC transport
• [x] TLS 1.3 encryption built-in (no separate SSL setup)
• [x] 0-RTT session resumption for fast reconnection
• [x] Multiple streams: control (urgency 0) + data (urgency 4-6)
• [x] Stream prioritization for tick/control messages
• [x] QUIC-level liveness detection (packet counts, not blocked by flow control)
• [x] Keep-alive PING frames for transport liveness
• [x] Backpressure mechanism for congestion control
• [x] Session ticket storage for 0-RTT

Modules

• quic_dist - Distribution protocol callbacks
• quic_dist_controller - Per-connection state machine
• quic_dist_sup - Distribution supervisor
• quic_dist_tickets - Session ticket storage
• quic_epmd - EPMD replacement module

Discovery Backends

• quic_discovery_static - Static node configuration
• quic_discovery_dns - DNS SRV-based discovery
• Custom backends via quic_discovery behaviour

Distribution API

• quic:get_stats/1 - Get packet counts for liveness detection
• quic:send_ping/1 - Send transport-level PING frame

Interop Runner Compliance

All 10 QUIC Interop Runner test cases pass: