QUIC event definitions for qlog

2.1.1. Raw packet and frame information

This document re-uses the definition of the RawInfo data class from [QLOG-MAIN].¶

Note:

QUIC packets always include an AEAD authentication tag ("trailer") at the end. As this tag is always the same size for a given connection (it depends on the used TLS cipher), this document does not define a separate "RawInfo:aead_tag_length" field here. Instead, this field is reflected in "transport:parameters_set" and can be logged only once.¶

Note:

As QUIC uses trailers in packets, packet header_lengths can be calculated as:¶

header_length = length - payload_length - aead_tag_length¶

For UDP datagrams, the calulation is simpler:¶

header_length = length - payload_length¶

Note:

In some cases, the length fields are also explicitly reflected inside of packet headers. For example, the QUIC STREAM frame has a "length" field indicating its payload size. Similarly, the QUIC Long Header has a "length" field which is equal to the payload length plus the packet number length. In these cases, those fields are intentionally preserved in the event definitions. Even though this can lead to duplicate data when the full RawInfo is logged, it allows a more direct mapping of the QUIC specifications to qlog, making it easier for users to interpret.¶

2.1.2. Events not belonging to a single connection

For several types of events, it is sometimes impossible to tie them to a specific conceptual QUIC connection (e.g., a packet_dropped event triggered because the packet has an unknown connection_id in the header). Since qlog events in a trace are typically associated with a single connection, it is unclear how to log these events.¶

Ideally, implementers SHOULD create a separate, individual "endpoint-level" trace file (or group_id value), not associated with a specific connection (for example a "server.qlog" or group_id = "client"), and log all events that do not belong to a single connection to this grouping trace. However, this is not always practical, depending on the implementation. Because the semantics of most of these events are well-defined in the protocols and because they are difficult to mis-interpret as belonging to a connection, implementers MAY choose to log events not belonging to a particular connection in any other trace, even those strongly associated with a single connection.¶

Note that this can make it difficult to match logs from different vantage points with each other. For example, from the client side, it is easy to log connections with version negotiation or retry in the same trace, while on the server they would most likely be logged in separate traces. Servers can take extra efforts (and keep additional state) to keep these events combined in a single trace however (for example by also matching connections on their four-tuple instead of just the connection ID).¶

3.1.1. server_listening

Importance: Extra¶

Emitted when the server starts accepting connections.¶

Definition:¶

ConnectivityServerListening = {
    ? ip_v4: IPAddress
    ? ip_v6: IPAddress
    ? port_v4: uint16
    ? port_v6: uint16

    ; the server will always answer client initials with a retry
    ; (no 1-RTT connection setups by choice)
    ? retry_required: bool
}

Note: some QUIC stacks do not handle sockets directly and are thus unable to log IP and/or port information.¶

3.1.2. connection_started

Importance: Base¶

Used for both attempting (client-perspective) and accepting (server-perspective) new connections. Note that this event has overlap with connection_state_updated and this is a separate event mainly because of all the additional data that should be logged.¶

Definition:¶

ConnectivityConnectionStarted = {
    ? ip_version: IPVersion
    src_ip: IPAddress
    dst_ip: IPAddress

    ; transport layer protocol
    ? protocol: text .default "QUIC"
    ? src_port: uint16
    ? dst_port: uint16

    ? src_cid: ConnectionID
    ? dst_cid: ConnectionID
}

Note: some QUIC stacks do not handle sockets directly and are thus unable to log IP and/or port information.¶

3.1.3. connection_closed

Importance: Base¶

Used for logging when a connection was closed, typically when an error or timeout occurred. Note that this event has overlap with connectivity:connection_state_updated, as well as the CONNECTION_CLOSE frame. However, in practice, when analyzing large deployments, it can be useful to have a single event representing a connection_closed event, which also includes an additional reason field to provide additional information. Additionally, it is useful to log closures due to timeouts, which are difficult to reflect using the other options.¶

In QUIC there are two main connection-closing error categories: connection and application errors. They have well-defined error codes and semantics. Next to these however, there can be internal errors that occur that may or may not get mapped to the official error codes in implementation-specific ways. As such, multiple error codes can be set on the same event to reflect this.¶

Definition:¶

ConnectivityConnectionClosed = {
    ; which side closed the connection
    ? owner: Owner

    ? connection_code: TransportError / CryptoError / uint32
    ? application_code: $ApplicationError / uint32
    ? internal_code: uint32

    ? reason: text
    ? trigger:
        "clean" /
        "handshake_timeout" /
        "idle_timeout" /
        ; this is called the "immediate close" in the QUIC RFC
        "error" /
        "stateless_reset" /
        "version_mismatch" /
        ; for example HTTP/3's GOAWAY frame
        "application"
}

3.1.4. connection_id_updated

Importance: Base¶

This event is emitted when either party updates their current Connection ID. As this typically happens only sparingly over the course of a connection, this event allows loggers to be more efficient than logging the observed CID with each packet in the .header field of the "packet_sent" or "packet_received" events.¶

This is viewed from the perspective of the one applying the new id. As such, if we receive a new connection id from our peer, we will see the dst_ fields are set. If we update our own connection id (e.g., NEW_CONNECTION_ID frame), we log the src_ fields.¶

Definition:¶

ConnectivityConnectionIDUpdated = {
    owner: Owner

    ? old: ConnectionID
    ? new: ConnectionID
}

3.1.5. spin_bit_updated

Importance: Base¶

To be emitted when the spin bit changes value. It SHOULD NOT be emitted if the spin bit is set without changing its value.¶

Definition:¶

ConnectivitySpinBitUpdated = {
    state: bool
}

3.1.6. connection_retried

TODO¶

3.1.7. connection_state_updated

Importance: Base¶

This event is used to track progress through QUIC's complex handshake and connection close procedures. It is intended to provide exhaustive options to log each state individually, but also provides a more basic, simpler set for implementations less interested in tracking each smaller state transition. As such, users should not expect to see -all- these states reflected in all qlogs and implementers should focus on support for the SimpleConnectionState set.¶

Definition:¶

ConnectivityConnectionStateUpdated = {
    ? old: ConnectionState / SimpleConnectionState
    new: ConnectionState / SimpleConnectionState
}

ConnectionState =
    ; initial sent/received
    "attempted" /
    ; peer address validated by: client sent Handshake packet OR
    ; client used CONNID chosen by the server.
    ; transport-draft-32, section-8.1
    "peer_validated" /
    "handshake_started" /
    ; 1 RTT can be sent, but handshake isn't done yet
    "early_write" /
    ; TLS handshake complete: Finished received and sent
    ; tls-draft-32, section-4.1.1
    "handshake_complete" /
    ; HANDSHAKE_DONE sent/received (connection is now "active", 1RTT
    ; can be sent). tls-draft-32, section-4.1.2
    "handshake_confirmed" /
    "closing" /
    ; connection_close sent/received
    "draining" /
    ; draining period done, connection state discarded
    "closed"

SimpleConnectionState =
    "attempted" /
    "handshake_started" /
    "handshake_confirmed" /
    "closed"

These states correspond to the following transitions for both client and server:¶

Client:¶

• send initial¶

  • state = attempted¶

• get initial¶

  • state = validated (not really "needed" at the client, but somewhat useful to indicate progress nonetheless)¶

• get first Handshake packet¶

  • state = handshake_started¶

• get Handshake packet containing ServerFinished¶

  • state = handshake_complete¶

• send ClientFinished¶

  • state = early_write (1RTT can now be sent)¶

• get HANDSHAKE_DONE¶

  • state = handshake_confirmed¶

Server:¶

• get initial¶

  • state = attempted¶
• send initial (TODO don't think this needs a separate state, since some handshake will always be sent in the same flight as this?)¶

• send handshake EE, CERT, CV, ...¶

  • state = handshake_started¶

• send ServerFinished¶

  • state = early_write (1RTT can now be sent)¶

• get first handshake packet / something using a server-issued CID of min length¶

  • state = validated¶

• get handshake packet containing ClientFinished¶

  • state = handshake_complete¶

• send HANDSHAKE_DONE¶

  • state = handshake_confirmed¶

Note:

connection_state_changed with a new state of "attempted" is the same conceptual event as the connection_started event above from the client's perspective. Similarly, a state of "closing" or "draining" corresponds to the connection_closed event.¶

3.1.8. MIGRATION-related events

e.g., path_updated¶

TODO: read up on the draft how migration works and whether to best fit this here or in TRANSPORT TODO: integrate https://tools.ietf.org/html/draft-deconinck-quic-multipath-02¶

For now, infer from other connectivity events and path_challenge/path_response frames¶

3.2.1. key_updated

Importance: Base¶

Note: secret_updated would be more correct, but in the draft it's called KEY_UPDATE, so stick with that for consistency¶

Definition:¶

SecurityKeyUpdated = {
    key_type: KeyType

    ? old: hexstring
    new: hexstring

    ; needed for 1RTT key updates
    ? generation: uint32

    ? trigger:
        ; (e.g., initial, handshake and 0-RTT keys
        ; are generated by TLS)
        "tls" /
        "remote_update" /
        "local_update"
}

3.2.2. key_retired

Importance: Base¶

Definition:¶

SecurityKeyRetired = {
    key_type: KeyType
    ? key: hexstring

    ; needed for 1RTT key updates
    ? generation: uint32

    ? trigger:
        ; (e.g., initial, handshake and 0-RTT keys
        ; are generated by TLS)
        "tls" /
        "remote_update" /
        "local_update"
}

3.3.1. version_information

Importance: Core¶

QUIC endpoints each have their own list of of QUIC versions they support. The client uses the most likely version in their first initial. If the server does support that version, it replies with a version_negotiation packet, containing supported versions. From this, the client selects a version. This event aggregates all this information in a single event type. It also allows logging of supported versions at an endpoint without actual version negotiation needing to happen.¶

Definition:¶

TransportVersionInformation = {
    ? server_versions: [+ QuicVersion]
    ? client_versions: [+ QuicVersion]
    ? chosen_version: QuicVersion
}

Intended use:¶

• When sending an initial, the client logs this event with client_versions and chosen_version set¶
• Upon receiving a client initial with a supported version, the server logs this event with server_versions and chosen_version set¶
• Upon receiving a client initial with an unsupported version, the server logs this event with server_versions set and client_versions to the single-element array containing the client's attempted version. The absence of chosen_version implies no overlap was found.¶
• Upon receiving a version negotiation packet from the server, the client logs this event with client_versions set and server_versions to the versions in the version negotiation packet and chosen_version to the version it will use for the next initial packet¶

3.3.2. alpn_information

Importance: Core¶

QUIC implementations each have their own list of application level protocols and versions thereof they support. The client includes a list of their supported options in its first initial as part of the TLS Application Layer Protocol Negotiation (alpn) extension. If there are common option(s), the server chooses the most optimal one and communicates this back to the client. If not, the connection is closed.¶

Definition:¶

TransportALPNInformation = {
    ? server_alpns: [* text]
    ? client_alpns: [* text]
    ? chosen_alpn: text
}

Intended use:¶

• When sending an initial, the client logs this event with client_alpns set¶
• When receiving an initial with a supported alpn, the server logs this event with server_alpns set, client_alpns equalling the client-provided list, and chosen_alpn to the value it will send back to the client.¶
• When receiving an initial with an alpn, the client logs this event with chosen_alpn to the received value.¶
• Alternatively, a client can choose to not log the first event, but wait for the receipt of the server initial to log this event with both client_alpns and chosen_alpn set.¶

3.3.3. parameters_set

Importance: Core¶

This event groups settings from several different sources (transport parameters, TLS ciphers, etc.) into a single event. This is done to minimize the amount of events and to decouple conceptual setting impacts from their underlying mechanism for easier high-level reasoning.¶

All these settings are typically set once and never change. However, they are typically set at different times during the connection, so there will typically be several instances of this event with different fields set.¶

Note that some settings have two variations (one set locally, one requested by the remote peer). This is reflected in the "owner" field. As such, this field MUST be correct for all settings included a single event instance. If you need to log settings from two sides, you MUST emit two separate event instances.¶

In the case of connection resumption and 0-RTT, some of the server's parameters are stored up-front at the client and used for the initial connection startup. They are later updated with the server's reply. In these cases, utilize the separate parameters_restored event to indicate the initial values, and this event to indicate the updated values, as normal.¶

Definition:¶

TransportParametersSet = {
    ? owner: Owner

    ; true if valid session ticket was received
    ? resumption_allowed: bool

    ; true if early data extension was enabled on the TLS layer
    ? early_data_enabled: bool

    ; e.g., "AES_128_GCM_SHA256"
    ? tls_cipher: text

    ; depends on the TLS cipher, but it's easier to be explicit.
    ; in bytes
    ? aead_tag_length: uint8 .default 16

    ; transport parameters from the TLS layer:
    ? original_destination_connection_id: ConnectionID
    ? initial_source_connection_id: ConnectionID
    ? retry_source_connection_id: ConnectionID
    ? stateless_reset_token: StatelessResetToken
    ? disable_active_migration: bool

    ? max_idle_timeout: uint64
    ? max_udp_payload_size: uint32
    ? ack_delay_exponent: uint16
    ? max_ack_delay: uint16
    ? active_connection_id_limit: uint32

    ? initial_max_data: uint64
    ? initial_max_stream_data_bidi_local: uint64
    ? initial_max_stream_data_bidi_remote: uint64
    ? initial_max_stream_data_uni: uint64
    ? initial_max_streams_bidi: uint64
    ? initial_max_streams_uni: uint64

    ? preferred_address: PreferredAddress
}

PreferredAddress = {
    ip_v4: IPAddress
    ip_v6: IPAddress

    port_v4: uint16
    port_v6: uint16

    connection_id: ConnectionID
    stateless_reset_token: StatelessResetToken
}

Additionally, this event can contain any number of unspecified fields. This is to reflect setting of for example unknown (greased) transport parameters or employed (proprietary) extensions.¶

3.3.4. parameters_restored

Importance: Base¶

When using QUIC 0-RTT, clients are expected to remember and restore the server's transport parameters from the previous connection. This event is used to indicate which parameters were restored and to which values when utilizing 0-RTT. Note that not all transport parameters should be restored (many are even prohibited from being re-utilized). The ones listed here are the ones expected to be useful for correct 0-RTT usage.¶

Definition:¶

TransportParametersRestored = {
    ? disable_active_migration: bool

    ? max_idle_timeout: uint64
    ? max_udp_payload_size: uint32
    ? active_connection_id_limit: uint32

    ? initial_max_data: uint64
    ? initial_max_stream_data_bidi_local: uint64
    ? initial_max_stream_data_bidi_remote: uint64,
    ? initial_max_stream_data_uni: uint64
    ? initial_max_streams_bidi: uint64
    ? initial_max_streams_uni: uint64
}

Note that, like parameters_set above, this event can contain any number of unspecified fields to allow for additional/custom parameters.¶

3.3.5. packet_sent

Importance: Core¶

Definition:¶

TransportPacketSent = {
    header: PacketHeader

    ; see appendix for the QuicFrame definitions
    ? frames: [* QuicFrame]

    ? is_coalesced: bool .default false

    ; only if header.packet_type === "retry"
    ? retry_token: Token

    ; only if header.packet_type === "stateless_reset"
    ; is always 128 bits in length.
    ? stateless_reset_token: StatelessResetToken

    ; only if header.packet_type === "version_negotiation"
    ? supported_versions: [+ QuicVersion]

    ? raw: RawInfo
    ? datagram_id: uint32

    ? trigger:
      ; draft-23 5.1.1
      "retransmit_reordered" /
      ; draft-23 5.1.2
      "retransmit_timeout" /
      ; draft-23 5.3.1
      "pto_probe" /
      ; draft-19 6.2
      "retransmit_crypto" /
      ; needed for some CCs to figure out bandwidth allocations
      ; when there are no normal sends
      "cc_bandwidth_probe"
}

Note: We do not explicitly log the encryption_level or packet_number_space: the header.packet_type specifies this by inference (assuming correct implementation)¶

Note: for more details on "datagram_id", see Section 3.3.10. It is only needed when keeping track of packet coalescing.¶

3.3.6. packet_received

Importance: Core¶

Definition:¶

TransportPacketReceived = {
    header: PacketHeader

    ; see appendix for the definitions
    ? frames: [* QuicFrame]

    ? is_coalesced: bool .default false

    ; only if header.packet_type === "retry"
    ? retry_token: Token

    ; only if header.packet_type === "stateless_reset"
    ; Is always 128 bits in length.
    ? stateless_reset_token: StatelessResetToken

    ; only if header.packet_type === "version_negotiation"
    ? supported_versions: [+ QuicVersion]

    ? raw: RawInfo
    ? datagram_id: uint32

    ? trigger:
        ; if packet was buffered because
        ; it couldn't be decrypted before
        "keys_available"
}

Note: We do not explicitly log the encryption_level or packet_number_space: the header.packet_type specifies this by inference (assuming correct implementation)¶

Note: for more details on "datagram_id", see Section 3.3.10. It is only needed when keeping track of packet coalescing.¶

3.3.7. packet_dropped

Importance: Base¶

This event indicates a QUIC-level packet was dropped after partial or no parsing.¶

Definition:¶

TransportPacketDropped = {
    ; primarily packet_type should be filled here,
    ; as other fields might not be parseable
    ? header: PacketHeader

    ? raw: RawInfo
    ? datagram_id: uint32

    ? trigger:
        "key_unavailable" /
        "unknown_connection_id" /
        "header_parse_error" /
        "payload_decrypt_error" /
        "protocol_violation" /
        "dos_prevention" /
        "unsupported_version" /
        "unexpected_packet" /
        "unexpected_source_connection_id" /
        "unexpected_version" /
        "duplicate" /
        "invalid_initial"
}

Note: sometimes packets are dropped before they can be associated with a particular connection (e.g., in case of "unsupported_version"). This situation is discussed more in Section 2.1.2.¶

Note: for more details on "datagram_id", see Section 3.3.10. It is only needed when keeping track of packet coalescing.¶

3.3.8. packet_buffered

Importance: Base¶

This event is emitted when a packet is buffered because it cannot be processed yet. Typically, this is because the packet cannot be parsed yet, and thus we only log the full packet contents when it was parsed in a packet_received event.¶

Definition:¶

TransportPacketBuffered = {
    ; primarily packet_type and possible packet_number should be
    ; filled here as other elements might not be available yet
    ? header: PacketHeader

    ? raw: RawInfo
    ? datagram_id: uint32

    ? trigger:
        ; indicates the parser cannot keep up, temporarily buffers
        ; packet for later processing
        "backpressure" /
        ; if packet cannot be decrypted because the proper keys were
        ; not yet available
        "keys_unavailable"
}

Note: for more details on "datagram_id", see Section 3.3.10. It is only needed when keeping track of packet coalescing.¶

3.3.9. packets_acked

Importance: Extra¶

This event is emitted when a (group of) sent packet(s) is acknowledged by the remote peer for the first time. This information could also be deduced from the contents of received ACK frames. However, ACK frames require additional processing logic to determine when a given packet is acknowledged for the first time, as QUIC uses ACK ranges which can include repeated ACKs. Additionally, this event can be used by implementations that do not log frame contents.¶

Definition:¶

TransportPacketsAcked = {
    ? packet_number_space: PacketNumberSpace

    ? packet_numbers: [+ uint64]
}

Note: if packet_number_space is omitted, it assumes the default value of PacketNumberSpace.application_data, as this is by far the most prevalent packet number space a typical QUIC connection will use.¶

3.3.10. datagrams_sent

Importance: Extra¶

When we pass one or more UDP-level datagrams to the socket. This is useful for determining how QUIC packet buffers are drained to the OS.¶

Definition:¶

TransportDatagramsSent = {
    ; to support passing multiple at once
    ? count: uint16

    ; RawInfo:length field indicates total length of the datagrams
    ; including UDP header length
    ? raw: [+ RawInfo]

    ? datagram_ids: [+ uint32]
}

Note: QUIC itself does not have a concept of a "datagram_id". This field is a purely qlog-specific construct to allow tracking how multiple QUIC packets are coalesced inside of a single UDP datagram, which is an important optimization during the QUIC handshake. For this, implementations assign a (per-endpoint) unique ID to each datagram and keep track of which packets were coalesced into the same datagram. As packet coalescing typically only happens during the handshake (as it requires at least one long header packet), this can be done without much overhead.¶

3.3.11. datagrams_received

Importance: Extra¶

When we receive one or more UDP-level datagrams from the socket. This is useful for determining how datagrams are passed to the user space stack from the OS.¶

Definition:¶

TransportDatagramsReceived = {
    ; to support passing multiple at once
    ? count: uint16

    ; RawInfo:length field indicates total length of the datagrams
    ; including UDP header length
    ? raw: [+ RawInfo]

    ? datagram_ids: [+ uint32]
}

Note: for more details on "datagram_ids", see Section 3.3.10.¶

3.3.12. datagram_dropped

Importance: Extra¶

When we drop a UDP-level datagram. This is typically if it does not contain a valid QUIC packet (in that case, use packet_dropped instead).¶

Definition:¶

TransportDatagramDropped = {
    ? raw: RawInfo
}

3.3.13. stream_state_updated

Importance: Base¶

This event is emitted whenever the internal state of a QUIC stream is updated, as described in QUIC transport draft-23 section 3. Most of this can be inferred from several types of frames going over the wire, but it's much easier to have explicit signals for these state changes.¶

Definition:¶

StreamType = "unidirectional" / "bidirectional"

TransportStreamStateUpdated = {
    stream_id: uint64

    ; mainly useful when opening the stream
    ? stream_type: StreamType

    ? old: StreamState
    new: StreamState

    ? stream_side: "sending" / "receiving"
}

StreamState =
    ; bidirectional stream states, draft-23 3.4.
    "idle" /
    "open" /
    "half_closed_local" /
    "half_closed_remote" /
    "closed" /

    ; sending-side stream states, draft-23 3.1.
    "ready" /
    "send" /
    "data_sent" /
    "reset_sent" /
    "reset_received" /

    ; receive-side stream states, draft-23 3.2.
    "receive" /
    "size_known" /
    "data_read" /
    "reset_read" /

    ; both-side states
    "data_received" /

    ; qlog-defined:
    ; memory actually freed
    "destroyed"

Note: QUIC implementations SHOULD mainly log the simplified bidirectional (HTTP/2-alike) stream states (e.g., idle, open, closed) instead of the more finegrained stream states (e.g., data_sent, reset_received). These latter ones are mainly for more in-depth debugging. Tools SHOULD be able to deal with both types equally.¶

3.3.14. frames_processed

Importance: Extra¶

This event's main goal is to prevent a large proliferation of specific purpose events (e.g., packets_acknowledged, flow_control_updated, stream_data_received). We want to give implementations the opportunity to (selectively) log this type of signal without having to log packet-level details (e.g., in packet_received). Since for almost all cases, the effects of applying a frame to the internal state of an implementation can be inferred from that frame's contents, we aggregate these events in this single "frames_processed" event.¶

Note: This event can be used to signal internal state change not resulting directly from the actual "parsing" of a frame (e.g., the frame could have been parsed, data put into a buffer, then later processed, then logged with this event).¶

Note: Implementations logging "packet_received" and which include all of the packet's constituent frames therein, are not expected to emit this "frames_processed" event. Rather, implementations not wishing to log full packets or that wish to explicitly convey extra information about when frames are processed (if not directly tied to their reception) can use this event.¶

Note: for some events, this approach will lose some information (e.g., for which encryption level are packets being acknowledged?). If this information is important, please use the packet_received event instead.¶

Note: in some implementations, it can be difficult to log frames directly, even when using packet_sent and packet_received events. For these cases, this event also contains the direct packet_number field, which can be used to more explicitly link this event to the packet_sent/received events.¶

Definition:¶

TransportFramesProcessed = {
    ; see appendix for the QuicFrame definitions
    frames: [* QuicFrame]

    ? packet_number: uint64
}

3.3.15. data_moved

Importance: Base¶

Used to indicate when data moves between the different layers (for example passing from the application protocol (e.g., HTTP) to QUIC stream buffers and vice versa) or between the application protocol (e.g., HTTP) and the actual user application on top (for example a browser engine). This helps make clear the flow of data, how long data remains in various buffers and the overheads introduced by individual layers.¶

For example, this helps make clear whether received data on a QUIC stream is moved to the application protocol immediately (for example per received packet) or in larger batches (for example, all QUIC packets are processed first and afterwards the application layer reads from the streams with newly available data). This in turn can help identify bottlenecks or scheduling problems.¶

Definition:¶

TransportDataMoved = {
    ? stream_id: uint64
    ? offset: uint64

    ; byte length of the moved data
    ? length: uint64

    ? from: "user" / "application" / "transport" / "network" / text
    ? to: "user" / "application" / "transport" / "network" / text

    ; raw bytes that were transferred
    ? data: hexstring
}

Note: we do not for example use a "direction" field (with values "up" and "down") to specify the data flow. This is because in some optimized implementations, data might skip some individual layers. Additionally, using explicit "from" and "to" fields is more flexible and allows the definition of other conceptual "layers" (for example to indicate data from QUIC CRYPTO frames being passed to a TLS library ("security") or from HTTP/3 to QPACK ("qpack")).¶

Note: this event type is part of the "transport" category, but really spans all the different layers. This means we have a few leaky abstractions here (for example, the stream_id or stream offset might not be available at some logging points, or the raw data might not be in a byte-array form). In these situations, implementers can decide to define new, in-context fields to aid in manual debugging.¶

3.4.1. parameters_set

Importance: Base¶

This event groups initial parameters from both loss detection and congestion control into a single event. All these settings are typically set once and never change. Implementation that do, for some reason, change these parameters during execution, MAY emit the parameters_set event twice.¶

Definition:¶

RecoveryParametersSet = {
    ; Loss detection, see recovery draft-23, Appendix A.2
    ; in amount of packets
    ? reordering_threshold: uint16

    ; as RTT multiplier
    ? time_threshold: float32

    ; in ms
    timer_granularity: uint16

    ; in ms
    ? initial_rtt:float32

    ; congestion control, Appendix B.1.
    ; in bytes. Note: this could be updated after pmtud
    ? max_datagram_size: uint32

    ; in bytes
    ? initial_congestion_window: uint64

    ; Note: this could change when max_datagram_size changes
    ; in bytes
    ? minimum_congestion_window: uint32
    ? loss_reduction_factor: float32

    ; as PTO multiplier
    ? persistent_congestion_threshold: uint16
}

Additionally, this event can contain any number of unspecified fields to support different recovery approaches.¶

3.4.2. metrics_updated

Importance: Core¶

This event is emitted when one or more of the observable recovery metrics changes value. This event SHOULD group all possible metric updates that happen at or around the same time in a single event (e.g., if min_rtt and smoothed_rtt change at the same time, they should be bundled in a single metrics_updated entry, rather than split out into two). Consequently, a metrics_updated event is only guaranteed to contain at least one of the listed metrics.¶

Definition:¶

RecoveryMetricsUpdated = {
    ; Loss detection, see recovery draft-23, Appendix A.3
    ; all following rtt fields are expressed in ms
    ? min_rtt: float32
    ? smoothed_rtt: float32
    ? latest_rtt: float32
    ? rtt_variance: float32

    ? pto_count: uint16

    ; Congestion control, Appendix B.2.
    ; in bytes
    ? congestion_window: uint64
    ? bytes_in_flight: uint64

    ; in bytes
    ? ssthresh: uint64

    ; qlog defined
    ; sum of all packet number spaces
    ? packets_in_flight: uint64

    ; in bits per second
    ? pacing_rate: uint64
}

Note: to make logging easier, implementations MAY log values even if they are the same as previously reported values (e.g., two subsequent RecoveryMetricsUpdated entries can both report the exact same value for min_rtt). However, applications SHOULD try to log only actual updates to values.¶

Additionally, this event can contain any number of unspecified fields to support different recovery approaches.¶

3.4.3. congestion_state_updated

Importance: Base¶

This event signifies when the congestion controller enters a significant new state and changes its behaviour. This event's definition is kept generic to support different Congestion Control algorithms. For example, for the algorithm defined in the Recovery draft ("enhanced" New Reno), the following states are defined:¶

• slow_start¶
• congestion_avoidance¶
• application_limited¶
• recovery¶

Definition:¶

RecoveryCongestionStateUpdated = {
    ? old: text
    new: text

    ? trigger:
        "persistent_congestion" /
        "ECN"
}

The "trigger" field SHOULD be logged if there are multiple ways in which a state change can occur but MAY be omitted if a given state can only be due to a single event occuring (e.g., slow start is exited only when ssthresh is exceeded).¶

3.4.4. loss_timer_updated

Importance: Extra¶

This event is emitted when a recovery loss timer changes state. The three main event types are:¶

• set: the timer is set with a delta timeout for when it will trigger next¶
• expired: when the timer effectively expires after the delta timeout¶
• cancelled: when a timer is cancelled (e.g., all outstanding packets are acknowledged, start idle period)¶

Note: to indicate an active timer's timeout update, a new "set" event is used.¶

Definition:¶

RecoveryLossTimerUpdated = {
    ; called "mode" in draft-23 A.9.
    ? timer_type: "ack" / "pto"
    ? packet_number_space: PacketNumberSpace

    event_type: "set" / "expired" / "cancelled"

    ; if event_type === "set": delta time is in ms from
    ; this event's timestamp until when the timer will trigger
    ? delta: float32
}

TODO: how about CC algo's that use multiple timers? How generic do these events need to be? Just support QUIC-style recovery from the spec or broader?¶

TODO: read up on the loss detection logic in draft-27 onward and see if this suffices¶

3.4.5. packet_lost

Importance: Core¶

This event is emitted when a packet is deemed lost by loss detection.¶

Definition:¶

RecoveryPacketLost = {
    ; should include at least the packet_type and packet_number
    ? header: PacketHeader

    ; not all implementations will keep track of full
    ; packets, so these are optional
    ; see appendix for the QuicFrame definitions
    ? frames: [* QuicFrame]

    ? trigger:
        "reordering_threshold" /
        "time_threshold" /
        ; draft-23 section 5.3.1, MAY
        "pto_expired"
}

For this event, the "trigger" field SHOULD be set (for example to one of the values below), as this helps tremendously in debugging.¶

3.4.6. marked_for_retransmit

Importance: Extra¶

This event indicates which data was marked for retransmit upon detecing a packet loss (see packet_lost). Similar to our reasoning for the "frames_processed" event, in order to keep the amount of different events low, we group this signal for all types of retransmittable data in a single event based on existing QUIC frame definitions.¶

Implementations retransmitting full packets or frames directly can just log the consituent frames of the lost packet here (or do away with this event and use the contents of the packet_lost event instead). Conversely, implementations that have more complex logic (e.g., marking ranges in a stream's data buffer as in-flight), or that do not track sent frames in full (e.g., only stream offset + length), can translate their internal behaviour into the appropriate frame instance here even if that frame was never or will never be put on the wire.¶

Note: much of this data can be inferred if implementations log packet_sent events (e.g., looking at overlapping stream data offsets and length, one can determine when data was retransmitted).¶

Definition:¶

RecoveryMarkedForRetransmit = {
    ; see appendix for the QuicFrame definitions
    frames: [+ QuicFrame]
}

A.12.1. PaddingFrame

In QUIC, PADDING frames are simply identified as a single byte of value 0. As such, each padding byte could be theoretically interpreted and logged as an individual PaddingFrame.¶

However, as this leads to heavy logging overhead, implementations SHOULD instead emit just a single PaddingFrame and set the payload_length property to the amount of PADDING bytes/frames included in the packet.¶

PaddingFrame = {
    frame_type: "padding"

    ; total frame length, including frame header
    ? length: uint32
    payload_length: uint32
}

A.12.2. PingFrame

PingFrame = {
    frame_type: "ping"

    ; total frame length, including frame header
    ? length: uint32
    ? payload_length: uint32
}

A.12.3. AckFrame

; either a single number (e.g., [1]) or two numbers (e.g., [1,2]).
; For two numbers:
; the first number is "from": lowest packet number in interval
; the second number is "to": up to and including the highest
; packet number in the interval
AckRange = [1*2 uint64]

AckFrame = {
    frame_type: "ack"

    ; in ms
    ? ack_delay: float32

    ; e.g., looks like [[1,2],[4,5], [7], [10,22]] serialized
    ? acked_ranges: [+ AckRange]

    ; ECN (explicit congestion notification) related fields
    ; (not always present)
    ? ect1: uint64
    ? ect0:uint64
    ? ce: uint64

    ; total frame length, including frame header
    ? length: uint32
    ? payload_length: uint32
}

Note: the packet ranges in AckFrame.acked_ranges do not necessarily have to be ordered (e.g., [[5,9],[1,4]] is a valid value).¶

Note: the two numbers in the packet range can be the same (e.g., [120,120] means that packet with number 120 was ACKed). However, in that case, implementers SHOULD log [120] instead and tools MUST be able to deal with both notations.¶

A.12.4. ResetStreamFrame

ResetStreamFrame = {
    frame_type: "reset_stream"

    stream_id: uint64
    error_code: $ApplicationError / uint32

    ; in bytes
    final_size: uint64

    ; total frame length, including frame header
    ? length: uint32
    ? payload_length: uint32
}

A.12.5. StopSendingFrame

StopSendingFrame = {
    frame_type: "stop_sending"

    stream_id: uint64
    error_code: $ApplicationError / uint32

    ; total frame length, including frame header
    ? length: uint32
    ? payload_length: uint32
}

A.12.6. CryptoFrame

CryptoFrame = {
    frame_type: "crypto"

    offset: uint64
    length: uint64

    ? payload_length: uint32
}

A.12.7. NewTokenFrame

NewTokenFrame = {
  frame_type: "new_token"

  token: Token
}

A.12.8. StreamFrame

StreamFrame = {
    frame_type: "stream"

    stream_id: uint64

    ; These two MUST always be set
    ; If not present in the Frame type, log their default values
    offset: uint64
    length: uint64

    ; this MAY be set any time,
    ; but MUST only be set if the value is true
    ; if absent, the value MUST be assumed to be false
    ? fin: bool .default false

    ? raw: hexstring
}

A.12.9. MaxDataFrame

MaxDataFrame = {
  frame_type: "max_data"

  maximum: uint64
}

A.12.10. MaxStreamDataFrame

MaxStreamDataFrame = {
  frame_type: "max_stream_data"

  stream_id: uint64
  maximum: uint64
}

A.12.11. MaxStreamsFrame

MaxStreamsFrame = {
  frame_type: "max_streams"

  stream_type: StreamType
  maximum: uint64
}

A.12.12. DataBlockedFrame

DataBlockedFrame = {
  frame_type: "data_blocked"

  limit: uint64
}

A.12.13. StreamDataBlockedFrame

StreamDataBlockedFrame = {
  frame_type: "stream_data_blocked"

  stream_id: uint64
  limit: uint64
}

A.12.14. StreamsBlockedFrame

StreamsBlockedFrame = {
  frame_type: "streams_blocked"

  stream_type: StreamType
  limit: uint64
}

A.12.15. NewConnectionIDFrame

NewConnectionIDFrame = {
  frame_type: "new_connection_id"

  sequence_number: uint32
  retire_prior_to: uint32

  ; mainly used if e.g., for privacy reasons the full
  ; connection_id cannot be logged
  ? connection_id_length: uint8
  connection_id: ConnectionID

  ? stateless_reset_token: StatelessResetToken
}

A.12.16. RetireConnectionIDFrame

RetireConnectionIDFrame = {
  frame_type: "retire_connection_id"

  sequence_number: uint32
}

A.12.17. PathChallengeFrame

PathChallengeFrame = {
  frame_type: "path_challenge"

  ; always 64-bit
  ? data: hexstring
}

A.12.18. PathResponseFrame

PathResponseFrame = {
  frame_type: "path_response"

  ; always 64-bit
  ? data: hexstring
}

A.12.19. ConnectionCloseFrame

raw_error_code is the actual, numerical code. This is useful because some error types are spread out over a range of codes (e.g., QUIC's crypto_error).¶

ErrorSpace = "transport" / "application"

ConnectionCloseFrame = {
    frame_type: "connection_close"

    ? error_space: ErrorSpace
    ? error_code: TransportError / $ApplicationError / uint32
    ? raw_error_code: uint32
    ? reason: text

    ; For known frame types, the appropriate "frame_type" string
    ; For unknown frame types, the hex encoded identifier value
    ? trigger_frame_type: uint64 / text
}

A.12.20. HandshakeDoneFrame

HandshakeDoneFrame = {
  frame_type: "handshake_done";
}

A.12.21. UnknownFrame

UnknownFrame = {
    frame_type: "unknown"
    raw_frame_type: uint64

    ? raw_length: uint32
    ? raw: hexstring
}

A.12.22. TransportError

TransportError = "no_error" / "internal_error" /
    "connection_refused" / "flow_control_error" /
    "stream_limit_error" / "stream_state_error" /
    "final_size_error" / "frame_encoding_error" /
    "transport_parameter_error" / "connection_id_limit_error" /
    "protocol_violation" / "invalid_token" / "application_error" /
    "crypto_buffer_exceeded"

A.12.23. ApplicationError

By definition, an application error is defined by the application-level protocol running on top of QUIC (e.g., HTTP/3).¶

As such, we cannot define it here directly. Though we provide an extension point through the use of the CDDL "socket" mechanism.¶

Application-level qlog definitions that wish to define new ApplicationError strings MUST do so by extending the $ApplicationError socket as such:¶

$ApplicationError /= "new_error_name" / "another_new_error_name"

A.12.24. CryptoError

These errors are defined in the TLS document as "A TLS alert is turned into a QUIC connection error by converting the one-byte alert description into a QUIC error code. The alert description is added to 0x100 to produce a QUIC error code from the range reserved for CRYPTO_ERROR."¶

This approach maps badly to a pre-defined enum. As such, we define the crypto_error string as having a dynamic component here, which should include the hex-encoded and zero-padded value of the TLS alert description.¶

; all strings from "crypto_error_0x100" to "crypto_error_0x199"
CryptoError = text .regexp "crypto_error_0x1[0-9][0-9]"