rx-depacketizer.md
RX depacketizer
===============
This component takes a QUIC packet and parses the frames contained therein,
to be forwarded to appropriate other components for further processing.
In the [overview], this is called the "RX Frame Handler". The name "RX
depacketizer" was chosen to reflect the kinship with the [TX packetizer].
Main structures
---------------
### Connection
Represented by an `QUIC_CONNECTION` object, defined in
[`include/internal/quic_ssl.h`](../../../include/internal/quic_ssl.h).
### Stream
Represented by an `QUIC_STREAM` object (yet to be defined).
### Packets
Represented by the `OSSL_QRX_PKT` structure, defined in
`include/internal/quic_record_rx.h` in [QUIC Demuxer and Record Layer (RX+TX)].
Interactions
------------
The RX depacketizer receives a packet from the QUIC Read Record Layer, and
then processes frames in two phases:
1. [Collect information for the ACK Manager](#collect-information-for-the-ack-manager)
2. [Pass frame data](#pass-frame-data)
### Other components
There are a number of other components that the RX depacketizer wants to
interact with:
- [ACK manager]
- Handshake manager, which is currently unspecified. It's assumed that
this will wrap around what is called the "TLS Handshake Record Layer",
in the [overview]
- Session manager, which is currently unspecified for QUIC, but may very
well be the existing `SSL_SESSION` functionality, extended to fit QUIC
purposes.
- Flow control, which is currently unspecified. In the [overview], it's
called the "Flow Controller And Statistics Collector"
- Connection manager, which is currently unspecified. In the [overview],
there's a "Connection State Machine" that the "RX Frame Handler" isn't
talking directly with, so it's possible that the Connection manager will
turn out to be the Handshake manager.
- Stream SSL objects, to pass the stream data to.
### Read and process a packet
Following how things are designed elsewhere, the depacketizer is assumed to
be called "from above" using the following function:
``` C
__owur int ossl_quic_depacketize(QUIC_CONNECTION *connection);
```
This function would create an `OSSL_QRX_PKT` and call the QUIC Read Record
Layer with a pointer to it, leaving it to the QUIC Read Record Layer to fill
in the data.
This uses the `ossl_qrx_read_pkt()` packet reading function from
[QUIC Demuxer and Record Layer (RX+TX)].
(the `OSSL_QRX_PKT` structure / sub-structure needs to be extended to take
an `OSSL_TIME`, possibly by reference, which should be filled in with the
packet reception time)
### Collect information for the [ACK manager]
This collects appropriate data into a `QUIC_ACKM_RX_PKT` structure:
- The packet number (`packet->packet_number`)
- The packet receive time (`received`)
- The packet space, which is always:
- `QUIC_PN_SPACE_INITIAL` when `packet->packet_type == pkt_initial`
- `QUIC_PN_SPACE_HANDSHAKE` when `packet->packet_type == pkt_handshake`
- `QUIC_PN_SPACE_APP` for all other packet types
- The ACK eliciting flag. This is calculated by looping through all
frames and noting those that are ACK eliciting, as determined from
[Table 1](#table-1) below)
### Passing frame data
This loops through all the frames, extracts data where there is any
and calls diverse other components as shown in the Passed to column in
[Table 1](#table-1) below.
#### Table 1
Taken from [RFC 9000 12.4 Frames and Frame Types]
| Type | Name | Passed to | ACK eliciting | I | H | 0 | 1 |
|------|-------------------------|--------------------------|---------------|----------|----------|----------|----------|
| 0x00 | [padding] | - | | ✔ | ✔ | ✔ | ✔ |
| 0x01 | [ping] | - | ✔ | ✔ | ✔ | ✔ | ✔ |
| 0x02 | [ack 0x02] | [ACK manager] [^1] | | ✔ | ✔ | | ✔ |
| 0x03 | [ack 0x03] | [ACK manager] [^1] | | ✔ | ✔ | | ✔ |
| 0x04 | [reset_stream] | - [^2] | ✔ | | | ✔ | ✔ |
| 0x05 | [stop_sending] | - [^3] | ✔ | | | ✔ | ✔ |
| 0x06 | [crypto] | Handshake manager | ✔ | ✔ | ✔ | | ✔ |
| 0x07 | [new_token] | Session manager | ✔ | | | | ✔ |
| 0x08 | [stream 0x08] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x09 | [stream 0x09] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x0A | [stream 0x0A] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x0B | [stream 0x0B] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x0C | [stream 0x0C] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x0D | [stream 0x0D] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x0E | [stream 0x0E] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x0F | [stream 0x0F] | Apprioriate stream [^4] | ✔ | | | ✔ | ✔ |
| 0x10 | [max_data] | Flow control [^5] | ✔ | | | ✔ | ✔ |
| 0x11 | [max_stream_data] | Flow control [^5] | ✔ | | | ✔ | ✔ |
| 0x12 | [max_streams 0x12] | Connection manager? [^6] | ✔ | | | ✔ | ✔ |
| 0x13 | [max_streams 0x13] | Connection manager? [^6] | ✔ | | | ✔ | ✔ |
| 0x14 | [data_blocked] | Flow control [^5] | ✔ | | | ✔ | ✔ |
| 0x15 | [stream_data_blocked] | Flow control [^5] | ✔ | | | ✔ | ✔ |
| 0x16 | [streams_blocked 0x16] | Connection manager? [^6] | ✔ | | | ✔ | ✔ |
| 0x17 | [streams_blocked 0x17] | Connection manager? [^6] | ✔ | | | ✔ | ✔ |
| 0x18 | [new_connection_id] | Connection manager | ✔ | | | ✔ | ✔ |
| 0x19 | [retire_connection_id] | Connection manager | ✔ | | | ✔ | ✔ |
| 0x1A | [path_challenge] | Connection manager? [^7] | ✔ | | | ✔ | ✔ |
| 0x1B | [path_response] | Connection manager? [^7] | ✔ | | | | ✔ |
| 0x1C | [connection_close 0x1C] | Connection manager | | ✔ | ✔ | ✔ | ✔ |
| 0x1D | [connection_close 0x1D] | Connection manager | | | | ✔ | ✔ |
| 0x1E | [handshake_done] | Handshake manager | ✔ | | | | ✔ |
| ???? | *[Extension Frames]* | - [^8] | ✔ | | | | |
The I, H, 0, and 1 columns are validity in different packet types, with this meaning:
| Pkts | Description |
|:----:|----------------------------|
| I | Valid in Initial packets |
| H | Valid in Handshake packets |
| 0 | Valid in 0-RTT packets |
| 1 | Valid in 1-RTT packets |
Notes:
[^1]: This creates and populates an `QUIC_ACKM_ACK` structure, then calls
`QUIC_ACKM_on_rx_ack_frame()`, with the appropriate context
(`QUIC_ACKM`, the created `QUIC_ACKM_ACK`, `pkt_space` and `rx_time`)
[^2]: Immediately terminates the appropriate receiving stream `QUIC_STREAM`
object.
This includes discarding any buffered application data.
For a stream that's send-only, the error `STREAM_STATE_ERROR` is raised,
and the `QUIC_CONNECTION` object is terminated.
[^3]: Immediately terminates the appropriate sending stream `QUIC_STREAM`
object.
For a stream that's receive-only, the error `STREAM_STATE_ERROR` is
raised, and the `QUIC_CONNECTION` object is terminated.
[^4]: The frame payload (Stream Data) is passed as is to the `QUIC_STREAM`
object, along with available metadata (offset and length, as determined
to be available from the lower 3 bits of the frame type).
[^5]: The details of what flow control will need are yet to be determined
[^6]: I imagine that `max_streams` and `streams_blocked` concern a Connection
manager before anything else.
[^7]: I imagine that path challenge/response concerns a Connection manager
before anything else.
[^8]: We have no idea what extension frames there will be. However, we
must at least acknowledge their presence, so much is clear from the RFC.
[overview]: https://github.com/openssl/openssl/blob/master/doc/designs/quic-design/quic-overview.md
[TX packetizer]: https://github.com/openssl/openssl/pull/18570
[SSL object refactoring using SSL_CONNECTION object]: https://github.com/openssl/openssl/pull/18612
[QUIC Demuxer and Record Layer (RX+TX)]: https://github.com/openssl/openssl/pull/18949
[ACK manager]: https://github.com/openssl/openssl/pull/18564
[RFC 9000 12.4 Frames and Frame Types]: https://datatracker.ietf.org/doc/html/rfc9000#section-12.4
[padding]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.1
[ping]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.2
[ack 0x02]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.3
[ack 0x03]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.3
[reset_stream]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.4
[stop_sending]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.5
[crypto]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.6
[new_token]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.7
[stream 0x08]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[stream 0x09]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[stream 0x0A]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[stream 0x0B]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[stream 0x0C]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[stream 0x0D]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[stream 0x0E]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[stream 0x0F]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.8
[max_data]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.9
[max_stream_data]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.10
[max_streams 0x12]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.11
[max_streams 0x13]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.11
[data_blocked]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.12
[stream_data_blocked]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.13
[streams_blocked 0x16]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.14
[streams_blocked 0x17]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.14
[new_connection_id]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.15
[retire_connection_id]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.16
[path_challenge]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.17
[path_response]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.18
[connection_close 0x1C]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.19
[connection_close 0x1D]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.19
[handshake_done]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.20
[Extension Frames]: https://datatracker.ietf.org/doc/html/rfc9000#section-19.21
