dcsctp 0.1.13

An SCTP implementation for WebRTC Data Channels
Documentation 
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// Copyright 2025 The dcSCTP Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::api::StreamId;
use crate::packet::ChunkParseError;
use crate::packet::SerializableTlv;
use crate::packet::ensure;
use crate::packet::parameter::RawParameter;
use crate::packet::parameter::write_parameter_header;
use crate::packet::read_u16_be;
use crate::packet::read_u32_be;
use crate::packet::write_u16_be;
use crate::packet::write_u32_be;
use crate::types::Tsn;
use core::fmt;

pub(crate) const PARAMETER_TYPE: u16 = 13;

/// Outgoing SSN Reset Request parameter
///
/// See <https://datatracker.ietf.org/doc/html/rfc6525#section-4.1>.
///
/// ```txt
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |     Parameter Type = 13       | Parameter Length = 16 + 2 * N |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |           Re-configuration Request Sequence Number            |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |           Re-configuration Response Sequence Number           |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |                Sender's Last Assigned TSN                     |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |  Stream Number 1 (optional)   |    Stream Number 2 (optional) |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// /                            ......                             /
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |  Stream Number N-1 (optional) |    Stream Number N (optional) |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// ```
#[derive(Debug)]
pub struct OutgoingSsnResetRequestParameter {
    pub(crate) request_seq_nbr: u32,
    pub(crate) response_seq_nbr: u32,
    pub(crate) sender_last_assigned_tsn: Tsn,
    pub(crate) streams: Vec<StreamId>,
}

impl TryFrom<RawParameter<'_>> for OutgoingSsnResetRequestParameter {
    type Error = ChunkParseError;

    fn try_from(raw: RawParameter<'_>) -> Result<Self, ChunkParseError> {
        ensure!(raw.typ == PARAMETER_TYPE, ChunkParseError::InvalidType);
        ensure!(
            raw.value.len() >= 12 && raw.value.len().is_multiple_of(2),
            ChunkParseError::InvalidLength
        );

        let streams = raw.value[12..].chunks_exact(2).map(|c| StreamId(read_u16_be!(c))).collect();

        Ok(Self {
            request_seq_nbr: read_u32_be!(&raw.value[0..4]),
            response_seq_nbr: read_u32_be!(&raw.value[4..8]),
            sender_last_assigned_tsn: Tsn(read_u32_be!(&raw.value[8..12])),
            streams,
        })
    }
}

impl SerializableTlv for OutgoingSsnResetRequestParameter {
    fn serialize_to(&self, output: &mut [u8]) {
        let value = write_parameter_header(PARAMETER_TYPE, self.value_size(), output);
        write_u32_be!(&mut value[0..4], self.request_seq_nbr);
        write_u32_be!(&mut value[4..8], self.response_seq_nbr);
        write_u32_be!(&mut value[8..12], self.sender_last_assigned_tsn.0);
        let mut chunks = value[12..].chunks_exact_mut(2);
        for (stream_id, chunk) in self.streams.iter().zip(&mut chunks) {
            write_u16_be!(chunk, stream_id.0);
        }
    }

    fn value_size(&self) -> usize {
        12 + self.streams.len() * 2
    }
}

impl fmt::Display for OutgoingSsnResetRequestParameter {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "Incoming SSN Reset Request, req_seq_nbr={}, resp_seq_nbr={}, slatsn={}",
            self.request_seq_nbr, self.response_seq_nbr, self.sender_last_assigned_tsn,
        )
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn serialize_and_deserialize() {
        let cause = OutgoingSsnResetRequestParameter {
            request_seq_nbr: 1,
            response_seq_nbr: 2,
            sender_last_assigned_tsn: Tsn(3),
            streams: vec![StreamId(4), StreamId(5), StreamId(6)],
        };

        let mut serialized = vec![0; cause.serialized_size()];
        cause.serialize_to(&mut serialized);

        let param = OutgoingSsnResetRequestParameter::try_from(
            RawParameter::from_bytes(&serialized).unwrap().0,
        )
        .unwrap();
        assert_eq!(param.request_seq_nbr, 1);
        assert_eq!(param.response_seq_nbr, 2);
        assert_eq!(param.sender_last_assigned_tsn, Tsn(3));
        assert_eq!(param.streams, vec![StreamId(4), StreamId(5), StreamId(6)]);
    }
}