mpeg-ps 0.5.0

//! Program Stream Map — ISO/IEC 13818-1 §2.5.4, Table 2-41.
//!
//! The PSM provides a mapping from `stream_type`/`elementary_stream_id`
//! to descriptors, tied to the Program Stream with a CRC-32 trailer.
//! It uses start-code prefix `0x000001` + `map_stream_id` `0xBC`.

use alloc::vec::Vec;

use crate::error::{Error, Result};
use broadcast_common::{Parse, Serialize, crc32_mpeg2};

/// `packet_start_code_prefix` — `0x000001`.
pub const PACKET_START_CODE_PREFIX: u32 = 0x00_0001;
/// `map_stream_id` — `0xBC`, combined with the prefix forms the PSM start code.
pub const MAP_STREAM_ID: u8 = 0xBC;
/// Combined PSM start code: `0x000001BC`.
pub const PSM_START_CODE: u32 = (PACKET_START_CODE_PREFIX << 8) | MAP_STREAM_ID as u32;

/// Bytes before the map body: prefix(3) + map_stream_id(1) + psm_length(2) = 6.
const PREFIX_LEN: usize = 6;

/// `program_stream_map_length` upper bound (ISO/IEC 13818-1 Table 2-41).
const MAP_LENGTH_MAX: usize = 1018;
/// Bytes after the prefix that are always present: flags(1) + reserved(1) +
/// `program_stream_info_length`(2) + `elementary_stream_map_length`(2).
const FIXED_BODY_LEN: usize = 6;
/// CRC-32 trailer length (Table 2-41).
const CRC_LEN: usize = 4;
/// `stream_type`(1) + `elementary_stream_id`(1) + `ES_info_length`(2).
const ES_ENTRY_HEADER_LEN: usize = 4;
/// Pseudo descriptor carrying `elementary_stream_id_extension` (Table 2-41):
/// tag(1) + length(1) + marker+extension(1).
const PSEUDO_DESCRIPTOR_LEN: usize = 3;
/// `pseudo_descriptor_tag` — Table 2-41 allows any value.
const PSEUDO_DESCRIPTOR_TAG: u8 = 0x00;
/// Marker bit in the `elementary_stream_id_extension` byte (Table 2-41).
const MARKER_BIT: u8 = 0x80;
/// 7-bit `elementary_stream_id_extension`.
const EXTENSION_MASK: u8 = 0x7F;
/// `flags` byte reserved bit 5 — conventionally set (Table 2-41).
const FLAGS_RESERVED_BIT: u8 = 0x20;
/// `program_stream_map_version` width in bits (Table 2-41).
const VERSION_BITS: u32 = 5;
/// Mask of the 5-bit `program_stream_map_version` in the flags byte.
const VERSION_MASK: u8 = 0x1F;

/// An elementary stream descriptor entry with optional stream_id_extension.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
pub struct EsMapEntry<'a> {
    /// `stream_type` per ISO/IEC 13818-1 Table 2-29.
    pub stream_type: u8,
    /// `elementary_stream_id`.
    pub elementary_stream_id: u8,
    /// If `elementary_stream_id == 0xFD` and `single_extension_stream_flag == 0`,
    /// this holds the `elementary_stream_id_extension`. Otherwise `None`.
    pub stream_id_extension: Option<u8>,
    /// Descriptor bytes for this elementary stream.
    #[cfg_attr(feature = "serde", serde(skip))]
    pub descriptors: &'a [u8],
}

/// A parsed Program Stream Map.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
pub struct ProgramStreamMap<'a> {
    /// `current_next_indicator` (1 bit).
    pub current_next_indicator: bool,
    /// `single_extension_stream_flag` (1 bit).
    pub single_extension_stream_flag: bool,
    /// `program_stream_map_version` (5 bits).
    pub version: u8,
    /// Descriptors for the program stream itself.
    #[cfg_attr(feature = "serde", serde(skip))]
    pub program_stream_info: &'a [u8],
    /// Per-elementary-stream entries.
    pub elementary_stream_map: Vec<EsMapEntry<'a>>,
    /// The raw CRC-32 value in the trailer (validated on parse).
    pub crc: u32,
}

impl<'a> Parse<'a> for ProgramStreamMap<'a> {
    type Error = Error;

    fn parse(b: &'a [u8]) -> Result<Self> {
        if b.len() < PREFIX_LEN + 2 + 4 {
            // prefix + psm_length(2) + CRC(4) = minimum
            return Err(Error::BufferTooShort {
                need: PREFIX_LEN + 2 + 4,
                have: b.len(),
                what: "program_stream_map",
            });
        }

        // packet_start_code_prefix (3 bytes) + map_stream_id (1 byte)
        let start = u32::from_be_bytes([0, b[0], b[1], b[2]]);
        if start != PACKET_START_CODE_PREFIX {
            return Err(Error::BadMapStreamId(b[3]));
        }
        if b[3] != MAP_STREAM_ID {
            return Err(Error::BadMapStreamId(b[3]));
        }

        let map_length = u16::from_be_bytes([b[4], b[5]]) as usize;
        let crc_end = PREFIX_LEN + map_length + 4;
        if b.len() < crc_end {
            return Err(Error::MapLengthOverflow {
                map_length,
                available: b.len().saturating_sub(PREFIX_LEN),
            });
        }

        // Validate CRC before trusting the parsed content
        let crc_data_end = crc_end - 4;
        let crc_data = &b[0..crc_data_end];
        let stored_crc = u32::from_be_bytes([
            b[crc_data_end],
            b[crc_data_end + 1],
            b[crc_data_end + 2],
            b[crc_data_end + 3],
        ]);
        let computed_crc = crc32_mpeg2::compute(crc_data);
        if computed_crc != stored_crc {
            return Err(Error::BadCrc {
                computed: computed_crc,
                stored: stored_crc,
            });
        }

        // flags byte: current_next(1) | single_extension(1) | reserved(1) | version(5)
        let flags = b[6];
        let current_next_indicator = flags & 0x80 != 0;
        let single_extension_stream_flag = flags & 0x40 != 0;
        let version = flags & VERSION_MASK;

        // reserved byte (7 bits reserved + marker_bit)
        if b[7] & 0x01 == 0 {
            return Err(Error::BadMarker("program_stream_map marker_bit"));
        }

        let program_stream_info_length = u16::from_be_bytes([b[8], b[9]]) as usize;

        let info_start = PREFIX_LEN + 4; // after flags(1)+reserved(1)+prog_info_len(2)
        let info_end = info_start + program_stream_info_length;

        // Table 2-41 order: program_stream_info_length(16), descriptor()×N,
        // THEN elementary_stream_map_length(16) — the length field follows
        // the program descriptor loop, not the reverse (#1050).
        if crc_data_end < info_end + 2 {
            return Err(Error::MapLengthOverflow {
                map_length,
                available: b.len().saturating_sub(PREFIX_LEN),
            });
        }
        let elementary_stream_map_length =
            u16::from_be_bytes([b[info_end], b[info_end + 1]]) as usize;

        let es_start = info_end + 2; // after elementary_stream_map_length(2)
        let es_end = es_start + elementary_stream_map_length;

        if crc_data_end < es_end {
            return Err(Error::MapLengthOverflow {
                map_length,
                available: b.len().saturating_sub(PREFIX_LEN),
            });
        }

        let program_stream_info = &b[info_start..info_end];

        // Parse elementary stream loop
        let es_data = &b[es_start..es_end];
        let elementary_stream_map = parse_es_loop(es_data, single_extension_stream_flag)?;

        Ok(ProgramStreamMap {
            current_next_indicator,
            single_extension_stream_flag,
            version,
            program_stream_info,
            elementary_stream_map,
            crc: stored_crc,
        })
    }
}

fn parse_es_loop(data: &[u8], single_flag: bool) -> Result<Vec<EsMapEntry<'_>>> {
    let mut entries = Vec::new();
    let mut pos = 0;
    while pos + 4 <= data.len() {
        let stream_type = data[pos];
        let elementary_stream_id = data[pos + 1];
        let es_info_length = u16::from_be_bytes([data[pos + 2], data[pos + 3]]) as usize;
        let entry_hdr_end = pos + 4;
        let entry_end = entry_hdr_end + es_info_length;
        if entry_end > data.len() {
            return Err(Error::BufferTooShort {
                need: entry_end,
                have: data.len(),
                what: "elementary_stream_map entry descriptors",
            });
        }

        let (stream_id_extension, descriptors) = if elementary_stream_id == 0xFD && !single_flag {
            // Extension form with pseudo descriptor
            if es_info_length < 3 {
                return Err(Error::BufferTooShort {
                    need: 3,
                    have: es_info_length,
                    what: "pseudo descriptor for stream_id_extension",
                });
            }
            // pseudo_descriptor_tag + pseudo_descriptor_length + marker+extension
            if data[entry_hdr_end + 2] & 0x80 == 0 {
                return Err(Error::BadMarker("elementary_stream_id_extension marker"));
            }
            let ext = data[entry_hdr_end + 2] & 0x7F;
            let desc = &data[entry_hdr_end + 3..entry_end];
            (Some(ext), desc)
        } else {
            let desc = &data[entry_hdr_end..entry_end];
            (None, desc)
        };

        entries.push(EsMapEntry {
            stream_type,
            elementary_stream_id,
            stream_id_extension,
            descriptors,
        });

        pos = entry_end;
    }
    Ok(entries)
}

/// Bytes one elementary-stream entry occupies on the wire:
/// `stream_type(1) + elementary_stream_id(1) + ES_info_length(2)` + the
/// optional 3-byte pseudo descriptor + the descriptor bytes.
fn es_entry_len(e: &EsMapEntry<'_>) -> usize {
    ES_ENTRY_HEADER_LEN
        + if e.stream_id_extension.is_some() {
            PSEUDO_DESCRIPTOR_LEN
        } else {
            0
        }
        + e.descriptors.len()
}

/// Write the elementary-stream loop straight into `out` (exactly the sum of
/// [`es_entry_len`], checked by the caller), no intermediate owned copies
/// (audit r14-MPS-O1).
fn write_es_loop(entries: &[EsMapEntry<'_>], out: &mut [u8]) -> Result<()> {
    let mut at = 0usize;
    for e in entries {
        let entry_len = es_entry_len(e);
        let dst = &mut out[at..at + entry_len];
        dst[0] = e.stream_type;
        dst[1] = e.elementary_stream_id;
        let info_len = entry_len - ES_ENTRY_HEADER_LEN;
        let info_len =
            broadcast_common::len::fit_u16(info_len, "elementary_stream_map.ES_info_length")?;
        dst[2..4].copy_from_slice(&info_len.to_be_bytes());
        let mut c = ES_ENTRY_HEADER_LEN;
        if let Some(ext) = e.stream_id_extension {
            dst[c] = PSEUDO_DESCRIPTOR_TAG;
            // pseudo_descriptor_length: 8-bit field covering the marker+
            // extension byte plus the descriptors. Checked in usize before
            // narrowing — `1 + len as u8` used to overflow at 255 (#1129).
            dst[c + 1] = broadcast_common::len::fit_u8(
                1 + e.descriptors.len(),
                "elementary_stream_map.pseudo_descriptor_length",
            )?;
            dst[c + 2] = MARKER_BIT | (ext & EXTENSION_MASK);
            c += PSEUDO_DESCRIPTOR_LEN;
        }
        dst[c..].copy_from_slice(e.descriptors);
        at += entry_len;
    }
    Ok(())
}

impl Serialize for ProgramStreamMap<'_> {
    type Error = Error;

    fn serialized_len(&self) -> usize {
        let prog_info_len = self.program_stream_info.len();
        let es_loop_len: usize = self.elementary_stream_map.iter().map(es_entry_len).sum();
        // PREFIX_LEN + flags(1) + reserved(1) + prog_info_len(2) + prog_info
        // + es_map_len(2) + es_loop + CRC(4)
        PREFIX_LEN + FIXED_BODY_LEN + prog_info_len + es_loop_len + CRC_LEN
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        let total = self.serialized_len();
        if buf.len() < total {
            return Err(Error::BufferTooShort {
                need: total,
                have: buf.len(),
                what: "program_stream_map serialize output",
            });
        }

        // packet_start_code_prefix (3 bytes)
        buf[0..3].copy_from_slice(&PACKET_START_CODE_PREFIX.to_be_bytes()[1..]);
        // map_stream_id
        buf[3] = MAP_STREAM_ID;

        let prog_info_len = self.program_stream_info.len();
        let es_loop_len: usize = self.elementary_stream_map.iter().map(es_entry_len).sum();

        // map_length = flags(1) + reserved(1) + prog_info_len(2) + es_loop_len(2) + prog_info + es_loop
        let map_length = FIXED_BODY_LEN + prog_info_len + es_loop_len;
        // program_stream_map_length max is 1018 (0x3FA) per Table 2-41 — checked
        // in usize before any narrowing (#1129).
        if map_length > MAP_LENGTH_MAX {
            return Err(broadcast_common::len::FieldOverflow {
                field: "program_stream_map.program_stream_map_length",
                value: map_length as u64,
                max: MAP_LENGTH_MAX as u64,
            }
            .into());
        }
        let map_length = broadcast_common::len::fit_u16(
            map_length,
            "program_stream_map.program_stream_map_length",
        )?;
        buf[4..6].copy_from_slice(&map_length.to_be_bytes());

        // flags: current_next(1) + single_extension(1) + reserved(1, convention
        // is set) + version(5). W8 (#1119): the reserved bit (bit 5) was
        // always written 0 instead of the conventional 1.
        let version = broadcast_common::len::fit_bits(
            u64::from(self.version),
            VERSION_BITS,
            "program_stream_map.program_stream_map_version",
        )? as u8;
        buf[6] = (u8::from(self.current_next_indicator) << 7)
            | (u8::from(self.single_extension_stream_flag) << 6)
            | FLAGS_RESERVED_BIT
            | version;

        // reserved(7, convention is all set) + marker_bit(1).
        // W8 (#1119): `0x7F | 0x01` is a no-op (`0x7F` already has bit 0
        // set) and leaves the MSB reserved bit `0` instead of the
        // conventional `1` — real encoders write this byte `0xFF`, so this
        // did not round-trip byte-identically against a real capture.
        buf[7] = 0xFF;

        // program_stream_info_length and elementary_stream_map_length are
        // both 16-bit fields; `map_length <= MAP_LENGTH_MAX` above already
        // bounds each of them well under `u16::MAX`, but check explicitly
        // rather than relying on that aggregate bound holding (#1129).
        let prog_info_len_u16 = broadcast_common::len::fit_u16(
            prog_info_len,
            "program_stream_map.program_stream_info_length",
        )?;
        let es_loop_len_u16 = broadcast_common::len::fit_u16(
            es_loop_len,
            "program_stream_map.elementary_stream_map_length",
        )?;
        buf[8..10].copy_from_slice(&prog_info_len_u16.to_be_bytes());

        // program_stream_info descriptors (Table 2-41: the program descriptor
        // loop comes immediately after program_stream_info_length, at byte
        // 10, BEFORE elementary_stream_map_length — #1050)
        buf[10..10 + prog_info_len].copy_from_slice(self.program_stream_info);

        // elementary_stream_map_length, then the elementary stream loop
        let es_len_start = 10 + prog_info_len;
        buf[es_len_start..es_len_start + 2].copy_from_slice(&es_loop_len_u16.to_be_bytes());
        let es_start = es_len_start + 2;
        write_es_loop(
            &self.elementary_stream_map,
            &mut buf[es_start..es_start + es_loop_len],
        )?;

        // CRC-32 over everything before it
        let crc_offset = es_start + es_loop_len;
        let crc = crc32_mpeg2::compute(&buf[0..crc_offset]);
        buf[crc_offset..crc_offset + 4].copy_from_slice(&crc.to_be_bytes());

        Ok(total)
    }
}

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

    #[test]
    fn serialize_rejects_version_over_5_bits() {
        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 0x20,
            program_stream_info: &[],
            elementary_stream_map: vec![],
            crc: 0,
        };
        let mut buf = vec![0u8; 64];
        assert!(matches!(
            psm.serialize_into(&mut buf),
            Err(Error::FieldOverflow(_))
        ));
    }

    /// Build a valid PSM programmatically and verify round-trip.
    #[test]
    fn psm_build_and_round_trip() {
        let entries = vec![EsMapEntry {
            stream_type: 0x02, // MPEG-2 video
            elementary_stream_id: 0xE0,
            stream_id_extension: None,
            descriptors: &[0x0A, 0x04, b'H', b'E', b'L', b'L'], // registration descriptor
        }];

        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 3,
            program_stream_info: &[],
            elementary_stream_map: entries,
            crc: 0, // will be overwritten by serialize
        };

        let mut buf = vec![0u8; psm.serialized_len()];
        psm.serialize_into(&mut buf).unwrap();

        // Parse back
        let parsed = ProgramStreamMap::parse(&buf).unwrap();
        assert!(parsed.current_next_indicator);
        assert!(!parsed.single_extension_stream_flag);
        assert_eq!(parsed.version, 3);
        assert!(parsed.program_stream_info.is_empty());
        assert_eq!(parsed.elementary_stream_map.len(), 1);
        assert_eq!(parsed.elementary_stream_map[0].stream_type, 0x02);
        assert_eq!(parsed.elementary_stream_map[0].elementary_stream_id, 0xE0);
        assert!(
            parsed.elementary_stream_map[0]
                .stream_id_extension
                .is_none()
        );
        assert_eq!(
            parsed.elementary_stream_map[0].descriptors,
            &[0x0A, 0x04, b'H', b'E', b'L', b'L']
        );

        // Byte-exact round-trip
        let mut out2 = vec![0u8; parsed.serialized_len()];
        parsed.serialize_into(&mut out2).unwrap();
        assert_eq!(&out2[..], &buf[..], "byte-exact round-trip mismatch");

        // Mutation test: change version, output must differ
        let psm_mut = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 7,
            program_stream_info: &[],
            elementary_stream_map: vec![EsMapEntry {
                stream_type: 0x02,
                elementary_stream_id: 0xE0,
                stream_id_extension: None,
                descriptors: &[0x0A, 0x04, b'H', b'E', b'L', b'L'],
            }],
            crc: 0,
        };
        let mut out3 = vec![0u8; psm_mut.serialized_len()];
        psm_mut.serialize_into(&mut out3).unwrap();
        assert_ne!(&buf[..], &out3[..]);
    }

    #[test]
    fn psm_with_stream_id_extension() {
        let entries = vec![EsMapEntry {
            stream_type: 0x06, // subtitles
            elementary_stream_id: 0xFD,
            stream_id_extension: Some(0x0F),
            descriptors: &[0x59, 0x02, 0x01, 0x02], // subtitling descriptor
        }];

        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 1,
            program_stream_info: &[],
            elementary_stream_map: entries,
            crc: 0,
        };

        let mut buf = vec![0u8; psm.serialized_len()];
        psm.serialize_into(&mut buf).unwrap();

        let parsed = ProgramStreamMap::parse(&buf).unwrap();
        assert_eq!(parsed.elementary_stream_map.len(), 1);
        assert_eq!(
            parsed.elementary_stream_map[0].stream_id_extension,
            Some(0x0F)
        );
        assert_eq!(
            parsed.elementary_stream_map[0].descriptors,
            &[0x59, 0x02, 0x01, 0x02]
        );

        // Byte-exact round-trip
        let mut out2 = vec![0u8; parsed.serialized_len()];
        parsed.serialize_into(&mut out2).unwrap();
        assert_eq!(&out2[..], &buf[..]);
    }

    /// MPS-W6 (#1129): `pseudo_descriptor_length` is `1 + descriptors.len()`,
    /// written as `1 + (descriptors.len() as u8)` — the cast happened before
    /// the add, so a 255-byte descriptor overflowed the `u8` addition
    /// (panicking in debug, wrapping in release) rather than being checked.
    #[test]
    fn pseudo_descriptor_length_overflow_is_rejected_not_wrapped() {
        let entries = vec![EsMapEntry {
            stream_type: 0x06,
            elementary_stream_id: 0xFD,
            stream_id_extension: Some(0x01),
            descriptors: &[0u8; 255],
        }];
        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 0,
            program_stream_info: &[],
            elementary_stream_map: entries,
            crc: 0,
        };
        let mut buf = vec![0u8; psm.serialized_len()];
        assert!(psm.serialize_into(&mut buf).is_err());
    }

    /// MPS-W6 (#1129): `program_stream_map_length` (spec max 1018, Table
    /// 2-41) was written unchecked with `as u16`.
    #[test]
    fn program_stream_map_length_over_spec_max_is_rejected() {
        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 0,
            program_stream_info: &[0u8; 1019],
            elementary_stream_map: vec![],
            crc: 0,
        };
        let mut buf = vec![0u8; psm.serialized_len()];
        assert!(psm.serialize_into(&mut buf).is_err());
    }

    /// The boundary: exactly the spec max still serializes and round-trips.
    #[test]
    fn program_stream_map_length_at_spec_max_round_trips() {
        // map_length = 6 + prog_info_len + es_loop_len; want map_length == 1018.
        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 0,
            program_stream_info: &[0u8; 1012],
            elementary_stream_map: vec![],
            crc: 0,
        };
        let mut buf = vec![0u8; psm.serialized_len()];
        psm.serialize_into(&mut buf).unwrap();
        let parsed = ProgramStreamMap::parse(&buf).unwrap();
        assert_eq!(parsed.program_stream_info.len(), 1012);
    }

    /// #1050 regression: a conformant PSM with a non-empty program
    /// descriptor loop. TSDuck cannot generate PS, and the committed
    /// ffmpeg fixture (`fixtures/mpeg-ps/ffmpeg-mpeg2-ps.mpg`) carries no
    /// PSM at all (VOB/MPEG-PS from ffmpeg's muxer omits it), so this is
    /// hand-built directly from ISO/IEC 13818-1 Table 2-41's field order —
    /// the oracle: `program_stream_info_length(16)`, `descriptor()×N`,
    /// THEN `elementary_stream_map_length(16)`, `stream_map()×N`, `CRC_32`.
    /// Before the fix, parse took the program loop's first descriptor
    /// bytes (tag=0x05 'C'=0x43 here) as `elementary_stream_map_length`
    /// (0x0543 = 1347), which overflows the buffer and fails with
    /// `MapLengthOverflow` instead of parsing the one ES entry.
    #[test]
    fn psm_with_nonempty_program_descriptor_loop() {
        // One program-level registration descriptor (tag 0x05, len 4, "TEST").
        let prog_descriptor: &[u8] = &[0x05, 0x04, b'T', b'E', b'S', b'T'];
        let entries = vec![EsMapEntry {
            stream_type: 0x02, // MPEG-2 video
            elementary_stream_id: 0xE0,
            stream_id_extension: None,
            descriptors: &[],
        }];

        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 5,
            program_stream_info: prog_descriptor,
            elementary_stream_map: entries,
            crc: 0,
        };

        let mut buf = vec![0u8; psm.serialized_len()];
        psm.serialize_into(&mut buf).unwrap();

        // Table 2-41 byte layout check: the program descriptor loop (6 bytes)
        // sits at buf[10..16], directly after program_stream_info_length;
        // elementary_stream_map_length sits at buf[16..18], AFTER it.
        assert_eq!(&buf[10..16], prog_descriptor);
        let es_map_len = u16::from_be_bytes([buf[16], buf[17]]);
        assert_eq!(es_map_len, 4, "one ES entry: stream_type+id+info_len(0)");

        let parsed = ProgramStreamMap::parse(&buf).unwrap();
        assert_eq!(parsed.program_stream_info, prog_descriptor);
        assert_eq!(parsed.elementary_stream_map.len(), 1);
        assert_eq!(parsed.elementary_stream_map[0].stream_type, 0x02);
        assert_eq!(parsed.elementary_stream_map[0].elementary_stream_id, 0xE0);

        // Byte-exact round-trip
        let mut out2 = vec![0u8; parsed.serialized_len()];
        parsed.serialize_into(&mut out2).unwrap();
        assert_eq!(&out2[..], &buf[..]);
    }

    /// W8 (#1119): reserved bits in the flags byte (bit 5) and the
    /// following reserved+marker byte (bits 7-1) are conventionally `1` —
    /// real encoders write byte 6's reserved bit set and byte 7 as `0xFF`.
    /// The flags byte used to always clear bit 5, and byte 7 was written
    /// `0x7F | 0x01` (a no-op, since `0x7F` already has bit 0 set) instead
    /// of `0xFF`, leaving the MSB reserved bit `0`.
    #[test]
    fn reserved_bits_are_set_by_convention() {
        let psm = ProgramStreamMap {
            current_next_indicator: false,
            single_extension_stream_flag: false,
            version: 0,
            program_stream_info: &[],
            elementary_stream_map: vec![],
            crc: 0,
        };
        let mut buf = vec![0u8; psm.serialized_len()];
        psm.serialize_into(&mut buf).unwrap();
        assert_eq!(
            buf[6], 0x20,
            "flags byte reserved bit (0x20) must be set even with both flags clear"
        );
        assert_eq!(buf[7], 0xFF, "reserved(7)+marker_bit(1) byte must be 0xFF");
    }

    #[test]
    fn psm_bad_crc_rejected() {
        let psm = ProgramStreamMap {
            current_next_indicator: true,
            single_extension_stream_flag: false,
            version: 0,
            program_stream_info: &[],
            elementary_stream_map: vec![],
            crc: 0,
        };
        let mut buf = vec![0u8; psm.serialized_len()];
        psm.serialize_into(&mut buf).unwrap();
        // Corrupt CRC (last 4 bytes)
        let crc_off = buf.len() - 4;
        buf[crc_off] ^= 0xFF;
        assert!(matches!(
            ProgramStreamMap::parse(&buf),
            Err(Error::BadCrc { .. })
        ));
    }
}