dvb_si/tables/

protection_message.rs

//! Protection message sections — ETSI TS 102 809 v1.3.1 §9 (table_id 0x7B).
//!
//! Protection messages are MPEG-2 private sections (ISO/IEC 13818-1) used by
//! the application-signalling authentication scheme. They share one table_id
//! (0x7B) and are discriminated by the 16-bit `table_id_extension`
//! ([`ProtectionMessageBody`], §9.3.4 Table 41, PDF p. 66):
//!
//! - `0x0000..=0x00FF` — **authentication message** (§9.4.3 Table 42, PDF
//!   pp. 70-71). The extension *is* the `authentication_group_id`. Carries a
//!   loop of section hashes plus a detached signature.
//! - `0x0100` — **certificate collection message** (§9.5.4.9 Table 51, PDF
//!   p. 91). The extension is the fixed `trust_message_id` 0x0100. Carries a
//!   count-prefixed list of DER-encoded DVBCertificates.
//! - `0x0101..=0xFFFF` — reserved for future use; preserved as a raw body so
//!   parse → serialize stays byte-exact ([`ProtectionMessageBody::Raw`]).
//!
//! Mirrors the SAT precedent (`sat.rs`): a typed common section header plus a
//! discriminated typed body. Variable-length inner loops (hash entries,
//! certificate slices) are exposed as borrowed slices.
//!
//! Per crate contract this parser does NOT verify CRC_32 (use
//! `Section::validate_crc`). Reserved bits are ignored on parse and emitted as
//! 1s on serialize, except spec-mandated zero fields which are emitted 0.

use crate::error::{Error, Result};
use alloc::vec::Vec;
use broadcast_common::{Parse, Serialize};

/// table_id for all protection messages (TS 102 809 §9.3.4; coded per EN 300 468 §5.1.3).
pub const TABLE_ID: u8 = 0x7B;
// No fixed PID: this table's PID is signalled (PMT / descriptors). A `PID`
// constant of `0x0000` used to sit here, which is the real PAT PID, so a
// caller filtering on it would pick up PAT traffic (audit r02-W15/O12).

/// `table_id_extension` value (inclusive) of the first authentication message (§9.3.4 Table 41).
pub const AUTH_EXTENSION_FIRST: u16 = 0x0000;
/// `table_id_extension` value (inclusive) of the last authentication message (§9.3.4 Table 41).
pub const AUTH_EXTENSION_LAST: u16 = 0x00FF;
/// `table_id_extension` (`trust_message_id`) of the certificate collection message (§9.3.4 Table 41).
pub const CERTIFICATE_COLLECTION_EXTENSION: u16 = 0x0100;

/// Reference type coding — ETSI TS 102 809 §9.4.3 Table 45.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[non_exhaustive]
pub enum ReferenceType {
    /// 0x0 — reserved for future use.
    Reserved,
    /// 0x1 — same ES (table_id of the payload section).
    SameEs,
    /// 0x2 — component tag ES (component_tag of the payload section).
    ComponentTagEs,
    /// 0x3..=0xF — reserved.
    Unallocated(u8),
}

impl ReferenceType {
    #[must_use]
    /// Decode from the wire value.  Every value maps (lossless).
    pub fn from_u8(v: u8) -> Self {
        match v & 0x0F {
            0x0 => Self::Reserved,
            0x1 => Self::SameEs,
            0x2 => Self::ComponentTagEs,
            v => Self::Unallocated(v),
        }
    }

    #[must_use]
    /// Encode to the wire value.  Inverse of `from_u8` / `from_u16`.
    pub const fn to_u8(self) -> u8 {
        match self {
            Self::Reserved => 0x0,
            Self::SameEs => 0x1,
            Self::ComponentTagEs => 0x2,
            Self::Unallocated(v) => v,
        }
    }

    #[must_use]
    /// Human-readable spec display name.
    pub fn name(self) -> &'static str {
        match self {
            Self::Reserved => "Reserved",
            Self::SameEs => "Same ES",
            Self::ComponentTagEs => "Component Tag ES",
            Self::Unallocated(_) => "Unallocated",
        }
    }
}
broadcast_common::impl_spec_display!(ReferenceType, Unallocated);

/// table_id(1) + section_length hi/lo(2) + extension(2) + version/cni(1)
/// + section_number(1) + last_section_number(1) = 8-byte common header.
const HEADER_LEN: usize = 8;
/// `section_length` counts from just after the field (byte 3) to end of section.
const SECTION_LENGTH_PREFIX: usize = 3;
use super::CRC_LEN;

/// Authentication-message fixed body bytes after the common header, before the
/// hash loop: section_hash_algorithm_identifier(1) + section_hash_length(1)
/// + signature_algorithm_identifier(1) + reserved(4)|section_hashes_loop_length(12)(2).
const AUTH_FIXED_PREFIX: usize = 5;

/// The 12-bit `section_hashes_loop_length` / `certificate_length` maximum
/// (ETSI TS 103 192 §9.4.3/§9.4.4).
const LOOP_LEN_MAX: usize = 0x0FFF;
/// The 4-bit `reference_length` / `certificate_count` maximum.
const NIBBLE_MAX: usize = 0x0F;
/// The four `reserved = '1111'` bits preceding a 4-bit length/count field.
/// The four `reserved = '1111'` bits preceding the 12-bit loop-length field
/// (low nibble of the field's first wire byte).
const LOOP_LEN_HI_MASK: u8 = 0x0F;

/// One entry in the authentication message section-hash loop (§9.4.3 Table 42).
///
/// Each entry pairs a reference (locating the payload section the hash covers)
/// with the truncated hash itself. `reference` length is the 4-bit
/// `reference_length`; `hash` length is the section-wide `section_hash_length`.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
pub struct SectionHashEntry<'a> {
    /// 4-bit `reference_type` (§9.4.3 Table 45): 1 = same ES, 2 = component_tag ES.
    pub reference_type: ReferenceType,
    /// `reference_byte` field — its semantics depend on `reference_type`.
    pub reference: &'a [u8],
    /// The (possibly truncated) section hash, `section_hash_length` bytes.
    pub hash: &'a [u8],
}

/// Discriminated protection-message body, selected by `table_id_extension`.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[non_exhaustive]
pub enum ProtectionMessageBody<'a> {
    /// Authentication message (extension `0x0000..=0x00FF`; §9.4.3 Table 42).
    AuthenticationMessage {
        /// `section_hash_algorithm_identifier` (§9.4.3 Table 43): 0 = SHA-256, 1 = SHA-512.
        section_hash_algorithm_identifier: u8,
        /// `section_hash_length` — bytes per hash in each loop entry.
        section_hash_length: u8,
        /// `signature_algorithm_identifier` (§9.4.3 Table 44).
        signature_algorithm_identifier: u8,
        /// Section-hash loop entries in wire order.
        hashes: Vec<SectionHashEntry<'a>>,
        /// `extension_byte` payload (length-prefixed by `extension_bytes_length`).
        extension_bytes: &'a [u8],
        /// `signature_key_identifier_byte` payload (length-prefixed).
        signature_key_identifier: &'a [u8],
        /// Detached signature — runs from after the key identifier to the CRC.
        signature: &'a [u8],
        /// `reserved(4)` before `section_hashes_loop_length` (`1111`);
        /// preserved from the wire.
        #[cfg_attr(feature = "serde", serde(skip))]
        reserved_section_hashes_loop_length: u8,
    },
    /// Certificate collection message (extension `0x0100`; §9.5.4.9 Table 51).
    CertificateCollection {
        /// DER-encoded DVBCertificate byte runs, one slice per `certificate_length` loop entry.
        certificates: Vec<&'a [u8]>,
        /// `reserved(4)` before `certificate_count` (`1111`); preserved from
        /// the wire.
        #[cfg_attr(feature = "serde", serde(skip))]
        reserved_certificate_count: u8,
        /// `reserved(4)` before each `certificate_length` (`1111`), parallel
        /// to `certificates`; entries missing from the vector default to
        /// all-ones on serialize. Preserved from the wire.
        #[cfg_attr(feature = "serde", serde(skip))]
        reserved_certificate_lengths: Vec<u8>,
    },
    /// Reserved extension (`0x0101..=0xFFFF`) — body preserved verbatim.
    Raw(&'a [u8]),
}

impl<'a> ProtectionMessageBody<'a> {
    /// A certificate-collection body with the spec `reserved` fill.
    #[must_use]
    pub fn certificate_collection(certificates: Vec<&'a [u8]>) -> Self {
        Self::CertificateCollection {
            certificates,
            reserved_certificate_count: super::RESERVED_4,
            reserved_certificate_lengths: Vec::new(),
        }
    }
}

/// Protection message section (TS 102 809 §9; Tables 42 / 51).
///
/// Typed fields cover the common section header; [`ProtectionMessageSection::body`]
/// carries the typed, discriminated body.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
#[non_exhaustive]
pub struct ProtectionMessageSection<'a> {
    /// `table_id_extension` — `authentication_group_id` for authentication
    /// messages, `trust_message_id` (0x0100) for certificate collections.
    pub table_id_extension: u16,
    /// 5-bit version_number.
    pub version_number: u8,
    /// current_next_indicator bit (spec mandates 1).
    pub current_next_indicator: bool,
    /// section_number.
    pub section_number: u8,
    /// last_section_number.
    pub last_section_number: u8,
    /// Discriminated body, selected by `table_id_extension`.
    pub body: ProtectionMessageBody<'a>,
    /// Header bit fields (`reserved_future_use`, `reserved(2)` x2; default
    /// [`SectionBits::dvb`](super::SectionBits::dvb)).
    #[cfg_attr(feature = "serde", serde(skip))]
    pub bits: super::SectionBits,
}

impl<'a> ProtectionMessageSection<'a> {
    /// Construct a protection message section with the spec `reserved` fill.
    #[must_use]
    pub fn new(
        table_id_extension: u16,
        version_number: u8,
        current_next_indicator: bool,
        section_number: u8,
        last_section_number: u8,
        body: ProtectionMessageBody<'a>,
    ) -> Self {
        Self {
            table_id_extension,
            version_number,
            current_next_indicator,
            section_number,
            last_section_number,
            body,
            bits: super::SectionBits::dvb(),
        }
    }
}

impl<'a> Parse<'a> for ProtectionMessageSection<'a> {
    type Error = crate::error::Error;
    fn parse(bytes: &'a [u8]) -> Result<Self> {
        let min_len = HEADER_LEN + CRC_LEN;
        if bytes.len() < min_len {
            return Err(Error::BufferTooShort {
                need: min_len,
                have: bytes.len(),
                what: "ProtectionMessageSection",
            });
        }
        if bytes[0] != TABLE_ID {
            return Err(Error::UnexpectedTableId {
                table_id: bytes[0],
                what: "ProtectionMessageSection",
                expected: &[TABLE_ID],
            });
        }
        let section_length = super::section_length_of(bytes);
        let total = super::check_section_length(
            bytes.len(),
            SECTION_LENGTH_PREFIX,
            section_length,
            HEADER_LEN + CRC_LEN,
        )?;

        let table_id_extension = crate::wire::be_u16(bytes, 3, "protection_message")?;
        let version_number = super::version_number_of(bytes[5]);
        let current_next_indicator = super::current_next_of(bytes[5]);
        let section_number = bytes[6];
        let last_section_number = bytes[7];

        let body_bytes = &bytes[HEADER_LEN..total - CRC_LEN];
        let body = match table_id_extension {
            AUTH_EXTENSION_FIRST..=AUTH_EXTENSION_LAST => parse_authentication_message(body_bytes)?,
            CERTIFICATE_COLLECTION_EXTENSION => parse_certificate_collection(body_bytes)?,
            _ => ProtectionMessageBody::Raw(body_bytes),
        };

        Ok(ProtectionMessageSection {
            table_id_extension,
            version_number,
            current_next_indicator,
            section_number,
            last_section_number,
            body,
            bits: super::SectionBits::parse(bytes[1], Some(bytes[5])),
        })
    }
}

/// Parse the authentication-message body (§9.4.3 Table 42, PDF pp. 70-71).
fn parse_authentication_message(body: &[u8]) -> Result<ProtectionMessageBody<'_>> {
    if body.len() < AUTH_FIXED_PREFIX {
        return Err(Error::BufferTooShort {
            need: AUTH_FIXED_PREFIX,
            have: body.len(),
            what: "ProtectionMessageSection::AuthenticationMessage",
        });
    }
    let section_hash_algorithm_identifier = body[0];
    let section_hash_length = body[1];
    let signature_algorithm_identifier = body[2];
    // bytes[3] high nibble = reserved; section_hashes_loop_length is 12 bits.
    let section_hashes_loop_length = super::desc_loop_len_of(body[3], body[4]);

    let loop_start = AUTH_FIXED_PREFIX;
    let loop_end = loop_start + section_hashes_loop_length;
    if loop_end > body.len() {
        return Err(Error::SectionLengthOverflow {
            declared: section_hashes_loop_length,
            available: body.len() - loop_start,
        });
    }

    let hash_len = section_hash_length as usize;
    let mut hashes = Vec::new();
    let mut pos = loop_start;
    while pos < loop_end {
        // reference_type(4) | reference_length(4)
        let lead = body[pos];
        let reference_type = ReferenceType::from_u8(lead >> 4);
        let reference_length = (lead & LOOP_LEN_HI_MASK) as usize;
        let ref_start = pos + 1;
        let ref_end = ref_start + reference_length;
        let hash_end = ref_end + hash_len;
        if hash_end > loop_end {
            return Err(Error::SectionLengthOverflow {
                declared: reference_length + hash_len,
                available: loop_end - ref_start,
            });
        }
        hashes.push(SectionHashEntry {
            reference_type,
            reference: &body[ref_start..ref_end],
            hash: &body[ref_end..hash_end],
        });
        pos = hash_end;
    }

    // extension_bytes_length(8) + extension bytes (§9.4.3 Table 42 tail).
    if loop_end >= body.len() {
        return Err(Error::BufferTooShort {
            need: loop_end + 1,
            have: body.len(),
            what: "ProtectionMessageSection::extension_bytes_length",
        });
    }
    let extension_bytes_length = body[loop_end] as usize;
    let ext_start = loop_end + 1;
    let ext_end = ext_start + extension_bytes_length;
    if ext_end > body.len() {
        return Err(Error::SectionLengthOverflow {
            declared: extension_bytes_length,
            available: body.len() - ext_start,
        });
    }

    // signature_key_identifier_length(8) + key id bytes (Table 43 spillover, PDF p. 71).
    if ext_end >= body.len() {
        return Err(Error::BufferTooShort {
            need: ext_end + 1,
            have: body.len(),
            what: "ProtectionMessageSection::signature_key_identifier_length",
        });
    }
    let key_id_length = body[ext_end] as usize;
    let key_start = ext_end + 1;
    let key_end = key_start + key_id_length;
    if key_end > body.len() {
        return Err(Error::SectionLengthOverflow {
            declared: key_id_length,
            available: body.len() - key_start,
        });
    }

    // signature_byte loop runs to the end of the body (i.e. up to the CRC_32).
    let signature = &body[key_end..];

    Ok(ProtectionMessageBody::AuthenticationMessage {
        section_hash_algorithm_identifier,
        section_hash_length,
        signature_algorithm_identifier,
        hashes,
        extension_bytes: &body[ext_start..ext_end],
        signature_key_identifier: &body[key_start..key_end],
        signature,
        reserved_section_hashes_loop_length: super::len_reserved_of(body[3]),
    })
}

/// Parse the certificate-collection body (§9.5.4.9 Table 51, PDF p. 91).
fn parse_certificate_collection(body: &[u8]) -> Result<ProtectionMessageBody<'_>> {
    if body.is_empty() {
        return Err(Error::BufferTooShort {
            need: 1,
            have: 0,
            what: "ProtectionMessageSection::CertificateCollection",
        });
    }
    // byte 0: reserved(4) | certificate_count(4)
    let certificate_count = (body[0] & LOOP_LEN_HI_MASK) as usize;
    let mut certificates = Vec::with_capacity(certificate_count);
    let mut reserved_certificate_lengths = Vec::with_capacity(certificate_count);
    let mut pos = 1;
    for _ in 0..certificate_count {
        if pos + 2 > body.len() {
            return Err(Error::BufferTooShort {
                need: pos + 2,
                have: body.len(),
                what: "ProtectionMessageSection::certificate_length",
            });
        }
        // reserved(4) | certificate_length(12)
        let certificate_length = super::desc_loop_len_of(body[pos], body[pos + 1]);
        let cert_start = pos + 2;
        let cert_end = cert_start + certificate_length;
        if cert_end > body.len() {
            return Err(Error::SectionLengthOverflow {
                declared: certificate_length,
                available: body.len() - cert_start,
            });
        }
        reserved_certificate_lengths.push(super::len_reserved_of(body[pos]));
        certificates.push(&body[cert_start..cert_end]);
        pos = cert_end;
    }
    // Reject trailing bytes after the last certificate (r02-W18): silently
    // dropping them would break the parse -> serialize byte-identity
    // invariant.
    if pos != body.len() {
        return Err(Error::BufferTooShort {
            need: body.len() - pos,
            have: 0,
            what: "ProtectionMessageSection::CertificateCollection trailing bytes",
        });
    }
    Ok(ProtectionMessageBody::CertificateCollection {
        certificates,
        reserved_certificate_count: super::len_reserved_of(body[0]),
        reserved_certificate_lengths,
    })
}

impl ProtectionMessageBody<'_> {
    /// Serialized length of the body (excluding common header and CRC).
    fn body_len(&self) -> usize {
        match self {
            ProtectionMessageBody::AuthenticationMessage {
                hashes,
                extension_bytes,
                signature_key_identifier,
                signature,
                ..
            } => {
                let loop_bytes: usize = hashes
                    .iter()
                    .map(|h| 1 + h.reference.len() + h.hash.len())
                    .sum();
                AUTH_FIXED_PREFIX
                    + loop_bytes
                    + 1
                    + extension_bytes.len()
                    + 1
                    + signature_key_identifier.len()
                    + signature.len()
            }
            ProtectionMessageBody::CertificateCollection { certificates, .. } => {
                1 + certificates.iter().map(|c| 2 + c.len()).sum::<usize>()
            }
            ProtectionMessageBody::Raw(raw) => raw.len(),
        }
    }

    /// Write the body into `buf`, returning the number of bytes written.
    fn write_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            ProtectionMessageBody::AuthenticationMessage {
                section_hash_algorithm_identifier,
                section_hash_length,
                signature_algorithm_identifier,
                hashes,
                extension_bytes,
                signature_key_identifier,
                signature,
                reserved_section_hashes_loop_length,
            } => {
                buf[0] = *section_hash_algorithm_identifier;
                buf[1] = *section_hash_length;
                buf[2] = *signature_algorithm_identifier;
                let loop_bytes: usize = hashes
                    .iter()
                    .map(|h| 1 + h.reference.len() + h.hash.len())
                    .sum();
                if loop_bytes > LOOP_LEN_MAX {
                    return Err(Error::SectionLengthOverflow {
                        declared: loop_bytes,
                        available: LOOP_LEN_MAX,
                    });
                }
                if extension_bytes.len() > u8::MAX as usize {
                    return Err(Error::SectionLengthOverflow {
                        declared: extension_bytes.len(),
                        available: u8::MAX as usize,
                    });
                }
                if signature_key_identifier.len() > u8::MAX as usize {
                    return Err(Error::SectionLengthOverflow {
                        declared: signature_key_identifier.len(),
                        available: u8::MAX as usize,
                    });
                }
                // reserved(4) emitted 1s | section_hashes_loop_length(12).
                super::write_desc_loop_len_r(
                    &mut buf[3..5],
                    loop_bytes,
                    *reserved_section_hashes_loop_length,
                )?;
                let mut pos = AUTH_FIXED_PREFIX;
                for h in hashes {
                    if h.reference.len() > NIBBLE_MAX {
                        return Err(Error::SectionLengthOverflow {
                            declared: h.reference.len(),
                            available: NIBBLE_MAX,
                        });
                    }
                    // Every hash entry is exactly `section_hash_length`
                    // bytes on the wire (the parser slices it that way
                    // unconditionally) — a different length here would
                    // misframe every later entry (r02-W18).
                    if h.hash.len() != *section_hash_length as usize {
                        return Err(Error::ValueOutOfRange {
                            field: "Hash.hash",
                            reason: "length must equal section_hash_length",
                        });
                    }
                    buf[pos] = (broadcast_common::len::fit_mask(
                        h.reference_type.to_u8(),
                        0x0F,
                        "reference_type",
                    )? << 4)
                        | broadcast_common::len::fit_bits(
                            h.reference.len() as u64,
                            4,
                            "h.reference",
                        )? as u8;
                    pos += 1;
                    buf[pos..pos + h.reference.len()].copy_from_slice(h.reference);
                    pos += h.reference.len();
                    buf[pos..pos + h.hash.len()].copy_from_slice(h.hash);
                    pos += h.hash.len();
                }
                buf[pos] = broadcast_common::len::fit_u8(extension_bytes.len(), "extension_bytes")?;
                pos += 1;
                buf[pos..pos + extension_bytes.len()].copy_from_slice(extension_bytes);
                pos += extension_bytes.len();
                buf[pos] = broadcast_common::len::fit_u8(
                    signature_key_identifier.len(),
                    "signature_key_identifier",
                )?;
                pos += 1;
                buf[pos..pos + signature_key_identifier.len()]
                    .copy_from_slice(signature_key_identifier);
                pos += signature_key_identifier.len();
                buf[pos..pos + signature.len()].copy_from_slice(signature);
                pos += signature.len();
                Ok(pos)
            }
            ProtectionMessageBody::CertificateCollection {
                certificates,
                reserved_certificate_count,
                reserved_certificate_lengths,
            } => {
                if certificates.len() > NIBBLE_MAX {
                    return Err(Error::SectionLengthOverflow {
                        declared: certificates.len(),
                        available: NIBBLE_MAX,
                    });
                }
                // reserved(4) emitted 1s | certificate_count(4).
                buf[0] = (broadcast_common::len::fit_mask(
                    *reserved_certificate_count,
                    super::RESERVED_4,
                    "reserved(4)",
                )? << 4)
                    | broadcast_common::len::fit_bits(certificates.len() as u64, 4, "certificates")?
                        as u8;
                let mut pos = 1;
                for (i, c) in certificates.iter().enumerate() {
                    if c.len() > LOOP_LEN_MAX {
                        return Err(Error::SectionLengthOverflow {
                            declared: c.len(),
                            available: LOOP_LEN_MAX,
                        });
                    }
                    // reserved(4) emitted 1s | certificate_length(12).
                    super::write_desc_loop_len_r(
                        &mut buf[pos..pos + 2],
                        c.len(),
                        reserved_certificate_lengths
                            .get(i)
                            .copied()
                            .unwrap_or(super::RESERVED_4),
                    )?;
                    pos += 2;
                    buf[pos..pos + c.len()].copy_from_slice(c);
                    pos += c.len();
                }
                Ok(pos)
            }
            ProtectionMessageBody::Raw(raw) => {
                buf[..raw.len()].copy_from_slice(raw);
                Ok(raw.len())
            }
        }
    }
}

impl Serialize for ProtectionMessageSection<'_> {
    type Error = crate::error::Error;
    fn serialized_len(&self) -> usize {
        HEADER_LEN + self.body.body_len() + CRC_LEN
    }
    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        let len = self.serialized_len();
        if buf.len() < len {
            return Err(Error::OutputBufferTooSmall {
                need: len,
                have: buf.len(),
            });
        }
        buf[0] = TABLE_ID;
        buf[1] = self.bits.b1()?;
        super::write_section_length(buf, len - SECTION_LENGTH_PREFIX)?;
        buf[3..5].copy_from_slice(&self.table_id_extension.to_be_bytes());
        // reserved(2)=11, version_number(5), current_next_indicator(1).
        buf[5] = self
            .bits
            .b5(self.version_number, self.current_next_indicator)?;
        buf[6] = self.section_number;
        buf[7] = self.last_section_number;
        let body_written = self.body.write_into(&mut buf[HEADER_LEN..])?;
        let body_end = HEADER_LEN + body_written;
        super::write_crc(buf, body_end);
        Ok(len)
    }
}
impl<'a> crate::traits::TableDef<'a> for ProtectionMessageSection<'a> {
    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
    const NAME: &'static str = "PROTECTION_MESSAGE";
}

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

    /// Wrap a body in the 8-byte common header + placeholder CRC.
    fn build_section(extension: u16, version: u8, body: &[u8]) -> Vec<u8> {
        let section_length = (HEADER_LEN - SECTION_LENGTH_PREFIX + body.len() + CRC_LEN) as u16;
        let mut v = vec![
            TABLE_ID,
            super::super::SECTION_B1_FLAGS_DVB | ((section_length >> 8) as u8 & 0x0F),
            (section_length & 0xFF) as u8,
            (extension >> 8) as u8,
            (extension & 0xFF) as u8,
            0xC0 | (version << 1) | 0x01,
            0x00,
            0x00,
        ];
        v.extend_from_slice(body);
        v.extend_from_slice(&[0, 0, 0, 0]);
        v
    }

    /// Build an authentication-message body: one hash entry + ext + key id + signature.
    fn auth_body() -> Vec<u8> {
        let reference = [0x01]; // reference_type 1 => table_id of payload section
        let hash = [0xAA, 0xBB, 0xCC, 0xDD]; // section_hash_length = 4
        let mut hashes_loop = vec![(1u8 << 4) | (reference.len() as u8)]; // reference_type 1, length 1
        hashes_loop.extend_from_slice(&reference);
        hashes_loop.extend_from_slice(&hash);
        let loop_len = hashes_loop.len();

        let mut b = vec![
            0x00,                                  // section_hash_algorithm_identifier = SHA-256
            hash.len() as u8,                      // section_hash_length = 4
            0x01,                                  // signature_algorithm_identifier = ed25519
            0xF0 | ((loop_len >> 8) as u8 & 0x0F), // reserved | loop_length hi
            (loop_len & 0xFF) as u8,               // loop_length lo
        ];
        b.extend_from_slice(&hashes_loop);
        // extension_bytes_length + bytes
        b.push(2);
        b.extend_from_slice(&[0xDE, 0xAD]);
        // signature_key_identifier_length + bytes
        b.push(3);
        b.extend_from_slice(&[0x11, 0x22, 0x33]);
        // signature (runs to CRC)
        b.extend_from_slice(&[0x90, 0x91, 0x92, 0x93, 0x94, 0x95]);
        b
    }

    /// Build a certificate-collection body with two certificate slices.
    fn cert_body() -> Vec<u8> {
        let c0: &[u8] = &[0x30, 0x82, 0x01, 0x02];
        let c1: &[u8] = &[0xAB, 0xCD];
        let mut b = vec![0xF0 | 0x02]; // reserved | certificate_count = 2
        b.push(0xF0 | ((c0.len() >> 8) as u8 & 0x0F));
        b.push((c0.len() & 0xFF) as u8);
        b.extend_from_slice(c0);
        b.push(0xF0 | ((c1.len() >> 8) as u8 & 0x0F));
        b.push((c1.len() & 0xFF) as u8);
        b.extend_from_slice(c1);
        b
    }

    #[test]
    fn parse_authentication_message() {
        let bytes = build_section(0x0042, 5, &auth_body());
        let sec = ProtectionMessageSection::parse(&bytes).unwrap();
        assert_eq!(sec.table_id_extension, 0x0042);
        assert_eq!(sec.version_number, 5);
        assert!(sec.current_next_indicator);
        match sec.body {
            ProtectionMessageBody::AuthenticationMessage {
                section_hash_algorithm_identifier,
                section_hash_length,
                signature_algorithm_identifier,
                hashes,
                extension_bytes,
                signature_key_identifier,
                signature,
                ..
            } => {
                assert_eq!(section_hash_algorithm_identifier, 0x00);
                assert_eq!(section_hash_length, 4);
                assert_eq!(signature_algorithm_identifier, 0x01);
                assert_eq!(hashes.len(), 1);
                assert_eq!(hashes[0].reference_type, ReferenceType::SameEs);
                assert_eq!(hashes[0].reference, &[0x01]);
                assert_eq!(hashes[0].hash, &[0xAA, 0xBB, 0xCC, 0xDD]);
                assert_eq!(extension_bytes, &[0xDE, 0xAD]);
                assert_eq!(signature_key_identifier, &[0x11, 0x22, 0x33]);
                assert_eq!(signature, &[0x90, 0x91, 0x92, 0x93, 0x94, 0x95]);
            }
            other => panic!("expected AuthenticationMessage, got {other:?}"),
        }
    }

    #[test]
    fn parse_certificate_collection() {
        let bytes = build_section(CERTIFICATE_COLLECTION_EXTENSION, 0, &cert_body());
        let sec = ProtectionMessageSection::parse(&bytes).unwrap();
        assert_eq!(sec.table_id_extension, 0x0100);
        match sec.body {
            ProtectionMessageBody::CertificateCollection { certificates, .. } => {
                assert_eq!(certificates.len(), 2);
                assert_eq!(certificates[0], &[0x30, 0x82, 0x01, 0x02]);
                assert_eq!(certificates[1], &[0xAB, 0xCD]);
            }
            other => panic!("expected CertificateCollection, got {other:?}"),
        }
    }

    #[test]
    fn reserved_extension_kept_raw() {
        let raw = [0x01, 0x02, 0x03, 0x04];
        let bytes = build_section(0x0200, 0, &raw);
        let sec = ProtectionMessageSection::parse(&bytes).unwrap();
        assert!(matches!(sec.body, ProtectionMessageBody::Raw(b) if b == raw));
    }

    #[test]
    fn parse_rejects_wrong_tag() {
        let mut bytes = build_section(0x0000, 0, &auth_body());
        bytes[0] = 0x4D;
        assert!(matches!(
            ProtectionMessageSection::parse(&bytes).unwrap_err(),
            Error::UnexpectedTableId { table_id: 0x4D, .. }
        ));
    }

    #[test]
    fn rejects_short_buffer() {
        assert!(matches!(
            ProtectionMessageSection::parse(&[0x7B, 0xB0]).unwrap_err(),
            Error::BufferTooShort {
                what: "ProtectionMessageSection",
                ..
            }
        ));
    }

    #[test]
    fn auth_loop_overflow_rejected() {
        let mut body = vec![0x00, 0x04, 0x01, 0xF0, 0xFF];
        body.extend_from_slice(&[0x00]);
        let bytes = build_section(0x0000, 0, &body);
        assert!(matches!(
            ProtectionMessageSection::parse(&bytes).unwrap_err(),
            Error::SectionLengthOverflow { .. }
        ));
    }

    #[test]
    fn cert_length_overflow_rejected() {
        let body = vec![0xF0 | 0x01, 0x00, 0x10, 0x01];
        let bytes = build_section(CERTIFICATE_COLLECTION_EXTENSION, 0, &body);
        assert!(matches!(
            ProtectionMessageSection::parse(&bytes).unwrap_err(),
            Error::SectionLengthOverflow { .. }
        ));
    }

    #[test]
    fn round_trip_authentication_message() {
        let bytes = build_section(0x0042, 7, &auth_body());
        let sec = ProtectionMessageSection::parse(&bytes).unwrap();
        let mut buf = vec![0u8; sec.serialized_len()];
        sec.serialize_into(&mut buf).unwrap();
        let re = ProtectionMessageSection::parse(&buf).unwrap();
        assert_eq!(sec, re);
    }

    #[test]
    fn round_trip_certificate_collection() {
        let bytes = build_section(CERTIFICATE_COLLECTION_EXTENSION, 3, &cert_body());
        let sec = ProtectionMessageSection::parse(&bytes).unwrap();
        let mut buf = vec![0u8; sec.serialized_len()];
        sec.serialize_into(&mut buf).unwrap();
        let re = ProtectionMessageSection::parse(&buf).unwrap();
        assert_eq!(sec, re);
    }

    /// Regression for r02-W18: a `Hash.hash` whose length disagrees with
    /// `section_hash_length` must be rejected, not written verbatim (which
    /// would misframe every later hash entry on re-parse).
    #[test]
    fn serialize_rejects_hash_length_disagreeing_with_section_hash_length() {
        let bytes = build_section(0x0042, 5, &auth_body());
        let mut sec = ProtectionMessageSection::parse(&bytes).unwrap();
        match &mut sec.body {
            ProtectionMessageBody::AuthenticationMessage { hashes, .. } => {
                hashes[0].hash = &[0xAA, 0xBB]; // section_hash_length is 4
            }
            other => panic!("expected AuthenticationMessage, got {other:?}"),
        }
        let mut buf = vec![0u8; sec.serialized_len()];
        assert!(matches!(
            sec.serialize_into(&mut buf).unwrap_err(),
            Error::ValueOutOfRange { .. }
        ));
    }

    /// Regression for r02-W18: bytes left over after the last certificate in
    /// a `CertificateCollection` body must be rejected, not silently
    /// dropped.
    #[test]
    fn parse_certificate_collection_rejects_trailing_bytes() {
        let mut body = cert_body();
        body.push(0xFF); // one byte past the last certificate
        let bytes = build_section(CERTIFICATE_COLLECTION_EXTENSION, 0, &body);
        assert!(matches!(
            ProtectionMessageSection::parse(&bytes).unwrap_err(),
            Error::BufferTooShort { .. }
        ));
    }

    #[test]
    fn round_trip_raw_reserved() {
        let bytes = build_section(0xABCD, 1, &[0xDE, 0xAD, 0xBE, 0xEF]);
        let sec = ProtectionMessageSection::parse(&bytes).unwrap();
        let mut buf = vec![0u8; sec.serialized_len()];
        sec.serialize_into(&mut buf).unwrap();
        let re = ProtectionMessageSection::parse(&buf).unwrap();
        assert_eq!(sec, re);
    }

    #[test]
    fn table_trait_constants() {
        assert_eq!(TABLE_ID, 0x7B);
    }

    #[test]
    #[cfg(feature = "serde")]
    fn serde_json_round_trip() {
        let bytes = build_section(0x0042, 5, &auth_body());
        let sec = ProtectionMessageSection::parse(&bytes).unwrap();
        let j = serde_json::to_string(&sec).unwrap();
        let reparsed = ProtectionMessageSection::parse(&bytes).unwrap();
        assert_eq!(serde_json::to_string(&reparsed).unwrap(), j);
        assert!(j.contains("\"signature_algorithm_identifier\":1"));
    }

    #[test]
    fn parse_rejects_zero_section_length() {
        let mut buf = vec![0u8; 64];
        buf[0] = TABLE_ID;
        buf[1] = 0xF0;
        buf[2] = 0x00;
        for b in &mut buf[3..] {
            *b = 0xFF;
        }
        assert!(matches!(
            ProtectionMessageSection::parse(&buf).unwrap_err(),
            Error::SectionLengthOverflow { .. }
        ));
    }

    /// section_length is 12 bits (max 4095 = HEADER_LEN(8) -
    /// SECTION_LENGTH_PREFIX(3) + body_len + CRC_LEN(4), so 4086 is the
    /// largest Raw body that fits).
    #[test]
    fn serialize_rejects_raw_body_exceeding_section_length() {
        let raw = vec![0xAAu8; 4087];
        let sec =
            ProtectionMessageSection::new(0x0200, 0, true, 0, 0, ProtectionMessageBody::Raw(&raw));
        let mut buf = vec![0u8; sec.serialized_len()];
        assert!(matches!(
            sec.serialize_into(&mut buf).unwrap_err(),
            Error::FieldOverflow(_)
        ));
    }

    #[test]
    fn serialize_accepts_raw_body_at_section_length_boundary() {
        let raw = vec![0xAAu8; 4086];
        let sec =
            ProtectionMessageSection::new(0x0200, 0, true, 0, 0, ProtectionMessageBody::Raw(&raw));
        let mut buf = vec![0u8; sec.serialized_len()];
        sec.serialize_into(&mut buf).expect("boundary fits");
        let reparsed = ProtectionMessageSection::parse(&buf).expect("reparse");
        assert_eq!(sec, reparsed);
    }

    #[test]
    fn reference_type_full_range_round_trip() {
        for v in 0u8..=0x0F {
            let rt = ReferenceType::from_u8(v);
            assert_eq!(
                rt.to_u8(),
                v,
                "ReferenceType round-trip failed for {v:#04x}"
            );
        }
    }
}