domain 0.12.0

//! DNS records.

use core::{borrow::Borrow, cmp::Ordering, fmt, ops::Deref};

use crate::utils::dst::UnsizedCopy;

use super::build::{BuildInMessage, NameCompressor};
use super::parse::{ParseMessageBytes, SplitMessageBytes};
use super::wire::{
    AsBytes, BuildBytes, ParseBytes, ParseBytesZC, ParseError, SizePrefixed,
    SplitBytes, SplitBytesZC, TruncationError, U16, U32,
};

//----------- Record ---------------------------------------------------------

/// A DNS record.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct Record<N, D> {
    /// The name of the record.
    pub rname: N,

    /// The type of the record.
    pub rtype: RType,

    /// The class of the record.
    pub rclass: RClass,

    /// How long the record is reliable for.
    pub ttl: TTL,

    /// Unparsed record data.
    pub rdata: D,
}

//--- Construction

impl<N, D> Record<N, D> {
    /// Construct a new [`Record`].
    pub fn new(
        rname: N,
        rtype: RType,
        rclass: RClass,
        ttl: TTL,
        rdata: D,
    ) -> Self {
        Self {
            rname,
            rtype,
            rclass,
            ttl,
            rdata,
        }
    }
}

//--- Transformation

impl<N, D> Record<N, D> {
    /// Transform this type's generic parameters.
    pub fn transform<NN, ND>(
        self,
        name_map: impl FnOnce(N) -> NN,
        data_map: impl FnOnce(D) -> ND,
    ) -> Record<NN, ND> {
        Record {
            rname: (name_map)(self.rname),
            rtype: self.rtype,
            rclass: self.rclass,
            ttl: self.ttl,
            rdata: (data_map)(self.rdata),
        }
    }

    /// Transform this type's generic parameters by reference.
    pub fn transform_ref<'a, NN, ND>(
        &'a self,
        name_map: impl FnOnce(&'a N) -> NN,
        data_map: impl FnOnce(&'a D) -> ND,
    ) -> Record<NN, ND> {
        Record {
            rname: (name_map)(&self.rname),
            rtype: self.rtype,
            rclass: self.rclass,
            ttl: self.ttl,
            rdata: (data_map)(&self.rdata),
        }
    }
}

//--- Parsing from DNS messages

impl<'a, N, D> SplitMessageBytes<'a> for Record<N, D>
where
    N: SplitMessageBytes<'a>,
    D: ParseRecordData<'a>,
{
    fn split_message_bytes(
        contents: &'a [u8],
        start: usize,
    ) -> Result<(Self, usize), ParseError> {
        let (rname, rest) = N::split_message_bytes(contents, start)?;
        let (&rtype, rest) = <&RType>::split_message_bytes(contents, rest)?;
        let (&rclass, rest) = <&RClass>::split_message_bytes(contents, rest)?;
        let (&ttl, rest) = <&TTL>::split_message_bytes(contents, rest)?;
        let rdata_start = rest;
        let (_, rest) =
            <&SizePrefixed<U16, [u8]>>::split_message_bytes(contents, rest)?;
        let rdata =
            D::parse_record_data(&contents[..rest], rdata_start + 2, rtype)?;

        Ok((Self::new(rname, rtype, rclass, ttl, rdata), rest))
    }
}

impl<'a, N, D> ParseMessageBytes<'a> for Record<N, D>
where
    N: SplitMessageBytes<'a>,
    D: ParseRecordData<'a>,
{
    fn parse_message_bytes(
        contents: &'a [u8],
        start: usize,
    ) -> Result<Self, ParseError> {
        match Self::split_message_bytes(contents, start) {
            Ok((this, rest)) if rest == contents.len() => Ok(this),
            _ => Err(ParseError),
        }
    }
}

//--- Building into DNS messages

impl<N, D> BuildInMessage for Record<N, D>
where
    N: BuildInMessage,
    D: BuildInMessage,
{
    fn build_in_message(
        &self,
        contents: &mut [u8],
        mut start: usize,
        compressor: &mut NameCompressor,
    ) -> Result<usize, TruncationError> {
        start = self.rname.build_in_message(contents, start, compressor)?;
        // For more efficiency, copy the bytes manually.
        let end = start + 8;
        let bytes = contents.get_mut(start..end).ok_or(TruncationError)?;
        bytes[0..2].copy_from_slice(self.rtype.as_bytes());
        bytes[2..4].copy_from_slice(self.rclass.as_bytes());
        bytes[4..8].copy_from_slice(self.ttl.as_bytes());
        start = end;
        // Build the record data with a 16-bit size prefix.
        start = SizePrefixed::<U16, _>::new(&self.rdata)
            .build_in_message(contents, start, compressor)?;
        Ok(start)
    }
}

//--- Parsing from bytes

impl<'a, N, D> SplitBytes<'a> for Record<N, D>
where
    N: SplitBytes<'a>,
    D: ParseRecordDataBytes<'a>,
{
    fn split_bytes(bytes: &'a [u8]) -> Result<(Self, &'a [u8]), ParseError> {
        let (rname, rest) = N::split_bytes(bytes)?;
        let (rtype, rest) = RType::split_bytes(rest)?;
        let (rclass, rest) = RClass::split_bytes(rest)?;
        let (ttl, rest) = TTL::split_bytes(rest)?;
        let (rdata, rest) = <&SizePrefixed<U16, [u8]>>::split_bytes(rest)?;
        let rdata = D::parse_record_data_bytes(rdata, rtype)?;

        Ok((Self::new(rname, rtype, rclass, ttl, rdata), rest))
    }
}

impl<'a, N, D> ParseBytes<'a> for Record<N, D>
where
    N: SplitBytes<'a>,
    D: ParseRecordDataBytes<'a>,
{
    fn parse_bytes(bytes: &'a [u8]) -> Result<Self, ParseError> {
        match Self::split_bytes(bytes) {
            Ok((this, &[])) => Ok(this),
            _ => Err(ParseError),
        }
    }
}

//--- Building into byte sequences

impl<N, D> BuildBytes for Record<N, D>
where
    N: BuildBytes,
    D: BuildBytes,
{
    fn build_bytes<'b>(
        &self,
        mut bytes: &'b mut [u8],
    ) -> Result<&'b mut [u8], TruncationError> {
        bytes = self.rname.build_bytes(bytes)?;
        bytes = self.rtype.as_bytes().build_bytes(bytes)?;
        bytes = self.rclass.as_bytes().build_bytes(bytes)?;
        bytes = self.ttl.as_bytes().build_bytes(bytes)?;
        bytes =
            SizePrefixed::<U16, _>::new(&self.rdata).build_bytes(bytes)?;

        Ok(bytes)
    }

    fn built_bytes_size(&self) -> usize {
        self.rname.built_bytes_size() + 10 + self.rdata.built_bytes_size()
    }
}

//----------- RType ----------------------------------------------------------

/// The type of a record.
#[derive(
    Copy,
    Clone,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
    Hash,
    AsBytes,
    BuildBytes,
    ParseBytes,
    ParseBytesZC,
    SplitBytes,
    SplitBytesZC,
    UnsizedCopy,
)]
#[repr(transparent)]
pub struct RType {
    /// The type code.
    pub code: U16,
}

//--- Associated Constants

impl RType {
    /// Create a new [`RType`].
    const fn new(value: u16) -> Self {
        Self {
            code: U16::new(value),
        }
    }

    /// The type of an [`A`](crate::new::rdata::A) record.
    pub const A: Self = Self::new(1);

    /// The type of an [`Ns`](crate::new::rdata::Ns) record.
    pub const NS: Self = Self::new(2);

    /// The type of a [`CName`](crate::new::rdata::CName) record.
    pub const CNAME: Self = Self::new(5);

    /// The type of an [`Soa`](crate::new::rdata::Soa) record.
    pub const SOA: Self = Self::new(6);

    /// The type of a [`Ptr`](crate::new::rdata::Ptr) record.
    pub const PTR: Self = Self::new(12);

    /// The type of a [`HInfo`](crate::new::rdata::HInfo) record.
    pub const HINFO: Self = Self::new(13);

    /// The type of a [`Mx`](crate::new::rdata::Mx) record.
    pub const MX: Self = Self::new(15);

    /// The type of a [`Txt`](crate::new::rdata::Txt) record.
    pub const TXT: Self = Self::new(16);

    /// The type of an [`Rp`](crate::new::rdata::Rp) record.
    pub const RP: Self = Self::new(17);

    /// The type of an [`Aaaa`](crate::new::rdata::Aaaa) record.
    pub const AAAA: Self = Self::new(28);

    /// The type of a [`DName`](crate::new::rdata::DName) record.
    pub const DNAME: Self = Self::new(39);

    /// The type of an [`Opt`](crate::new::rdata::Opt) record.
    pub const OPT: Self = Self::new(41);

    /// The type of a [`Ds`](crate::new::rdata::Ds) record.
    pub const DS: Self = Self::new(43);

    /// The type of an [`RRSig`](crate::new::rdata::RRSig) record.
    pub const RRSIG: Self = Self::new(46);

    /// The type of an [`NSec`](crate::new::rdata::NSec) record.
    pub const NSEC: Self = Self::new(47);

    /// The type of a [`DNSKey`](crate::new::rdata::DNSKey) record.
    pub const DNSKEY: Self = Self::new(48);

    /// The type of an [`NSec3`](crate::new::rdata::NSec3) record.
    pub const NSEC3: Self = Self::new(50);

    /// The type of an [`NSec3Param`](crate::new::rdata::NSec3Param) record.
    pub const NSEC3PARAM: Self = Self::new(51);

    /// The type of a `Cds` record.
    pub const CDS: Self = Self::new(59);

    /// The type of a `CDNSKey` record.
    pub const CDNSKEY: Self = Self::new(60);

    /// The type of a [`ZoneMD`](crate::new::rdata::ZoneMD) record.
    pub const ZONEMD: Self = Self::new(63);

    /// The type of a `TSig` record.
    pub const TSIG: Self = Self::new(250);
}

//--- Interaction

impl RType {
    /// Whether this type uses lowercased domain names in canonical form.
    ///
    /// As specified by [RFC 4034, section 6.2] (and updated by [RFC 6840,
    /// section 5.1]), the canonical form of the record data of any of the
    /// following types will have its domain names lowercased:
    ///
    /// - [`NS`](RType::NS)
    /// - `MD` (obsolete)
    /// - `MF` (obsolete)
    /// - [`CNAME`](RType::CNAME)
    /// - [`SOA`](RType::SOA)
    /// - `MB`
    /// - `MG`
    /// - `MR`
    /// - [`PTR`](RType::PTR)
    /// - `MINFO`
    /// - [`MX`](RType::MX)
    /// - [`RP`](RType::RP)
    /// - `AFSDB`
    /// - `RT`
    /// - `SIG` (obsolete)
    /// - `PX`
    /// - `NXT` (obsolete)
    /// - `NAPTR`
    /// - `KX`
    /// - `SRV`
    /// - [`DNAME`](RType::DNAME)
    /// - `A6` (obsolete)
    /// - [`RRSIG`](RType::RRSIG)
    ///
    /// [RFC 4034, section 6.2]: https://datatracker.ietf.org/doc/html/rfc4034#section-6.2
    /// [RFC 6840, section 5.1]: https://datatracker.ietf.org/doc/html/rfc6840#section-5.1
    pub const fn uses_lowercase_canonical_form(&self) -> bool {
        // TODO: Update this as more types are added.
        matches!(
            *self,
            Self::NS
                | Self::CNAME
                | Self::SOA
                | Self::PTR
                | Self::MX
                | Self::RP
                | Self::DNAME
                | Self::RRSIG
        )
    }
}

//--- Conversion to and from 'u16'

impl From<u16> for RType {
    fn from(value: u16) -> Self {
        Self {
            code: U16::new(value),
        }
    }
}

impl From<RType> for u16 {
    fn from(value: RType) -> Self {
        value.code.get()
    }
}

//--- Formatting

impl fmt::Debug for RType {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(match *self {
            Self::A => "RType::A",
            Self::NS => "RType::NS",
            Self::CNAME => "RType::CNAME",
            Self::SOA => "RType::SOA",
            Self::PTR => "RType::PTR",
            Self::HINFO => "RType::HINFO",
            Self::MX => "RType::MX",
            Self::TXT => "RType::TXT",
            Self::RP => "RType::RP",
            Self::AAAA => "RType::AAAA",
            Self::DNAME => "RType::DNAME",
            Self::OPT => "RType::OPT",
            Self::DS => "RType::DS",
            Self::RRSIG => "RType::RRSIG",
            Self::NSEC => "RType::NSEC",
            Self::DNSKEY => "RType::DNSKEY",
            Self::NSEC3 => "RType::NSEC3",
            Self::NSEC3PARAM => "RType::NSEC3PARAM",
            Self::CDS => "RType::CDS",
            Self::CDNSKEY => "RType::CDNSKEY",
            Self::ZONEMD => "RType::ZONEMD",
            Self::TSIG => "RType::TSIG",
            _ => return write!(f, "RType({})", self.code),
        })
    }
}

//----------- RClass ---------------------------------------------------------

/// The class of a record.
#[derive(
    Copy,
    Clone,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
    Hash,
    AsBytes,
    BuildBytes,
    ParseBytes,
    ParseBytesZC,
    SplitBytes,
    SplitBytesZC,
    UnsizedCopy,
)]
#[repr(transparent)]
pub struct RClass {
    /// The class code.
    pub code: U16,
}

//--- Associated Constants

impl RClass {
    /// Create a new [`RType`].
    const fn new(value: u16) -> Self {
        Self {
            code: U16::new(value),
        }
    }

    /// The Internet class.
    pub const IN: Self = Self::new(1);

    /// The CHAOS class.
    pub const CH: Self = Self::new(3);
}

//--- Formatting

impl fmt::Debug for RClass {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(match *self {
            Self::IN => "RClass::IN",
            Self::CH => "RClass::CH",
            _ => return write!(f, "RClass({})", self.code),
        })
    }
}

//----------- TTL ------------------------------------------------------------

/// How long a record can be cached.
#[derive(
    Copy,
    Clone,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
    Hash,
    AsBytes,
    BuildBytes,
    ParseBytes,
    ParseBytesZC,
    SplitBytes,
    SplitBytesZC,
    UnsizedCopy,
)]
#[repr(transparent)]
pub struct TTL {
    /// The underlying value.
    pub value: U32,
}

//--- Conversion to and from integers

impl From<u32> for TTL {
    fn from(value: u32) -> Self {
        Self {
            value: U32::new(value),
        }
    }
}

impl From<TTL> for u32 {
    fn from(value: TTL) -> Self {
        value.value.get()
    }
}

//--- Formatting

impl fmt::Debug for TTL {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "TTL({})", self.value)
    }
}

//----------- ParseRecordData ------------------------------------------------

/// Parsing DNS record data.
pub trait ParseRecordData<'a>: ParseRecordDataBytes<'a> {
    /// Parse DNS record data of the given type from a DNS message.
    fn parse_record_data(
        contents: &'a [u8],
        start: usize,
        rtype: RType,
    ) -> Result<Self, ParseError> {
        Self::parse_record_data_bytes(&contents[start..], rtype)
    }
}

/// Parsing DNS record data without name compression.
pub trait ParseRecordDataBytes<'a>: Sized {
    /// Parse DNS record data of the given type from a byte sequence.
    fn parse_record_data_bytes(
        bytes: &'a [u8],
        rtype: RType,
    ) -> Result<Self, ParseError>;
}

//----------- CanonicalRecordData --------------------------------------------

/// DNSSEC-conformant operations for resource records.
///
/// As specified by [RFC 4034, section 6], there is a "canonical form" for
/// DNS resource records, used for ordering records and computing signatures.
/// This trait defines operations for working with the canonical form.
///
/// [RFC 4034, section 6]: https://datatracker.ietf.org/doc/html/rfc4034#section-6
pub trait CanonicalRecordData: BuildBytes {
    /// Serialize record data in the canonical form.
    ///
    /// This is subtly different from [`BuildBytes`]: for certain special
    /// record data types, it causes embedded domain names to be lowercased.
    /// By default, it will fall back to [`BuildBytes`].
    fn build_canonical_bytes<'b>(
        &self,
        bytes: &'b mut [u8],
    ) -> Result<&'b mut [u8], TruncationError> {
        self.build_bytes(bytes)
    }

    /// Compare record data in the canonical form.
    ///
    /// This is equivalent to serializing both record data instances using
    /// [`build_canonical_bytes()`] and comparing the resulting byte sequences.
    ///
    /// [`build_canonical_bytes()`]: Self::build_canonical_bytes()
    fn cmp_canonical(&self, other: &Self) -> Ordering;
}

/// Implement [`CanonicalRecordData`] for a [`Deref`]-based generic container.
macro_rules! impl_canonical_record_data_for_deref {
    {$(
        $(#[$attr:meta])*
        impl[$($args:tt)*] CanonicalRecordData for $subject:ty;
    )*} => {$(
        $(#[$attr])*
        impl<$($args)*> CanonicalRecordData for $subject {
            fn build_canonical_bytes<'b>(
                &self,
                bytes: &'b mut [u8],
            ) -> Result<&'b mut [u8], TruncationError> {
                (**self).build_canonical_bytes(bytes)
            }

            fn cmp_canonical(&self, other: &Self) -> Ordering {
                (**self).cmp_canonical(&**other)
            }
        }
    )*};
}

impl_canonical_record_data_for_deref! {
    impl[T: ?Sized + CanonicalRecordData] CanonicalRecordData for &T;
    impl[T: ?Sized + CanonicalRecordData] CanonicalRecordData for &mut T;

    #[cfg(feature = "alloc")]
    impl[T: ?Sized + CanonicalRecordData] CanonicalRecordData for alloc::boxed::Box<T>;
    #[cfg(feature = "alloc")]
    impl[T: ?Sized + CanonicalRecordData] CanonicalRecordData for alloc::rc::Rc<T>;
    #[cfg(feature = "alloc")]
    impl[T: ?Sized + CanonicalRecordData] CanonicalRecordData for alloc::sync::Arc<T>;
}

//----------- UnparsedRecordData ---------------------------------------------

/// Unparsed DNS record data.
#[derive(AsBytes, BuildBytes, UnsizedCopy)]
#[repr(transparent)]
pub struct UnparsedRecordData([u8]);

//--- Construction

impl UnparsedRecordData {
    /// Assume a byte sequence is a valid [`UnparsedRecordData`].
    ///
    /// # Safety
    ///
    /// The byte sequence must be 65,535 bytes or shorter.
    pub const unsafe fn new_unchecked(bytes: &[u8]) -> &Self {
        // SAFETY: 'UnparsedRecordData' is 'repr(transparent)' to '[u8]', so
        // casting a '[u8]' into an 'UnparsedRecordData' is sound.
        core::mem::transmute(bytes)
    }
}

//--- Parsing record data

impl<'a> ParseRecordData<'a> for &'a UnparsedRecordData {}

impl<'a> ParseRecordDataBytes<'a> for &'a UnparsedRecordData {
    fn parse_record_data_bytes(
        bytes: &'a [u8],
        _rtype: RType,
    ) -> Result<Self, ParseError> {
        if bytes.len() > 65535 {
            // Too big to fit in an 'UnparsedRecordData'.
            return Err(ParseError);
        }

        // SAFETY: 'bytes.len()' fits within a 'u16'.
        Ok(unsafe { UnparsedRecordData::new_unchecked(bytes) })
    }
}

//--- Building into DNS messages

impl BuildInMessage for UnparsedRecordData {
    fn build_in_message(
        &self,
        contents: &mut [u8],
        start: usize,
        _compressor: &mut NameCompressor,
    ) -> Result<usize, TruncationError> {
        let end = start + self.0.len();
        contents
            .get_mut(start..end)
            .ok_or(TruncationError)?
            .copy_from_slice(&self.0);
        Ok(end)
    }
}

//--- Access to the underlying bytes

impl Deref for UnparsedRecordData {
    type Target = [u8];

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl Borrow<[u8]> for UnparsedRecordData {
    fn borrow(&self) -> &[u8] {
        self
    }
}

impl AsRef<[u8]> for UnparsedRecordData {
    fn as_ref(&self) -> &[u8] {
        self
    }
}

//--- Cloning

#[cfg(feature = "alloc")]
impl Clone for alloc::boxed::Box<UnparsedRecordData> {
    fn clone(&self) -> Self {
        (*self).unsized_copy_into()
    }
}

//============ Tests =========================================================

#[cfg(test)]
mod test {
    use super::{RClass, RType, Record, UnparsedRecordData, TTL};

    use crate::new::base::{
        name::Name,
        wire::{AsBytes, BuildBytes, ParseBytes, SplitBytes},
    };

    #[test]
    fn parse_build() {
        type Subject<'a> = Record<&'a Name, &'a UnparsedRecordData>;

        let bytes =
            b"\x03com\x00\x00\x01\x00\x01\x00\x00\x00\x2A\x00\x00\x54";
        let (record, rest) = Subject::split_bytes(bytes).unwrap();
        assert_eq!(record.rname.as_bytes(), b"\x03com\x00");
        assert_eq!(record.rtype, RType::A);
        assert_eq!(record.rclass, RClass::IN);
        assert_eq!(record.ttl, TTL::from(42));
        assert_eq!(record.rdata.as_bytes(), b"");
        assert_eq!(rest, b"\x54");

        assert!(Subject::parse_bytes(bytes).is_err());
        assert!(Subject::parse_bytes(&bytes[..15]).is_ok());

        let mut buffer = [0u8; 15];
        assert_eq!(record.build_bytes(&mut buffer), Ok(&mut [] as &mut [u8]));
        assert_eq!(buffer, &bytes[..15]);
    }
}