// Copyright 2015-2021 Benjamin Fry <benjaminfry@me.com>
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

//! SVCB records, see [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03)

use std::{
    cmp::{Ord, Ordering, PartialOrd},
    convert::TryFrom,
    fmt,
    net::Ipv4Addr,
    net::Ipv6Addr,
};

use enum_as_inner::EnumAsInner;

use crate::error::*;
use crate::rr::Name;
use crate::serialize::binary::*;

///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.2)
///
/// ```text
/// 2.2.  RDATA wire format
///
///   The RDATA for the SVCB RR consists of:
///
///   *  a 2 octet field for SvcPriority as an integer in network byte
///      order.
///   *  the uncompressed, fully-qualified TargetName, represented as a
///      sequence of length-prefixed labels as in Section 3.1 of [RFC1035].
///   *  the SvcParams, consuming the remainder of the record (so smaller
///      than 65535 octets and constrained by the RDATA and DNS message
///      sizes).
///
///   When the list of SvcParams is non-empty (ServiceMode), it contains a
///   series of SvcParamKey=SvcParamValue pairs, represented as:
///
///   *  a 2 octet field containing the SvcParamKey as an integer in
///      network byte order.  (See Section 14.3.2 for the defined values.)
///   *  a 2 octet field containing the length of the SvcParamValue as an
///      integer between 0 and 65535 in network byte order (but constrained
///      by the RDATA and DNS message sizes).
///   *  an octet string of this length whose contents are in a format
///      determined by the SvcParamKey.
///
///   SvcParamKeys SHALL appear in increasing numeric order.
///
///   Clients MUST consider an RR malformed if:
///
///   *  the end of the RDATA occurs within a SvcParam.
///   *  SvcParamKeys are not in strictly increasing numeric order.
///   *  the SvcParamValue for an SvcParamKey does not have the expected
///      format.
///
///   Note that the second condition implies that there are no duplicate
///   SvcParamKeys.
///
///   If any RRs are malformed, the client MUST reject the entire RRSet and
///   fall back to non-SVCB connection establishment.
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct SVCB {
    svc_priority: u16,
    target_name: Name,
    svc_params: Vec<(SvcParamKey, SvcParamValue)>,
}

impl SVCB {
    /// Create a new SVCB record from parts
    ///
    /// It is up to the caller to validate the data going into the record
    pub fn new(
        svc_priority: u16,
        target_name: Name,
        svc_params: Vec<(SvcParamKey, SvcParamValue)>,
    ) -> Self {
        Self {
            svc_priority,
            target_name,
            svc_params,
        }
    }

    ///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.4.1)
    /// ```text
    /// 2.4.1.  SvcPriority
    ///
    ///   When SvcPriority is 0 the SVCB record is in AliasMode
    ///   (Section 2.4.2).  Otherwise, it is in ServiceMode (Section 2.4.3).
    ///
    ///   Within a SVCB RRSet, all RRs SHOULD have the same Mode.  If an RRSet
    ///   contains a record in AliasMode, the recipient MUST ignore any
    ///   ServiceMode records in the set.
    ///
    ///   RRSets are explicitly unordered collections, so the SvcPriority field
    ///   is used to impose an ordering on SVCB RRs.  SVCB RRs with a smaller
    ///   SvcPriority value SHOULD be given preference over RRs with a larger
    ///   SvcPriority value.
    ///
    ///   When receiving an RRSet containing multiple SVCB records with the
    ///   same SvcPriority value, clients SHOULD apply a random shuffle within
    ///   a priority level to the records before using them, to ensure uniform
    ///   load-balancing.
    /// ```
    pub fn svc_priority(&self) -> u16 {
        self.svc_priority
    }

    ///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.5)
    /// ```text
    /// 2.5.  Special handling of "." in TargetName
    ///
    ///   If TargetName has the value "." (represented in the wire format as a
    ///    zero-length label), special rules apply.
    ///
    /// 2.5.1.  AliasMode
    ///
    ///    For AliasMode SVCB RRs, a TargetName of "." indicates that the
    ///    service is not available or does not exist.  This indication is
    ///    advisory: clients encountering this indication MAY ignore it and
    ///    attempt to connect without the use of SVCB.
    ///
    /// 2.5.2.  ServiceMode
    ///
    ///    For ServiceMode SVCB RRs, if TargetName has the value ".", then the
    ///    owner name of this record MUST be used as the effective TargetName.
    ///
    ///    For example, in the following example "svc2.example.net" is the
    ///    effective TargetName:
    ///
    ///    example.com.      7200  IN HTTPS 0 svc.example.net.
    ///    svc.example.net.  7200  IN CNAME svc2.example.net.
    ///    svc2.example.net. 7200  IN HTTPS 1 . port=8002 echconfig="..."
    ///    svc2.example.net. 300   IN A     192.0.2.2
    ///    svc2.example.net. 300   IN AAAA  2001:db8::2
    /// ```
    pub fn target_name(&self) -> &Name {
        &self.target_name
    }

    /// See [`SvcParamKey`] for details on each parameter
    pub fn svc_params(&self) -> &[(SvcParamKey, SvcParamValue)] {
        &self.svc_params
    }
}

/// ```text
/// 14.3.2.  Initial contents
///
///   The "Service Binding (SVCB) Parameter Registry" shall initially be
///   populated with the registrations below:
///
///   +=============+=================+======================+===========+
///   | Number      | Name            | Meaning              | Reference |
///   +=============+=================+======================+===========+
///   | 0           | mandatory       | Mandatory keys in    | (This     |
///   |             |                 | this RR              | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 1           | alpn            | Additional supported | (This     |
///   |             |                 | protocols            | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 2           | no-default-alpn | No support for       | (This     |
///   |             |                 | default protocol     | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 3           | port            | Port for alternative | (This     |
///   |             |                 | endpoint             | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 4           | ipv4hint        | IPv4 address hints   | (This     |
///   |             |                 |                      | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 5           | echconfig       | Encrypted            | (This     |
///   |             |                 | ClientHello info     | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 6           | ipv6hint        | IPv6 address hints   | (This     |
///   |             |                 |                      | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 65280-65534 | keyNNNNN        | Private Use          | (This     |
///   |             |                 |                      | document) |
///   +-------------+-----------------+----------------------+-----------+
///   | 65535       | key65535        | Reserved ("Invalid   | (This     |
///   |             |                 | key")                | document) |
///   +-------------+-----------------+----------------------+-----------+
///
/// parsing done via:
///   *  a 2 octet field containing the SvcParamKey as an integer in
///      network byte order.  (See Section 14.3.2 for the defined values.)
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
pub enum SvcParamKey {
    /// Mandatory keys in this RR
    Mandatory,
    /// Additional supported protocols
    Alpn,
    /// No support for default protocol
    NoDefaultAlpn,
    /// Port for alternative endpoint
    Port,
    /// IPv4 address hints
    Ipv4Hint,
    /// Encrypted ClientHello info
    EchConfig,
    /// IPv6 address hints
    Ipv6Hint,
    /// Private Use
    Key(u16),
    /// Reserved ("Invalid key")
    Key65535,
    /// Unknown
    Unknown(u16),
}

impl From<u16> for SvcParamKey {
    fn from(val: u16) -> Self {
        match val {
            0 => SvcParamKey::Mandatory,
            1 => SvcParamKey::Alpn,
            2 => SvcParamKey::NoDefaultAlpn,
            3 => SvcParamKey::Port,
            4 => SvcParamKey::Ipv4Hint,
            5 => SvcParamKey::EchConfig,
            6 => SvcParamKey::Ipv6Hint,
            65280..=65534 => SvcParamKey::Key(val),
            65535 => SvcParamKey::Key65535,
            _ => SvcParamKey::Unknown(val),
        }
    }
}

impl From<SvcParamKey> for u16 {
    fn from(val: SvcParamKey) -> Self {
        match val {
            SvcParamKey::Mandatory => 0,
            SvcParamKey::Alpn => 1,
            SvcParamKey::NoDefaultAlpn => 2,
            SvcParamKey::Port => 3,
            SvcParamKey::Ipv4Hint => 4,
            SvcParamKey::EchConfig => 5,
            SvcParamKey::Ipv6Hint => 6,
            SvcParamKey::Key(val) => val,
            SvcParamKey::Key65535 => 65535,
            SvcParamKey::Unknown(val) => val,
        }
    }
}

impl<'r> BinDecodable<'r> for SvcParamKey {
    // a 2 octet field containing the SvcParamKey as an integer in
    //      network byte order.  (See Section 14.3.2 for the defined values.)
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        Ok(decoder.read_u16()?.unverified(/*any u16 is valid*/).into())
    }
}

impl BinEncodable for SvcParamKey {
    // a 2 octet field containing the SvcParamKey as an integer in
    //      network byte order.  (See Section 14.3.2 for the defined values.)
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        encoder.emit_u16((*self).into())
    }
}

impl fmt::Display for SvcParamKey {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        let mut write_key = |name| write!(f, "{}", name);

        match *self {
            SvcParamKey::Mandatory => write_key("mandatory")?,
            SvcParamKey::Alpn => write_key("alpn")?,
            SvcParamKey::NoDefaultAlpn => write_key("no-default-alpn")?,
            SvcParamKey::Port => write_key("port")?,
            SvcParamKey::Ipv4Hint => write_key("ipv4hint")?,
            SvcParamKey::EchConfig => write_key("echconfig")?,
            SvcParamKey::Ipv6Hint => write_key("ipv6hint")?,
            SvcParamKey::Key(val) => write!(f, "key{}", val)?,
            SvcParamKey::Key65535 => write_key("key65535")?,
            SvcParamKey::Unknown(val) => write!(f, "unknown{}", val)?,
        }

        Ok(())
    }
}

impl std::str::FromStr for SvcParamKey {
    type Err = ProtoError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        /// keys are in the format of key#, e.g. key12344, with a max value of u16
        fn parse_unknown_key(key: &str) -> Result<SvcParamKey, ProtoError> {
            let key_value = key.strip_prefix("key").ok_or_else(|| {
                ProtoError::from(ProtoErrorKind::Msg(format!(
                    "bad formatted key ({}), expected key1234",
                    key
                )))
            })?;

            let key_value = u16::from_str(key_value)?;
            let key = SvcParamKey::from(key_value);
            Ok(key)
        }

        let key = match s {
            "mandatory" => SvcParamKey::Mandatory,
            "alpn" => SvcParamKey::Alpn,
            "no-default-alpn" => SvcParamKey::NoDefaultAlpn,
            "port" => SvcParamKey::Port,
            "ipv4hint" => SvcParamKey::Ipv4Hint,
            "echconfig" => SvcParamKey::EchConfig,
            "ipv6hint" => SvcParamKey::Ipv6Hint,
            "key65535" => SvcParamKey::Key65535,
            _ => parse_unknown_key(s)?,
        };

        Ok(key)
    }
}

impl Ord for SvcParamKey {
    fn cmp(&self, other: &Self) -> Ordering {
        u16::from(*self).cmp(&u16::from(*other))
    }
}

impl PartialOrd for SvcParamKey {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

/// Warning, it is currently up to users of this type to validate the data against that expected by the key
///
/// ```text
///   *  a 2 octet field containing the length of the SvcParamValue as an
///      integer between 0 and 65535 in network byte order (but constrained
///      by the RDATA and DNS message sizes).
///   *  an octet string of this length whose contents are in a format
///      determined by the SvcParamKey.
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone, EnumAsInner)]
pub enum SvcParamValue {
    ///    In a ServiceMode RR, a SvcParamKey is considered "mandatory" if the
    ///    RR will not function correctly for clients that ignore this
    ///    SvcParamKey.  Each SVCB protocol mapping SHOULD specify a set of keys
    ///    that are "automatically mandatory", i.e. mandatory if they are
    ///    present in an RR.  The SvcParamKey "mandatory" is used to indicate
    ///    any mandatory keys for this RR, in addition to any automatically
    ///    mandatory keys that are present.
    ///
    /// see `Mandatory`
    Mandatory(Mandatory),
    /// The "alpn" and "no-default-alpn" SvcParamKeys together indicate the
    ///    set of Application Layer Protocol Negotiation (ALPN) protocol
    ///    identifiers [ALPN] and associated transport protocols supported by
    ///    this service endpoint.
    Alpn(Alpn),
    /// For "no-default-alpn", the presentation and wire format values MUST
    ///    be empty.
    /// See also `Alpn`
    NoDefaultAlpn,
    /// ```text
    ///    6.2.  "port"
    ///
    ///   The "port" SvcParamKey defines the TCP or UDP port that should be
    ///   used to reach this alternative endpoint.  If this key is not present,
    ///   clients SHALL use the authority endpoint's port number.
    ///
    ///   The presentation "value" of the SvcParamValue is a single decimal
    ///   integer between 0 and 65535 in ASCII.  Any other "value" (e.g. an
    ///   empty value) is a syntax error.  To enable simpler parsing, this
    ///   SvcParam MUST NOT contain escape sequences.
    ///
    ///   The wire format of the SvcParamValue is the corresponding 2 octet
    ///   numeric value in network byte order.
    ///
    ///   If a port-restricting firewall is in place between some client and
    ///   the service endpoint, changing the port number might cause that
    ///   client to lose access to the service, so operators should exercise
    ///   caution when using this SvcParamKey to specify a non-default port.
    /// ```
    Port(u16),
    ///   The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients
    ///   MAY use to reach the service.  If A and AAAA records for TargetName
    ///   are locally available, the client SHOULD ignore these hints.
    ///   Otherwise, clients SHOULD perform A and/or AAAA queries for
    ///   TargetName as in Section 3, and clients SHOULD use the IP address in
    ///   those responses for future connections.  Clients MAY opt to terminate
    ///   any connections using the addresses in hints and instead switch to
    ///   the addresses in response to the TargetName query.  Failure to use A
    ///   and/or AAAA response addresses could negatively impact load balancing
    ///   or other geo-aware features and thereby degrade client performance.
    ///
    /// see `IpHint`
    Ipv4Hint(IpHint<Ipv4Addr>),
    /// ```text
    /// 6.3.  "echconfig"
    ///
    ///   The SvcParamKey to enable Encrypted ClientHello (ECH) is "echconfig".
    ///   Its value is defined in Section 9.  It is applicable to most TLS-
    ///   based protocols.
    ///
    ///   When publishing a record containing an "echconfig" parameter, the
    ///   publisher MUST ensure that all IP addresses of TargetName correspond
    ///   to servers that have access to the corresponding private key or are
    ///   authoritative for the public name.  (See Section 7.2.2 of [ECH] for
    ///   more details about the public name.)  This yields an anonymity set of
    ///   cardinality equal to the number of ECH-enabled server domains
    ///   supported by a given client-facing server.  Thus, even with an
    ///   encrypted ClientHello, an attacker who can enumerate the set of ECH-
    ///   enabled domains supported by a client-facing server can guess the
    ///   correct SNI with probability at least 1/K, where K is the size of
    ///   this ECH-enabled server anonymity set.  This probability may be
    ///   increased via traffic analysis or other mechanisms.
    /// ```
    EchConfig(EchConfig),
    /// See `IpHint`
    Ipv6Hint(IpHint<Ipv6Addr>),
    /// Unparsed network data. Refer to documents on the associated key value
    ///
    /// This will be left as is when read off the wire, and encoded in bas64
    ///    for presentation.
    Unknown(Unknown),
}

impl SvcParamValue {
    // a 2 octet field containing the length of the SvcParamValue as an
    //      integer between 0 and 65535 in network byte order (but constrained
    //      by the RDATA and DNS message sizes).
    fn read(key: SvcParamKey, decoder: &mut BinDecoder<'_>) -> ProtoResult<Self> {
        let len: usize = decoder
            .read_u16()?
            .verify_unwrap(|len| *len as usize <= decoder.len())
            .map(|len| len as usize)
            .map_err(|u| {
                ProtoError::from(format!(
                    "length of SvcParamValue ({}) exceeds remainder in RDATA ({})",
                    u,
                    decoder.len()
                ))
            })?;

        let param_data = decoder.read_slice(len)?.unverified(/*verification to be done by individual param types*/);
        let mut decoder = BinDecoder::new(param_data);

        let value = match key {
            SvcParamKey::Mandatory => Self::Mandatory(Mandatory::read(&mut decoder)?),
            SvcParamKey::Alpn => Self::Alpn(Alpn::read(&mut decoder)?),
            // should always be empty
            SvcParamKey::NoDefaultAlpn => {
                if len > 0 {
                    return Err(ProtoError::from("Alpn expects at least one value"));
                }

                Self::NoDefaultAlpn
            }
            // The wire format of the SvcParamValue is the corresponding 2 octet
            // numeric value in network byte order.
            SvcParamKey::Port => {
                let port = decoder.read_u16()?.unverified(/*all values are legal ports*/);
                Self::Port(port)
            }
            SvcParamKey::Ipv4Hint => Self::Ipv4Hint(IpHint::<Ipv4Addr>::read(&mut decoder)?),
            SvcParamKey::EchConfig => Self::EchConfig(EchConfig::read(&mut decoder)?),
            SvcParamKey::Ipv6Hint => Self::Ipv6Hint(IpHint::<Ipv6Addr>::read(&mut decoder)?),
            SvcParamKey::Key(_) | SvcParamKey::Key65535 | SvcParamKey::Unknown(_) => {
                Self::Unknown(Unknown::read(&mut decoder)?)
            }
        };

        Ok(value)
    }
}

impl BinEncodable for SvcParamValue {
    // a 2 octet field containing the length of the SvcParamValue as an
    //      integer between 0 and 65535 in network byte order (but constrained
    //      by the RDATA and DNS message sizes).
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        // set the place for the length...
        let place = encoder.place::<u16>()?;

        match self {
            SvcParamValue::Mandatory(mandatory) => mandatory.emit(encoder)?,
            SvcParamValue::Alpn(alpn) => alpn.emit(encoder)?,
            SvcParamValue::NoDefaultAlpn => (),
            SvcParamValue::Port(port) => encoder.emit_u16(*port)?,
            SvcParamValue::Ipv4Hint(ip_hint) => ip_hint.emit(encoder)?,
            SvcParamValue::EchConfig(ech_config) => ech_config.emit(encoder)?,
            SvcParamValue::Ipv6Hint(ip_hint) => ip_hint.emit(encoder)?,
            SvcParamValue::Unknown(unknown) => unknown.emit(encoder)?,
        }

        // go back and set the length
        let len = u16::try_from(encoder.len_since_place(&place))
            .map_err(|_| ProtoError::from("Total length of SvcParamValue exceeds u16::MAX"))?;
        place.replace(encoder, len)?;

        Ok(())
    }
}

impl fmt::Display for SvcParamValue {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        match self {
            SvcParamValue::Mandatory(mandatory) => write!(f, "{}", mandatory)?,
            SvcParamValue::Alpn(alpn) => write!(f, "{}", alpn)?,
            SvcParamValue::NoDefaultAlpn => (),
            SvcParamValue::Port(port) => write!(f, "{}", port)?,
            SvcParamValue::Ipv4Hint(ip_hint) => write!(f, "{}", ip_hint)?,
            SvcParamValue::EchConfig(ech_config) => write!(f, "{}", ech_config)?,
            SvcParamValue::Ipv6Hint(ip_hint) => write!(f, "{}", ip_hint)?,
            SvcParamValue::Unknown(unknown) => write!(f, "{}", unknown)?,
        }

        Ok(())
    }
}

/// ```text
/// 7.  ServiceMode RR compatibility and mandatory keys
///
///    In a ServiceMode RR, a SvcParamKey is considered "mandatory" if the
///    RR will not function correctly for clients that ignore this
///    SvcParamKey.  Each SVCB protocol mapping SHOULD specify a set of keys
///    that are "automatically mandatory", i.e. mandatory if they are
///    present in an RR.  The SvcParamKey "mandatory" is used to indicate
///    any mandatory keys for this RR, in addition to any automatically
///    mandatory keys that are present.
///
///    A ServiceMode RR is considered "compatible" with a client if the
///    client recognizes all the mandatory keys, and their values indicate
///    that successful connection establishment is possible.  If the SVCB
///    RRSet contains no compatible RRs, the client will generally act as if
///    the RRSet is empty.
///
///    The presentation "value" SHALL be a comma-separated list
///    (Appendix A.1) of one or more valid SvcParamKeys, either by their
///    registered name or in the unknown-key format (Section 2.1).  Keys MAY
///    appear in any order, but MUST NOT appear more than once.  For self-
///    consistency (Section 2.4.3), listed keys MUST also appear in the
///    SvcParams.
///
///    To enable simpler parsing, this SvcParamValue MUST NOT contain escape
///    sequences.
///
///    For example, the following is a valid list of SvcParams:
///
///    echconfig=... key65333=ex1 key65444=ex2 mandatory=key65444,echconfig
///
///    In wire format, the keys are represented by their numeric values in
///    network byte order, concatenated in ascending order.
///
///    This SvcParamKey is always automatically mandatory, and MUST NOT
///    appear in its own value-list.  Other automatically mandatory keys
///    SHOULD NOT appear in the list either.  (Including them wastes space
///    and otherwise has no effect.)
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct Mandatory(pub Vec<SvcParamKey>);

impl<'r> BinDecodable<'r> for Mandatory {
    /// This expects the decoder to be limited to only this field, i.e. the end of input for the decoder
    ///   is the end of input for the fields
    ///
    /// ```text
    ///    In wire format, the keys are represented by their numeric values in
    ///    network byte order, concatenated in ascending order.
    /// ```
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut keys = Vec::with_capacity(1);

        while decoder.peek().is_some() {
            keys.push(SvcParamKey::read(decoder)?);
        }

        if keys.is_empty() {
            return Err(ProtoError::from("Mandatory expects at least one value"));
        }

        Ok(Mandatory(keys))
    }
}

impl BinEncodable for Mandatory {
    /// This expects the decoder to be limited to only this field, i.e. the end of input for the decoder
    ///   is the end of input for the fields
    ///
    /// ```text
    ///    In wire format, the keys are represented by their numeric values in
    ///    network byte order, concatenated in ascending order.
    /// ```
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        if self.0.is_empty() {
            return Err(ProtoError::from("Alpn expects at least one value"));
        }

        // TODO: order by key value
        for key in self.0.iter() {
            key.emit(encoder)?
        }

        Ok(())
    }
}

impl fmt::Display for Mandatory {
    ///    The presentation "value" SHALL be a comma-separated list
    ///    (Appendix A.1) of one or more valid SvcParamKeys, either by their
    ///    registered name or in the unknown-key format (Section 2.1).  Keys MAY
    ///    appear in any order, but MUST NOT appear more than once.  For self-
    ///    consistency (Section 2.4.3), listed keys MUST also appear in the
    ///    SvcParams.
    ///
    ///    To enable simpler parsing, this SvcParamValue MUST NOT contain escape
    ///    sequences.
    ///
    ///    For example, the following is a valid list of SvcParams:
    ///
    ///    echconfig=... key65333=ex1 key65444=ex2 mandatory=key65444,echconfig
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for key in self.0.iter() {
            // TODO: confirm in the RFC that trailing commas are ok
            write!(f, "{},", key)?;
        }

        Ok(())
    }
}

///  [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-6.1)
///
/// ```text
/// 6.1.  "alpn" and "no-default-alpn"
///
///   The "alpn" and "no-default-alpn" SvcParamKeys together indicate the
///   set of Application Layer Protocol Negotiation (ALPN) protocol
///   identifiers [ALPN] and associated transport protocols supported by
///   this service endpoint.
///
///   As with Alt-Svc [AltSvc], the ALPN protocol identifier is used to
///   identify the application protocol and associated suite of protocols
///   supported by the endpoint (the "protocol suite").  Clients filter the
///   set of ALPN identifiers to match the protocol suites they support,
///   and this informs the underlying transport protocol used (such as
///   QUIC-over-UDP or TLS-over-TCP).
///
///   ALPNs are identified by their registered "Identification Sequence"
///   ("alpn-id"), which is a sequence of 1-255 octets.
///
///   alpn-id = 1*255OCTET
///
///   The presentation "value" SHALL be a comma-separated list
///   (Appendix A.1) of one or more "alpn-id"s.
///
///   The wire format value for "alpn" consists of at least one "alpn-id"
///   prefixed by its length as a single octet, and these length-value
///   pairs are concatenated to form the SvcParamValue.  These pairs MUST
///   exactly fill the SvcParamValue; otherwise, the SvcParamValue is
///   malformed.
///
///   For "no-default-alpn", the presentation and wire format values MUST
///   be empty.  When "no-default-alpn" is specified in an RR, "alpn" must
///   also be specified in order for the RR to be "self-consistent"
///   (Section 2.4.3).
///
///   Each scheme that uses this SvcParamKey defines a "default set" of
///   supported ALPNs, which SHOULD NOT be empty.  To determine the set of
///   protocol suites supported by an endpoint (the "SVCB ALPN set"), the
///   client adds the default set to the list of "alpn-id"s unless the "no-
///   default-alpn" SvcParamKey is present.  The presence of an ALPN
///   protocol in the SVCB ALPN set indicates that this service endpoint,
///   described by TargetName and the other parameters (e.g. "port") offers
///   service with the protocol suite associated with this ALPN protocol.
///
///   ALPN protocol names that do not uniquely identify a protocol suite
///   (e.g. an Identification Sequence that can be used with both TLS and
///   DTLS) are not compatible with this SvcParamKey and MUST NOT be
///   included in the SVCB ALPN set.
///
///   To establish a connection to the endpoint, clients MUST
///
///   1.  Let SVCB-ALPN-Intersection be the set of protocols in the SVCB
///       ALPN set that the client supports.
///
///   2.  Let Intersection-Transports be the set of transports (e.g.  TLS,
///       DTLS, QUIC) implied by the protocols in SVCB-ALPN-Intersection.
///
///   3.  For each transport in Intersection-Transports, construct a
///       ProtocolNameList containing the Identification Sequences of all
///       the client's supported ALPN protocols for that transport, without
///       regard to the SVCB ALPN set.
///
///   For example, if the SVCB ALPN set is ["http/1.1", "h3"], and the
///   client supports HTTP/1.1, HTTP/2, and HTTP/3, the client could
///   attempt to connect using TLS over TCP with a ProtocolNameList of
///   ["http/1.1", "h2"], and could also attempt a connection using QUIC,
///   with a ProtocolNameList of ["h3"].
///
///   Once the client has constructed a ClientHello, protocol negotiation
///   in that handshake proceeds as specified in [ALPN], without regard to
///   the SVCB ALPN set.
///
///   With this procedure in place, an attacker who can modify DNS and
///   network traffic can prevent a successful transport connection, but
///   cannot otherwise interfere with ALPN protocol selection.  This
///   procedure also ensures that each ProtocolNameList includes at least
///   one protocol from the SVCB ALPN set.
///
///   Clients SHOULD NOT attempt connection to a service endpoint whose
///   SVCB ALPN set does not contain any supported protocols.  To ensure
///   consistency of behavior, clients MAY reject the entire SVCB RRSet and
///   fall back to basic connection establishment if all of the RRs
///   indicate "no-default-alpn", even if connection could have succeeded
///   using a non-default alpn.
///
///   For compatibility with clients that require default transports, zone
///   operators SHOULD ensure that at least one RR in each RRSet supports
///   the default transports.
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct Alpn(pub Vec<String>);

impl<'r> BinDecodable<'r> for Alpn {
    /// This expects the decoder to be limited to only this field, i.e. the end of input for the decoder
    ///   is the end of input for the fields
    ///
    /// ```text
    ///   The wire format value for "alpn" consists of at least one "alpn-id"
    ///   prefixed by its length as a single octet, and these length-value
    ///   pairs are concatenated to form the SvcParamValue.  These pairs MUST
    ///   exactly fill the SvcParamValue; otherwise, the SvcParamValue is
    ///   malformed.
    /// ```
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut alpns = Vec::with_capacity(1);

        while decoder.peek().is_some() {
            let alpn = decoder.read_character_data()?.unverified(/*will rely on string parser*/);
            let alpn = String::from_utf8(alpn.to_vec())?;
            alpns.push(alpn);
        }

        if alpns.is_empty() {
            return Err(ProtoError::from("Alpn expects at least one value"));
        }

        Ok(Alpn(alpns))
    }
}

impl BinEncodable for Alpn {
    ///   The wire format value for "alpn" consists of at least one "alpn-id"
    ///   prefixed by its length as a single octet, and these length-value
    ///   pairs are concatenated to form the SvcParamValue.  These pairs MUST
    ///   exactly fill the SvcParamValue; otherwise, the SvcParamValue is
    ///   malformed.
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        if self.0.is_empty() {
            return Err(ProtoError::from("Alpn expects at least one value"));
        }

        for alpn in self.0.iter() {
            encoder.emit_character_data(alpn)?
        }

        Ok(())
    }
}

impl fmt::Display for Alpn {
    ///   The presentation "value" SHALL be a comma-separated list
    ///   (Appendix A.1) of one or more "alpn-id"s.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for alpn in self.0.iter() {
            // TODO: confirm in the RFC that trailing commas are ok
            write!(f, "{},", alpn)?;
        }

        Ok(())
    }
}

/// ```text
/// 9.  SVCB/HTTPS RR parameter for ECH configuration
///
///   The SVCB "echconfig" parameter is defined for conveying the ECH
///   configuration of an alternative endpoint.  In wire format, the value
///   of the parameter is an ECHConfigs vector [ECH], including the
///   redundant length prefix.  In presentation format, the value is a
///   single ECHConfigs encoded in Base64 [base64].  Base64 is used here to
///   simplify integration with TLS server software.  To enable simpler
///   parsing, this SvcParam MUST NOT contain escape sequences.
///
///   When ECH is in use, the TLS ClientHello is divided into an
///   unencrypted "outer" and an encrypted "inner" ClientHello.  The outer
///   ClientHello is an implementation detail of ECH, and its contents are
///   controlled by the ECHConfig in accordance with [ECH].  The inner
///   ClientHello is used for establishing a connection to the service, so
///   its contents may be influenced by other SVCB parameters.  For
///   example, the requirements on the ProtocolNameList in Section 6.1
///   apply only to the inner ClientHello.  Similarly, it is the inner
///   ClientHello whose Server Name Indication identifies the desired
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct EchConfig(pub Vec<u8>);

impl<'r> BinDecodable<'r> for EchConfig {
    /// In wire format, the value
    ///   of the parameter is an ECHConfigs vector [ECH], including the
    ///   redundant length prefix (a 2 octet field containing the length of the SvcParamValue
    ///   as an integer between 0 and 65535 in network byte order).
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let redundant_len = decoder
            .read_u16()?
            .map(|len| len as usize)
            .verify_unwrap(|len| *len <= decoder.len())
            .map_err(|_| ProtoError::from("ECH value length exceeds max size of u16::MAX"))?;

        let data =
            decoder.read_vec(redundant_len)?.unverified(/*up to consumer to validate this data*/);

        Ok(EchConfig(data))
    }
}

impl BinEncodable for EchConfig {
    /// In wire format, the value
    ///   of the parameter is an ECHConfigs vector [ECH], including the
    ///   redundant length prefix (a 2 octet field containing the length of the SvcParamValue
    ///   as an integer between 0 and 65535 in network byte order).
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        let len = u16::try_from(self.0.len())
            .map_err(|_| ProtoError::from("ECH value length exceeds max size of u16::MAX"))?;

        // redundant length...
        encoder.emit_u16(len)?;
        encoder.emit_vec(&self.0)?;

        Ok(())
    }
}

impl fmt::Display for EchConfig {
    /// In presentation format, the value is a
    ///   single ECHConfigs encoded in Base64 [base64].  Base64 is used here to
    ///   simplify integration with TLS server software.  To enable simpler
    ///   parsing, this SvcParam MUST NOT contain escape sequences.
    ///
    /// *note* while the on the wire the EchConfig has a redundant length,
    ///   the RFC is not explicit about including it in the base64
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        write!(f, "\"{}\"", data_encoding::BASE64.encode(&self.0))
    }
}

/// ```text
///    6.4.  "ipv4hint" and "ipv6hint"
///
///   The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients
///   MAY use to reach the service.  If A and AAAA records for TargetName
///   are locally available, the client SHOULD ignore these hints.
///   Otherwise, clients SHOULD perform A and/or AAAA queries for
///   TargetName as in Section 3, and clients SHOULD use the IP address in
///   those responses for future connections.  Clients MAY opt to terminate
///   any connections using the addresses in hints and instead switch to
///   the addresses in response to the TargetName query.  Failure to use A
///   and/or AAAA response addresses could negatively impact load balancing
///   or other geo-aware features and thereby degrade client performance.
///
///   The presentation "value" SHALL be a comma-separated list
///   (Appendix A.1) of one or more IP addresses of the appropriate family
///   in standard textual format [RFC5952].  To enable simpler parsing,
///   this SvcParamValue MUST NOT contain escape sequences.
///
///   The wire format for each parameter is a sequence of IP addresses in
///   network byte order.  Like an A or AAAA RRSet, the list of addresses
///   represents an unordered collection, and clients SHOULD pick addresses
///   to use in a random order.  An empty list of addresses is invalid.
///
///   When selecting between IPv4 and IPv6 addresses to use, clients may
///   use an approach such as Happy Eyeballs [HappyEyeballsV2].  When only
///   "ipv4hint" is present, IPv6-only clients may synthesize IPv6
///   addresses as specified in [RFC7050] or ignore the "ipv4hint" key and
///   wait for AAAA resolution (Section 3).  Recursive resolvers MUST NOT
///   perform DNS64 ([RFC6147]) on parameters within a SVCB record.  For
///   best performance, server operators SHOULD include an "ipv6hint"
///   parameter whenever they include an "ipv4hint" parameter.
///
///   These parameters are intended to minimize additional connection
///   latency when a recursive resolver is not compliant with the
///   requirements in Section 4, and SHOULD NOT be included if most clients
///   are using compliant recursive resolvers.  When TargetName is the
///   origin hostname or the owner name (which can be written as "."),
///   server operators SHOULD NOT include these hints, because they are
///   unlikely to convey any performance benefit.
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct IpHint<T>(pub Vec<T>);

impl<'r, T> BinDecodable<'r> for IpHint<T>
where
    T: BinDecodable<'r>,
{
    ///   The wire format for each parameter is a sequence of IP addresses in
    ///   network byte order.  Like an A or AAAA RRSet, the list of addresses
    ///   represents an unordered collection, and clients SHOULD pick addresses
    ///   to use in a random order.  An empty list of addresses is invalid.
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut ips = Vec::new();

        while decoder.peek().is_some() {
            ips.push(T::read(decoder)?)
        }

        Ok(IpHint(ips))
    }
}

impl<T> BinEncodable for IpHint<T>
where
    T: BinEncodable,
{
    ///   The wire format for each parameter is a sequence of IP addresses in
    ///   network byte order.  Like an A or AAAA RRSet, the list of addresses
    ///   represents an unordered collection, and clients SHOULD pick addresses
    ///   to use in a random order.  An empty list of addresses is invalid.
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        for ip in self.0.iter() {
            ip.emit(encoder)?;
        }

        Ok(())
    }
}

impl<T> fmt::Display for IpHint<T>
where
    T: fmt::Display,
{
    ///   The presentation "value" SHALL be a comma-separated list
    ///   (Appendix A.1) of one or more IP addresses of the appropriate family
    ///   in standard textual format [RFC5952].  To enable simpler parsing,
    ///   this SvcParamValue MUST NOT contain escape sequences.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for ip in self.0.iter() {
            write!(f, "{},", ip)?;
        }

        Ok(())
    }
}

/// [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-2.1)
/// ```text
/// Unrecognized keys are represented in presentation format as
///   "keyNNNNN" where NNNNN is the numeric value of the key type without
///   leading zeros.  A SvcParam in this form SHALL be parsed as specified
///   above, and the decoded "value" SHALL be used as its wire format
///   encoding.
///
///   For some SvcParamKeys, the "value" corresponds to a list or set of
///   items.  Presentation formats for such keys SHOULD use a comma-
///   separated list (Appendix A.1).
///
///   SvcParams in presentation format MAY appear in any order, but keys
///   MUST NOT be repeated.
/// ```
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
#[repr(transparent)]
pub struct Unknown(pub Vec<Vec<u8>>);

impl<'r> BinDecodable<'r> for Unknown {
    fn read(decoder: &mut BinDecoder<'r>) -> ProtoResult<Self> {
        let mut unknowns = Vec::new();

        while decoder.peek().is_some() {
            let data = decoder.read_character_data()?;
            let data = data.unverified(/*any data is valid here*/).to_vec();
            unknowns.push(data)
        }

        Ok(Unknown(unknowns))
    }
}

impl BinEncodable for Unknown {
    fn emit(&self, encoder: &mut BinEncoder<'_>) -> ProtoResult<()> {
        for unknown in self.0.iter() {
            encoder.emit_character_data(unknown)?;
        }

        Ok(())
    }
}

impl fmt::Display for Unknown {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        for unknown in self.0.iter() {
            // TODO: this needs to be properly encoded
            write!(f, "\"{}\",", String::from_utf8_lossy(unknown))?;
        }

        Ok(())
    }
}

/// Reads the SVCB record from the decoder.
///
/// ```text
///   Clients MUST consider an RR malformed if:
///
///   *  the end of the RDATA occurs within a SvcParam.
///   *  SvcParamKeys are not in strictly increasing numeric order.
///   *  the SvcParamValue for an SvcParamKey does not have the expected
///      format.
///
///   Note that the second condition implies that there are no duplicate
///   SvcParamKeys.
///
///   If any RRs are malformed, the client MUST reject the entire RRSet and
///   fall back to non-SVCB connection establishment.
/// ```
pub fn read(decoder: &mut BinDecoder<'_>, rdata_length: Restrict<u16>) -> ProtoResult<SVCB> {
    let start_index = decoder.index();

    let svc_priority = decoder.read_u16()?.unverified(/*any u16 is valid*/);
    let target_name = Name::read(decoder)?;

    let mut remainder_len = rdata_length.map(|len| len as usize - (decoder.index() - start_index)).unverified(/*valid len*/);
    let mut svc_params: Vec<(SvcParamKey, SvcParamValue)> = Vec::new();

    // must have at least 4 bytes left for the key and the length
    while remainder_len >= 4 {
        // a 2 octet field containing the SvcParamKey as an integer in
        //      network byte order.  (See Section 14.3.2 for the defined values.)
        let key = SvcParamKey::read(decoder)?;

        // a 2 octet field containing the length of the SvcParamValue as an
        //      integer between 0 and 65535 in network byte order (but constrained
        //      by the RDATA and DNS message sizes).
        let value = SvcParamValue::read(key, decoder)?;

        if let Some(last_key) = svc_params.last().map(|(key, _)| key) {
            if last_key >= &key {
                return Err(ProtoError::from("SvcParams out of order"));
            }
        }

        svc_params.push((key, value));
        remainder_len = rdata_length.map(|len| len as usize - (decoder.index() - start_index)).unverified(/*valid len*/);
    }

    Ok(SVCB {
        svc_priority,
        target_name,
        svc_params,
    })
}

/// Write the RData from the given Decoder
pub fn emit(encoder: &mut BinEncoder<'_>, svcb: &SVCB) -> ProtoResult<()> {
    svcb.svc_priority.emit(encoder)?;
    svcb.target_name.emit(encoder)?;

    let mut last_key: Option<SvcParamKey> = None;
    for (key, param) in svcb.svc_params.iter() {
        if let Some(last_key) = last_key {
            if key <= &last_key {
                return Err(ProtoError::from("SvcParams out of order"));
            }
        }

        key.emit(encoder)?;
        param.emit(encoder)?;

        last_key = Some(*key);
    }

    Ok(())
}

/// [draft-ietf-dnsop-svcb-https-03 SVCB and HTTPS RRs for DNS, February 2021](https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-03#section-10.3)
///
/// ```text
/// simple.example. 7200 IN HTTPS 1 . alpn=h3
/// pool  7200 IN HTTPS 1 h3pool alpn=h2,h3 echconfig="123..."
///               HTTPS 2 .      alpn=h2 echconfig="abc..."
/// @     7200 IN HTTPS 0 www
/// _8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net.
/// ```
impl fmt::Display for SVCB {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        write!(
            f,
            "{svc_priority} {target_name}",
            svc_priority = self.svc_priority,
            target_name = self.target_name,
        )?;

        for (key, param) in self.svc_params.iter() {
            write!(f, " {key}={param}", key = key, param = param)?
        }

        Ok(())
    }
}

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

    #[test]
    fn read_svcb_key() {
        assert_eq!(SvcParamKey::Mandatory, 0.into());
        assert_eq!(SvcParamKey::Alpn, 1.into());
        assert_eq!(SvcParamKey::NoDefaultAlpn, 2.into());
        assert_eq!(SvcParamKey::Port, 3.into());
        assert_eq!(SvcParamKey::Ipv4Hint, 4.into());
        assert_eq!(SvcParamKey::EchConfig, 5.into());
        assert_eq!(SvcParamKey::Ipv6Hint, 6.into());
        assert_eq!(SvcParamKey::Key(65280), 65280.into());
        assert_eq!(SvcParamKey::Key(65534), 65534.into());
        assert_eq!(SvcParamKey::Key65535, 65535.into());
        assert_eq!(SvcParamKey::Unknown(65279), 65279.into());
    }

    #[test]
    fn read_svcb_key_to_u16() {
        assert_eq!(u16::from(SvcParamKey::Mandatory), 0);
        assert_eq!(u16::from(SvcParamKey::Alpn), 1);
        assert_eq!(u16::from(SvcParamKey::NoDefaultAlpn), 2);
        assert_eq!(u16::from(SvcParamKey::Port), 3);
        assert_eq!(u16::from(SvcParamKey::Ipv4Hint), 4);
        assert_eq!(u16::from(SvcParamKey::EchConfig), 5);
        assert_eq!(u16::from(SvcParamKey::Ipv6Hint), 6);
        assert_eq!(u16::from(SvcParamKey::Key(65280)), 65280);
        assert_eq!(u16::from(SvcParamKey::Key(65534)), 65534);
        assert_eq!(u16::from(SvcParamKey::Key65535), 65535);
        assert_eq!(u16::from(SvcParamKey::Unknown(65279)), 65279);
    }

    // TODO: add this back after upgrading rustc version to 1.46
    // #[track_caller]
    fn test_encode_decode(rdata: SVCB) {
        let mut bytes = Vec::new();
        let mut encoder: BinEncoder<'_> = BinEncoder::new(&mut bytes);
        emit(&mut encoder, &rdata).expect("failed to emit SVCB");
        let bytes = encoder.into_bytes();

        println!("svcb: {}", rdata);
        println!("bytes: {:?}", bytes);

        let mut decoder: BinDecoder<'_> = BinDecoder::new(bytes);
        let read_rdata =
            read(&mut decoder, Restrict::new(bytes.len() as u16)).expect("failed to read back");
        assert_eq!(rdata, read_rdata);
    }

    #[test]
    fn test_encode_decode_svcb() {
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8("www.example.com.").unwrap(),
            vec![],
        ));
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8(".").unwrap(),
            vec![(
                SvcParamKey::Alpn,
                SvcParamValue::Alpn(Alpn(vec!["h2".to_string()])),
            )],
        ));
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8("example.com.").unwrap(),
            vec![
                (
                    SvcParamKey::Mandatory,
                    SvcParamValue::Mandatory(Mandatory(vec![SvcParamKey::Alpn])),
                ),
                (
                    SvcParamKey::Alpn,
                    SvcParamValue::Alpn(Alpn(vec!["h2".to_string()])),
                ),
            ],
        ));
    }

    #[test]
    #[should_panic]
    fn test_encode_decode_svcb_bad_order() {
        test_encode_decode(SVCB::new(
            0,
            Name::from_utf8(".").unwrap(),
            vec![
                (
                    SvcParamKey::Alpn,
                    SvcParamValue::Alpn(Alpn(vec!["h2".to_string()])),
                ),
                (
                    SvcParamKey::Mandatory,
                    SvcParamValue::Mandatory(Mandatory(vec![SvcParamKey::Alpn])),
                ),
            ],
        ));
    }
}