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/*
* Copyright (C) 2015 Benjamin Fry <benjaminfry@me.com>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
//! mail exchange, email, record
use std::fmt;
#[cfg(feature = "serde-config")]
use serde::{Deserialize, Serialize};
use crate::error::*;
use crate::rr::domain::Name;
use crate::serialize::binary::*;
/// [RFC 1035, DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION, November 1987](https://tools.ietf.org/html/rfc1035)
///
/// ```text
/// 3.3.9. MX RDATA format
///
/// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/// | PREFERENCE |
/// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/// / EXCHANGE /
/// / /
/// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
///
/// MX records cause type A additional section processing for the host
/// specified by EXCHANGE. The use of MX RRs is explained in detail in
/// [RFC-974].
///
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct MX {
preference: u16,
exchange: Name,
}
impl MX {
/// Constructs a new MX RData
///
/// # Arguments
///
/// * `preference` - weight of this MX record as opposed to others, lower values have the higher preference
/// * `exchange` - Name labels for the mail server
///
/// # Returns
///
/// A new MX RData for use in a Resource Record
pub fn new(preference: u16, exchange: Name) -> Self {
Self {
preference,
exchange,
}
}
/// [RFC 1035, DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION, November 1987](https://tools.ietf.org/html/rfc1035)
///
/// ```text
/// PREFERENCE A 16 bit integer which specifies the preference given to
/// this RR among others at the same owner. Lower values
/// are preferred.
/// ```
pub fn preference(&self) -> u16 {
self.preference
}
/// [RFC 1035, DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION, November 1987](https://tools.ietf.org/html/rfc1035)
///
/// ```text
/// EXCHANGE A <domain-name> which specifies a host willing to act as
/// a mail exchange for the owner name.
/// ```
pub fn exchange(&self) -> &Name {
&self.exchange
}
}
/// Read the RData from the given Decoder
pub fn read(decoder: &mut BinDecoder<'_>) -> ProtoResult<MX> {
Ok(MX::new(
decoder.read_u16()?.unverified(/*any u16 is valid*/),
Name::read(decoder)?,
))
}
/// [RFC 4034](https://tools.ietf.org/html/rfc4034#section-6), DNSSEC Resource Records, March 2005
///
/// ```text
/// 6.2. Canonical RR Form
///
/// For the purposes of DNS security, the canonical form of an RR is the
/// wire format of the RR where:
///
/// ...
///
/// 3. if the type of the RR is NS, MD, MF, CNAME, SOA, MB, MG, MR, PTR,
/// HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, NAPTR, KX,
/// SRV, DNAME, A6, RRSIG, or NSEC (rfc6840 removes NSEC), all uppercase
/// US-ASCII letters in the DNS names contained within the RDATA are replaced
/// by the corresponding lowercase US-ASCII letters;
/// ```
pub fn emit(encoder: &mut BinEncoder<'_>, mx: &MX) -> ProtoResult<()> {
let is_canonical_names = encoder.is_canonical_names();
encoder.emit_u16(mx.preference())?;
mx.exchange()
.emit_with_lowercase(encoder, is_canonical_names)?;
Ok(())
}
/// [RFC 1033](https://tools.ietf.org/html/rfc1033), DOMAIN OPERATIONS GUIDE, November 1987
/// ```text
/// MX (Mail Exchanger) (See RFC-974 for more details.)
///
/// <name> [<ttl>] [<class>] MX <preference> <host>
///
/// MX records specify where mail for a domain name should be delivered.
/// There may be multiple MX records for a particular name. The
/// preference value specifies the order a mailer should try multiple MX
/// records when delivering mail. Zero is the highest preference.
/// Multiple records for the same name may have the same preference.
///
/// A host BAR.FOO.COM may want its mail to be delivered to the host
/// PO.FOO.COM and would then use the MX record:
///
/// BAR.FOO.COM. MX 10 PO.FOO.COM.
///
/// A host BAZ.FOO.COM may want its mail to be delivered to one of three
/// different machines, in the following order:
///
/// BAZ.FOO.COM. MX 10 PO1.FOO.COM.
/// MX 20 PO2.FOO.COM.
/// MX 30 PO3.FOO.COM.
///
/// An entire domain of hosts not connected to the Internet may want
/// their mail to go through a mail gateway that knows how to deliver
/// mail to them. If they would like mail addressed to any host in the
/// domain FOO.COM to go through the mail gateway they might use:
///
/// FOO.COM. MX 10 RELAY.CS.NET.
/// *.FOO.COM. MX 20 RELAY.CS.NET.
///
/// Note that you can specify a wildcard in the MX record to match on
/// anything in FOO.COM, but that it won't match a plain FOO.COM.
impl fmt::Display for MX {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
write!(f, "{pref} {ex}", pref = self.preference, ex = self.exchange)
}
}
#[cfg(test)]
mod tests {
#![allow(clippy::dbg_macro, clippy::print_stdout)]
use super::*;
#[test]
fn test() {
use std::str::FromStr;
let rdata = MX::new(16, Name::from_str("mail.example.com").unwrap());
let mut bytes = Vec::new();
let mut encoder: BinEncoder<'_> = BinEncoder::new(&mut bytes);
assert!(emit(&mut encoder, &rdata).is_ok());
let bytes = encoder.into_bytes();
println!("bytes: {:?}", bytes);
let mut decoder: BinDecoder<'_> = BinDecoder::new(bytes);
let read_rdata = read(&mut decoder).expect("Decoding error");
assert_eq!(rdata, read_rdata);
}
}