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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.
*/
//! service records for identify port mapping for specific services on a host
use std::fmt;
#[cfg(feature = "serde-config")]
use serde::{Deserialize, Serialize};
use crate::error::*;
use crate::rr::domain::Name;
use crate::serialize::binary::*;
/// [RFC 2782, DNS SRV RR, February 2000](https://tools.ietf.org/html/rfc2782)
///
/// ```text
/// Introductory example
///
/// If a SRV-cognizant LDAP client wants to discover a LDAP server that
/// supports TCP protocol and provides LDAP service for the domain
/// example.com., it does a lookup of
///
/// _ldap._tcp.example.com
///
/// as described in [ARM]. The example zone file near the end of this
/// memo contains answering RRs for an SRV query.
///
/// Note: LDAP is chosen as an example for illustrative purposes only,
/// and the LDAP examples used in this document should not be considered
/// a definitive statement on the recommended way for LDAP to use SRV
/// records. As described in the earlier applicability section, consult
/// the appropriate LDAP documents for the recommended procedures.
///
/// The format of the SRV RR
///
/// Here is the format of the SRV RR, whose DNS type code is 33:
///
/// _Service._Proto.Name TTL Class SRV Priority Weight Port Target
///
/// (There is an example near the end of this document.)
///
/// Service
/// The symbolic name of the desired service, as defined in Assigned
/// Numbers [STD 2] or locally. An underscore (_) is prepended to
/// the service identifier to avoid collisions with DNS labels that
/// occur in nature.
///
/// Some widely used services, notably POP, don't have a single
/// universal name. If Assigned Numbers names the service
/// indicated, that name is the only name which is legal for SRV
/// lookups. The Service is case insensitive.
///
/// Proto
/// The symbolic name of the desired protocol, with an underscore
/// (_) prepended to prevent collisions with DNS labels that occur
/// in nature. _TCP and _UDP are at present the most useful values
/// for this field, though any name defined by Assigned Numbers or
/// locally may be used (as for Service). The Proto is case
/// insensitive.
///
/// Name
/// The domain this RR refers to. The SRV RR is unique in that the
/// name one searches for is not this name; the example near the end
/// shows this clearly.
///
/// TTL
/// Standard DNS meaning [RFC 1035].
///
/// Class
/// Standard DNS meaning [RFC 1035]. SRV records occur in the IN
/// Class.
///
/// ```
#[cfg_attr(feature = "serde-config", derive(Deserialize, Serialize))]
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct SRV {
priority: u16,
weight: u16,
port: u16,
target: Name,
}
impl SRV {
/// Creates a new SRV record data.
///
/// # Arguments
///
/// * `priority` - lower values have a higher priority and clients will attempt to use these
/// first.
/// * `weight` - for servers with the same priority, higher weights will be chosen more often.
/// * `port` - the socket port number on which the service is listening.
/// * `target` - like CNAME, this is the target domain name to which the service is associated.
///
/// # Return value
///
/// The newly constructed SRV record data.
pub fn new(priority: u16, weight: u16, port: u16, target: Name) -> Self {
Self {
priority,
weight,
port,
target,
}
}
/// ```text
/// Priority
/// The priority of this target host. A client MUST attempt to
/// contact the target host with the lowest-numbered priority it can
/// reach; target hosts with the same priority SHOULD be tried in an
/// order defined by the weight field. The range is 0-65535. This
/// is a 16 bit unsigned integer in network byte order.
/// ```
pub fn priority(&self) -> u16 {
self.priority
}
/// ```text
/// Weight
/// A server selection mechanism. The weight field specifies a
/// relative weight for entries with the same priority. Larger
/// weights SHOULD be given a proportionately higher probability of
/// being selected. The range of this number is 0-65535. This is a
/// 16 bit unsigned integer in network byte order. Domain
/// administrators SHOULD use Weight 0 when there isn't any server
/// selection to do, to make the RR easier to read for humans (less
/// noisy). In the presence of records containing weights greater
/// than 0, records with weight 0 should have a very small chance of
/// being selected.
///
/// In the absence of a protocol whose specification calls for the
/// use of other weighting information, a client arranges the SRV
/// RRs of the same Priority in the order in which target hosts,
/// specified by the SRV RRs, will be contacted. The following
/// algorithm SHOULD be used to order the SRV RRs of the same
/// priority:
///
/// To select a target to be contacted next, arrange all SRV RRs
/// (that have not been ordered yet) in any order, except that all
/// those with weight 0 are placed at the beginning of the list.
///
/// Compute the sum of the weights of those RRs, and with each RR
/// associate the running sum in the selected order. Then choose a
/// uniform random number between 0 and the sum computed
/// (inclusive), and select the RR whose running sum value is the
/// first in the selected order which is greater than or equal to
/// the random number selected. The target host specified in the
/// selected SRV RR is the next one to be contacted by the client.
/// Remove this SRV RR from the set of the unordered SRV RRs and
/// apply the described algorithm to the unordered SRV RRs to select
/// the next target host. Continue the ordering process until there
/// are no unordered SRV RRs. This process is repeated for each
/// Priority.
/// ```
pub fn weight(&self) -> u16 {
self.weight
}
/// ```text
/// Port
/// The port on this target host of this service. The range is 0-
/// 65535. This is a 16 bit unsigned integer in network byte order.
/// This is often as specified in Assigned Numbers but need not be.
///
/// ```
pub fn port(&self) -> u16 {
self.port
}
/// ```text
/// Target
/// The domain name of the target host. There MUST be one or more
/// address records for this name, the name MUST NOT be an alias (in
/// the sense of RFC 1034 or RFC 2181). Implementors are urged, but
/// not required, to return the address record(s) in the Additional
/// Data section. Unless and until permitted by future standards
/// action, name compression is not to be used for this field.
///
/// A Target of "." means that the service is decidedly not
/// available at this domain.
/// ```
pub fn target(&self) -> &Name {
&self.target
}
}
/// Read the RData from the given Decoder
pub fn read(decoder: &mut BinDecoder<'_>) -> ProtoResult<SRV> {
// SRV { priority: u16, weight: u16, port: u16, target: Name, },
Ok(SRV::new(
decoder.read_u16()?.unverified(/*any u16 is valid*/),
decoder.read_u16()?.unverified(/*any u16 is valid*/),
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
///
/// This is accurate for all currently known name records.
///
/// ```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 (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<'_>, srv: &SRV) -> ProtoResult<()> {
let is_canonical_names = encoder.is_canonical_names();
encoder.emit_u16(srv.priority())?;
encoder.emit_u16(srv.weight())?;
encoder.emit_u16(srv.port())?;
srv.target()
.emit_with_lowercase(encoder, is_canonical_names)?;
Ok(())
}
/// [RFC 2782, DNS SRV RR, February 2000](https://tools.ietf.org/html/rfc2782)
///
/// ```text
/// The format of the SRV RR
///
/// Here is the format of the SRV RR, whose DNS type code is 33:
///
/// _Service._Proto.Name TTL Class SRV Priority Weight Port Target
///
/// (There is an example near the end of this document.)
/// ```
impl fmt::Display for SRV {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
write!(
f,
"{priority} {weight} {port} {target}",
priority = self.priority,
weight = self.weight,
port = self.port,
target = self.target,
)
}
}
#[cfg(test)]
mod tests {
#![allow(clippy::dbg_macro, clippy::print_stdout)]
use super::*;
#[test]
fn test() {
use std::str::FromStr;
let rdata = SRV::new(1, 2, 3, Name::from_str("_dns._tcp.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);
}
}