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use std::net::IpAddr;
use self::{header::DnsHeader, question::DnsQuestion, record::DnsRecord, query::QueryType};
type Error = Box<dyn std::error::Error>;
pub type Result<T> = std::result::Result<T, Error>;
mod buffer;
mod header;
mod query;
mod question;
mod record;
mod result;
#[derive(Clone, Debug)]
pub struct Packet {
pub header: DnsHeader,
pub questions: Vec<DnsQuestion>,
pub answers: Vec<DnsRecord>,
pub authorities: Vec<DnsRecord>,
pub resources: Vec<DnsRecord>,
}
pub use buffer::PacketBuffer;
pub use result::ResultCode;
pub use query::QueryType as PacketType;
pub use question::DnsQuestion as PacketQuestion;
impl Packet {
pub fn new() -> Self {
Self {
header: DnsHeader::new(),
questions: Vec::new(),
answers: Vec::new(),
authorities: Vec::new(),
resources: Vec::new(),
}
}
pub fn from_buffer(buffer: &mut PacketBuffer) -> Result<Self> {
let mut result = Self::new();
result.header.read(buffer)?;
for _ in 0..result.header.questions {
let mut question = DnsQuestion::new("".to_string(), QueryType::UNKNOWN(0));
question.read(buffer)?;
result.questions.push(question);
}
for _ in 0..result.header.answers {
let rec = DnsRecord::read(buffer)?;
result.answers.push(rec);
}
for _ in 0..result.header.authoritative_entries {
let rec = DnsRecord::read(buffer)?;
result.authorities.push(rec);
}
for _ in 0..result.header.resource_entries {
let rec = DnsRecord::read(buffer)?;
result.resources.push(rec);
}
Ok(result)
}
pub fn write(&mut self, buffer: &mut PacketBuffer) -> Result<()> {
self.header.questions = self.questions.len() as u16;
self.header.answers = self.answers.len() as u16;
self.header.authoritative_entries = self.authorities.len() as u16;
self.header.resource_entries = self.resources.len() as u16;
self.header.write(buffer)?;
for question in &self.questions {
question.write(buffer)?;
}
for rec in &self.answers {
rec.write(buffer)?;
}
for rec in &self.authorities {
rec.write(buffer)?;
}
for rec in &self.resources {
rec.write(buffer)?;
}
Ok(())
}
/// It's useful to be able to pick a random A record from a packet. When we
/// get multiple IP's for a single name, it doesn't matter which one we
/// choose, so in those cases we can now pick one at random.
pub fn get_random_a(&self) -> Option<IpAddr> {
self.answers
.iter()
.filter_map(|record| match record {
DnsRecord::A { addr, .. } => Some(IpAddr::V4(*addr)),
DnsRecord::AAAA { addr, .. } => Some(IpAddr::V6(*addr)),
_ => None,
})
.next()
}
/// A helper function which returns an iterator over all name servers in
/// the authorities section, represented as (domain, host) tuples
fn get_ns<'a>(&'a self, qname: &'a str) -> impl Iterator<Item = (&'a str, &'a str)> {
self.authorities
.iter()
// In practice, these are always NS records in well formed packages.
// Convert the NS records to a tuple which has only the data we need
// to make it easy to work with.
.filter_map(|record| match record {
DnsRecord::NS { domain, host, .. } => Some((domain.as_str(), host.as_str())),
_ => None,
})
// Discard servers which aren't authoritative to our query
.filter(move |(domain, _)| qname.ends_with(*domain))
}
/// We'll use the fact that name servers often bundle the corresponding
/// A records when replying to an NS query to implement a function that
/// returns the actual IP for an NS record if possible.
pub fn get_resolved_ns(&self, qname: &str) -> Option<IpAddr> {
// Get an iterator over the nameservers in the authorities section
self.get_ns(qname)
// Now we need to look for a matching A record in the additional
// section. Since we just want the first valid record, we can just
// build a stream of matching records.
.flat_map(|(_, host)| {
self.resources
.iter()
// Filter for A records where the domain match the host
// of the NS record that we are currently processing
.filter_map(move |record| match record {
DnsRecord::A { domain, addr, .. } if domain == host => Some(IpAddr::V4(*addr)),
DnsRecord::AAAA { domain, addr, .. } if domain == host => Some(IpAddr::V6(*addr)),
_ => None,
})
})
// Finally, pick the first valid entry
.next()
}
/// However, not all name servers are as that nice. In certain cases there won't
/// be any A records in the additional section, and we'll have to perform *another*
/// lookup in the midst. For this, we introduce a method for returning the host
/// name of an appropriate name server.
pub fn get_unresolved_ns<'a>(&'a self, qname: &'a str) -> Option<&'a str> {
// Get an iterator over the nameservers in the authorities section
self.get_ns(qname)
.map(|(_, host)| host)
// Finally, pick the first valid entry
.next()
}
}
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