inital working dns

1 files changed, 157 insertions, 0 deletions

diff --git a/packet/src/lib.rs b/packet/src/lib.rs
new file mode 100644
index 0000000..6c9a097
--- /dev/null
+++ b/packet/src/lib.rs
@@ -0,0 +1,157 @@
+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() -> Packet {
+        Packet {
+            header: DnsHeader::new(),
+            questions: Vec::new(),
+            answers: Vec::new(),
+            authorities: Vec::new(),
+            resources: Vec::new(),
+        }
+    }
+
+    pub fn from_buffer(buffer: &mut PacketBuffer) -> Result<Packet> {
+        let mut result = Packet::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,
+                    })
+            })
+            .map(|addr| addr)
+            // 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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