1 files changed, 165 insertions, 0 deletions
diff --git a/src/server/resolver.rs b/src/server/resolver.rs
new file mode 100644
index 0000000..464620c
--- /dev/null
+++ b/src/server/resolver.rs
@@ -0,0 +1,165 @@
+use super::binding::Connection;
+use crate::{
+    config::Config,
+    packet::{
+        query::QueryType, question::DnsQuestion, result::ResultCode, Packet,
+        Result,
+    }, get_time,
+};
+use async_recursion::async_recursion;
+use moka::future::Cache;
+use std::{net::IpAddr, sync::Arc, time::Duration};
+use tracing::{error, trace};
+
+pub struct Resolver {
+    request_id: u16,
+    connection: Connection,
+    config: Arc<Config>,
+    cache: Cache<DnsQuestion, (Packet, u64)>,
+}
+
+impl Resolver {
+    pub fn new(
+        request_id: u16,
+        connection: Connection,
+        config: Arc<Config>,
+        cache: Cache<DnsQuestion, (Packet, u64)>,
+    ) -> Self {
+        Self {
+            request_id,
+            connection,
+            config,
+            cache,
+        }
+    }
+
+    async fn lookup_cache(&mut self, qname: &str, qtype: QueryType) -> Option<Packet> {
+        let question = DnsQuestion::new(qname.to_string(), qtype);
+        let Some((packet, date)) = self.cache.get(&question) else {
+            return None
+        };
+
+        let now = get_time();
+        let diff = Duration::from_millis(now - date).as_secs() as u32;
+
+        for answer in &packet.answers {
+            let ttl = answer.get_ttl();
+            if diff > ttl {
+                self.cache.invalidate(&question).await;
+                return None
+            }
+        }
+
+        trace!("Found cached value for {qtype:?} {qname}");
+
+        Some(packet)
+    }
+
+    async fn lookup(&mut self, qname: &str, qtype: QueryType, server: (IpAddr, u16)) -> Packet {
+        let mut packet = Packet::new();
+
+        packet.header.id = self.request_id;
+        packet.header.questions = 1;
+        packet.header.recursion_desired = true;
+        packet
+            .questions
+            .push(DnsQuestion::new(qname.to_string(), qtype));
+
+        let packet = match self.connection.request_packet(packet, server).await {
+            Ok(packet) => packet,
+            Err(e) => {
+                error!("Failed to complete nameserver request: {e}");
+                let mut packet = Packet::new();
+                packet.header.rescode = ResultCode::SERVFAIL;
+                packet
+            }
+        };
+
+        packet
+    }
+
+    #[async_recursion]
+    async fn recursive_lookup(&mut self, qname: &str, qtype: QueryType) -> Packet {
+        let question = DnsQuestion::new(qname.to_string(), qtype);
+        let mut ns = self.config.get_fallback_ns().clone();
+
+        if let Some(packet) = self.lookup_cache(qname, qtype).await { return packet }
+
+        loop {
+            trace!("Attempting lookup of {qtype:?} {qname} with ns {ns}");
+
+            let ns_copy = ns;
+
+            let server = (ns_copy, 53);
+            let response = self.lookup(qname, qtype, server).await;
+
+            if !response.answers.is_empty() && response.header.rescode == ResultCode::NOERROR {
+                self.cache.insert(question, (response.clone(), get_time())).await;
+                return response;
+            }
+
+            if response.header.rescode == ResultCode::NXDOMAIN {
+                self.cache.insert(question, (response.clone(), get_time())).await;
+                return response;
+            }
+
+            if let Some(new_ns) = response.get_resolved_ns(qname) {
+                ns = new_ns;
+                continue;
+            }
+
+            let new_ns_name = match response.get_unresolved_ns(qname) {
+                Some(x) => x,
+                None => {
+                    self.cache.insert(question, (response.clone(), get_time())).await;
+                    return response
+                },
+            };
+
+            let recursive_response = self.recursive_lookup(new_ns_name, QueryType::A).await;
+
+            if let Some(new_ns) = recursive_response.get_random_a() {
+                ns = new_ns;
+            } else {
+                self.cache.insert(question, (response.clone(), get_time())).await;
+                return response;
+            }
+        }
+    }
+
+    pub async fn handle_query(mut self) -> Result<()> {
+        let mut request = self.connection.read_packet().await?;
+
+        let mut packet = Packet::new();
+        packet.header.id = request.header.id;
+        packet.header.recursion_desired = true;
+        packet.header.recursion_available = true;
+        packet.header.response = true;
+
+        if let Some(question) = request.questions.pop() {
+            trace!("Received query: {question:?}");
+
+            let result = self.recursive_lookup(&question.name, question.qtype).await;
+            packet.questions.push(question.clone());
+            packet.header.rescode = result.header.rescode;
+
+            for rec in result.answers {
+                trace!("Answer: {rec:?}");
+                packet.answers.push(rec);
+            }
+            for rec in result.authorities {
+                trace!("Authority: {rec:?}");
+                packet.authorities.push(rec);
+            }
+            for rec in result.resources {
+                trace!("Resource: {rec:?}");
+                packet.resources.push(rec);
+            }
+        } else {
+            packet.header.rescode = ResultCode::FORMERR;
+        }
+
+        self.connection.write_packet(packet).await?;
+        Ok(())
+    }
+}