.

.gitignore

@@ -1,3 +1,4 @@
 /target
 .env
+nanodns.toml
 test.sh

src/config.rs

@@ -1,16 +1,69 @@
-use anyhow::Result;
+use anyhow::{Result, ensure};
 use serde::Deserialize;
 
 #[derive(Deserialize)]
-pub struct ConfigData {
+pub struct Entry {
+    pub name: String,
+    pub address: String,
+    #[serde(skip)]
+    pub address_bytes: [u8; 4],
+}
+
+#[derive(Deserialize)]
+struct EnvConfigData {
     pub port: u16,
 }
 
+#[derive(Deserialize)]
+struct FileConfigData {
+    #[serde(default, rename = "entry")]
+    pub entries: Vec<Entry>,
+}
+
+pub struct ConfigData {
+    pub port: u16,
+    pub entries: Vec<Entry>,
+}
+
+impl ConfigData {
+    pub fn get_address_by_domain(&self, domain: &str) -> Option<[u8; 4]> {
+        self.entries
+            .iter()
+            .find(|e| e.name.as_str() == domain)
+            .map(|e| e.address_bytes)
+    }
+}
+
 pub fn load() -> Result<ConfigData> {
+    let env_config = {
         let source = config::Environment::default();
         let builder = config::Config::builder()
             .add_source(source)
             .set_default("port", 53)?;
-    let config = builder.build()?.try_deserialize()?;
-    Ok(config)
+        let config: EnvConfigData = builder.build()?.try_deserialize()?;
+        config
+    };
+
+    let mut file_config = {
+        let source = config::File::with_name("nanodns").required(false);
+        let builder = config::Config::builder().add_source(source);
+        let config: FileConfigData = builder.build()?.try_deserialize()?;
+        config
+    };
+
+    for entry in &mut file_config.entries {
+        let address_parts: Vec<&str> = entry.address.split(".").collect();
+        ensure!(address_parts.len() == 4, "Invalid IP address");
+        entry.address_bytes = [
+            address_parts[0].parse()?,
+            address_parts[1].parse()?,
+            address_parts[2].parse()?,
+            address_parts[3].parse()?,
+        ];
+    }
+
+    Ok(ConfigData {
+        port: env_config.port,
+        entries: file_config.entries,
+    })
 }

src/dns.rs

@@ -1,179 +0,0 @@
-#![allow(unused)]
-use std::fmt::Display;
-
-use anyhow::{Result, bail};
-
-const QUESTION_TYPE_A: u16 = 0x01;
-const QUESTION_TYPE_NS: u16 = 0x02;
-const QUESTION_TYPE_CNAME: u16 = 0x05;
-const QUESTION_TYPE_AAAA: u16 = 0x1C;
-const QUESTION_TYPE_MX: u16 = 0x0F;
-
-const QUESTION_CLASS_IN: u16 = 0x01;
-const QUESTION_CLASS_CHAOS: u16 = 0x03;
-const QUESTION_CLASS_HS: u16 = 0x04;
-const QUESTION_CLASS_ANY: u16 = 0xFF;
-
-pub struct DnsHeader {
-    pub transaction_id: [u8; 2],
-    pub query_response: bool,
-    pub op_code: u8, // 4 bits
-    pub authoritative_answer: bool,
-    pub truncation: bool,
-    pub recursion_desired: bool,
-    pub recursion_available: bool,
-    pub authentic_data: bool,
-    pub checking_disabled: bool,
-    pub response_code: u8, // 4 bits
-    pub number_of_questions: u16,
-    pub number_of_answers: u16,
-    pub number_of_authority_resource_records: u16,
-    pub number_of_additional_resource_records: u16,
-}
-
-impl DnsHeader {
-    pub fn parse(packet: &[u8]) -> Result<DnsHeader> {
-        if packet.len() < 12 {
-            bail!("malformed datagram");
-        }
-
-        let datagram = DnsHeader {
-            transaction_id: [packet[0], packet[1]],
-            query_response: packet[2] & (1 << 7) > 0,
-            op_code: (packet[2] >> 3) & 0x0F,
-            authoritative_answer: packet[2] & (1 << 2) > 0,
-            truncation: packet[2] & (1 << 1) > 0,
-            recursion_desired: packet[2] & (1 << 0) > 0,
-            recursion_available: packet[3] & (1 << 7) > 0,
-            authentic_data: packet[3] & (1 << 5) > 0,
-            checking_disabled: packet[3] & (1 << 4) > 0,
-            response_code: packet[3] & 0xF,
-            number_of_questions: u16::from_be_bytes([packet[4], packet[5]]),
-            number_of_answers: u16::from_be_bytes([packet[6], packet[7]]),
-            number_of_authority_resource_records: u16::from_be_bytes([packet[8], packet[9]]),
-            number_of_additional_resource_records: u16::from_be_bytes([packet[10], packet[11]]),
-        };
-
-        Ok(datagram)
-    }
-}
-
-impl Display for DnsHeader {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        writeln!(
-            f,
-            "transaction_id: {:x}{:x}",
-            self.transaction_id[0], self.transaction_id[1]
-        )?;
-        writeln!(f, "query_response: {}", self.query_response)?;
-        writeln!(f, "op_code: {}", self.op_code)?;
-        writeln!(f, "authoritative_answer: {}", self.authoritative_answer)?;
-        writeln!(f, "truncation: {}", self.truncation)?;
-        writeln!(f, "recursion_desired: {}", self.recursion_desired)?;
-        writeln!(f, "recursion_available: {}", self.recursion_available)?;
-        writeln!(f, "authentic_data: {}", self.authentic_data)?;
-        writeln!(f, "checking_disabled: {}", self.checking_disabled)?;
-        writeln!(f, "response_code: {}", self.response_code)?;
-        writeln!(f, "number_of_questions: {}", self.number_of_questions)?;
-        writeln!(f, "number_of_answers: {}", self.number_of_answers)?;
-        writeln!(
-            f,
-            "number_of_authority_rr: {}",
-            self.number_of_authority_resource_records
-        )?;
-        writeln!(
-            f,
-            "number_of_additional_rr: {}",
-            self.number_of_additional_resource_records
-        )?;
-        Ok(())
-    }
-}
-
-pub struct DnsQuestion {
-    pub domain: String,
-    pub question_type: u16,
-    pub question_class: u16,
-}
-
-impl DnsQuestion {
-    pub fn parse(packet: &[u8], pos: &mut usize) -> Result<DnsQuestion> {
-        let domain = parse_domain(packet, pos)?;
-
-        if *pos + 4 > packet.len() {
-            bail!("malformed datagram");
-        }
-
-        let question_type = ((packet[*pos] as u16) << 8) | (packet[*pos + 1] as u16);
-        let question_class = ((packet[*pos + 2] as u16) << 8) | (packet[*pos + 3] as u16);
-        *pos += 4;
-
-        let question = DnsQuestion {
-            domain,
-            question_type,
-            question_class,
-        };
-
-        Ok(question)
-    }
-}
-
-impl Display for DnsQuestion {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(
-            f,
-            "{}, {}, {}",
-            self.domain, self.question_type, self.question_class
-        )
-    }
-}
-
-pub struct DnsAnswer {
-    pub domain: String,
-    // TODO missing fields
-}
-
-impl DnsAnswer {
-    pub fn to_bytes(&self) -> Vec<u8> {
-        let mut result = vec![];
-
-        for part in self.domain.split(".") {
-            result.push(part.len() as u8);
-            part.bytes().for_each(|c| result.push(c));
-        }
-
-        result.push(0);
-        result
-    }
-}
-
-fn parse_domain(packet: &[u8], pos: &mut usize) -> Result<String> {
-    let packet_size = packet.len();
-    let mut domain_parts: Vec<String> = vec![];
-
-    loop {
-        if *pos >= packet_size {
-            bail!("malformed datagram");
-        }
-
-        let len = packet[*pos] as usize;
-        if len > 63 {
-            bail!("malformed datagram");
-        }
-        if len == 0 {
-            *pos += 1;
-            break;
-        }
-
-        if (*pos + 1 + len) > packet_size {
-            bail!("malformed datagram");
-        }
-
-        let domain_part_bytes = &packet[(*pos + 1)..(*pos + 1 + len)];
-        let domain_part = String::from_utf8_lossy(&domain_part_bytes);
-        domain_parts.push(domain_part.to_string());
-        *pos += 1 + len;
-    }
-
-    Ok(domain_parts.join("."))
-}

src/dns/answer.rs

@@ -0,0 +1,60 @@
+use anyhow::{Result, bail};
+
+use crate::dns::{domain_to_bytes, parse_domain};
+
+#[derive(Debug, Clone)]
+pub struct Answer {
+    pub domain: String,
+    pub record_type: u16,
+    pub class: u16,
+    pub ttl: u32,
+    pub data: Vec<u8>,
+}
+
+impl Answer {
+    pub fn parse(datagram: &[u8], pos: &mut usize) -> Result<Answer> {
+        let domain = parse_domain(datagram, pos)?;
+
+        if *pos + 10 > datagram.len() {
+            bail!("malformed datagram");
+        }
+
+        let record_type = u16::from_be_bytes([datagram[*pos], datagram[*pos + 1]]);
+        let class = u16::from_be_bytes([datagram[*pos + 2], datagram[*pos + 3]]);
+        let ttl = u32::from_be_bytes([
+            datagram[*pos + 4],
+            datagram[*pos + 5],
+            datagram[*pos + 6],
+            datagram[*pos + 7],
+        ]);
+        let data_length = u16::from_be_bytes([datagram[*pos + 8], datagram[*pos + 9]]) as usize;
+        *pos += 10;
+
+        if *pos + data_length > datagram.len() {
+            bail!("malformed datagram");
+        }
+
+        let data = datagram[*pos..*pos + data_length].to_vec();
+        *pos += data_length;
+
+        Ok(Answer {
+            domain,
+            record_type,
+            class,
+            ttl,
+            data,
+        })
+    }
+
+    pub fn to_bytes(&self) -> Result<Vec<u8>> {
+        let mut result = vec![];
+        result.extend(domain_to_bytes(&self.domain)?);
+        result.extend(self.record_type.to_be_bytes());
+        result.extend(self.class.to_be_bytes());
+        result.extend(self.ttl.to_be_bytes());
+        result.extend((self.data.len() as u16).to_be_bytes());
+        result.extend_from_slice(&self.data);
+
+        Ok(result)
+    }
+}

src/dns/constants.rs

@@ -0,0 +1,25 @@
+pub const RECORD_TYPE_A: u16 = 0x01;
+#[allow(dead_code)]
+pub const RECORD_TYPE_NS: u16 = 0x02;
+#[allow(dead_code)]
+pub const RECORD_TYPE_CNAME: u16 = 0x05;
+#[allow(dead_code)]
+pub const RECORD_TYPE_AAAA: u16 = 0x1C;
+#[allow(dead_code)]
+pub const RECORD_TYPE_MX: u16 = 0x0F;
+
+pub const CLASS_IN: u16 = 0x01;
+#[allow(dead_code)]
+pub const CLASS_CHAOS: u16 = 0x03;
+#[allow(dead_code)]
+pub const CLASS_HS: u16 = 0x04;
+#[allow(dead_code)]
+pub const CLASS_ANY: u16 = 0xFF;
+
+pub const RESPONSE_CODE_NO_ERROR: u8 = 0x00;
+#[allow(dead_code)]
+pub const RESPONSE_CODE_NXDOMAIN: u8 = 0x03;
+#[allow(dead_code)]
+pub const RESPONSE_CODE_NOT_IMPLEMENTED: u8 = 0x04;
+#[allow(dead_code)]
+pub const RESPONSE_CODE_REFUSED: u8 = 0x05;

src/dns/domainname.rs

@@ -0,0 +1,83 @@
+use anyhow::{Result, bail};
+
+pub fn parse_domain(datagram: &[u8], pos: &mut usize) -> Result<String> {
+    let mut domain_parts: Vec<String> = vec![];
+    let mut cursor = *pos;
+    let mut jumped = false;
+    let mut jumps = 0usize;
+
+    loop {
+        if cursor >= datagram.len() {
+            bail!("malformed datagram");
+        }
+
+        let len = datagram[cursor] as usize;
+        if (len & 0xC0) == 0xC0 {
+            if cursor + 1 >= datagram.len() {
+                bail!("malformed datagram");
+            }
+
+            let pointer = ((len & 0x3F) << 8) | datagram[cursor + 1] as usize;
+            if pointer >= datagram.len() {
+                bail!("malformed datagram");
+            }
+            if !jumped {
+                *pos = cursor + 2;
+                jumped = true;
+            }
+
+            jumps += 1;
+            if jumps > datagram.len() {
+                bail!("malformed datagram");
+            }
+
+            cursor = pointer;
+            continue;
+        }
+        if (len & 0xC0) != 0 {
+            bail!("malformed datagram");
+        }
+        if len > 63 {
+            bail!("malformed datagram");
+        }
+        if len == 0 {
+            if !jumped {
+                *pos = cursor + 1;
+            }
+            break;
+        }
+
+        if (cursor + 1 + len) > datagram.len() {
+            bail!("malformed datagram");
+        }
+
+        let domain_part_bytes = &datagram[(cursor + 1)..(cursor + 1 + len)];
+        let domain_part = String::from_utf8_lossy(&domain_part_bytes);
+        domain_parts.push(domain_part.to_string());
+        cursor += 1 + len;
+    }
+
+    Ok(domain_parts.join("."))
+}
+
+pub fn domain_to_bytes(domain: &str) -> Result<Vec<u8>> {
+    let mut result = Vec::new();
+    if domain.is_empty() {
+        result.push(0);
+        return Ok(result);
+    }
+
+    for part in domain.split(".") {
+        if part.len() > 63 {
+            bail!("domain label too long");
+        }
+        if part.is_empty() {
+            bail!("empty domain label");
+        }
+
+        result.push(part.len() as u8);
+        result.extend_from_slice(part.as_bytes());
+    }
+    result.push(0);
+    Ok(result)
+}

src/dns/header.rs

@@ -0,0 +1,92 @@
+use anyhow::{Result, bail};
+
+#[derive(Debug, Clone)]
+pub struct Header {
+    pub transaction_id: [u8; 2],
+    pub query_response: bool,
+    pub op_code: u8, // 4 bits
+    pub authoritative_answer: bool,
+    pub truncation: bool,
+    pub recursion_desired: bool,
+    pub recursion_available: bool,
+    pub authentic_data: bool,
+    pub checking_disabled: bool,
+    pub response_code: u8, // 4 bits
+    pub number_of_questions: u16,
+    pub number_of_answers: u16,
+    pub number_of_authority_resource_records: u16,
+    pub number_of_additional_resource_records: u16,
+}
+
+impl Header {
+    pub fn parse(datagram: &[u8]) -> Result<Header> {
+        if datagram.len() < 12 {
+            bail!("malformed datagram");
+        }
+
+        let datagram = Header {
+            transaction_id: [datagram[0], datagram[1]],
+            query_response: datagram[2] & (1 << 7) > 0,
+            op_code: (datagram[2] >> 3) & 0x0F,
+            authoritative_answer: datagram[2] & (1 << 2) > 0,
+            truncation: datagram[2] & (1 << 1) > 0,
+            recursion_desired: datagram[2] & (1 << 0) > 0,
+            recursion_available: datagram[3] & (1 << 7) > 0,
+            authentic_data: datagram[3] & (1 << 5) > 0,
+            checking_disabled: datagram[3] & (1 << 4) > 0,
+            response_code: datagram[3] & 0xF,
+            number_of_questions: u16::from_be_bytes([datagram[4], datagram[5]]),
+            number_of_answers: u16::from_be_bytes([datagram[6], datagram[7]]),
+            number_of_authority_resource_records: u16::from_be_bytes([datagram[8], datagram[9]]),
+            number_of_additional_resource_records: u16::from_be_bytes([datagram[10], datagram[11]]),
+        };
+
+        Ok(datagram)
+    }
+
+    pub fn to_bytes(&self) -> Result<Vec<u8>> {
+        let mut buffer = [0u8; 12];
+        let number_of_questions = self.number_of_questions.to_be_bytes();
+        let number_of_answers = self.number_of_answers.to_be_bytes();
+        let number_of_authority_resource_records =
+            self.number_of_authority_resource_records.to_be_bytes();
+        let number_of_additional_resource_records =
+            self.number_of_additional_resource_records.to_be_bytes();
+
+        buffer[0] = self.transaction_id[0];
+        buffer[1] = self.transaction_id[1];
+        if self.query_response {
+            buffer[2] |= 1 << 7;
+        }
+        buffer[2] |= (self.op_code & 0x0F) << 3;
+        if self.authoritative_answer {
+            buffer[2] |= 1 << 2;
+        }
+        if self.truncation {
+            buffer[2] |= 1 << 1;
+        }
+        if self.recursion_desired {
+            buffer[2] |= 1 << 0;
+        }
+        if self.recursion_available {
+            buffer[3] |= 1 << 7;
+        }
+        if self.authentic_data {
+            buffer[3] |= 1 << 5;
+        }
+        if self.checking_disabled {
+            buffer[3] |= 1 << 4;
+        }
+        buffer[3] |= self.response_code & 0x0F;
+        buffer[4] = number_of_questions[0];
+        buffer[5] = number_of_questions[1];
+        buffer[6] = number_of_answers[0];
+        buffer[7] = number_of_answers[1];
+        buffer[8] = number_of_authority_resource_records[0];
+        buffer[9] = number_of_authority_resource_records[1];
+        buffer[10] = number_of_additional_resource_records[0];
+        buffer[11] = number_of_additional_resource_records[1];
+
+        Ok(buffer.into())
+    }
+}

src/dns/message.rs

@@ -0,0 +1,69 @@
+use anyhow::Result;
+
+use crate::dns::{Answer, Header, Question, RESPONSE_CODE_NO_ERROR};
+
+#[derive(Debug, Clone)]
+pub struct Message {
+    pub header: Header,
+    pub questions: Vec<Question>,
+    pub answers: Vec<Answer>,
+}
+
+impl Message {
+    pub fn parse(datagram: &[u8]) -> Result<Message> {
+        let header = Header::parse(datagram)?;
+
+        let mut message = Message {
+            header: header,
+            questions: vec![],
+            answers: vec![],
+        };
+
+        let mut pos = 12usize;
+        for _ in 0..(message.header.number_of_questions) {
+            let question = Question::parse(datagram, &mut pos)?;
+            message.questions.push(question);
+        }
+        for _ in 0..(message.header.number_of_answers) {
+            let answer = Answer::parse(datagram, &mut pos)?;
+            message.answers.push(answer);
+        }
+
+        Ok(message)
+    }
+
+    pub fn to_bytes(&self) -> Result<Vec<u8>> {
+        let mut result: Vec<u8> = vec![];
+        result.extend(self.header.to_bytes()?);
+        for question in &self.questions {
+            result.extend(question.to_bytes()?);
+        }
+        for answer in &self.answers {
+            result.extend(answer.to_bytes()?);
+        }
+        Ok(result)
+    }
+
+    pub fn prepare_response(&self) -> Message {
+        Message {
+            header: Header {
+                transaction_id: self.header.transaction_id,
+                query_response: true,
+                op_code: self.header.op_code,
+                authoritative_answer: true,
+                truncation: false,
+                recursion_desired: self.header.recursion_desired,
+                recursion_available: false,
+                authentic_data: false,
+                checking_disabled: self.header.checking_disabled,
+                response_code: RESPONSE_CODE_NO_ERROR,
+                number_of_questions: self.header.number_of_questions,
+                number_of_answers: 0,
+                number_of_authority_resource_records: 0,
+                number_of_additional_resource_records: 0,
+            },
+            questions: self.questions.clone(),
+            answers: vec![],
+        }
+    }
+}

src/dns/mod.rs

@@ -0,0 +1,64 @@
+mod answer;
+mod constants;
+mod domainname;
+mod header;
+mod message;
+mod question;
+
+pub use answer::*;
+pub use constants::*;
+pub use domainname::*;
+pub use header::*;
+pub use message::*;
+pub use question::*;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn a_query_datagram() -> Vec<u8> {
+        let mut datagram = vec![
+            0x12, 0x34, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        ];
+        datagram.extend_from_slice(&domain_to_bytes("example.com").unwrap());
+        datagram.extend_from_slice(&RECORD_TYPE_A.to_be_bytes());
+        datagram.extend_from_slice(&CLASS_IN.to_be_bytes());
+        datagram
+    }
+
+    #[test]
+    fn response_keeps_original_question_section() {
+        let query = Message::parse(&a_query_datagram()).unwrap();
+        let mut response = query.prepare_response();
+        response.answers.push(Answer {
+            domain: "example.com".to_string(),
+            record_type: RECORD_TYPE_A,
+            class: CLASS_IN,
+            ttl: 1,
+            data: vec![127, 0, 0, 1],
+        });
+        response.header.number_of_answers = 1;
+
+        let bytes = response.to_bytes().unwrap();
+        assert_eq!(u16::from_be_bytes([bytes[4], bytes[5]]), 1);
+        assert_eq!(u16::from_be_bytes([bytes[6], bytes[7]]), 1);
+        assert_eq!(&bytes[12..29], &a_query_datagram()[12..29]);
+    }
+
+    #[test]
+    fn parses_compressed_answer_names() {
+        let mut datagram = a_query_datagram();
+        datagram[2] = 0x81;
+        datagram[3] = 0x80;
+        datagram[6] = 0x00;
+        datagram[7] = 0x01;
+        datagram.extend_from_slice(&[
+            0xC0, 0x0C, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x04, 127, 0, 0, 1,
+        ]);
+
+        let message = Message::parse(&datagram).unwrap();
+        assert_eq!(message.answers.len(), 1);
+        assert_eq!(message.answers[0].domain, "example.com");
+        assert_eq!(message.answers[0].data, vec![127, 0, 0, 1]);
+    }
+}

src/dns/question.rs

@@ -0,0 +1,39 @@
+use anyhow::{Result, bail};
+
+use crate::dns::{domain_to_bytes, parse_domain};
+
+#[derive(Debug, Clone)]
+pub struct Question {
+    pub domain: String,
+    pub question_type: u16,
+    pub question_class: u16,
+}
+
+impl Question {
+    pub fn parse(datagram: &[u8], pos: &mut usize) -> Result<Question> {
+        let domain = parse_domain(datagram, pos)?;
+
+        if *pos + 4 > datagram.len() {
+            bail!("malformed datagram");
+        }
+
+        let question_type = ((datagram[*pos] as u16) << 8) | (datagram[*pos + 1] as u16);
+        let question_class = ((datagram[*pos + 2] as u16) << 8) | (datagram[*pos + 3] as u16);
+        *pos += 4;
+
+        let question = Question {
+            domain,
+            question_type,
+            question_class,
+        };
+
+        Ok(question)
+    }
+
+    pub fn to_bytes(&self) -> Result<Vec<u8>> {
+        let mut result = domain_to_bytes(&self.domain)?;
+        result.extend(self.question_type.to_be_bytes());
+        result.extend(self.question_class.to_be_bytes());
+        Ok(result)
+    }
+}

src/macros.rs

@@ -0,0 +1,6 @@
+#[macro_export]
+macro_rules! txid {
+    ($bytes:expr) => {
+        format!("{:02x}{:02x}", $bytes[0], $bytes[1])
+    };
+}

src/main.rs

@@ -1,42 +1,106 @@
 mod config;
 mod dns;
 mod logging;
+mod macros;
+
+use std::net::SocketAddr;
 
 use anyhow::Result;
 use dotenv::dotenv;
 use tokio::net::UdpSocket;
+use tracing::{Instrument, Level};
 
 use crate::dns::*;
 
 #[tokio::main]
 async fn main() -> Result<()> {
     dotenv().ok();
-    let config = config::load()?;
     logging::setup();
+    let config = config::load()?;
 
     tracing::info!("start server on port {}", config.port);
     let sock = UdpSocket::bind(("0.0.0.0", config.port)).await?;
-
     let mut buffer = [0u8; 512];
 
     loop {
         let (size, addr) = sock.recv_from(&mut buffer).await?;
-        tracing::info!("Received datagram from {}", addr.to_string());
-        if let Err(err) = handle_datagram(&buffer[..size]) {
+        let result = handle_datagram(&config, &sock, &addr, &buffer[..size]).await;
+        if let Err(err) = result {
             tracing::error!("failed to handle datagram: {err}");
         }
     }
 }
 
-fn handle_datagram(packet: &[u8]) -> Result<()> {
-    let header = DnsHeader::parse(packet)?;
-    println!("Received:\n{}", header);
+async fn handle_datagram(
+    config: &config::ConfigData,
+    sock: &UdpSocket,
+    addr: &SocketAddr,
+    datagram: &[u8],
+) -> Result<()> {
+    let message = Message::parse(datagram)?;
+    let span = tracing::span!(
+        Level::INFO,
+        "handle_datagram",
+        transaction_id = %txid!(message.header.transaction_id),
+        client = %addr,
+    );
 
-    let mut pos = 12usize;
-    for _ in 0..(header.number_of_questions) {
-        let question = DnsQuestion::parse(packet, &mut pos)?;
-        println!("Question: {}", question);
+    let result: Result<()> = async {
+        tracing::info!("received message");
+
+        if message.header.query_response {
+            tracing::error!("message is response, drop");
+            return Ok(());
+        }
+        if message.header.op_code != 0 {
+            tracing::error!("op code is not 0, drop");
+            return Ok(());
         }
 
+        let mut response = message.prepare_response();
+        for question in message.questions {
+            if question.question_type != RECORD_TYPE_A {
+                tracing::error!(
+                    "only A records are supported yet, requested: {}",
+                    question.question_type
+                );
+                return Ok(());
+            }
+            if question.question_class != CLASS_IN {
+                tracing::error!(
+                    "only IN class records are supported yet, requested: {}",
+                    question.question_class
+                );
+                return Ok(());
+            }
+
+            let address = config.get_address_by_domain(&question.domain);
+            match address {
+                Some(address) => {
+                    let answer = Answer {
+                        domain: question.domain,
+                        record_type: RECORD_TYPE_A,
+                        class: CLASS_IN,
+                        ttl: 1,
+                        data: address.to_vec(),
+                    };
+
+                    response.answers.push(answer);
+                    response.header.number_of_answers += 1;
+                }
+                None => {
+                    response.header.response_code = RESPONSE_CODE_NXDOMAIN;
+                }
+            }
+        }
+
+        let response_bytes = response.to_bytes()?;
+        sock.send_to(&response_bytes, addr).await?;
+
         Ok(())
+    }
+    .instrument(span)
+    .await;
+
+    result
 }