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Public repository / 853296b98de062273b7165b3e8dc1131a50a5c8b
AkurAI-DNS / src/dns.rs
Latest change 43d77bcd39e1042ed35120cd427d306a7b2fb530 - feat: implement RFC-compliant DNS wire protocol parser and serializer by Ólafur Búi Ólafsson
use std::collections::HashMap;
use std::fmt;
use std::net::{Ipv4Addr, Ipv6Addr};
// ---------------------------------------------------------------------------
// Record type constants
// ---------------------------------------------------------------------------
pub const TYPE_A: u16 = 1;
pub const TYPE_NS: u16 = 2;
pub const TYPE_CNAME: u16 = 5;
pub const TYPE_SOA: u16 = 6;
pub const TYPE_MX: u16 = 15;
pub const TYPE_TXT: u16 = 16;
pub const TYPE_AAAA: u16 = 28;
pub const TYPE_SRV: u16 = 33;
pub const TYPE_OPT: u16 = 41;
pub const TYPE_CAA: u16 = 257;
pub const TYPE_ANY: u16 = 255;
pub const CLASS_IN: u16 = 1;
// ---------------------------------------------------------------------------
// RCODE constants
// ---------------------------------------------------------------------------
pub const RCODE_NOERROR: u8 = 0;
pub const RCODE_FORMERR: u8 = 1;
pub const RCODE_SERVFAIL: u8 = 2;
pub const RCODE_NXDOMAIN: u8 = 3;
pub const RCODE_REFUSED: u8 = 5;
/// Maximum number of compression pointer jumps before we declare a loop.
const MAX_COMPRESSION_JUMPS: usize = 256;
// ---------------------------------------------------------------------------
// Error type
// ---------------------------------------------------------------------------
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum DnsError {
TooShort,
InvalidHeader,
InvalidName,
InvalidRecord,
CompressionLoop,
BufferOverflow,
}
impl fmt::Display for DnsError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
DnsError::TooShort => write!(f, "packet too short"),
DnsError::InvalidHeader => write!(f, "invalid header"),
DnsError::InvalidName => write!(f, "invalid domain name"),
DnsError::InvalidRecord => write!(f, "invalid resource record"),
DnsError::CompressionLoop => write!(f, "compression pointer loop"),
DnsError::BufferOverflow => write!(f, "buffer overflow"),
}
}
}
impl std::error::Error for DnsError {}
// ---------------------------------------------------------------------------
// Data types
// ---------------------------------------------------------------------------
#[derive(Debug, Clone)]
pub struct Header {
pub id: u16,
pub qr: bool,
pub opcode: u8,
pub aa: bool,
pub tc: bool,
pub rd: bool,
pub ra: bool,
pub rcode: u8,
pub qdcount: u16,
pub ancount: u16,
pub nscount: u16,
pub arcount: u16,
}
#[derive(Debug, Clone)]
pub struct Question {
pub name: String,
pub qtype: u16,
pub qclass: u16,
}
#[derive(Debug, Clone)]
pub enum RData {
A([u8; 4]),
AAAA([u8; 16]),
CNAME(String),
MX { preference: u16, exchange: String },
TXT(String),
NS(String),
SOA {
mname: String,
rname: String,
serial: u32,
refresh: u32,
retry: u32,
expire: u32,
minimum: u32,
},
SRV {
priority: u16,
weight: u16,
port: u16,
target: String,
},
CAA {
flags: u8,
tag: String,
value: String,
},
OPT {
udp_size: u16,
},
Unknown(Vec<u8>),
}
impl RData {
/// Returns the DNS type code for this rdata variant.
pub fn type_code(&self) -> u16 {
match self {
RData::A(_) => TYPE_A,
RData::AAAA(_) => TYPE_AAAA,
RData::CNAME(_) => TYPE_CNAME,
RData::MX { .. } => TYPE_MX,
RData::TXT(_) => TYPE_TXT,
RData::NS(_) => TYPE_NS,
RData::SOA { .. } => TYPE_SOA,
RData::SRV { .. } => TYPE_SRV,
RData::CAA { .. } => TYPE_CAA,
RData::OPT { .. } => TYPE_OPT,
RData::Unknown(_) => 0,
}
}
}
#[derive(Debug, Clone)]
pub struct Record {
pub name: String,
pub rtype: u16,
pub class: u16,
pub ttl: u32,
pub rdata: RData,
}
#[derive(Debug, Clone)]
pub struct Message {
pub header: Header,
pub questions: Vec<Question>,
pub answers: Vec<Record>,
pub authority: Vec<Record>,
pub additional: Vec<Record>,
}
// ---------------------------------------------------------------------------
// Record constructors
// ---------------------------------------------------------------------------
impl Record {
pub fn new_a(name: &str, ttl: u32, ip: [u8; 4]) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_A,
class: CLASS_IN,
ttl,
rdata: RData::A(ip),
}
}
pub fn new_aaaa(name: &str, ttl: u32, ip: [u8; 16]) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_AAAA,
class: CLASS_IN,
ttl,
rdata: RData::AAAA(ip),
}
}
pub fn new_cname(name: &str, ttl: u32, target: &str) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_CNAME,
class: CLASS_IN,
ttl,
rdata: RData::CNAME(normalize_name(target)),
}
}
pub fn new_mx(name: &str, ttl: u32, preference: u16, exchange: &str) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_MX,
class: CLASS_IN,
ttl,
rdata: RData::MX {
preference,
exchange: normalize_name(exchange),
},
}
}
pub fn new_txt(name: &str, ttl: u32, text: &str) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_TXT,
class: CLASS_IN,
ttl,
rdata: RData::TXT(text.to_string()),
}
}
pub fn new_ns(name: &str, ttl: u32, nsdname: &str) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_NS,
class: CLASS_IN,
ttl,
rdata: RData::NS(normalize_name(nsdname)),
}
}
pub fn new_soa(
name: &str,
ttl: u32,
mname: &str,
rname: &str,
serial: u32,
refresh: u32,
retry: u32,
expire: u32,
minimum: u32,
) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_SOA,
class: CLASS_IN,
ttl,
rdata: RData::SOA {
mname: normalize_name(mname),
rname: normalize_name(rname),
serial,
refresh,
retry,
expire,
minimum,
},
}
}
pub fn new_srv(
name: &str,
ttl: u32,
priority: u16,
weight: u16,
port: u16,
target: &str,
) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_SRV,
class: CLASS_IN,
ttl,
rdata: RData::SRV {
priority,
weight,
port,
target: normalize_name(target),
},
}
}
pub fn new_caa(name: &str, ttl: u32, flags: u8, tag: &str, value: &str) -> Record {
Record {
name: normalize_name(name),
rtype: TYPE_CAA,
class: CLASS_IN,
ttl,
rdata: RData::CAA {
flags,
tag: tag.to_string(),
value: value.to_string(),
},
}
}
}
// ---------------------------------------------------------------------------
// Name normalization
// ---------------------------------------------------------------------------
/// Ensure a name is lowercase and FQDN (ends with '.').
fn normalize_name(name: &str) -> String {
let lower = name.to_ascii_lowercase();
if lower.ends_with('.') {
lower
} else {
format!("{lower}.")
}
}
// ---------------------------------------------------------------------------
// Parsing helpers
// ---------------------------------------------------------------------------
/// A cursor over a byte slice for parsing DNS messages.
struct Cursor<'a> {
data: &'a [u8],
pos: usize,
}
impl<'a> Cursor<'a> {
fn new(data: &'a [u8]) -> Self {
Cursor { data, pos: 0 }
}
fn remaining(&self) -> usize {
self.data.len().saturating_sub(self.pos)
}
fn read_u8(&mut self) -> Result<u8, DnsError> {
if self.pos >= self.data.len() {
return Err(DnsError::TooShort);
}
let v = self.data[self.pos];
self.pos += 1;
Ok(v)
}
fn read_u16(&mut self) -> Result<u16, DnsError> {
if self.pos + 2 > self.data.len() {
return Err(DnsError::TooShort);
}
let v = u16::from_be_bytes([self.data[self.pos], self.data[self.pos + 1]]);
self.pos += 2;
Ok(v)
}
fn read_u32(&mut self) -> Result<u32, DnsError> {
if self.pos + 4 > self.data.len() {
return Err(DnsError::TooShort);
}
let v = u32::from_be_bytes([
self.data[self.pos],
self.data[self.pos + 1],
self.data[self.pos + 2],
self.data[self.pos + 3],
]);
self.pos += 4;
Ok(v)
}
fn read_bytes(&mut self, n: usize) -> Result<&'a [u8], DnsError> {
if self.pos + n > self.data.len() {
return Err(DnsError::TooShort);
}
let slice = &self.data[self.pos..self.pos + n];
self.pos += n;
Ok(slice)
}
}
/// Parse a DNS domain name from the packet, following compression pointers.
/// `data` is the full original packet (needed for pointer offsets).
/// `pos` is the current read position; returns the new position after the name
/// (which may differ from where the pointer chain ends).
fn parse_name(data: &[u8], start: usize) -> Result<(String, usize), DnsError> {
let mut labels: Vec<String> = Vec::new();
let mut pos = start;
let mut jumps = 0;
// The position after the first pointer (or after the null terminator if no pointer).
let mut end_pos: Option<usize> = None;
loop {
if pos >= data.len() {
return Err(DnsError::TooShort);
}
let len_byte = data[pos];
if len_byte == 0 {
// End of name
if end_pos.is_none() {
end_pos = Some(pos + 1);
}
break;
}
// Check for compression pointer: top 2 bits are 11
if len_byte & 0xC0 == 0xC0 {
if pos + 1 >= data.len() {
return Err(DnsError::TooShort);
}
let pointer = ((len_byte as u16 & 0x3F) << 8) | data[pos + 1] as u16;
if end_pos.is_none() {
end_pos = Some(pos + 2);
}
jumps += 1;
if jumps > MAX_COMPRESSION_JUMPS {
return Err(DnsError::CompressionLoop);
}
pos = pointer as usize;
continue;
}
// Regular label
let label_len = len_byte as usize;
if label_len > 63 {
return Err(DnsError::InvalidName);
}
if pos + 1 + label_len > data.len() {
return Err(DnsError::TooShort);
}
let label = &data[pos + 1..pos + 1 + label_len];
// Validate label bytes (RFC allows any octet, but we lowercase for storage)
let label_str = std::str::from_utf8(label)
.map_err(|_| DnsError::InvalidName)?
.to_ascii_lowercase();
labels.push(label_str);
pos += 1 + label_len;
}
// Build FQDN
let mut name = labels.join(".");
name.push('.');
// Total name length check (RFC 1035: 255 octets max)
if name.len() > 255 {
return Err(DnsError::InvalidName);
}
Ok((name, end_pos.unwrap_or(pos)))
}
/// Parse a name using the cursor's position, advancing the cursor.
fn parse_name_from_cursor(cursor: &mut Cursor<'_>) -> Result<String, DnsError> {
let (name, new_pos) = parse_name(cursor.data, cursor.pos)?;
cursor.pos = new_pos;
Ok(name)
}
// ---------------------------------------------------------------------------
// Header parsing / serialization
// ---------------------------------------------------------------------------
impl Header {
fn parse(cursor: &mut Cursor<'_>) -> Result<Header, DnsError> {
if cursor.remaining() < 12 {
return Err(DnsError::InvalidHeader);
}
let id = cursor.read_u16().map_err(|_| DnsError::InvalidHeader)?;
let flags = cursor.read_u16().map_err(|_| DnsError::InvalidHeader)?;
let qdcount = cursor.read_u16().map_err(|_| DnsError::InvalidHeader)?;
let ancount = cursor.read_u16().map_err(|_| DnsError::InvalidHeader)?;
let nscount = cursor.read_u16().map_err(|_| DnsError::InvalidHeader)?;
let arcount = cursor.read_u16().map_err(|_| DnsError::InvalidHeader)?;
Ok(Header {
id,
qr: (flags >> 15) & 1 == 1,
opcode: ((flags >> 11) & 0xF) as u8,
aa: (flags >> 10) & 1 == 1,
tc: (flags >> 9) & 1 == 1,
rd: (flags >> 8) & 1 == 1,
ra: (flags >> 7) & 1 == 1,
rcode: (flags & 0xF) as u8,
qdcount,
ancount,
nscount,
arcount,
})
}
fn serialize(&self, buf: &mut Vec<u8>) {
buf.extend_from_slice(&self.id.to_be_bytes());
let mut flags: u16 = 0;
if self.qr {
flags |= 1 << 15;
}
flags |= (self.opcode as u16 & 0xF) << 11;
if self.aa {
flags |= 1 << 10;
}
if self.tc {
flags |= 1 << 9;
}
if self.rd {
flags |= 1 << 8;
}
if self.ra {
flags |= 1 << 7;
}
flags |= self.rcode as u16 & 0xF;
buf.extend_from_slice(&flags.to_be_bytes());
buf.extend_from_slice(&self.qdcount.to_be_bytes());
buf.extend_from_slice(&self.ancount.to_be_bytes());
buf.extend_from_slice(&self.nscount.to_be_bytes());
buf.extend_from_slice(&self.arcount.to_be_bytes());
}
}
// ---------------------------------------------------------------------------
// Question parsing / serialization
// ---------------------------------------------------------------------------
impl Question {
fn parse(cursor: &mut Cursor<'_>) -> Result<Question, DnsError> {
let name = parse_name_from_cursor(cursor)?;
let qtype = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
let qclass = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
Ok(Question {
name,
qtype,
qclass,
})
}
fn serialize(&self, buf: &mut Vec<u8>, compression: &mut CompressionMap) {
write_name(buf, &self.name, compression);
buf.extend_from_slice(&self.qtype.to_be_bytes());
buf.extend_from_slice(&self.qclass.to_be_bytes());
}
}
// ---------------------------------------------------------------------------
// Record parsing / serialization
// ---------------------------------------------------------------------------
impl Record {
fn parse(cursor: &mut Cursor<'_>) -> Result<Record, DnsError> {
let name = parse_name_from_cursor(cursor)?;
let rtype = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
let class = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
let ttl = cursor.read_u32().map_err(|_| DnsError::InvalidRecord)?;
let rdlength = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)? as usize;
if cursor.remaining() < rdlength {
return Err(DnsError::InvalidRecord);
}
let rdata_start = cursor.pos;
let rdata_end = rdata_start + rdlength;
let rdata = match rtype {
TYPE_A => {
if rdlength != 4 {
return Err(DnsError::InvalidRecord);
}
let bytes = cursor.read_bytes(4).map_err(|_| DnsError::InvalidRecord)?;
RData::A([bytes[0], bytes[1], bytes[2], bytes[3]])
}
TYPE_AAAA => {
if rdlength != 16 {
return Err(DnsError::InvalidRecord);
}
let bytes = cursor
.read_bytes(16)
.map_err(|_| DnsError::InvalidRecord)?;
let mut addr = [0u8; 16];
addr.copy_from_slice(bytes);
RData::AAAA(addr)
}
TYPE_CNAME => {
let cname = parse_name_from_cursor(cursor)?;
RData::CNAME(cname)
}
TYPE_NS => {
let ns = parse_name_from_cursor(cursor)?;
RData::NS(ns)
}
TYPE_MX => {
let preference = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
let exchange = parse_name_from_cursor(cursor)?;
RData::MX {
preference,
exchange,
}
}
TYPE_TXT => {
// TXT records contain one or more character strings.
// Each is length-prefixed. We concatenate them.
let mut text = String::new();
while cursor.pos < rdata_end {
let str_len =
cursor.read_u8().map_err(|_| DnsError::InvalidRecord)? as usize;
if cursor.pos + str_len > rdata_end {
return Err(DnsError::InvalidRecord);
}
let bytes = cursor
.read_bytes(str_len)
.map_err(|_| DnsError::InvalidRecord)?;
let s = std::str::from_utf8(bytes).map_err(|_| DnsError::InvalidRecord)?;
text.push_str(s);
}
RData::TXT(text)
}
TYPE_SOA => {
let mname = parse_name_from_cursor(cursor)?;
let rname = parse_name_from_cursor(cursor)?;
let serial = cursor.read_u32().map_err(|_| DnsError::InvalidRecord)?;
let refresh = cursor.read_u32().map_err(|_| DnsError::InvalidRecord)?;
let retry = cursor.read_u32().map_err(|_| DnsError::InvalidRecord)?;
let expire = cursor.read_u32().map_err(|_| DnsError::InvalidRecord)?;
let minimum = cursor.read_u32().map_err(|_| DnsError::InvalidRecord)?;
RData::SOA {
mname,
rname,
serial,
refresh,
retry,
expire,
minimum,
}
}
TYPE_SRV => {
let priority = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
let weight = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
let port = cursor.read_u16().map_err(|_| DnsError::InvalidRecord)?;
let target = parse_name_from_cursor(cursor)?;
RData::SRV {
priority,
weight,
port,
target,
}
}
TYPE_CAA => {
if rdlength < 2 {
return Err(DnsError::InvalidRecord);
}
let flags = cursor.read_u8().map_err(|_| DnsError::InvalidRecord)?;
let tag_len =
cursor.read_u8().map_err(|_| DnsError::InvalidRecord)? as usize;
if cursor.pos + tag_len > rdata_end {
return Err(DnsError::InvalidRecord);
}
let tag_bytes = cursor
.read_bytes(tag_len)
.map_err(|_| DnsError::InvalidRecord)?;
let tag =
std::str::from_utf8(tag_bytes).map_err(|_| DnsError::InvalidRecord)?;
let value_len = rdata_end - cursor.pos;
let value_bytes = cursor
.read_bytes(value_len)
.map_err(|_| DnsError::InvalidRecord)?;
let value =
std::str::from_utf8(value_bytes).map_err(|_| DnsError::InvalidRecord)?;
RData::CAA {
flags,
tag: tag.to_string(),
value: value.to_string(),
}
}
TYPE_OPT => {
// OPT pseudo-record: class field = UDP payload size, name = "."
// Skip rdata (options we don't process)
cursor.pos = rdata_end;
RData::OPT { udp_size: class }
}
_ => {
let bytes = cursor
.read_bytes(rdlength)
.map_err(|_| DnsError::InvalidRecord)?;
RData::Unknown(bytes.to_vec())
}
};
// Ensure cursor is at rdata_end (some parsers may under-read)
if cursor.pos != rdata_end {
// For name-containing records the cursor may have advanced past rdata_end
// due to compression. But it should never be before.
if cursor.pos < rdata_end {
cursor.pos = rdata_end;
}
}
Ok(Record {
name,
rtype,
class,
ttl,
rdata,
})
}
fn serialize(&self, buf: &mut Vec<u8>, compression: &mut CompressionMap) {
// OPT is special: name is root ".", class is UDP size, TTL encodes extended rcode/flags
if self.rtype == TYPE_OPT {
buf.push(0); // root name
buf.extend_from_slice(&self.rtype.to_be_bytes());
// class = udp size
if let RData::OPT { udp_size } = &self.rdata {
buf.extend_from_slice(&udp_size.to_be_bytes());
} else {
buf.extend_from_slice(&self.class.to_be_bytes());
}
buf.extend_from_slice(&self.ttl.to_be_bytes()); // extended rcode + flags
buf.extend_from_slice(&0u16.to_be_bytes()); // rdlength = 0 (no options)
return;
}
write_name(buf, &self.name, compression);
buf.extend_from_slice(&self.rtype.to_be_bytes());
buf.extend_from_slice(&self.class.to_be_bytes());
buf.extend_from_slice(&self.ttl.to_be_bytes());
// Placeholder for rdlength
let rdlength_pos = buf.len();
buf.extend_from_slice(&0u16.to_be_bytes());
let rdata_start = buf.len();
match &self.rdata {
RData::A(ip) => {
buf.extend_from_slice(ip);
}
RData::AAAA(ip) => {
buf.extend_from_slice(ip);
}
RData::CNAME(name) => {
write_name(buf, name, compression);
}
RData::NS(name) => {
write_name(buf, name, compression);
}
RData::MX {
preference,
exchange,
} => {
buf.extend_from_slice(&preference.to_be_bytes());
write_name(buf, exchange, compression);
}
RData::TXT(text) => {
// Split into 255-byte chunks
let bytes = text.as_bytes();
if bytes.is_empty() {
// Empty TXT: single zero-length character string
buf.push(0);
} else {
let mut offset = 0;
while offset < bytes.len() {
let chunk_len = std::cmp::min(255, bytes.len() - offset);
buf.push(chunk_len as u8);
buf.extend_from_slice(&bytes[offset..offset + chunk_len]);
offset += chunk_len;
}
}
}
RData::SOA {
mname,
rname,
serial,
refresh,
retry,
expire,
minimum,
} => {
write_name(buf, mname, compression);
write_name(buf, rname, compression);
buf.extend_from_slice(&serial.to_be_bytes());
buf.extend_from_slice(&refresh.to_be_bytes());
buf.extend_from_slice(&retry.to_be_bytes());
buf.extend_from_slice(&expire.to_be_bytes());
buf.extend_from_slice(&minimum.to_be_bytes());
}
RData::SRV {
priority,
weight,
port,
target,
} => {
buf.extend_from_slice(&priority.to_be_bytes());
buf.extend_from_slice(&weight.to_be_bytes());
buf.extend_from_slice(&port.to_be_bytes());
write_name(buf, target, compression);
}
RData::CAA { flags, tag, value } => {
buf.push(*flags);
buf.push(tag.len() as u8);
buf.extend_from_slice(tag.as_bytes());
buf.extend_from_slice(value.as_bytes());
}
RData::OPT { .. } => {
// Handled above, should not reach here
}
RData::Unknown(data) => {
buf.extend_from_slice(data);
}
}
// Patch rdlength
let rdlength = (buf.len() - rdata_start) as u16;
buf[rdlength_pos] = (rdlength >> 8) as u8;
buf[rdlength_pos + 1] = (rdlength & 0xFF) as u8;
}
}
// ---------------------------------------------------------------------------
// Name compression for serialization
// ---------------------------------------------------------------------------
type CompressionMap = HashMap<String, u16>;
/// Write a DNS name with compression. The `compression` map tracks
/// previously written name suffixes and their offsets.
fn write_name(buf: &mut Vec<u8>, name: &str, compression: &mut CompressionMap) {
// Strip trailing dot for processing, we'll handle it
let name = if name.ends_with('.') {
&name[..name.len() - 1]
} else {
name
};
if name.is_empty() {
// Root name
buf.push(0);
return;
}
let labels: Vec<&str> = name.split('.').collect();
for i in 0..labels.len() {
// Check if the suffix from this label onwards has been seen
let suffix = labels[i..].join(".");
let suffix_key = suffix.to_ascii_lowercase();
if let Some(&offset) = compression.get(&suffix_key) {
// Emit a compression pointer
let pointer = 0xC000 | offset;
buf.extend_from_slice(&(pointer as u16).to_be_bytes());
return;
}
// Record this suffix's offset (only if it fits in 14 bits)
let current_offset = buf.len();
if current_offset < 0x3FFF {
compression.insert(suffix_key, current_offset as u16);
}
// Write the label
let label = labels[i].as_bytes();
buf.push(label.len() as u8);
buf.extend_from_slice(label);
}
// Null terminator
buf.push(0);
}
// ---------------------------------------------------------------------------
// Message implementation
// ---------------------------------------------------------------------------
impl Message {
/// Parse a DNS message from raw bytes.
pub fn parse(data: &[u8]) -> Result<Message, DnsError> {
if data.len() < 12 {
return Err(DnsError::TooShort);
}
let mut cursor = Cursor::new(data);
let header = Header::parse(&mut cursor)?;
let mut questions = Vec::with_capacity(header.qdcount as usize);
for _ in 0..header.qdcount {
questions.push(Question::parse(&mut cursor)?);
}
let mut answers = Vec::with_capacity(header.ancount as usize);
for _ in 0..header.ancount {
answers.push(Record::parse(&mut cursor)?);
}
let mut authority = Vec::with_capacity(header.nscount as usize);
for _ in 0..header.nscount {
authority.push(Record::parse(&mut cursor)?);
}
let mut additional = Vec::with_capacity(header.arcount as usize);
for _ in 0..header.arcount {
additional.push(Record::parse(&mut cursor)?);
}
Ok(Message {
header,
questions,
answers,
authority,
additional,
})
}
/// Serialize this message to wire format.
pub fn serialize(&self) -> Vec<u8> {
let mut buf = Vec::with_capacity(512);
let mut compression = CompressionMap::new();
// Update header counts to match actual section lengths
let mut header = self.header.clone();
header.qdcount = self.questions.len() as u16;
header.ancount = self.answers.len() as u16;
header.nscount = self.authority.len() as u16;
header.arcount = self.additional.len() as u16;
header.serialize(&mut buf);
for q in &self.questions {
q.serialize(&mut buf, &mut compression);
}
for r in &self.answers {
r.serialize(&mut buf, &mut compression);
}
for r in &self.authority {
r.serialize(&mut buf, &mut compression);
}
for r in &self.additional {
r.serialize(&mut buf, &mut compression);
}
buf
}
/// Serialize with a size limit. Returns (bytes, was_truncated).
/// If the full message exceeds `max_size`, records are dropped from
/// additional, then authority, then answers until it fits. If still
/// too large, TC is set and only the header+questions are returned.
pub fn serialize_with_limit(&self, max_size: usize) -> (Vec<u8>, bool) {
// Try full serialization first
let full = self.serialize();
if full.len() <= max_size {
return (full, false);
}
// Try progressively dropping sections
let sections: &[(&[Record], &[Record], &[Record])] = &[
(&self.answers, &self.authority, &[]), // drop additional
(&self.answers, &[], &[]), // drop authority too
(&[], &[], &[]), // drop answers too
];
for &(answers, authority, additional) in sections {
let mut msg = self.clone();
msg.answers = answers.to_vec();
msg.authority = authority.to_vec();
msg.additional = additional.to_vec();
msg.header.tc = true;
let bytes = msg.serialize();
if bytes.len() <= max_size {
return (bytes, true);
}
}
// Last resort: header + questions only, TC=1
let mut msg = self.clone();
msg.answers.clear();
msg.authority.clear();
msg.additional.clear();
msg.header.tc = true;
let bytes = msg.serialize();
(bytes, true)
}
/// Create a response skeleton from a query. Copies the ID, sets QR=1, AA=1,
/// copies RD from the query, and copies the question section.
pub fn new_response(query: &Message) -> Message {
Message {
header: Header {
id: query.header.id,
qr: true,
opcode: query.header.opcode,
aa: true,
tc: false,
rd: query.header.rd,
ra: false,
rcode: RCODE_NOERROR,
qdcount: query.questions.len() as u16,
ancount: 0,
nscount: 0,
arcount: 0,
},
questions: query.questions.clone(),
answers: Vec::new(),
authority: Vec::new(),
additional: Vec::new(),
}
}
/// Set the response code.
pub fn set_rcode(&mut self, rcode: u8) {
self.header.rcode = rcode;
}
/// Check if the query contains an EDNS0 OPT record.
pub fn has_edns(&self) -> bool {
self.additional.iter().any(|r| r.rtype == TYPE_OPT)
}
/// Get the EDNS0 UDP payload size from the query, if present.
pub fn edns_udp_size(&self) -> Option<u16> {
self.additional.iter().find_map(|r| {
if r.rtype == TYPE_OPT {
if let RData::OPT { udp_size } = &r.rdata {
Some(*udp_size)
} else {
Some(r.class)
}
} else {
None
}
})
}
/// Add an EDNS0 OPT record to the additional section advertising the given
/// UDP payload size.
pub fn add_edns(&mut self, udp_size: u16) {
self.additional.push(Record {
name: ".".to_string(),
rtype: TYPE_OPT,
class: udp_size,
ttl: 0,
rdata: RData::OPT { udp_size },
});
}
}
// ---------------------------------------------------------------------------
// Display implementations for debugging
// ---------------------------------------------------------------------------
impl fmt::Display for RData {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
RData::A(ip) => write!(f, "{}", Ipv4Addr::from(*ip)),
RData::AAAA(ip) => write!(f, "{}", Ipv6Addr::from(*ip)),
RData::CNAME(name) => write!(f, "{name}"),
RData::NS(name) => write!(f, "{name}"),
RData::MX {
preference,
exchange,
} => write!(f, "{preference} {exchange}"),
RData::TXT(text) => write!(f, "\"{text}\""),
RData::SOA {
mname,
rname,
serial,
refresh,
retry,
expire,
minimum,
} => write!(
f,
"{mname} {rname} {serial} {refresh} {retry} {expire} {minimum}"
),
RData::SRV {
priority,
weight,
port,
target,
} => write!(f, "{priority} {weight} {port} {target}"),
RData::CAA { flags, tag, value } => write!(f, "{flags} {tag} \"{value}\""),
RData::OPT { udp_size } => write!(f, "OPT udp_size={udp_size}"),
RData::Unknown(data) => write!(f, "<unknown {} bytes>", data.len()),
}
}
}
// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------
#[cfg(test)]
mod tests {
use super::*;
/// Build a minimal DNS query packet for "example.com" A record.
fn build_query_packet(name: &str, qtype: u16) -> Vec<u8> {
let mut buf = Vec::new();
// Header
buf.extend_from_slice(&0x1234u16.to_be_bytes()); // ID
buf.extend_from_slice(&0x0100u16.to_be_bytes()); // flags: RD=1
buf.extend_from_slice(&1u16.to_be_bytes()); // QDCOUNT
buf.extend_from_slice(&0u16.to_be_bytes()); // ANCOUNT
buf.extend_from_slice(&0u16.to_be_bytes()); // NSCOUNT
buf.extend_from_slice(&0u16.to_be_bytes()); // ARCOUNT
// Question: name
let name = if name.ends_with('.') {
&name[..name.len() - 1]
} else {
name
};
for label in name.split('.') {
buf.push(label.len() as u8);
buf.extend_from_slice(label.as_bytes());
}
buf.push(0); // null terminator
// QTYPE, QCLASS
buf.extend_from_slice(&qtype.to_be_bytes());
buf.extend_from_slice(&CLASS_IN.to_be_bytes());
buf
}
#[test]
fn test_parse_simple_query() {
let packet = build_query_packet("example.com", TYPE_A);
let msg = Message::parse(&packet).unwrap();
assert_eq!(msg.header.id, 0x1234);
assert!(!msg.header.qr);
assert!(msg.header.rd);
assert_eq!(msg.questions.len(), 1);
assert_eq!(msg.questions[0].name, "example.com.");
assert_eq!(msg.questions[0].qtype, TYPE_A);
assert_eq!(msg.questions[0].qclass, CLASS_IN);
}
#[test]
fn test_roundtrip_response() {
let query_pkt = build_query_packet("golfsetridak.is", TYPE_A);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response
.answers
.push(Record::new_a("golfsetridak.is.", 300, [93, 95, 230, 10]));
response
.answers
.push(Record::new_a("golfsetridak.is.", 300, [93, 95, 230, 11]));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
assert!(parsed.header.qr);
assert!(parsed.header.aa);
assert_eq!(parsed.header.rcode, RCODE_NOERROR);
assert_eq!(parsed.questions.len(), 1);
assert_eq!(parsed.questions[0].name, "golfsetridak.is.");
assert_eq!(parsed.answers.len(), 2);
if let RData::A(ip) = &parsed.answers[0].rdata {
assert_eq!(ip, &[93, 95, 230, 10]);
} else {
panic!("expected A record");
}
}
#[test]
fn test_name_compression() {
let query_pkt = build_query_packet("example.com", TYPE_A);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
// Add multiple records with the same name — compression should kick in
for i in 0..5 {
response
.answers
.push(Record::new_a("example.com.", 300, [10, 0, 0, i]));
}
let bytes = response.serialize();
// The serialized form should be significantly smaller than without compression.
// Without compression, each name would be 13 bytes. With compression, subsequent
// names are 2 bytes (pointer).
assert!(bytes.len() < 12 + 17 + 5 * (13 + 10 + 4)); // rough upper bound
// Verify it parses back correctly
let parsed = Message::parse(&bytes).unwrap();
assert_eq!(parsed.answers.len(), 5);
for (i, rec) in parsed.answers.iter().enumerate() {
assert_eq!(rec.name, "example.com.");
if let RData::A(ip) = &rec.rdata {
assert_eq!(ip[3], i as u8);
}
}
}
#[test]
fn test_compression_pointer_parsing() {
// Build a packet with a compression pointer in the answer section
let mut pkt = Vec::new();
// Header
pkt.extend_from_slice(&0xABCDu16.to_be_bytes());
pkt.extend_from_slice(&0x8400u16.to_be_bytes()); // QR=1, AA=1
pkt.extend_from_slice(&1u16.to_be_bytes()); // QDCOUNT
pkt.extend_from_slice(&1u16.to_be_bytes()); // ANCOUNT
pkt.extend_from_slice(&0u16.to_be_bytes()); // NSCOUNT
pkt.extend_from_slice(&0u16.to_be_bytes()); // ARCOUNT
// Question: "test.example.com."
let name_offset = pkt.len(); // offset of "test"
pkt.push(4);
pkt.extend_from_slice(b"test");
let example_offset = pkt.len(); // offset of "example"
pkt.push(7);
pkt.extend_from_slice(b"example");
pkt.push(3);
pkt.extend_from_slice(b"com");
pkt.push(0);
pkt.extend_from_slice(&TYPE_A.to_be_bytes());
pkt.extend_from_slice(&CLASS_IN.to_be_bytes());
// Answer: name uses pointer to "test.example.com." at name_offset
let pointer = 0xC000 | name_offset as u16;
pkt.extend_from_slice(&pointer.to_be_bytes());
pkt.extend_from_slice(&TYPE_A.to_be_bytes());
pkt.extend_from_slice(&CLASS_IN.to_be_bytes());
pkt.extend_from_slice(&300u32.to_be_bytes());
pkt.extend_from_slice(&4u16.to_be_bytes()); // rdlength
pkt.extend_from_slice(&[1, 2, 3, 4]);
let msg = Message::parse(&pkt).unwrap();
assert_eq!(msg.answers[0].name, "test.example.com.");
if let RData::A(ip) = &msg.answers[0].rdata {
assert_eq!(ip, &[1, 2, 3, 4]);
} else {
panic!("expected A record");
}
}
#[test]
fn test_too_short_packet() {
assert!(Message::parse(&[0; 5]).is_err());
assert!(Message::parse(&[]).is_err());
}
#[test]
fn test_compression_loop_detection() {
// Create a packet where a name pointer points to itself
let mut pkt = vec![0u8; 12]; // header
pkt[4] = 0; // QDCOUNT = 1
pkt[5] = 1;
// Name at offset 12 is a pointer to offset 12 (self-referencing)
pkt.push(0xC0);
pkt.push(12);
// QTYPE and QCLASS
pkt.extend_from_slice(&TYPE_A.to_be_bytes());
pkt.extend_from_slice(&CLASS_IN.to_be_bytes());
let result = Message::parse(&pkt);
assert!(matches!(result, Err(DnsError::CompressionLoop)));
}
#[test]
fn test_txt_record_roundtrip() {
let query_pkt = build_query_packet("example.com", TYPE_TXT);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response
.answers
.push(Record::new_txt("example.com.", 300, "v=spf1 include:_spf.google.com ~all"));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
assert_eq!(parsed.answers.len(), 1);
if let RData::TXT(text) = &parsed.answers[0].rdata {
assert_eq!(text, "v=spf1 include:_spf.google.com ~all");
} else {
panic!("expected TXT record");
}
}
#[test]
fn test_soa_record_roundtrip() {
let query_pkt = build_query_packet("example.com", TYPE_SOA);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response.answers.push(Record::new_soa(
"example.com.",
3600,
"ns1.example.com.",
"admin.example.com.",
2024010101,
3600,
900,
604800,
86400,
));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
assert_eq!(parsed.answers.len(), 1);
if let RData::SOA {
mname,
rname,
serial,
refresh,
retry,
expire,
minimum,
} = &parsed.answers[0].rdata
{
assert_eq!(mname, "ns1.example.com.");
assert_eq!(rname, "admin.example.com.");
assert_eq!(*serial, 2024010101);
assert_eq!(*refresh, 3600);
assert_eq!(*retry, 900);
assert_eq!(*expire, 604800);
assert_eq!(*minimum, 86400);
} else {
panic!("expected SOA record");
}
}
#[test]
fn test_mx_record_roundtrip() {
let query_pkt = build_query_packet("example.com", TYPE_MX);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response
.answers
.push(Record::new_mx("example.com.", 3600, 10, "mail.example.com."));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
if let RData::MX {
preference,
exchange,
} = &parsed.answers[0].rdata
{
assert_eq!(*preference, 10);
assert_eq!(exchange, "mail.example.com.");
} else {
panic!("expected MX record");
}
}
#[test]
fn test_aaaa_record_roundtrip() {
let query_pkt = build_query_packet("example.com", TYPE_AAAA);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
let ipv6: [u8; 16] = [
0x20, 0x01, 0x0d, 0xb8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
];
response
.answers
.push(Record::new_aaaa("example.com.", 300, ipv6));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
if let RData::AAAA(ip) = &parsed.answers[0].rdata {
assert_eq!(ip, &ipv6);
} else {
panic!("expected AAAA record");
}
}
#[test]
fn test_cname_record_roundtrip() {
let query_pkt = build_query_packet("www.example.com", TYPE_CNAME);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response.answers.push(Record::new_cname(
"www.example.com.",
300,
"example.com.",
));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
if let RData::CNAME(target) = &parsed.answers[0].rdata {
assert_eq!(target, "example.com.");
} else {
panic!("expected CNAME record");
}
}
#[test]
fn test_ns_record_roundtrip() {
let query_pkt = build_query_packet("example.com", TYPE_NS);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response
.answers
.push(Record::new_ns("example.com.", 3600, "ns1.example.com."));
response
.answers
.push(Record::new_ns("example.com.", 3600, "ns2.example.com."));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
assert_eq!(parsed.answers.len(), 2);
if let RData::NS(name) = &parsed.answers[0].rdata {
assert_eq!(name, "ns1.example.com.");
} else {
panic!("expected NS record");
}
}
#[test]
fn test_srv_record_roundtrip() {
let query_pkt = build_query_packet("_sip._tcp.example.com", TYPE_SRV);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response.answers.push(Record::new_srv(
"_sip._tcp.example.com.",
300,
10,
60,
5060,
"sipserver.example.com.",
));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
if let RData::SRV {
priority,
weight,
port,
target,
} = &parsed.answers[0].rdata
{
assert_eq!(*priority, 10);
assert_eq!(*weight, 60);
assert_eq!(*port, 5060);
assert_eq!(target, "sipserver.example.com.");
} else {
panic!("expected SRV record");
}
}
#[test]
fn test_caa_record_roundtrip() {
let query_pkt = build_query_packet("example.com", TYPE_CAA);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response.answers.push(Record::new_caa(
"example.com.",
3600,
0,
"issue",
"letsencrypt.org",
));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
if let RData::CAA { flags, tag, value } = &parsed.answers[0].rdata {
assert_eq!(*flags, 0);
assert_eq!(tag, "issue");
assert_eq!(value, "letsencrypt.org");
} else {
panic!("expected CAA record");
}
}
#[test]
fn test_edns_opt_roundtrip() {
// Build a query with EDNS0 OPT in additional
let mut pkt = build_query_packet("example.com", TYPE_A);
// Fix ARCOUNT to 1
pkt[10] = 0;
pkt[11] = 1;
// OPT record: name = root (0x00), type = 41, class (UDP size) = 4096,
// TTL = 0 (extended rcode + version + flags), rdlength = 0
pkt.push(0x00); // root name
pkt.extend_from_slice(&TYPE_OPT.to_be_bytes());
pkt.extend_from_slice(&4096u16.to_be_bytes()); // class = UDP payload size
pkt.extend_from_slice(&0u32.to_be_bytes()); // TTL
pkt.extend_from_slice(&0u16.to_be_bytes()); // rdlength
let query = Message::parse(&pkt).unwrap();
assert!(query.has_edns());
assert_eq!(query.edns_udp_size(), Some(4096));
let mut response = Message::new_response(&query);
response.add_edns(4096);
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
assert!(parsed.has_edns());
}
#[test]
fn test_serialize_with_limit_truncation() {
let query_pkt = build_query_packet("example.com", TYPE_A);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
// Add many records to exceed 512 bytes
for i in 0..50u8 {
response
.answers
.push(Record::new_a("example.com.", 300, [10, 0, 0, i]));
}
let (bytes, truncated) = response.serialize_with_limit(512);
assert!(truncated);
assert!(bytes.len() <= 512);
// Verify the TC bit is set
let parsed = Message::parse(&bytes).unwrap();
assert!(parsed.header.tc);
}
#[test]
fn test_set_rcode() {
let query_pkt = build_query_packet("example.com", TYPE_A);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response.set_rcode(RCODE_NXDOMAIN);
assert_eq!(response.header.rcode, RCODE_NXDOMAIN);
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
assert_eq!(parsed.header.rcode, RCODE_NXDOMAIN);
}
#[test]
fn test_case_insensitive_names() {
let mut pkt = Vec::new();
pkt.extend_from_slice(&0x1234u16.to_be_bytes());
pkt.extend_from_slice(&0x0100u16.to_be_bytes());
pkt.extend_from_slice(&1u16.to_be_bytes());
pkt.extend_from_slice(&0u16.to_be_bytes());
pkt.extend_from_slice(&0u16.to_be_bytes());
pkt.extend_from_slice(&0u16.to_be_bytes());
// "EXAMPLE.COM" in uppercase
pkt.push(7);
pkt.extend_from_slice(b"EXAMPLE");
pkt.push(3);
pkt.extend_from_slice(b"COM");
pkt.push(0);
pkt.extend_from_slice(&TYPE_A.to_be_bytes());
pkt.extend_from_slice(&CLASS_IN.to_be_bytes());
let msg = Message::parse(&pkt).unwrap();
assert_eq!(msg.questions[0].name, "example.com.");
}
#[test]
fn test_rdata_type_code() {
assert_eq!(RData::A([0; 4]).type_code(), TYPE_A);
assert_eq!(RData::AAAA([0; 16]).type_code(), TYPE_AAAA);
assert_eq!(RData::CNAME("x.".into()).type_code(), TYPE_CNAME);
assert_eq!(RData::NS("x.".into()).type_code(), TYPE_NS);
assert_eq!(
RData::MX {
preference: 10,
exchange: "x.".into()
}
.type_code(),
TYPE_MX
);
assert_eq!(RData::TXT("x".into()).type_code(), TYPE_TXT);
assert_eq!(
RData::SOA {
mname: "a.".into(),
rname: "b.".into(),
serial: 1,
refresh: 2,
retry: 3,
expire: 4,
minimum: 5,
}
.type_code(),
TYPE_SOA
);
assert_eq!(
RData::SRV {
priority: 0,
weight: 0,
port: 0,
target: "x.".into()
}
.type_code(),
TYPE_SRV
);
assert_eq!(
RData::CAA {
flags: 0,
tag: "issue".into(),
value: "x".into()
}
.type_code(),
TYPE_CAA
);
assert_eq!(RData::OPT { udp_size: 4096 }.type_code(), TYPE_OPT);
assert_eq!(RData::Unknown(vec![]).type_code(), 0);
}
#[test]
fn test_long_txt_record() {
// TXT with > 255 bytes should be split into multiple character strings
let long_text = "a".repeat(300);
let query_pkt = build_query_packet("example.com", TYPE_TXT);
let query = Message::parse(&query_pkt).unwrap();
let mut response = Message::new_response(&query);
response
.answers
.push(Record::new_txt("example.com.", 300, &long_text));
let bytes = response.serialize();
let parsed = Message::parse(&bytes).unwrap();
if let RData::TXT(text) = &parsed.answers[0].rdata {
assert_eq!(text, &long_text);
} else {
panic!("expected TXT record");
}
}
#[test]
fn test_normalize_name() {
assert_eq!(normalize_name("example.com"), "example.com.");
assert_eq!(normalize_name("example.com."), "example.com.");
assert_eq!(normalize_name("EXAMPLE.COM"), "example.com.");
}
#[test]
fn test_new_response_copies_query_id() {
let query_pkt = build_query_packet("test.example.com", TYPE_A);
let query = Message::parse(&query_pkt).unwrap();
let response = Message::new_response(&query);
assert_eq!(response.header.id, query.header.id);
assert!(response.header.qr);
assert!(response.header.aa);
assert_eq!(response.header.rd, query.header.rd);
assert_eq!(response.questions.len(), query.questions.len());
assert_eq!(response.questions[0].name, query.questions[0].name);
}
}