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Update examples with modernized code

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Emil Hernvall 2020-06-18 01:47:09 +02:00
parent 31369696d9
commit f815075ae4
10 changed files with 708 additions and 627 deletions
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chapter1.md
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@ -323,43 +323,43 @@ we'll use a `struct` called `BytePacketBuffer`.
```rust
pub struct BytePacketBuffer {
pub buf: [u8; 512],
pub pos: usize
pub pos: usize,
}
impl BytePacketBuffer {
// This gives us a fresh buffer for holding the packet contents, and a field for
// keeping track of where we are.
/// This gives us a fresh buffer for holding the packet contents, and a
/// field for keeping track of where we are.
pub fn new() -> BytePacketBuffer {
BytePacketBuffer {
buf: [0; 512],
pos: 0
pos: 0,
}
}
// When handling the reading of domain names, we'll need a way of
// reading and manipulating our buffer position.
/// Current position within buffer
fn pos(&self) -> usize {
self.pos
}
/// Step the buffer position forward a specific number of steps
fn step(&mut self, steps: usize) -> Result<()> {
self.pos += steps;
Ok(())
}
/// Change the buffer position
fn seek(&mut self, pos: usize) -> Result<()> {
self.pos = pos;
Ok(())
}
// A method for reading a single byte, and moving one step forward
/// Read a single byte and move the position one step forward
fn read(&mut self) -> Result<u8> {
if self.pos >= 512 {
return Err(Error::new(ErrorKind::InvalidInput, "End of buffer"));
return Err("End of buffer".into());
}
let res = self.buf[self.pos];
self.pos += 1;
@ -367,49 +367,46 @@ impl BytePacketBuffer {
Ok(res)
}
// Methods for fetching data at a specified position, without modifying
// the internal position
/// Get a single byte, without changing the buffer position
fn get(&mut self, pos: usize) -> Result<u8> {
if pos >= 512 {
return Err(Error::new(ErrorKind::InvalidInput, "End of buffer"));
return Err("End of buffer".into());
}
Ok(self.buf[pos])
}
/// Get a range of bytes
fn get_range(&mut self, start: usize, len: usize) -> Result<&[u8]> {
if start + len >= 512 {
return Err(Error::new(ErrorKind::InvalidInput, "End of buffer"));
return Err("End of buffer".into());
}
Ok(&self.buf[start..start + len as usize])
}
// Methods for reading a u16 and u32 from the buffer, while stepping
// forward 2 or 4 bytes
fn read_u16(&mut self) -> Result<u16>
{
let res = ((try!(self.read()) as u16) << 8) |
(try!(self.read()) as u16);
/// Read two bytes, stepping two steps forward
fn read_u16(&mut self) -> Result<u16> {
let res = ((self.read()? as u16) << 8) | (self.read()? as u16);
Ok(res)
}
fn read_u32(&mut self) -> Result<u32>
{
let res = ((try!(self.read()) as u32) << 24) |
((try!(self.read()) as u32) << 16) |
((try!(self.read()) as u32) << 8) |
((try!(self.read()) as u32) << 0);
/// Read four bytes, stepping four steps forward
fn read_u32(&mut self) -> Result<u32> {
let res = ((self.read()? as u32) << 24)
| ((self.read()? as u32) << 16)
| ((self.read()? as u32) << 8)
| ((self.read()? as u32) << 0);
Ok(res)
}
// The tricky part: Reading domain names, taking labels into consideration.
// Will take something like [3]www[6]google[3]com[0] and append
// www.google.com to outstr.
fn read_qname(&mut self, outstr: &mut String) -> Result<()>
{
/// Read a qname
///
/// The tricky part: Reading domain names, taking labels into consideration.
/// Will take something like [3]www[6]google[3]com[0] and append
/// www.google.com to outstr.
fn read_qname(&mut self, outstr: &mut String) -> Result<()> {
// Since we might encounter jumps, we'll keep track of our position
// locally as opposed to using the position within the struct. This
// allows us to move the shared position to a point past our current
@ -419,43 +416,54 @@ impl BytePacketBuffer {
// track whether or not we've jumped
let mut jumped = false;
let max_jumps = 5;
let mut jumps_performed = 0;
// Our delimiter which we append for each label. Since we don't want a dot at the
// beginning of the domain name we'll leave it empty for now and set it to "." at
// the end of the first iteration.
// Our delimiter which we append for each label. Since we don't want a
// dot at the beginning of the domain name we'll leave it empty for now
// and set it to "." at the end of the first iteration.
let mut delim = "";
loop {
// Dns Packets are untrusted data, so we need to be paranoid. Someone
// can craft a packet with a cycle in the jump instructions. This guards
// against such packets.
if jumps_performed > max_jumps {
return Err(format!("Limit of {} jumps exceeded", max_jumps).into());
}
// At this point, we're always at the beginning of a label. Recall
// that labels start with a length byte.
let len = try!(self.get(pos));
let len = self.get(pos)?;
// If len has the two most significant bit are set, it represents a jump to
// some other offset in the packet:
// If len has the two most significant bit are set, it represents a
// jump to some other offset in the packet:
if (len & 0xC0) == 0xC0 {
// Update the buffer position to a point past the current
// label. We don't need to touch it any further.
if !jumped {
try!(self.seek(pos+2));
self.seek(pos + 2)?;
}
// Read another byte, calculate offset and perform the jump by
// updating our local position variable
let b2 = try!(self.get(pos+1)) as u16;
let b2 = self.get(pos + 1)? as u16;
let offset = (((len as u16) ^ 0xC0) << 8) | b2;
pos = offset as usize;
// Indicate that a jump was performed.
jumped = true;
}
jumps_performed += 1;
continue;
}
// The base scenario, where we're reading a single label and
// appending it to the output:
else {
// Move a single byte forward to move past the length byte.
pos += 1;
// Domain names are terminated by an empty label of length 0, so if the length is zero
// we're done.
// Domain names are terminated by an empty label of length 0,
// so if the length is zero we're done.
if len == 0 {
break;
}
@ -463,9 +471,9 @@ impl BytePacketBuffer {
// Append the delimiter to our output buffer first.
outstr.push_str(delim);
// Extract the actual ASCII bytes for this label and append them to the output buffer.
let str_buffer = try!(self.get_range(pos, len as usize));
// Extract the actual ASCII bytes for this label and append them
// to the output buffer.
let str_buffer = self.get_range(pos, len as usize)?;
outstr.push_str(&String::from_utf8_lossy(str_buffer).to_lowercase());
delim = ".";
@ -475,16 +483,13 @@ impl BytePacketBuffer {
}
}
// If a jump has been performed, we've already modified the buffer position state and
// shouldn't do so again.
if !jumped {
try!(self.seek(pos));
self.seek(pos)?;
}
Ok(())
} // End of read_qname
} // End of BytePacketBuffer
}
}
```
### ResultCode
@ -499,7 +504,7 @@ pub enum ResultCode {
SERVFAIL = 2,
NXDOMAIN = 3,
NOTIMP = 4,
REFUSED = 5
REFUSED = 5,
}
impl ResultCode {
@ -510,7 +515,7 @@ impl ResultCode {
3 => ResultCode::NXDOMAIN,
4 => ResultCode::NOTIMP,
5 => ResultCode::REFUSED,
0 | _ => ResultCode::NOERROR
0 | _ => ResultCode::NOERROR,
}
}
}
@ -540,7 +545,7 @@ pub struct DnsHeader {
pub questions: u16, // 16 bits
pub answers: u16, // 16 bits
pub authoritative_entries: u16, // 16 bits
pub resource_entries: u16 // 16 bits
pub resource_entries: u16, // 16 bits
}
```
@ -549,7 +554,8 @@ The implementation involves a lot of bit twiddling:
```rust
impl DnsHeader {
pub fn new() -> DnsHeader {
DnsHeader { id: 0,
DnsHeader {
id: 0,
recursion_desired: false,
truncated_message: false,
@ -566,13 +572,14 @@ impl DnsHeader {
questions: 0,
answers: 0,
authoritative_entries: 0,
resource_entries: 0 }
resource_entries: 0,
}
}
pub fn read(&mut self, buffer: &mut BytePacketBuffer) -> Result<()> {
self.id = try!(buffer.read_u16());
self.id = buffer.read_u16()?;
let flags = try!(buffer.read_u16());
let flags = buffer.read_u16()?;
let a = (flags >> 8) as u8;
let b = (flags & 0xFF) as u8;
self.recursion_desired = (a & (1 << 0)) > 0;
@ -587,10 +594,10 @@ impl DnsHeader {
self.z = (b & (1 << 6)) > 0;
self.recursion_available = (b & (1 << 7)) > 0;
self.questions = try!(buffer.read_u16());
self.answers = try!(buffer.read_u16());
self.authoritative_entries = try!(buffer.read_u16());
self.resource_entries = try!(buffer.read_u16());
self.questions = buffer.read_u16()?;
self.answers = buffer.read_u16()?;
self.authoritative_entries = buffer.read_u16()?;
self.resource_entries = buffer.read_u16()?;
// Return the constant header size
Ok(())
@ -621,7 +628,7 @@ impl QueryType {
pub fn from_num(num: u16) -> QueryType {
match num {
1 => QueryType::A,
_ => QueryType::UNKNOWN(num)
_ => QueryType::UNKNOWN(num),
}
}
}
@ -636,21 +643,21 @@ question entries:
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DnsQuestion {
pub name: String,
pub qtype: QueryType
pub qtype: QueryType,
}
impl DnsQuestion {
pub fn new(name: String, qtype: QueryType) -> DnsQuestion {
DnsQuestion {
name: name,
qtype: qtype
qtype: qtype,
}
}
pub fn read(&mut self, buffer: &mut BytePacketBuffer) -> Result<()> {
try!(buffer.read_qname(&mut self.name));
self.qtype = QueryType::from_num(try!(buffer.read_u16())); // qtype
let _ = try!(buffer.read_u16()); // class
buffer.read_qname(&mut self.name)?;
self.qtype = QueryType::from_num(buffer.read_u16()?); // qtype
let _ = buffer.read_u16()?; // class
Ok(())
}
@ -673,12 +680,12 @@ pub enum DnsRecord {
domain: String,
qtype: u16,
data_len: u16,
ttl: u32
ttl: u32,
}, // 0
A {
domain: String,
addr: Ipv4Addr,
ttl: u32
ttl: u32,
}, // 1
}
```
@ -690,39 +697,40 @@ this:
```rust
impl DnsRecord {
pub fn read(buffer: &mut BytePacketBuffer) -> Result<DnsRecord> {
let mut domain = String::new();
try!(buffer.read_qname(&mut domain));
buffer.read_qname(&mut domain)?;
let qtype_num = try!(buffer.read_u16());
let qtype_num = buffer.read_u16()?;
let qtype = QueryType::from_num(qtype_num);
let _ = try!(buffer.read_u16()); // class, which we ignore
let ttl = try!(buffer.read_u32());
let data_len = try!(buffer.read_u16());
let _ = buffer.read_u16()?;
let ttl = buffer.read_u32()?;
let data_len = buffer.read_u16()?;
match qtype {
QueryType::A => {
let raw_addr = try!(buffer.read_u32());
let addr = Ipv4Addr::new(((raw_addr >> 24) & 0xFF) as u8,
let raw_addr = buffer.read_u32()?;
let addr = Ipv4Addr::new(
((raw_addr >> 24) & 0xFF) as u8,
((raw_addr >> 16) & 0xFF) as u8,
((raw_addr >> 8) & 0xFF) as u8,
((raw_addr >> 0) & 0xFF) as u8);
((raw_addr >> 0) & 0xFF) as u8,
);
Ok(DnsRecord::A {
domain: domain,
addr: addr,
ttl: ttl
ttl: ttl,
})
},
}
QueryType::UNKNOWN(_) => {
try!(buffer.step(data_len as usize));
buffer.step(data_len as usize)?;
Ok(DnsRecord::UNKNOWN {
domain: domain,
qtype: qtype_num,
data_len: data_len,
ttl: ttl
ttl: ttl,
})
}
}
@ -741,7 +749,7 @@ pub struct DnsPacket {
pub questions: Vec<DnsQuestion>,
pub answers: Vec<DnsRecord>,
pub authorities: Vec<DnsRecord>,
pub resources: Vec<DnsRecord>
pub resources: Vec<DnsRecord>,
}
impl DnsPacket {
@ -751,31 +759,30 @@ impl DnsPacket {
questions: Vec::new(),
answers: Vec::new(),
authorities: Vec::new(),
resources: Vec::new()
resources: Vec::new(),
}
}
pub fn from_buffer(buffer: &mut BytePacketBuffer) -> Result<DnsPacket> {
let mut result = DnsPacket::new();
try!(result.header.read(buffer));
result.header.read(buffer)?;
for _ in 0..result.header.questions {
let mut question = DnsQuestion::new("".to_string(),
QueryType::UNKNOWN(0));
try!(question.read(buffer));
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 = try!(DnsRecord::read(buffer));
let rec = DnsRecord::read(buffer)?;
result.answers.push(rec);
}
for _ in 0..result.header.authoritative_entries {
let rec = try!(DnsRecord::read(buffer));
let rec = DnsRecord::read(buffer)?;
result.authorities.push(rec);
}
for _ in 0..result.header.resource_entries {
let rec = try!(DnsRecord::read(buffer));
let rec = DnsRecord::read(buffer)?;
result.resources.push(rec);
}
@ -789,26 +796,28 @@ impl DnsPacket {
Let's use the `response_packet.txt` we generated earlier to try it out!
```rust
fn main() {
let mut f = File::open("response_packet.txt").unwrap();
fn main() -> Result<()> {
let mut f = File::open("response_packet.txt")?;
let mut buffer = BytePacketBuffer::new();
f.read(&mut buffer.buf).unwrap();
f.read(&mut buffer.buf)?;
let packet = DnsPacket::from_buffer(&mut buffer).unwrap();
println!("{:?}", packet.header);
let packet = DnsPacket::from_buffer(&mut buffer)?;
println!("{:#?}", packet.header);
for q in packet.questions {
println!("{:?}", q);
println!("{:#?}", q);
}
for rec in packet.answers {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in packet.authorities {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in packet.resources {
println!("{:?}", rec);
println!("{:#?}", rec);
}
Ok(())
}
```

138
chapter2.md
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@ -21,7 +21,7 @@ impl BytePacketBuffer {
fn write(&mut self, val: u8) -> Result<()> {
if self.pos >= 512 {
return Err(Error::new(ErrorKind::InvalidInput, "End of buffer"));
return Err("End of buffer".into());
}
self.buf[self.pos] = val;
self.pos += 1;
@ -29,23 +29,23 @@ impl BytePacketBuffer {
}
fn write_u8(&mut self, val: u8) -> Result<()> {
try!(self.write(val));
self.write(val)?;
Ok(())
}
fn write_u16(&mut self, val: u16) -> Result<()> {
try!(self.write((val >> 8) as u8));
try!(self.write((val & 0xFF) as u8));
self.write((val >> 8) as u8)?;
self.write((val & 0xFF) as u8)?;
Ok(())
}
fn write_u32(&mut self, val: u32) -> Result<()> {
try!(self.write(((val >> 24) & 0xFF) as u8));
try!(self.write(((val >> 16) & 0xFF) as u8));
try!(self.write(((val >> 8) & 0xFF) as u8));
try!(self.write(((val >> 0) & 0xFF) as u8));
self.write(((val >> 24) & 0xFF) as u8)?;
self.write(((val >> 16) & 0xFF) as u8)?;
self.write(((val >> 8) & 0xFF) as u8)?;
self.write(((val >> 0) & 0xFF) as u8)?;
Ok(())
}
@ -55,22 +55,19 @@ We'll also need a function for writing query names in labeled form:
```rust
fn write_qname(&mut self, qname: &str) -> Result<()> {
let split_str = qname.split('.').collect::<Vec<&str>>();
for label in split_str {
for label in qname.split('.') {
let len = label.len();
if len > 0x34 {
return Err(Error::new(ErrorKind::InvalidInput, "Single label exceeds 63 characters of length"));
return Err("Single label exceeds 63 characters of length".into());
}
try!(self.write_u8(len as u8));
self.write_u8(len as u8)?;
for b in label.as_bytes() {
try!(self.write_u8(*b));
self.write_u8(*b)?;
}
}
try!(self.write_u8(0));
self.write_u8(0)?;
Ok(())
}
@ -89,24 +86,28 @@ impl DnsHeader {
- snip -
pub fn write(&self, buffer: &mut BytePacketBuffer) -> Result<()> {
try!(buffer.write_u16(self.id));
buffer.write_u16(self.id)?;
try!(buffer.write_u8( ((self.recursion_desired as u8)) |
((self.truncated_message as u8) << 1) |
((self.authoritative_answer as u8) << 2) |
(self.opcode << 3) |
((self.response as u8) << 7) as u8) );
buffer.write_u8(
(self.recursion_desired as u8)
| ((self.truncated_message as u8) << 1)
| ((self.authoritative_answer as u8) << 2)
| (self.opcode << 3)
| ((self.response as u8) << 7) as u8,
)?;
try!(buffer.write_u8( (self.rescode.clone() as u8) |
((self.checking_disabled as u8) << 4) |
((self.authed_data as u8) << 5) |
((self.z as u8) << 6) |
((self.recursion_available as u8) << 7) ));
buffer.write_u8(
(self.rescode.clone() as u8)
| ((self.checking_disabled as u8) << 4)
| ((self.authed_data as u8) << 5)
| ((self.z as u8) << 6)
| ((self.recursion_available as u8) << 7),
)?;
try!(buffer.write_u16(self.questions));
try!(buffer.write_u16(self.answers));
try!(buffer.write_u16(self.authoritative_entries));
try!(buffer.write_u16(self.resource_entries));
buffer.write_u16(self.questions)?;
buffer.write_u16(self.answers)?;
buffer.write_u16(self.authoritative_entries)?;
buffer.write_u16(self.resource_entries)?;
Ok(())
}
@ -124,12 +125,11 @@ impl DnsQuestion {
- snip -
pub fn write(&self, buffer: &mut BytePacketBuffer) -> Result<()> {
try!(buffer.write_qname(&self.name));
buffer.write_qname(&self.name)?;
let typenum = self.qtype.to_num();
try!(buffer.write_u16(typenum));
try!(buffer.write_u16(1));
buffer.write_u16(typenum)?;
buffer.write_u16(1)?;
Ok(())
}
@ -148,23 +148,26 @@ impl DnsRecord {
- snip -
pub fn write(&self, buffer: &mut BytePacketBuffer) -> Result<usize> {
let start_pos = buffer.pos();
match *self {
DnsRecord::A { ref domain, ref addr, ttl } => {
try!(buffer.write_qname(domain));
try!(buffer.write_u16(QueryType::A.to_num()));
try!(buffer.write_u16(1));
try!(buffer.write_u32(ttl));
try!(buffer.write_u16(4));
DnsRecord::A {
ref domain,
ref addr,
ttl,
} => {
buffer.write_qname(domain)?;
buffer.write_u16(QueryType::A.to_num())?;
buffer.write_u16(1)?;
buffer.write_u32(ttl)?;
buffer.write_u16(4)?;
let octets = addr.octets();
try!(buffer.write_u8(octets[0]));
try!(buffer.write_u8(octets[1]));
try!(buffer.write_u8(octets[2]));
try!(buffer.write_u8(octets[3]));
},
buffer.write_u8(octets[0])?;
buffer.write_u8(octets[1])?;
buffer.write_u8(octets[2])?;
buffer.write_u8(octets[3])?;
}
DnsRecord::UNKNOWN { .. } => {
println!("Skipping record: {:?}", self);
}
@ -185,26 +188,25 @@ impl DnsPacket {
- snip -
pub fn write(&mut self, buffer: &mut BytePacketBuffer) -> Result<()>
{
pub fn write(&mut self, buffer: &mut BytePacketBuffer) -> 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;
try!(self.header.write(buffer));
self.header.write(buffer)?;
for question in &self.questions {
try!(question.write(buffer));
question.write(buffer)?;
}
for rec in &self.answers {
try!(rec.write(buffer));
rec.write(buffer)?;
}
for rec in &self.authorities {
try!(rec.write(buffer));
rec.write(buffer)?;
}
for rec in &self.resources {
try!(rec.write(buffer));
rec.write(buffer)?;
}
Ok(())
@ -219,7 +221,7 @@ We're ready to implement our stub resolver. Rust includes a convenient
`UDPSocket` which does most of the work.
```rust
fn main() {
fn main() -> Result<()> {
// Perform an A query for google.com
let qname = "google.com";
let qtype = QueryType::A;
@ -228,7 +230,7 @@ fn main() {
let server = ("8.8.8.8", 53);
// Bind a UDP socket to an arbitrary port
let socket = UdpSocket::bind(("0.0.0.0", 43210)).unwrap();
let socket = UdpSocket::bind(("0.0.0.0", 43210))?;
// Build our query packet. It's important that we remember to set the
// `recursion_desired` flag. As noted earlier, the packet id is arbitrary.
@ -237,37 +239,41 @@ fn main() {
packet.header.id = 6666;
packet.header.questions = 1;
packet.header.recursion_desired = true;
packet.questions.push(DnsQuestion::new(qname.to_string(), qtype));
packet
.questions
.push(DnsQuestion::new(qname.to_string(), qtype));
// Use our new write method to write the packet to a buffer...
let mut req_buffer = BytePacketBuffer::new();
packet.write(&mut req_buffer).unwrap();
packet.write(&mut req_buffer)?;
// ...and send it off to the server using our socket:
socket.send_to(&req_buffer.buf[0..req_buffer.pos], server).unwrap();
socket.send_to(&req_buffer.buf[0..req_buffer.pos], server)?;
// To prepare for receiving the response, we'll create a new `BytePacketBuffer`,
// and ask the socket to write the response directly into our buffer.
let mut res_buffer = BytePacketBuffer::new();
socket.recv_from(&mut res_buffer.buf).unwrap();
socket.recv_from(&mut res_buffer.buf)?;
// As per the previous section, `DnsPacket::from_buffer()` is then used to
// actually parse the packet after which we can print the response.
let res_packet = DnsPacket::from_buffer(&mut res_buffer).unwrap();
println!("{:?}", res_packet.header);
let res_packet = DnsPacket::from_buffer(&mut res_buffer)?;
println!("{:#?}", res_packet.header);
for q in res_packet.questions {
println!("{:?}", q);
println!("{:#?}", q);
}
for rec in res_packet.answers {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in res_packet.authorities {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in res_packet.resources {
println!("{:?}", rec);
println!("{:#?}", rec);
}
Ok(())
}
```

225
chapter3.md
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@ -101,7 +101,7 @@ impl QueryType {
5 => QueryType::CNAME,
15 => QueryType::MX,
28 => QueryType::AAAA,
_ => QueryType::UNKNOWN(num)
_ => QueryType::UNKNOWN(num),
}
}
}
@ -120,33 +120,33 @@ pub enum DnsRecord {
domain: String,
qtype: u16,
data_len: u16,
ttl: u32
ttl: u32,
}, // 0
A {
domain: String,
addr: Ipv4Addr,
ttl: u32
ttl: u32,
}, // 1
NS {
domain: String,
host: String,
ttl: u32
ttl: u32,
}, // 2
CNAME {
domain: String,
host: String,
ttl: u32
ttl: u32,
}, // 5
MX {
domain: String,
priority: u16,
host: String,
ttl: u32
ttl: u32,
}, // 15
AAAA {
domain: String,
addr: Ipv6Addr,
ttl: u32
ttl: u32,
}, // 28
}
```
@ -156,107 +156,102 @@ and reading records. Starting with read, we amend it with additional code for
each record type. First off, we've got the common preamble:
```rust
impl DnsRecord {
pub fn read(buffer: &mut BytePacketBuffer) -> Result<DnsRecord> {
let mut domain = String::new();
try!(buffer.read_qname(&mut domain));
buffer.read_qname(&mut domain)?;
let qtype_num = try!(buffer.read_u16());
let qtype_num = buffer.read_u16()?;
let qtype = QueryType::from_num(qtype_num);
let _ = try!(buffer.read_u16());
let ttl = try!(buffer.read_u32());
let data_len = try!(buffer.read_u16());
let _ = buffer.read_u16()?;
let ttl = buffer.read_u32()?;
let data_len = buffer.read_u16()?;
match qtype {
// Handle each record type separately, starting with the A record
// type which remains the same as before.
QueryType::A => {
let raw_addr = try!(buffer.read_u32());
let addr = Ipv4Addr::new(((raw_addr >> 24) & 0xFF) as u8,
let raw_addr = buffer.read_u32()?;
let addr = Ipv4Addr::new(
((raw_addr >> 24) & 0xFF) as u8,
((raw_addr >> 16) & 0xFF) as u8,
((raw_addr >> 8) & 0xFF) as u8,
((raw_addr >> 0) & 0xFF) as u8);
((raw_addr >> 0) & 0xFF) as u8,
);
Ok(DnsRecord::A {
domain: domain,
addr: addr,
ttl: ttl
ttl: ttl,
})
},
// The AAAA record type follows the same logic, but with more numbers to keep
// track off.
}
QueryType::AAAA => {
let raw_addr1 = try!(buffer.read_u32());
let raw_addr2 = try!(buffer.read_u32());
let raw_addr3 = try!(buffer.read_u32());
let raw_addr4 = try!(buffer.read_u32());
let addr = Ipv6Addr::new(((raw_addr1 >> 16) & 0xFFFF) as u16,
let raw_addr1 = buffer.read_u32()?;
let raw_addr2 = buffer.read_u32()?;
let raw_addr3 = buffer.read_u32()?;
let raw_addr4 = buffer.read_u32()?;
let addr = Ipv6Addr::new(
((raw_addr1 >> 16) & 0xFFFF) as u16,
((raw_addr1 >> 0) & 0xFFFF) as u16,
((raw_addr2 >> 16) & 0xFFFF) as u16,
((raw_addr2 >> 0) & 0xFFFF) as u16,
((raw_addr3 >> 16) & 0xFFFF) as u16,
((raw_addr3 >> 0) & 0xFFFF) as u16,
((raw_addr4 >> 16) & 0xFFFF) as u16,
((raw_addr4 >> 0) & 0xFFFF) as u16);
((raw_addr4 >> 0) & 0xFFFF) as u16,
);
Ok(DnsRecord::AAAA {
domain: domain,
addr: addr,
ttl: ttl
ttl: ttl,
})
},
// NS and CNAME both have the same structure.
}
QueryType::NS => {
let mut ns = String::new();
try!(buffer.read_qname(&mut ns));
buffer.read_qname(&mut ns)?;
Ok(DnsRecord::NS {
domain: domain,
host: ns,
ttl: ttl
ttl: ttl,
})
},
}
QueryType::CNAME => {
let mut cname = String::new();
try!(buffer.read_qname(&mut cname));
buffer.read_qname(&mut cname)?;
Ok(DnsRecord::CNAME {
domain: domain,
host: cname,
ttl: ttl
ttl: ttl,
})
},
// MX is almost like the previous two, but with one extra field for priority.
}
QueryType::MX => {
let priority = try!(buffer.read_u16());
let priority = buffer.read_u16()?;
let mut mx = String::new();
try!(buffer.read_qname(&mut mx));
buffer.read_qname(&mut mx)?;
Ok(DnsRecord::MX {
domain: domain,
priority: priority,
host: mx,
ttl: ttl
ttl: ttl,
})
},
// And we end with some code for handling unknown record types, as before.
}
QueryType::UNKNOWN(_) => {
try!(buffer.step(data_len as usize));
buffer.step(data_len as usize)?;
Ok(DnsRecord::UNKNOWN {
domain: domain,
qtype: qtype_num,
data_len: data_len,
ttl: ttl
ttl: ttl,
})
}
}
}
- snip -
}
```
It's a bit of a mouthful, but there are no especially complicated records in
@ -280,8 +275,8 @@ impl BytePacketBuffer {
}
fn set_u16(&mut self, pos: usize, val: u16) -> Result<()> {
try!(self.set(pos,(val >> 8) as u8));
try!(self.set(pos+1,(val & 0xFF) as u8));
self.set(pos, (val >> 8) as u8)?;
self.set(pos + 1, (val & 0xFF) as u8)?;
Ok(())
}
@ -289,83 +284,112 @@ impl BytePacketBuffer {
}
```
When writing the labels of a record, we don't know ahead of time the number of
bytes needed, since we might end up using jumps to compress the size. We'll
solve this by writing a zero size and then going back to fill in the size
needed.
### Extending DnsRecord for writing new record types
Now we can amend `DnsRecord::write`. Here's our new function:
```rust
pub fn write(&self, buffer: &mut BytePacketBuffer) -> Result<usize> {
impl DnsRecord {
- snip -
pub fn write(&self, buffer: &mut BytePacketBuffer) -> Result<usize> {
let start_pos = buffer.pos();
match *self {
DnsRecord::A { ref domain, ref addr, ttl } => {
try!(buffer.write_qname(domain));
try!(buffer.write_u16(QueryType::A.to_num()));
try!(buffer.write_u16(1));
try!(buffer.write_u32(ttl));
try!(buffer.write_u16(4));
DnsRecord::A {
ref domain,
ref addr,
ttl,
} => {
buffer.write_qname(domain)?;
buffer.write_u16(QueryType::A.to_num())?;
buffer.write_u16(1)?;
buffer.write_u32(ttl)?;
buffer.write_u16(4)?;
let octets = addr.octets();
try!(buffer.write_u8(octets[0]));
try!(buffer.write_u8(octets[1]));
try!(buffer.write_u8(octets[2]));
try!(buffer.write_u8(octets[3]));
},
DnsRecord::NS { ref domain, ref host, ttl } => {
try!(buffer.write_qname(domain));
try!(buffer.write_u16(QueryType::NS.to_num()));
try!(buffer.write_u16(1));
try!(buffer.write_u32(ttl));
buffer.write_u8(octets[0])?;
buffer.write_u8(octets[1])?;
buffer.write_u8(octets[2])?;
buffer.write_u8(octets[3])?;
}
DnsRecord::NS {
ref domain,
ref host,
ttl,
} => {
buffer.write_qname(domain)?;
buffer.write_u16(QueryType::NS.to_num())?;
buffer.write_u16(1)?;
buffer.write_u32(ttl)?;
let pos = buffer.pos();
try!(buffer.write_u16(0));
buffer.write_u16(0)?;
try!(buffer.write_qname(host));
buffer.write_qname(host)?;
let size = buffer.pos() - (pos + 2);
try!(buffer.set_u16(pos, size as u16));
},
DnsRecord::CNAME { ref domain, ref host, ttl } => {
try!(buffer.write_qname(domain));
try!(buffer.write_u16(QueryType::CNAME.to_num()));
try!(buffer.write_u16(1));
try!(buffer.write_u32(ttl));
buffer.set_u16(pos, size as u16)?;
}
DnsRecord::CNAME {
ref domain,
ref host,
ttl,
} => {
buffer.write_qname(domain)?;
buffer.write_u16(QueryType::CNAME.to_num())?;
buffer.write_u16(1)?;
buffer.write_u32(ttl)?;
let pos = buffer.pos();
try!(buffer.write_u16(0));
buffer.write_u16(0)?;
try!(buffer.write_qname(host));
buffer.write_qname(host)?;
let size = buffer.pos() - (pos + 2);
try!(buffer.set_u16(pos, size as u16));
},
DnsRecord::MX { ref domain, priority, ref host, ttl } => {
try!(buffer.write_qname(domain));
try!(buffer.write_u16(QueryType::MX.to_num()));
try!(buffer.write_u16(1));
try!(buffer.write_u32(ttl));
buffer.set_u16(pos, size as u16)?;
}
DnsRecord::MX {
ref domain,
priority,
ref host,
ttl,
} => {
buffer.write_qname(domain)?;
buffer.write_u16(QueryType::MX.to_num())?;
buffer.write_u16(1)?;
buffer.write_u32(ttl)?;
let pos = buffer.pos();
try!(buffer.write_u16(0));
buffer.write_u16(0)?;
try!(buffer.write_u16(priority));
try!(buffer.write_qname(host));
buffer.write_u16(priority)?;
buffer.write_qname(host)?;
let size = buffer.pos() - (pos + 2);
try!(buffer.set_u16(pos, size as u16));
},
DnsRecord::AAAA { ref domain, ref addr, ttl } => {
try!(buffer.write_qname(domain));
try!(buffer.write_u16(QueryType::AAAA.to_num()));
try!(buffer.write_u16(1));
try!(buffer.write_u32(ttl));
try!(buffer.write_u16(16));
buffer.set_u16(pos, size as u16)?;
}
DnsRecord::AAAA {
ref domain,
ref addr,
ttl,
} => {
buffer.write_qname(domain)?;
buffer.write_u16(QueryType::AAAA.to_num())?;
buffer.write_u16(1)?;
buffer.write_u32(ttl)?;
buffer.write_u16(16)?;
for octet in &addr.segments() {
try!(buffer.write_u16(*octet));
buffer.write_u16(*octet)?;
}
}
},
DnsRecord::UNKNOWN { .. } => {
println!("Skipping record: {:?}", self);
}
@ -373,6 +397,7 @@ pub fn write(&self, buffer: &mut BytePacketBuffer) -> Result<usize> {
Ok(buffer.pos() - start_pos)
}
}
```
Again, quite a bit of extra code, but thankfully the last thing we've got to

29
chapter4.md
View File

@ -141,26 +141,27 @@ work, it's a rather quick effort!
We'll start out by doing some quick refactoring, moving our lookup code into
a separate function. This is for the most part the same code as we had in our
`main` function in the previous chapter, with the only change being that we
handle errors gracefully using `try!`.
`main` function in the previous chapter.
```rust
fn lookup(qname: &str, qtype: QueryType, server: (&str, u16)) -> Result<DnsPacket> {
let socket = try!(UdpSocket::bind(("0.0.0.0", 43210)));
let socket = UdpSocket::bind(("0.0.0.0", 43210))?;
let mut packet = DnsPacket::new();
packet.header.id = 6666;
packet.header.questions = 1;
packet.header.recursion_desired = true;
packet.questions.push(DnsQuestion::new(qname.to_string(), qtype));
packet
.questions
.push(DnsQuestion::new(qname.to_string(), qtype));
let mut req_buffer = BytePacketBuffer::new();
packet.write(&mut req_buffer).unwrap();
try!(socket.send_to(&req_buffer.buf[0..req_buffer.pos], server));
packet.write(&mut req_buffer)?;
socket.send_to(&req_buffer.buf[0..req_buffer.pos], server)?;
let mut res_buffer = BytePacketBuffer::new();
socket.recv_from(&mut res_buffer.buf).unwrap();
socket.recv_from(&mut res_buffer.buf)?;
DnsPacket::from_buffer(&mut res_buffer)
}
@ -171,12 +172,12 @@ fn lookup(qname: &str, qtype: QueryType, server: (&str, u16)) -> Result<DnsPacke
Now we'll write our server code. First, we need get some things in order.
```rust
fn main() {
fn main() -> Result<()> {
// Forward queries to Google's public DNS
let server = ("8.8.8.8", 53);
// Bind an UDP socket on port 2053
let socket = UdpSocket::bind(("0.0.0.0", 2053)).unwrap();
let socket = UdpSocket::bind(("0.0.0.0", 2053))?;
// For now, queries are handled sequentially, so an infinite loop for servicing
// requests is initiated.
@ -224,7 +225,6 @@ fn main() {
if request.questions.is_empty() {
packet.header.rescode = ResultCode::FORMERR;
}
// Usually a question will be present, though.
else {
let question = &request.questions[0];
@ -254,12 +254,12 @@ fn main() {
} else {
packet.header.rescode = ResultCode::SERVFAIL;
}
}
// The only thing remaining is to encode our response and send it off!
let mut res_buffer = BytePacketBuffer::new();
match packet.write(&mut res_buffer) {
Ok(_) => {},
Ok(_) => {}
Err(e) => {
println!("Failed to encode UDP response packet: {:?}", e);
continue;
@ -276,15 +276,14 @@ fn main() {
};
match socket.send_to(data, src) {
Ok(_) => {},
Ok(_) => {}
Err(e) => {
println!("Failed to send response buffer: {:?}", e);
continue;
}
};
}
} // End of request loop
} // End of main
}
```
The match idiom for error handling is used again and again here, since we want to avoid

141
chapter5.md
View File

@ -168,90 +168,69 @@ impl DnsPacket {
- snip -
// 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.
/// 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<String> {
if !self.answers.is_empty() {
let idx = random::<usize>() % self.answers.len();
let a_record = &self.answers[idx];
if let DnsRecord::A{ ref addr, .. } = *a_record {
return Some(addr.to_string());
}
self.answers
.iter()
.filter_map(|record| match record {
DnsRecord::A { ref addr, .. } => Some(addr.to_string()),
_ => None,
})
.next()
}
None
/// 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.
/// When there is a NS record in the authorities section, there may also
/// be a matching A record in the additional section. This saves us
/// from doing a separate query to resolve the IP of the name server.
pub fn get_resolved_ns(&self, qname: &str) -> Option<String> {
// First, we scan the list of NS records in the authorities section:
let mut new_authorities = Vec::new();
for auth in &self.authorities {
if let DnsRecord::NS { ref domain, ref host, .. } = *auth {
if !qname.ends_with(domain) {
continue;
// 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(addr),
_ => None,
})
})
.map(|addr| addr.to_string())
// Finally, pick the first valid entry
.next()
}
// Once we've found an NS record, we scan the resources record for a matching
// A record...
for rsrc in &self.resources {
if let DnsRecord::A{ ref domain, ref addr, ttl } = *rsrc {
if domain != host {
continue;
}
let rec = DnsRecord::A {
domain: host.clone(),
addr: *addr,
ttl: ttl
};
// ...and push any matches to a list.
new_authorities.push(rec);
}
}
}
}
// If there are any matches, we pick the first one.
if !new_authorities.is_empty() {
if let DnsRecord::A { addr, .. } = new_authorities[0] {
return Some(addr.to_string());
}
}
None
} // End of get_resolved_ns
// 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.
/// 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 of our first. For this, we introduce a method for
returning the hostname of an appropriate name server.
pub fn get_unresolved_ns(&self, qname: &str) -> Option<String> {
let mut new_authorities = Vec::new();
for auth in &self.authorities {
if let DnsRecord::NS { ref domain, ref host, .. } = *auth {
if !qname.ends_with(domain) {
continue;
// Get an iterator over the nameservers in the authorities section
self.get_ns(qname)
.map(|(_, host)| host.to_string())
// Finally, pick the first valid entry
.next()
}
new_authorities.push(host);
}
}
if !new_authorities.is_empty() {
let idx = random::<usize>() % new_authorities.len();
return Some(new_authorities[idx].clone());
}
None
} // End of get_unresolved_ns
} // End of DnsPacket
```
@ -273,12 +252,10 @@ fn recursive_lookup(qname: &str, qtype: QueryType) -> Result<DnsPacket> {
let ns_copy = ns.clone();
let server = (ns_copy.as_str(), 53);
let response = try!(lookup(qname, qtype.clone(), server));
let response = lookup(qname, qtype.clone(), server)?;
// If there are entries in the answer section, and no errors, we are done!
if !response.answers.is_empty() &&
response.header.rescode == ResultCode::NOERROR {
if !response.answers.is_empty() && response.header.rescode == ResultCode::NOERROR {
return Ok(response.clone());
}
@ -301,23 +278,23 @@ fn recursive_lookup(qname: &str, qtype: QueryType) -> Result<DnsPacket> {
// we'll go with what the last server told us.
let new_ns_name = match response.get_unresolved_ns(qname) {
Some(x) => x,
None => return Ok(response.clone())
None => return Ok(response.clone()),
};
// Here we go down the rabbit hole by starting _another_ lookup sequence in the
// midst of our current one. Hopefully, this will give us the IP of an appropriate
// name server.
let recursive_response = try!(recursive_lookup(&new_ns_name, QueryType::A));
let recursive_response = recursive_lookup(&new_ns_name, QueryType::A)?;
// Finally, we pick a random ip from the result, and restart the loop. If no such
// record is available, we again return the last result we got.
if let Some(new_ns) = recursive_response.get_random_a() {
ns = new_ns.clone();
} else {
return Ok(response.clone())
return Ok(response.clone());
}
}
}
} // End of recursive_lookup
```
### Trying out recursive lookup
@ -326,7 +303,7 @@ The only thing remaining is to change our main function to use
`recursive_lookup`:
```rust
fn main() {
fn main() -> Result<()> {
- snip -

69
examples/sample1.rs
View File

@ -11,6 +11,8 @@ pub struct BytePacketBuffer {
}
impl BytePacketBuffer {
/// This gives us a fresh buffer for holding the packet contents, and a
/// field for keeping track of where we are.
pub fn new() -> BytePacketBuffer {
BytePacketBuffer {
buf: [0; 512],
@ -18,22 +20,26 @@ impl BytePacketBuffer {
}
}
/// Current position within buffer
fn pos(&self) -> usize {
self.pos
}
/// Step the buffer position forward a specific number of steps
fn step(&mut self, steps: usize) -> Result<()> {
self.pos += steps;
Ok(())
}
/// Change the buffer position
fn seek(&mut self, pos: usize) -> Result<()> {
self.pos = pos;
Ok(())
}
/// Read a single byte and move the position one step forward
fn read(&mut self) -> Result<u8> {
if self.pos >= 512 {
return Err("End of buffer".into());
@ -44,6 +50,7 @@ impl BytePacketBuffer {
Ok(res)
}
/// Get a single byte, without changing the buffer position
fn get(&mut self, pos: usize) -> Result<u8> {
if pos >= 512 {
return Err("End of buffer".into());
@ -51,6 +58,7 @@ impl BytePacketBuffer {
Ok(self.buf[pos])
}
/// Get a range of bytes
fn get_range(&mut self, start: usize, len: usize) -> Result<&[u8]> {
if start + len >= 512 {
return Err("End of buffer".into());
@ -58,12 +66,14 @@ impl BytePacketBuffer {
Ok(&self.buf[start..start + len as usize])
}
/// Read two bytes, stepping two steps forward
fn read_u16(&mut self) -> Result<u16> {
let res = ((self.read()? as u16) << 8) | (self.read()? as u16);
Ok(res)
}
/// Read four bytes, stepping four steps forward
fn read_u32(&mut self) -> Result<u32> {
let res = ((self.read()? as u32) << 24)
| ((self.read()? as u32) << 16)
@ -73,13 +83,28 @@ impl BytePacketBuffer {
Ok(res)
}
/// Read a qname
///
/// The tricky part: Reading domain names, taking labels into consideration.
/// Will take something like [3]www[6]google[3]com[0] and append
/// www.google.com to outstr.
fn read_qname(&mut self, outstr: &mut String) -> Result<()> {
// Since we might encounter jumps, we'll keep track of our position
// locally as opposed to using the position within the struct. This
// allows us to move the shared position to a point past our current
// qname, while keeping track of our progress on the current qname
// using this variable.
let mut pos = self.pos();
let mut jumped = false;
let mut delim = "";
// track whether or not we've jumped
let mut jumped = false;
let max_jumps = 5;
let mut jumps_performed = 0;
// Our delimiter which we append for each label. Since we don't want a
// dot at the beginning of the domain name we'll leave it empty for now
// and set it to "." at the end of the first iteration.
let mut delim = "";
loop {
// Dns Packets are untrusted data, so we need to be paranoid. Someone
// can craft a packet with a cycle in the jump instructions. This guards
@ -88,43 +113,57 @@ impl BytePacketBuffer {
return Err(format!("Limit of {} jumps exceeded", max_jumps).into());
}
// At this point, we're always at the beginning of a label. Recall
// that labels start with a length byte.
let len = self.get(pos)?;
// A two byte sequence, where the two highest bits of the first byte is
// set, represents a offset relative to the start of the buffer. We
// handle this by jumping to the offset, setting a flag to indicate
// that we shouldn't update the shared buffer position once done.
// If len has the two most significant bit are set, it represents a
// jump to some other offset in the packet:
if (len & 0xC0) == 0xC0 {
// When a jump is performed, we only modify the shared buffer
// position once, and avoid making the change later on.
// Update the buffer position to a point past the current
// label. We don't need to touch it any further.
if !jumped {
self.seek(pos + 2)?;
}
// Read another byte, calculate offset and perform the jump by
// updating our local position variable
let b2 = self.get(pos + 1)? as u16;
let offset = (((len as u16) ^ 0xC0) << 8) | b2;
pos = offset as usize;
// Indicate that a jump was performed.
jumped = true;
jumps_performed += 1;
continue;
}
// The base scenario, where we're reading a single label and
// appending it to the output:
else {
// Move a single byte forward to move past the length byte.
pos += 1;
// Names are terminated by an empty label of length 0
// Domain names are terminated by an empty label of length 0,
// so if the length is zero we're done.
if len == 0 {
break;
}
// Append the delimiter to our output buffer first.
outstr.push_str(delim);
// Extract the actual ASCII bytes for this label and append them
// to the output buffer.
let str_buffer = self.get_range(pos, len as usize)?;
outstr.push_str(&String::from_utf8_lossy(str_buffer).to_lowercase());
delim = ".";
// Move forward the full length of the label.
pos += len as usize;
}
}
if !jumped {
self.seek(pos)?;
@ -386,19 +425,19 @@ fn main() -> Result<()> {
f.read(&mut buffer.buf)?;
let packet = DnsPacket::from_buffer(&mut buffer)?;
println!("{:?}", packet.header);
println!("{:#?}", packet.header);
for q in packet.questions {
println!("{:?}", q);
println!("{:#?}", q);
}
for rec in packet.answers {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in packet.authorities {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in packet.resources {
println!("{:?}", rec);
println!("{:#?}", rec);
}
Ok(())

29
examples/sample2.rs
View File

@ -164,9 +164,7 @@ impl BytePacketBuffer {
}
fn write_qname(&mut self, qname: &str) -> Result<()> {
let split_str = qname.split('.').collect::<Vec<&str>>();
for label in split_str {
for label in qname.split('.') {
let len = label.len();
if len > 0x34 {
return Err("Single label exceeds 63 characters of length".into());
@ -521,12 +519,18 @@ impl DnsPacket {
}
fn main() -> Result<()> {
let qname = "www.yahoo.com";
// Perform an A query for google.com
let qname = "google.com";
let qtype = QueryType::A;
// Using googles public DNS server
let server = ("8.8.8.8", 53);
// Bind a UDP socket to an arbitrary port
let socket = UdpSocket::bind(("0.0.0.0", 43210))?;
// Build our query packet. It's important that we remember to set the
// `recursion_desired` flag. As noted earlier, the packet id is arbitrary.
let mut packet = DnsPacket::new();
packet.header.id = 6666;
@ -536,27 +540,34 @@ fn main() -> Result<()> {
.questions
.push(DnsQuestion::new(qname.to_string(), qtype));
// Use our new write method to write the packet to a buffer...
let mut req_buffer = BytePacketBuffer::new();
packet.write(&mut req_buffer)?;
// ...and send it off to the server using our socket:
socket.send_to(&req_buffer.buf[0..req_buffer.pos], server)?;
// To prepare for receiving the response, we'll create a new `BytePacketBuffer`,
// and ask the socket to write the response directly into our buffer.
let mut res_buffer = BytePacketBuffer::new();
socket.recv_from(&mut res_buffer.buf)?;
// As per the previous section, `DnsPacket::from_buffer()` is then used to
// actually parse the packet after which we can print the response.
let res_packet = DnsPacket::from_buffer(&mut res_buffer)?;
println!("{:?}", res_packet.header);
println!("{:#?}", res_packet.header);
for q in res_packet.questions {
println!("{:?}", q);
println!("{:#?}", q);
}
for rec in res_packet.answers {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in res_packet.authorities {
println!("{:?}", rec);
println!("{:#?}", rec);
}
for rec in res_packet.resources {
println!("{:?}", rec);
println!("{:#?}", rec);
}
Ok(())

4
examples/sample3.rs
View File

@ -164,9 +164,7 @@ impl BytePacketBuffer {
}
fn write_qname(&mut self, qname: &str) -> Result<()> {
let split_str = qname.split('.').collect::<Vec<&str>>();
for label in split_str {
for label in qname.split('.') {
let len = label.len();
if len > 0x34 {
return Err("Single label exceeds 63 characters of length".into());

34
examples/sample4.rs
View File

@ -164,9 +164,7 @@ impl BytePacketBuffer {
}
fn write_qname(&mut self, qname: &str) -> Result<()> {
let split_str = qname.split('.').collect::<Vec<&str>>();
for label in split_str {
for label in qname.split('.') {
let len = label.len();
if len > 0x34 {
return Err("Single label exceeds 63 characters of length".into());
@ -714,11 +712,17 @@ fn lookup(qname: &str, qtype: QueryType, server: (&str, u16)) -> Result<DnsPacke
}
fn main() -> Result<()> {
// Forward queries to Google's public DNS
let server = ("8.8.8.8", 53);
// Bind an UDP socket on port 2053
let socket = UdpSocket::bind(("0.0.0.0", 2053))?;
// For now, queries are handled sequentially, so an infinite loop for servicing
// requests is initiated.
loop {
// With a socket ready, we can go ahead and read a packet. This will
// block until one is received.
let mut req_buffer = BytePacketBuffer::new();
let (_, src) = match socket.recv_from(&mut req_buffer.buf) {
Ok(x) => x,
@ -728,6 +732,16 @@ fn main() -> Result<()> {
}
};
// Here we use match to safely unwrap the `Result`. If everything's as expected,
// the raw bytes are simply returned, and if not it'll abort by restarting the
// loop and waiting for the next request. The `recv_from` function will write the
// data into the provided buffer, and return the length of the data read as well
// as the source address. We're not interested in the length, but we need to keep
// track of the source in order to send our reply later on.
// Next, `DnsPacket::from_buffer` is used to parse the raw bytes into
// a `DnsPacket`. It uses the same error handling idiom as the previous statement.
let request = match DnsPacket::from_buffer(&mut req_buffer) {
Ok(x) => x,
Err(e) => {
@ -736,18 +750,29 @@ fn main() -> Result<()> {
}
};
// Create and initialize the response packet
let mut packet = DnsPacket::new();
packet.header.id = request.header.id;
packet.header.recursion_desired = true;
packet.header.recursion_available = true;
packet.header.response = true;
// Being mindful of how unreliable input data from arbitrary senders can be, we
// need make sure that a question is actually present. If not, we return `FORMERR`
// to indicate that the sender made something wrong.
if request.questions.is_empty() {
packet.header.rescode = ResultCode::FORMERR;
} else {
}
// Usually a question will be present, though.
else {
let question = &request.questions[0];
println!("Received query: {:?}", question);
// Since all is set up and as expected, the query can be forwarded to the target
// server. There's always the possibility that the query will fail, in which case
// the `SERVFAIL` response code is set to indicate as much to the client. If
// rather everything goes as planned, the question and response records as copied
// into our response packet.
if let Ok(result) = lookup(&question.name, question.qtype, server) {
packet.questions.push(question.clone());
packet.header.rescode = result.header.rescode;
@ -769,6 +794,7 @@ fn main() -> Result<()> {
}
}
// The only thing remaining is to encode our response and send it off!
let mut res_buffer = BytePacketBuffer::new();
match packet.write(&mut res_buffer) {
Ok(_) => {}

151
examples/sample5.rs
View File

@ -164,9 +164,7 @@ impl BytePacketBuffer {
}
fn write_qname(&mut self, qname: &str) -> Result<()> {
let split_str = qname.split('.').collect::<Vec<&str>>();
for label in split_str {
for label in qname.split('.') {
let len = label.len();
if len > 0x34 {
return Err("Single label exceeds 63 characters of length".into());
@ -690,84 +688,69 @@ impl DnsPacket {
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<String> {
if !self.answers.is_empty() {
let a_record = &self.answers[0];
if let DnsRecord::A { ref addr, .. } = *a_record {
return Some(addr.to_string());
}
self.answers
.iter()
.filter_map(|record| match record {
DnsRecord::A { ref addr, .. } => Some(addr.to_string()),
_ => None,
})
.next()
}
None
/// 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<String> {
let mut new_authorities = Vec::new();
for auth in &self.authorities {
if let DnsRecord::NS {
ref domain,
ref host,
..
} = *auth
{
if !qname.ends_with(domain) {
continue;
}
for rsrc in &self.resources {
if let DnsRecord::A {
ref domain,
ref addr,
ttl,
} = *rsrc
{
if domain != host {
continue;
}
let rec = DnsRecord::A {
domain: host.clone(),
addr: *addr,
ttl: ttl,
};
new_authorities.push(rec);
}
}
}
}
if !new_authorities.is_empty() {
if let DnsRecord::A { addr, .. } = new_authorities[0] {
return Some(addr.to_string());
}
}
None
// 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(addr),
_ => None,
})
})
.map(|addr| addr.to_string())
// 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(&self, qname: &str) -> Option<String> {
let mut new_authorities = Vec::new();
for auth in &self.authorities {
if let DnsRecord::NS {
ref domain,
ref host,
..
} = *auth
{
if !qname.ends_with(domain) {
continue;
}
new_authorities.push(host);
}
}
if !new_authorities.is_empty() {
return Some(new_authorities[0].clone());
}
None
// Get an iterator over the nameservers in the authorities section
self.get_ns(qname)
.map(|(_, host)| host.to_string())
// Finally, pick the first valid entry
.next()
}
}
@ -794,45 +777,53 @@ fn lookup(qname: &str, qtype: QueryType, server: (&str, u16)) -> Result<DnsPacke
}
fn recursive_lookup(qname: &str, qtype: QueryType) -> Result<DnsPacket> {
// For now we're always starting with *a.root-servers.net*.
let mut ns = "198.41.0.4".to_string();
// Start querying name servers
// Since it might take an arbitrary number of steps, we enter an unbounded loop.
loop {
println!("attempting lookup of {:?} {} with ns {}", qtype, qname, ns);
// The next step is to send the query to the active server.
let ns_copy = ns.clone();
let server = (ns_copy.as_str(), 53);
let response = lookup(qname, qtype.clone(), server)?;
// If we've got an actual answer, we're done!
// If there are entries in the answer section, and no errors, we are done!
if !response.answers.is_empty() && response.header.rescode == ResultCode::NOERROR {
return Ok(response.clone());
}
// We might also get a `NXDOMAIN` reply, which is the authoritative name servers
// way of telling us that the name doesn't exist.
if response.header.rescode == ResultCode::NXDOMAIN {
return Ok(response.clone());
}
// Otherwise, try to find a new nameserver based on NS and a
// corresponding A record in the additional section
// Otherwise, we'll try to find a new nameserver based on NS and a corresponding A
// record in the additional section. If this succeeds, we can switch name server
// and retry the loop.
if let Some(new_ns) = response.get_resolved_ns(qname) {
// If there is such a record, we can retry the loop with that NS
ns = new_ns.clone();
continue;
}
// If not, we'll have to resolve the ip of a NS record
// If not, we'll have to resolve the ip of a NS record. If no NS records exist,
// we'll go with what the last server told us.
let new_ns_name = match response.get_unresolved_ns(qname) {
Some(x) => x,
None => return Ok(response.clone()),
};
// Recursively resolve the NS
// Here we go down the rabbit hole by starting _another_ lookup sequence in the
// midst of our current one. Hopefully, this will give us the IP of an appropriate
// name server.
let recursive_response = recursive_lookup(&new_ns_name, QueryType::A)?;
// Pick a random IP and restart
// Finally, we pick a random ip from the result, and restart the loop. If no such
// record is available, we again return the last result we got.
if let Some(new_ns) = recursive_response.get_random_a() {
ns = new_ns.clone();
} else {