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use crate::Result;
pub struct PacketBuffer {
pub buf: Vec<u8>,
pub pos: usize,
pub size: usize,
}
impl PacketBuffer {
pub fn new(buf: Vec<u8>) -> Self {
Self {
size: buf.len(),
buf,
pos: 0,
}
}
pub fn pos(&self) -> usize {
self.pos
}
pub fn step(&mut self, steps: usize) -> Result<()> {
self.pos += steps;
Ok(())
}
pub fn seek(&mut self, pos: usize) -> Result<()> {
self.pos = pos;
Ok(())
}
pub fn read(&mut self) -> Result<u8> {
if self.pos >= self.size {
return Err("Tried to read past end of buffer".into());
}
let res = self.buf[self.pos];
self.pos += 1;
Ok(res)
}
pub fn get(&mut self, pos: usize) -> Result<u8> {
if pos >= self.size {
return Err("Tried to read past end of buffer".into());
}
Ok(self.buf[pos])
}
pub fn get_range(&mut self, start: usize, len: usize) -> Result<&[u8]> {
if start + len >= self.size {
return Err("Tried to read past end of buffer".into());
}
Ok(&self.buf[start..start + len])
}
pub fn read_u16(&mut self) -> Result<u16> {
let res = ((self.read()? as u16) << 8) | (self.read()? as u16);
Ok(res)
}
pub 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);
Ok(res)
}
pub fn read_qname(&mut self, outstr: &mut String) -> Result<()> {
let mut pos = self.pos();
let mut jumped = false;
let mut delim = "";
let max_jumps = 5;
let mut jumps_performed = 0;
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 {max_jumps} jumps exceeded").into());
}
let len = self.get(pos)?;
if (len & 0xC0) == 0xC0 {
if !jumped {
self.seek(pos + 2)?;
}
let b2 = self.get(pos + 1)? as u16;
let offset = (((len as u16) ^ 0xC0) << 8) | b2;
pos = offset as usize;
jumped = true;
jumps_performed += 1;
continue;
}
pos += 1;
if len == 0 {
break;
}
outstr.push_str(delim);
let str_buffer = self.get_range(pos, len as usize)?;
outstr.push_str(&String::from_utf8_lossy(str_buffer).to_lowercase());
delim = ".";
pos += len as usize;
}
if !jumped {
self.seek(pos)?;
}
Ok(())
}
pub fn read_string(&mut self, outstr: &mut String) -> Result<()> {
let len = self.read()?;
self.read_string_n(outstr, len)?;
Ok(())
}
pub fn read_string_n(&mut self, outstr: &mut String, len: u8) -> Result<()> {
let mut pos = self.pos;
let str_buffer = self.get_range(pos, len as usize)?;
let mut i = 0;
for b in str_buffer {
let c = *b as char;
if c == '\0' {
break;
}
outstr.push(c);
i += 1;
}
pos += i;
self.seek(pos)?;
Ok(())
}
pub fn write(&mut self, val: u8) -> Result<()> {
if self.size < self.pos {
self.size = self.pos;
}
if self.buf.len() <= self.size {
self.buf.resize(self.size + 1, 0x00);
}
self.buf[self.pos] = val;
self.pos += 1;
Ok(())
}
pub fn write_u8(&mut self, val: u8) -> Result<()> {
self.write(val)?;
Ok(())
}
pub fn write_u16(&mut self, val: u16) -> Result<()> {
self.write((val >> 8) as u8)?;
self.write((val & 0xFF) as u8)?;
Ok(())
}
pub fn write_u32(&mut self, val: u32) -> Result<()> {
self.write(((val >> 24) & 0xFF) as u8)?;
self.write(((val >> 16) & 0xFF) as u8)?;
self.write(((val >> 8) & 0xFF) as u8)?;
self.write((val & 0xFF) as u8)?;
Ok(())
}
pub fn write_qname(&mut self, qname: &str) -> Result<()> {
for label in qname.split('.') {
let len = label.len();
self.write_u8(len as u8)?;
for b in label.as_bytes() {
self.write_u8(*b)?;
}
}
if !qname.is_empty() {
self.write_u8(0)?;
}
Ok(())
}
pub fn write_string(&mut self, text: &str) -> Result<()> {
for b in text.as_bytes() {
self.write_u8(*b)?;
}
Ok(())
}
pub fn set(&mut self, pos: usize, val: u8) -> Result<()> {
self.buf[pos] = val;
Ok(())
}
pub fn set_u16(&mut self, pos: usize, val: u16) -> Result<()> {
self.set(pos, (val >> 8) as u8)?;
self.set(pos + 1, (val & 0xFF) as u8)?;
Ok(())
}
}
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