From e0cc79198f9f76c8ca528e1b85f4268d57cec914 Mon Sep 17 00:00:00 2001
From: fuckwit <me@fucktwit.dev>
Date: Mon, 22 May 2023 22:43:16 +0200
Subject: [PATCH] parse server name and file name

---
 src/lib.rs | 66 +++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 58 insertions(+), 8 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index e5329c6..17dc8e7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,8 @@
+#![allow(unused)]
 use std::{net::Ipv4Addr, path::Path};
 
 use nom::{
-    bytes::complete::take,
+    bytes::complete::{take, take_until},
     number::complete::{be_u16, be_u32, be_u8},
     IResult,
 };
@@ -14,15 +15,18 @@ struct DhcpMessage<'a> {
     hops: u8,
     transaction_id: u32,
     seconds: u16,
-    flags: u16,
+    flags: Flags,
     client_address: Ipv4Addr,
     server_address: Ipv4Addr,
     gateway_address: Ipv4Addr,
     client_hardware_address: &'a [u8],
-    server_hostname: &'a str,
-    boot_file_name: &'a Path,
+    server_name: &'a str,
+    file_name: &'a Path,
 }
 
+#[derive(Debug)]
+struct Flags(u16);
+
 #[derive(Debug)]
 enum Operation {
     Request = 1,
@@ -61,6 +65,10 @@ fn parse_dhcp_operation(i: &[u8]) -> IResult<&[u8], Operation> {
     be_u8(i).map(|(i, v)| (i, v.into()))
 }
 
+fn parse_dhcp_flags(i: &[u8]) -> IResult<&[u8], Flags> {
+    be_u16(i).map(|(i, v)| (i, Flags(v)))
+}
+
 fn parse_dhcp_hardware_type(i: &[u8]) -> IResult<&[u8], HardwareType> {
     be_u8(i).map(|(i, v)| (i, v.into()))
 }
@@ -71,6 +79,28 @@ fn parse_ipv4_address(i: &[u8]) -> IResult<&[u8], Ipv4Addr> {
     Ok((i, ip))
 }
 
+fn parse_client_hardware_address(i: &[u8], hardware_address_length: u8) -> IResult<&[u8], &[u8]> {
+    let (i, val) = take(hardware_address_length)(i)?;
+    let (i, _padding) = take(0x10 - hardware_address_length)(i)?;
+    Ok((i, val))
+}
+
+fn parse_server_name(i: &[u8]) -> IResult<&[u8], &str> {
+    let (i, val) = take(64usize)(i)?;
+    let nullbyte_position = val.iter().position(|v| *v == b'\0').unwrap_or(64);
+    let val = unsafe { std::str::from_utf8_unchecked(&val[..nullbyte_position]) };
+
+    Ok((i, val))
+}
+
+fn parse_file(i: &[u8]) -> IResult<&[u8], &Path> {
+    let (i, val) = take(128usize)(i)?;
+    let nullbyte_position = val.iter().position(|v| *v == b'\0').unwrap_or(128);
+    let val = unsafe { std::str::from_utf8_unchecked(&val[..nullbyte_position]) };
+
+    Ok((i, Path::new(val)))
+}
+
 fn parse_dhcp_packet(packet: &[u8]) -> IResult<&[u8], DhcpMessage> {
     let (packet, operation) = parse_dhcp_operation(packet)?;
     let (packet, hardware_type) = parse_dhcp_hardware_type(packet)?;
@@ -78,11 +108,16 @@ fn parse_dhcp_packet(packet: &[u8]) -> IResult<&[u8], DhcpMessage> {
     let (packet, hops) = be_u8(packet)?;
     let (packet, transaction_id) = be_u32(packet)?;
     let (packet, seconds) = be_u16(packet)?;
-    let (packet, flags) = be_u16(packet)?;
+    let (packet, flags) = parse_dhcp_flags(packet)?;
     let (packet, client_address) = parse_ipv4_address(packet)?;
     let (packet, server_address) = parse_ipv4_address(packet)?;
     let (packet, gateway_address) = parse_ipv4_address(packet)?;
-    let (packet, client_hardware_address) = take(6usize)(packet)?;
+    let (packet, client_hardware_address) =
+        parse_client_hardware_address(packet, hardware_address_length)?;
+    let potential_options = packet;
+    
+    let (packet, server_name) = parse_server_name(packet)?;
+    let (packet, file_name) = parse_file(packet)?;
 
     Ok((
         packet,
@@ -98,8 +133,8 @@ fn parse_dhcp_packet(packet: &[u8]) -> IResult<&[u8], DhcpMessage> {
             server_address,
             gateway_address,
             client_hardware_address,
-            server_hostname: "",
-            boot_file_name: Path::new(""),
+            server_name,
+            file_name,
         },
     ))
 }
@@ -110,6 +145,21 @@ mod tests {
     static DHCP_PACKET2: &'static [u8] = &[
         0x01, 0x01, 0x06, 0x05, 0x00, 0x00, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x7f, 0x00, 0x00,
         0x01, 0x7f, 0x00, 0x00, 0x01, 0x7f, 0x00, 0x00, 0x01, 0x54, 0x05, 0xdb, 0xa6, 0x96, 0xd0,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //CHADDR padding
+        0x49, 0x20, 0x62, 0x69, 0x6D, 0x73, 0x20, 0x31, 0x20, 0x44, 0x48, 0x43, 0x50, 0x20, 0x53,
+        0x65, 0x72, 0x76, 0x65, 0x72, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, // server name with padding
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // file with padding
     ];
 
     #[test]