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use crate::protocol::ip::{self, IPProtocol};
use nom::bits;
use nom::error::Error;
use nom::number;
use nom::sequence;
use nom::IResult;
use std::net::Ipv4Addr;
/******************************************************************************
* Struct
******************************************************************************/
/*
* Internet Header Format
*
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* |Version| IHL |Type of Service| Total Length |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | Identification |Flags| Fragment Offset |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | Time to Live | Protocol | Header Checksum |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | Source Address |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | Destination Address |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | Options | Padding |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct IPv4Header {
pub version: u8, // 4 bit
pub ihl: u8, // 4 bit
pub tos: u8,
pub length: u16,
pub id: u16,
pub flags: u8, // 3 bit
pub frag_offset: u16, // 13 bit
pub ttl: u8,
pub protocol: IPProtocol,
pub checksum: u16,
pub src_addr: Ipv4Addr,
pub dst_addr: Ipv4Addr,
}
/******************************************************************************
* Parse
******************************************************************************/
fn parse_flag_and_frag_offset(input: &[u8]) -> IResult<&[u8], (u8, u16)> {
bits::bits::<_, _, Error<_>, _, _>(sequence::pair(
bits::streaming::take(3u8),
bits::streaming::take(13u16),
))(input)
}
fn parse_version_and_header_length(input: &[u8]) -> IResult<&[u8], (u8, u8)> {
bits::bits::<_, _, Error<_>, _, _>(sequence::pair(
bits::streaming::take(4u8),
bits::streaming::take(4u8),
))(input)
}
fn parse_ipv4_address(input: &[u8]) -> IResult<&[u8], Ipv4Addr> {
let (input, ipv4) = nom::bytes::streaming::take(4u8)(input)?;
Ok((input, Ipv4Addr::from(<[u8; 4]>::try_from(ipv4).unwrap())))
}
pub fn parse_ipv4(input: &[u8]) -> IResult<&[u8], IPv4Header> {
let (input, verihl) = parse_version_and_header_length(input)?;
let (input, tos) = number::streaming::be_u8(input)?;
let (input, length) = number::streaming::be_u16(input)?;
let (input, id) = number::streaming::be_u16(input)?;
let (input, flag_frag_offset) = parse_flag_and_frag_offset(input)?;
let (input, ttl) = number::streaming::be_u8(input)?;
let (input, protocol) = ip::protocol(input)?;
let (input, checksum) = number::streaming::be_u16(input)?;
let (input, src_addr) = parse_ipv4_address(input)?;
let (input, dst_addr) = parse_ipv4_address(input)?;
Ok((
input,
IPv4Header {
version: verihl.0,
ihl: verihl.1,
tos,
length,
id,
flags: flag_frag_offset.0,
frag_offset: flag_frag_offset.1,
ttl,
protocol,
checksum,
src_addr,
dst_addr,
},
))
}
/******************************************************************************
* TEST
******************************************************************************/
#[cfg(test)]
mod tests {
use super::parse_ipv4;
use super::IPv4Header;
use crate::ip::IPProtocol;
use std::net::Ipv4Addr;
const LAST_SLICE: &'static [u8] = &[0xff];
#[test]
fn parse_ipv4_works() {
/*
* Internet Protocol Version 4, Src: 192.168.0.100, Dst: 14.215.177.38
* 0100 .... = Version: 4
* .... 0101 = Header Length: 20 bytes (5)
* Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
* Total Length: 64
* Identification: 0x0000 (0)
* Flags: 0x40, Don't fragment
* 0... .... = Reserved bit: Not set
* .1.. .... = Don't fragment: Set
* ..0. .... = More fragments: Not set
* ...0 0000 0000 0000 = Fragment Offset: 0
* Time to Live: 64
* Protocol: TCP (6)
* Header Checksum: 0xb9ae [correct]
* [Header checksum status: Good]
* [Calculated Checksum: 0xb9ae]
* Source Address: 192.168.0.100
* Destination Address: 14.215.177.38
*/
let bytes = [
0x45, /* Version and Header length */
0x00, /* Differentiated Services Field */
0x01, 0xda, /* Total Length */
0x00, 0x00, /* Identification */
0x40, 0x00, /* Flags and Fragment Offset */
0x40, /* Time to Live */
0x06, /* Protocol */
0xb8, 0x14, /* Header Checksum */
0xc0, 0xa8, 0x00, 0x64, /* Source Address */
0x0e, 0xd7, 0xb1, 0x26, /* Destination Address */
0xff, /* Payload */
];
let expectation = IPv4Header {
version: 4,
ihl: 5,
tos: 0,
length: 474,
id: 0x0000,
flags: 0x2,
frag_offset: 0,
ttl: 64,
protocol: IPProtocol::TCP,
checksum: 0xb814,
src_addr: Ipv4Addr::new(192, 168, 0, 100),
dst_addr: Ipv4Addr::new(14, 215, 177, 38),
};
assert_eq!(parse_ipv4(&bytes), Ok((LAST_SLICE, expectation)));
}
}
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