Dhole / rust-netcat

netcat clone implemented in Rust

Netcat in rust

This is a netcat implementation in rust, aiming for similar performance as original openbsd-netcat.

I originally started using mio, which in linux uses the epoll system call, but it had two problems:

1. Every loop requires several systemcalls beucase every file descriptor needs to be reregistered for every change in the polling events.
2. Regular files and others (like /dev/null) cannot be registered with epoll.

Problem 1. can be solved by using 4 epoll devices, one with each combination of file descriptor and polling event that is required. I didn't find any solution to problem 2.

So I moved to using the poll system call, using a wrap over the libc function (note that openbsd-netcat also uses poll).

Current status

Performance is similar to openbsd-netcat.

Here's the list of implemented options:

• -4 Use IPv4
• -6 Use IPv6
• -b Allow broadcast
• -C Send CRLF as line-ending
• -D Enable the debug socket option
• -d Detach from stdin
• -F Pass socket fd
• -h This help text
• -I length TCP receive buffer length
• -i interval Delay interval for lines sent, ports scanned
• -k Keep inbound sockets open for multiple connects
• -l Listen mode, for inbound connects
• -M ttl Outgoing TTL / Hop Limit
• -m minttl Minimum incoming TTL / Hop Limit
• -N Shutdown the network socket after EOF on stdin
• -n Suppress name/port resolutions
• -O length TCP send buffer length
• -P proxyuser Username for proxy authentication
• -p port Specify local port for remote connects
• -q secs quit after EOF on stdin and delay of secs
• -r Randomize remote ports
• -S Enable the TCP MD5 signature option
• -s source Local source address
• -T keyword TOS value
• -t Answer TELNET negotiation
• -U Use UNIX domain socket
• -u UDP mode
• -V rtable Specify alternate routing table
• -v Verbose
• -W recvlimit Terminate after receiving a number of packets
• -w timeout Timeout for connects and final net reads
• -X proto Proxy protocol: "4", "5" (SOCKS) or "connect"
• -x addr[:port] Specify proxy address and port
• -Z DCCP mode
• -z Zero-I/O mode [used for scanning]

Acknowledgements

• Nan Xiao for writing the gitbook OpenBSD netcat demystified which brought my attention to the design of netcat, and gave me the idea to reimplement it in rust.
• Israël Hallé and Daan Sprenkels for their libc's poll wrapper in rust, from which I've taken code for my own poll wrapper:
  • https://github.com/isra17/rust-poll
  • https://github.com/dsprenkels/rust-poll)
• Original nc implementer (Hobbit [e-mail]) and OpenBSD developers (Eric Jackson [e-mail] and Bob Beck) for the netcat code which I've used as a base (some parts are quite literal translations from C to Rust) for this project.