nfqueue-rs is a wrapper library for libnetfilter-queue. The goal is to provide a library to gain access to packets queued by the kernel packet filter.

It is important to note that these bindings will not follow blindly libnetfilter_queue API. For ex., some higher-level wrappers will be provided for the open/bind/create mechanism (using one function call instead of three).

The API is not yet stable.

To use the library, a program must

• open a queue
• bind to a network family (AF_PACKET for IPv4)
• provide a callback function, which will be automatically called when a packet is received. The callback must return a verdict
• create the queue, providing the queue number (which must match the --queue-num from the iptables rules, see below
• run a loop, waiting for events. The program should also provide a clean way to exit the loop (for ex on SIGINT)

See nfq-example for a minimal example.

You must add rules in netfilter to send packets to the userspace queue. The number of the queue (--queue-num option in netfilter) must match the number provided to create_queue().

Example of iptables rules:

iptables -A OUTPUT --destination 1.2.3.4 -j NFQUEUE --queue-num 0

Of course, you should be more restrictive, depending on your needs.

nfqueue-rs does not require root privileges, but needs to open a netlink socket and send/receive packets to the kernel.

You have several options:

• Use the CAP_NET_ADMIN capability in order to allow your application to receive from and to send packets to kernel-space: setcap 'cap_net_admin=+ep' /path/to/program
• Run your program as root and drop privileges