High-performance TCP proxy implemented in C.

cproxy -l <local addr>:<local port> [-l <local addr>:<local port>...] 
       -r <remote addr>:<remote port> [-b <buf size>] [-n] [-t <num io threads>]
Arguments:
  -l <local addr>:<local port>: specify listen address and port
  -r <remote addr>:<remote port>: specify remote address and port
  -b <buf size>: specify session buffer size in bytes
  -n: enable TCP no delay
  -t: <num io threads>: specify number of I/O threads

• 1 acceptor thread to accept incoming client connections.
• Pool of 1 to N I/O threads to handle read, write, and connect operations. Pool size is configurable with -t option. Client sessions assigned to I/O threads using round robin.
• 2 buffers per client session, one for each direction of traffic. Buffer size is configurable with -b option. Buffers are allocated from per-thread buffer pools in each I/O thread.
• All sockets are non-blocking. All read, write, connect, and accept operations are asynchronous.
• Automatically chooses between epoll, kqueue, and poll as the poll system call. epoll or kqueue are recommended because they allow storing pointers to connection state information in events passed to and from the kernel, eliminating lookup of state information every time through the event loop. If poll is used, connection state information is stored in a red-black tree from libavl 2.0.3.
• kqueue is currently only supported on FreeBSD because that's the only platform I have access to test. It should also work on OS X and other BSDs.