What SOCKS expects

The SOCKS library covers only some of the socket functions, which must be called in a particular order:

1. The first socket function invoked must be either connect() or rcmd().
2. If you call connect() on a nonblocking socket, no I/O can occur on that socket until another connect(), with the same arguments, returns -1 and sets errno to EISCONN. This is required even if you use select() on write to check the readiness of that socket.
   Note: While a connection is still pending, don't try to start another connection via connect(), or start a sequence of bind(), getsockname(), listen(), and accept().
3. You must call bind() after a successful connect() call to a host for a specific service.
4. You must follow the call to bind() by calls to getsockname(), listen(), and accept(), in that order.

Most client programs fit these assumptions very well and can be SOCKSified without changing the code at all using the steps described in “How to SOCKSify a client.”

Some client programs use a bind() before each connect(). If the bind() is used to claim a specific port or a specific network interface, the current SOCKS library can't accommodate such use. Very often though, such a bind() call is there for no specific reason and may simply be deleted.