Module Tcp = Async_extra.Tcp

with_connection ~host ~port f looks up host from a string (using DNS as needed), connects, then calls f, passing the connected socket and a reader and writer for it. When the deferred returned by f is determined, or any exception is thrown, the socket, reader and writer are closed. The return deferred is fulfilled after f has finished processing and the file descriptor for the socket is closed. If interrupt is supplied then the connection attempt will be aborted if interrupt is fulfilled before the connection has been established. Similarly, all connection attempts have a timeout (default 30s), that can be overridden with timeout.

It is fine for f to ignore the supplied socket and just use the reader and writer. The socket is there to make it convenient to call Socket functions.

connect_sock ~host ~port opens a TCP connection to the specified hostname and port, returning the socket.

Any errors in the connection will be reported to the monitor that was current when connect was called.

connect ~host ~port is a convenience wrapper around connect_sock that returns the socket, and a reader and writer for the socket. The reader and writer share a file descriptor, and so closing one will affect the other by closing its underlying fd. In particular, closing the reader before closing the writer will cause the writer to subsequently raise an exception when it attempts to flush internally-buffered bytes to the OS, due to a closed fd. You should close the Writer first to avoid this problem.

If possible, use with_connection, which automatically handles closing.

It is fine to ignore the returned socket and just use the reader and writer. The socket is there to make it convenient to call Socket functions.