# gen_tcp

### MODULE

gen_tcp

### MODULE SUMMARY

Interface to TCP/IP sockets

### DESCRIPTION

The `gen_tcp` module provides functions for communicating with sockets using the TCP/IP protocol.

The available options are described in the setopts/2 function in the `inet` manual page.

The possible `{error, Reason}` results are described in the inet manual page.

The following code fragment provides a simple example of a client connecting to a server at port 5678, transferring a binary and closing the connection.

    client() ->
        SomeHostInNet = "localhost" % to make it runnable on one machine
        {ok, Sock} = gen_tcp:connect(SomeHostInNet, 5678,
                                     [binary, {packet, 0}]),
        ok = gen_tcp:send(Sock, "Some Data"),
        ok = gen_tcp:close(Sock).

At the other end a server is listening on port 5678, accepts the connection and receives the binary.

    server() ->
        {ok, LSock} = gen_tcp:listen(5678, [binary, {packet, 0},
                                            {active, false}]),
        {ok, Sock} = gen_tcp:accept(LSock),
        {ok, Bin} = do_recv(Sock, []),
        ok = gen_tcp:close(Sock),
        Bin.

    do_recv(Sock, Bs) ->
        case gen_tcp:recv(Sock, 0) of
            {ok, B} ->
                do_recv(Sock, [Bs, B]);
            {error, closed} ->
                {ok, list_to_binary(Bs)}
        end.

### EXPORTS

`accept(ListenSocket) -> {ok, Socket} | {error, Reason}`
`accept(ListenSocket, Timeout) -> {ok, Socket} | {error, Reason}`

Types:

`ListenSocket = socket()`
`Socket = socket()`
`Timeout = integer()`
`Reason = atom()`

Accepts an incoming connection request on a listen socket. `Socket` must be a socket returned from `listen/1`. If no `Timeout` argument is specified, or it is `infinity`, the `accept` function will not return until a connection has been established or the `ListenSocket` has been closed. If accept returns because the `ListenSocket` has been closed `{error, closed}` is returned. If `Timeout` is specified and no connection is accepted within the given time, `accept` will return `{error, timeout}`.

Packets can be sent to the returned socket using the `send/2` function. Packets sent from the peer will be delivered as messages

            {tcp, Socket, Data}

unless `{active, false}` was specified in the option list for the listen socket, in which case packets should be retrieved by calling `recv/2`.

`close(Socket) -> ok | {error, Reason}`

Types:

`Socket = socket()`
`Reason = atom()`

Closes an TCP socket.

`connect(Address, Port, Options) -> {ok, Socket} | {error, Reason}`
`connect(Address, Port, Options, Timeout) -> {ok, Socket} | {error, Reason}`

Types:

`Address = string() | atom() | ip_address()`
`Port = Timeout = integer()`
`Options = list()`
`Socket = socket()`
`Reason = atom()`

Connects to a server on TCP port `Port` on the host with IP address `Address`. The `Address` argument can be either a hostname, or an IP address.

The available options are:

`list`
  Received `Packet` is delivered as a list.
`binary`
  Received `Packet` is delivered as a binary.
common `inet` options
  The common `inet` options available are described in the setopts/2 function in the `inet` manual page.

Packets can be sent to the returned socket using the `send/2` function. Packets sent from the peer will be delivered as messages

            {tcp, Socket, Data}

If the socket was closed the following message is delivered:

            {tcp_closed, Socket}

If an error occurred on the socket the following message is delivered:

            {tcp_error, Socket, Reason}

unless the socket is in passive mode, in which case packets are retrieved by calling `recv/2`.

The optional `Timeout` parameter specifies a timeout in milliseconds. The default value is `infinity`.

`controlling_process(Socket, NewOwner) -> ok | {error, eperm}`

Types:

`Socket = socket()`
`NewOwner = pid()`

Assigns a new controlling process to `Socket`. The controlling process is the process which will receive messages from the socket. If called by any other process than the current owner `{error, eperm}` will be returned.

`listen(Port, Options) -> {ok, Socket} | {error, Reason}`

Types:

`Port = integer()`
`Options = list()`
`Socket = socket()`
`Reason = atom()`

Sets up socket to listen on the port `Port` on the local host.

If the port number is zero, the `listen` function picks an available port number (use `inet:port/1` to retrieve it); otherwise, the specified port number is used.

The available options are described in the setopts/2 function in the `inet` manual page. Additionally, the option `{backlog, B}` can be given, where B is an integer >= 0. The backlog value defaults to 5. The backlog value defines the maximum length the queue of pending connections may grow to.

The returned socket can only be used in calls to `accept`.

`recv(Socket, Length) -> {ok, Packet} | {error, Reason}`
`recv(Socket, Length, Timeout)`

Types:

`Socket = socket()`
`Length = integer()`
`Packet = list() | binary()`
`Timeout = integer()`
`Reason = atom()`

This function receives a packet from a socket in passive mode. A closed socket is indicated by a return value of `{error, closed}`.

The `Length` argument is only meaningful when the socket is in `raw` mode and denotes number of bytes to read. If `Length` = 0 all available bytes are returned.

The optional `Timeout` parameter specifies a timeout in milliseconds. The default value is `infinity`.

`send(Socket, Packet) -> ok | {error, Reason}`

Types:

`Socket = socket()`
`Packet = list() | binary()`
`Reason = atom()`

Sends a packet on a socket.

### AUTHORS

tony@erix.ericsson.se - support@erlang.ericsson.se

kernel 2.7.2
Copyright © 1991-2002 Ericsson Utvecklings AB