gen_tcp(3)

MODULE
gen_tcp - 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.

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