path: root/erts/doc/src/socket.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2018</year><year>2018</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>socket</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>socket.xml</file>
  </header>
  <module>socket</module>
  <modulesummary>Socket interface.</modulesummary>
  <description>
    <p>This module provides an API for the socket interface.
      It is used to create, delete and manipulate sockets.</p>
  </description>

  <datatypes>
    <datatype>
      <name name="domain"/>
    </datatype>
    <datatype>
      <name name="type"/>
    </datatype>
    <datatype>
      <name name="protocol"/>
    </datatype>
    <datatype>
      <name>socket()</name>
      <desc><p>As returned by
        <seealso marker="#open/1"><c>open/2,3,4</c></seealso> and
        <seealso marker="#accept/1"><c>accept/1,2</c></seealso>.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="ip4_address"/>
    </datatype>
    <datatype>
      <name name="ip6_address"/>
    </datatype>
    <datatype>
      <name name="ip_address"/>
    </datatype>
    <datatype>
      <name name="sockaddr"/>
    </datatype>
    <datatype>
      <name name="sockaddr_in4"/>
    </datatype>
    <datatype>
      <name name="sockaddr_in6"/>
    </datatype>
    <datatype>
      <name name="sockaddr_un"/>
    </datatype>
    <datatype>
      <name name="port_number"/>
    </datatype>
    <datatype>
      <name name="accept_flags"/>
    </datatype>
    <datatype>
      <name name="accept_flag"/>
    </datatype>
    <datatype>
      <name name="send_flags"/>
    </datatype>
    <datatype>
      <name name="send_flag"/>
    </datatype>
    <datatype>
      <name name="shutdown_how"/>
    </datatype>
    <datatype>
      <name name="sockopt_level"/>
    </datatype>
    <datatype>
      <name name="otp_socket_option"/>
    </datatype>
    <datatype>
      <name name="socket_option"/>
    </datatype>
    <datatype>
      <name name="ip_socket_option"/>
    </datatype>
    <datatype>
      <name name="ipv6_socket_option"/>
    </datatype>
    <datatype>
      <name name="tcp_socket_option"/>
    </datatype>
    <datatype>
      <name name="udp_socket_option"/>
    </datatype>
    <datatype>
      <name name="sctp_socket_option"/>
    </datatype>
    <datatype>
      <name name="ip_tos_flag"/>
    </datatype>
    <datatype>
      <name name="ip_mreq"/>
    </datatype>
    <datatype>
      <name name="ip_mreq_source"/>
    </datatype>
    <datatype>
      <name name="ip_pmtudisc"/>
    </datatype>
    <datatype>
      <name name="ipv6_mreq"/>
    </datatype>
    <datatype>
      <name name="ipv6_pmtudisc"/>
    </datatype>
    <datatype>
      <name name="sctp_event_subscribe"/>
    </datatype>
    <datatype>
      <name name="sctp_assocparams"/>
    </datatype>
    <datatype>
      <name name="sctp_rtoinfo"/>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="accept" arity="1"/>
      <name name="accept" arity="2"/>
      <fsummary>Accept a connection on a socket.</fsummary>
      <desc>
        <p>Accept a connection on a socket.</p>
        <p>This call is used with connection-based socket types
	(<c>stream</c> or <c>seqpacket</c>). It extracs the first pending
	connection request for the listen socket and returns the (newly)
	connected socket.</p>
      </desc>
    </func>

    <func>
      <name name="bind" arity="2"/>
      <fsummary>Bind a name to a socket.</fsummary>
      <desc>
        <p>Bind a name to a socket.</p>
        <p>When a socket is created
	(with <seealso marker="#open/2"><c>open</c></seealso>),
	it has no address assigned to it. <c>bind</c> assigns the
	address specified by the <c>Addr</c> argument.</p>
	<p>The rules used for name binding vary between domains.</p>
      </desc>
    </func>

    <func>
      <name name="close" arity="1"/>
      <fsummary>Close a socket.</fsummary>
      <desc>
	<p>Closes the socket.</p>

	<note>
	  <p>Note that for e.g. <c>protocol</c> = <c>tcp</c>, most implementations
	  doing a close does not guarantee that any data sent is delivered to
	  the recipient before the close is detected at the remote side. </p>
	  <p>One way to handle this is to use the
	  <seealso marker="#shutdown/2"><c>shutdown</c></seealso> function
	  (<c>socket:shutdown(Socket, write)</c>) to signal that no more data is
	  to be sent and then wait for the read side of the socket to be closed.</p>
	</note>
      </desc>
    </func>

    <func>
      <name name="connect" arity="2"/>
      <name name="connect" arity="3"/>
      <fsummary>Initiate a connection on a socket.</fsummary>
      <desc>
        <p>This function connects the socket to the address
	specied by the <c>SockAddr</c> argument.</p>
      </desc>
    </func>

    <func>
      <name name="getopt" arity="3" clause_i="1"/>
      <name name="getopt" arity="3" clause_i="2"/>
      <name name="getopt" arity="3" clause_i="3"/>
      <name name="getopt" arity="3" clause_i="4"/>
      <name name="getopt" arity="3" clause_i="5"/>
      <name name="getopt" arity="3" clause_i="6"/>
      <name name="getopt" arity="3" clause_i="7"/>
      <fsummary>Get an option on a socket.</fsummary>
      <desc>
        <p>Get an option on a socket.</p>
	<p>What properties are valid depend  both on <c>Level</c> and
	on what kind of socket it is (<c>domain</c>, <c>type</c> and
	<c>protocol</c>).</p>

	<note><p>Not all options are valid on all platforms. That is,
	even if "we" support an option, that does not mean that the
	underlying OS does.</p></note>

	<!--
	    We need these tables (one for each level) somewhere,
	    but they don't work here, so where?

        <p>Socket level options: </p>
	<table>
	  <row>
	    <cell><em>Option Name</em></cell>
	    <cell><em>Value Type</em></cell>
	    <cell><em>Set</em></cell>
	    <cell><em>Get</em></cell>
	    <cell><em>Other</em></cell>
	  </row>
	  <row>
	    <cell>acceptcon</cell>
	    <cell>boolean()</cell>
	    <cell>no</cell>
	    <cell>yes</cell>
	    <cell>none</cell>
	  </row>
	  <row>
	    <cell>broadcast</cell>
	    <cell>boolean()</cell>
	    <cell>yes</cell>
	    <cell>yes</cell>
	    <cell>dgram</cell>
	  </row>
	  <row>
	    <cell>debug</cell>
	    <cell>integer()</cell>
	    <cell>yes</cell>
	    <cell>yes</cell>
	    <cell>may require admin capability</cell>
	  </row>
	  <row>
	    <cell>domain</cell>
	    <cell>domain()</cell>
	    <cell>no</cell>
	    <cell>yes</cell>
	    <cell>none</cell>
	  </row>
	</table>
	-->
      </desc>
    </func>

    <func>
      <name name="getopt" arity="3" clause_i="8"/>
      <fsummary>Get an option on a socket.</fsummary>
      <desc>
        <p>Get an option on a socket.</p>
	<p>What properties are valid depend  both on <c>Level</c> and
	on what kind of socket it is (<c>domain</c>, <c>type</c> and
	<c>protocol</c>).</p>
	<p>When specifying <c>Level</c> as an integer, and therefor
	using "native mode", it is *currently* up to the caller to
	know how to interpret the result.</p>

	<note><p>Not all options are valid on all platforms. That is,
	even if "we" support an option, that does not mean that the
	underlying OS does.</p></note>
      </desc>
    </func>

    <func>
      <name name="listen" arity="1"/>
      <name name="listen" arity="2"/>
      <fsummary>Listen for connections on a socket.</fsummary>
      <desc>
        <p>Listen for connections on a socket.</p>
      </desc>
    </func>

    <func>
      <name name="open" arity="2"/>
      <name name="open" arity="3"/>
      <name name="open" arity="4"/>
      <fsummary>Create an endpoint for communication.</fsummary>
      <desc>
        <p>Creates an endpoint (socket) for communication.</p>
        <p>For some <c>types</c> there is a default protocol, which will
	be used if no protocol is specified: </p>

	<list>
	  <item><p><c>stream</c>: <c>tcp</c></p></item>
          <item><p><c>dgram</c>: <c>udp</c></p></item>
          <item><p><c>seqpacket</c>: <c>sctp</c></p></item>
	</list>

	<p>The <c>Extra</c> argument is intended for "obscure" options.
	Currently the only supported option is <c>netns</c>, which
	is only supported on the linux platform.</p>
      </desc>
    </func>

    <func>
      <name name="peername" arity="1"/>
      <fsummary>Get name of connected socket peer.</fsummary>
      <desc>
        <p>Returns the address of the peer connected to the socket.</p>
      </desc>
    </func>

    <func>
      <name name="recv" arity="1"/>
      <name name="recv" arity="2"/>
      <name name="recv" arity="3" clause_i="1"/>
      <name name="recv" arity="3" clause_i="2"/>
      <name name="recv" arity="4"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>
	<p>There is a special case for the argument <c>Length</c>.
	If it is set to zero (0), it means "give me everything you 
	currently have".</p>
      </desc>
    </func>

    <func>
      <name name="recvfrom" arity="1"/>
      <name name="recvfrom" arity="2"/>
      <name name="recvfrom" arity="3" clause_i="1"/>
      <name name="recvfrom" arity="3" clause_i="2"/>
      <name name="recvfrom" arity="3" clause_i="3"/>
      <name name="recvfrom" arity="4"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>
        <p>This function reads "messages", which means that regardless of
	how much we want to read, it returns when we get a message.</p>
        <p>The <c>BufSz</c> argument basically defines the size of the
	receive buffer. By setting the value to zero (0), the configured
	size (setopt with <c>Level</c> = <c>otp</c>) is used.</p>
        <p>It may be impossible to know what (buffer) size is appropriate
	"in advance", and in those cases it may be convenient to use the
	(recv) 'peek' flag. When this flag is provided, the message is *not*
	"consumed" from the underlying buffers, so another recvfrom call
	is needed, possibly with a then adjusted buffer size.</p>
      </desc>
    </func>

    <func>
      <name name="send" arity="2"/>
      <name name="send" arity="3" clause_i="1"/>
      <name name="send" arity="3" clause_i="2"/>
      <name name="send" arity="4"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
        <p>Send a message on a connected socket.</p>
      </desc>
    </func>

    <func>
      <name name="sendto" arity="3"/>
      <name name="sendto" arity="4"/>
      <name name="sendto" arity="5"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
        <p>Send a message on a socket, to the specified destination.</p>
      </desc>
    </func>

    <func>
      <name name="setopt" arity="4" clause_i="1"/>
      <name name="setopt" arity="4" clause_i="2"/>
      <name name="setopt" arity="4" clause_i="3"/>
      <name name="setopt" arity="4" clause_i="4"/>
      <name name="setopt" arity="4" clause_i="5"/>
      <name name="setopt" arity="4" clause_i="6"/>
      <name name="setopt" arity="4" clause_i="7"/>
      <fsummary>Set options on a socket.</fsummary>
      <desc>
        <p>Set options on a socket.</p>
	<p>What properties are valid depend both on <c>Level</c> and on
	what kind of socket it is (<c>domain</c>, <c>type</c> and
	<c>protocol</c>).</p>

	<note><p>Not all options are valid on all platforms. That is,
	even if "we" support an option, that does not mean that the
	underlying OS does.</p></note>

	<note><p>Sockets are set 'non-blocking' when created, so this option
	is *not* available (as it would adversely effect the Erlang VM
	to set a socket 'blocking').</p></note>
      </desc>
    </func>

    <func>
      <name name="shutdown" arity="2"/>
      <fsummary>Shut down part of a full-duplex connection.</fsummary>
      <desc>
        <p>Shut down all or part of a full-duplex connection.</p>
      </desc>
    </func>

    <func>
      <name name="sockname" arity="1"/>
      <fsummary>Get socket name.</fsummary>
      <desc>
        <p>Returns the current address to which the socket is bound.</p>
      </desc>
    </func>

  </funcs>
  <section>
    <title>Examples</title>
    <marker id="examples"></marker>
    <p>TBD: Need to implement a receiver process in order to be able to
    implement active!</p>
    <p>x_tcp.erl:</p>
    <code type="none">
listen(Addr, Port) ->
  try
    begin
      Socket = case socket:open(inet, stream, tcp) of
          {ok, Socket} ->
             Socket;
          {error, _} = OERROR ->
             throw(OERROR)
      end,
      SockAddr = #in4_sockaddr{port = Port,
	                       addr = Addr},
      ok = case socket:bind(Socket, SockAddr) of
               ok ->
	         ok;
	       {error, _} = BERROR ->
	         throw(BERROR)
	   end,
      case socket:listen(Socket, 10) of
	  ok ->
	    {ok, Socket};
	  {error, _} = LERROR ->
	    throw(LERROR)
      end
    end
  catch
    throw:ERROR ->
       ERROR
end.
    </code>

    <code type="none">
connect(Addr, Port) ->
  try
    begin
      Socket = case socket:open(inet, stream, tcp) of
          {ok, Socket} ->
             Socket;
          {error, _} = OERROR ->
             throw(OERROR)
      end,
      BSockAddr = #in4_sockaddr{port = 0,
	                        addr = any},
      ok = case socket:bind(Socket, BSockAddr) of
               ok ->
	         ok;
	       {error, _} = BERROR ->
	         throw(BERROR)
	   end,
      CSockAddr = #in4_sockaddr{port = Port,
	                        addr = Addr},
      Socket = case socket:connect(Socket, CSockAddr) of
	  {ok, Sock} ->
	    Sock;
	  {error, _} = CERROR ->
	    throw(CERROR)
      end,
      case start_receiver(Socket) of
          {ok, Pid} ->
            ok = socket:ts_add(Socket, receiver, Pid),
            {ok, Socket};
          {error, _} = RERROR ->
            socket:close(Socket),
	    throw(RERROR)
      end
    end
  catch
    throw:ERROR ->
       ERROR
end.
    </code>

    <code type="none">
accept(LSocket) ->
  case socket:accept(LSocket) of
      {ok, Socket} ->
        case start_receiver(Socket) of
	    {ok, Pid} ->
	      ok = socket:ts_add(Socket, receiver, Pid),
              {ok, Socket};
            {error, _} = RERROR ->
	      socket:close(Socket),
              throw(RERROR)
	end,
      {error, _} = AERROR ->
	AERROR
  end.
    </code>

    <code type="none">
send(Socket, Data) ->
  socket:send(Socket, Data).
    </code>

    <code type="none">
setopt(Socket, controlling_process = Item, Pid) when is_pid(Pid) ->
  case socket:setopt(Socket, otp, Item, Pid) of
      ok ->
        {ok, Receiver} = socket:ts_get(Socket, receiver),
        update_receiver(Receiver, {controlling_process, Pid),
	ok;
      {error, _} = ERROR ->
        ERROR
  end;
setopt(Socket, active, Active) ->
  {ok, Receiver} = socket:ts_get(Socket, receiver),
  receiver_active(Receiver, Active),
  ok;
%% This is just to indicate that there will be more options
%% that needs to be handled
setopt(Socket, Item, Pid) when is_pid(Pid) ->
  socket:setopt(Socket, which_level(Item), Item, Pid). 
    </code>

    <p>The receiver process: </p>
    <code type="none">
start_receiver(Socket) ->
  CtrlProc = self(),
  Ref = make_ref(),
  Receiver = proc_lib:spawn_link(fun() -> receiver_init(CtrlProc, Ref) end),
  receive
      {?MODULE, started, Ref} ->
          Receiver ! {?MODULE, receiver, Ref, Sock, true},
          unlink(Receiver),
	  {ok, Receiver};
      {'EXIT', Receiver, Reason} ->
	  {error, Reason}
  end.

receiver_active(Receiver, Active)
  when (Active =:= false) orelse
       (Active =:= true) orelse
       (Active =:= once) orelse
       is_integer(Active) ->
  Receiver ! {?MODULE, active, What}.

receiver_update(Receiver, What) ->
  Ref = make_ref(),
  Receiver ! {?MODULE, receiver_update, Ref, What},
  receive
      {?MODULE, receiver_upadate, Ref, Result} ->
          Result
  end.

-record(receiver, {sock            :: socket:socket(),
		   ctrl            :: pid(),
		   num_packages    :: infinity | non_neg_ineteger()}).

receiver_init(Pid, Ref) ->
    receive
	{?MODULE, receiver, Ref, stop} ->
	    i("received stop"),
	    exit(normal);

	{?MODULE, receiver, Ref, Sock, InitialMode} ->
	    i("received socket: ~p", [Sock]),
	    NumPackages = mode2pkgcount(InitialMode),
	    receiver(#receiver{sock = Sock, ctrl = Pid})
    end.

mode2pkgcount(true) ->
    infinity;
mode2pkgcount(false) ->
    0;
mode2pkgcount(N) when is_integer(N) andalso (N >= 0) ->
    N.

receiver(#receiver{num_packages = 0} = State) ->
    receive
	{?MODULE, active, false} ->
	    receiver(State);
	{?MODULE, active, true} ->
	    receiver(State#receiver{num_packages = infinity});
	{?MODULE, active, once} ->
	    receiver(State#receiver{num_packages = 1});
	{?MODULE, active, N} when (N > 0) ->
	    receiver(State#receiver{num_packages = N})
    end;
receiver(#receiver{num_packages = N, sock = Sock, ctrl = Pid} = State) ->
    case socket:recv(Sock, 0) of
	{ok, Package} when size(Package) > 0 ->
	    Pid ! {tcp, Sock, Packege},
	    case next_active(N) of
		0 ->
		    Pid ! {tcp_passive, Sock},
		    receiver(State#{num_packages = 0});
		NextN ->
		    receiver(State#{num_packages = NextN})
	    end;
	{ok, Package} when size(Package) =:= 0 ->
	    receiver(State);

        {error, closed} ->
	    i("closed"), 
            Pid ! {tcp_closed, Sock},
	    exit(normal);

        {error, Reason} ->
	    i("error: ~p", [Reason]), 
            Pid ! {tcp_error, Sock, Reason},
	    exit(normal)
    end.
    </code>
    
  </section>
</erlref>