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Linux 2.6 - man page for erl_connect (linux section 3erl)

erl_connect(3erl)		       C Library Functions			erl_connect(3erl)

NAME
       erl_connect - Communicate with Distributed Erlang

DESCRIPTION
       This  module  provides  support	for  communication between distributed Erlang nodes and C
       nodes, in a manner that is transparent to Erlang processes.

       A C node appears to Erlang as a hidden node . That is, Erlang processes that know the name
       of  the	C node are able to communicate with it in a normal manner, but the node name will
       not appear in the listing provided by the Erlang function nodes/0 .

EXPORTS
       int erl_connect_init(number, cookie, creation)
       int erl_connect_xinit(host, alive, node, addr, cookie, creation)

	      Types  int number;
		     char *cookie;
		     short creation;
		     char *host,*alive,*node;
		     struct in_addr *addr;

	      These functions initialize the erl_connect module. In particular, they are used  to
	      identify	the name of the C-node from which they are called. One of these functions
	      must be called before any of the other functions	in  the  erl_connect  module  are
	      used.

	      erl_connect_xinit()  stores  for	later  use information about the node's host name
	      host , alive name alive , node name node , IP address addr , cookie  cookie  ,  and
	      creation	number	creation  .  erl_connect_init() provides an alternative interface
	      which does not require as much  information  from  the  caller.  Instead,  erl_con-
	      nect_init() uses gethostbyname() to obtain default values.

	      If  you  use erl_connect_init() your node will have a short name, i.e., it will not
	      be fully qualified. If you need to use fully qualified  (a.k.a.  long)  names,  use
	      erl_connect_xinit() instead.

	      host is the name of the host on which the node is running.

	      alive is the alivename of the node.

	      node is the name of the node. The nodename should be of the form alivename@hostname
	      .

	      addr is the 32-bit IP address of host .

	      cookie is the authorization string required for access to the remote node. If  NULL
	      the  user HOME directory is searched for a cookie file .erlang.cookie . The path to
	      the home directory is retrieved from the environment variable HOME on Unix and from
	      the  HOMEDRIVE and HOMEPATH variables on Windows. Refer to the auth module for more
	      details.

	      creation helps identify a particular instance of a C node. In  particular,  it  can
	      help  prevent  us  from receiving messages sent to an earlier process with the same
	      registered name.

	      A C node acting as a server will be  assigned  a	creation  number  when	it  calls
	      erl_publish() .

	      number is used by erl_connect_init() to construct the actual node name. In the sec-
	      ond example shown below, "c17@a.DNS.name" will be the resulting node name.

	      Example 1:

	      struct in_addr addr;
	      addr = inet_addr("150.236.14.75");
	      if (!erl_connect_xinit("chivas",
				     "madonna",
				     "madonna@chivas.du.etx.ericsson.se",
				     &addr;
				     "samplecookiestring..."),
				     0)
		erl_err_quit("<ERROR> when initializing !");

	      Example 2:

	      if (!erl_connect_init(17, "samplecookiestring...", 0))
		erl_err_quit("<ERROR> when initializing !");

       int erl_connect(node)
       int erl_xconnect(addr, alive)

	      Types  char *node, *alive;
		     struct in_addr *addr;

	      These functions set up a connection to an Erlang node.

	      erl_xconnect() requires the IP address of the remote host and the alive name of the
	      remote  node  to be specified. erl_connect() provides an alternative interface, and
	      determines the information from the node name provided.

	      addr is the 32-bit IP address of the remote host.

	      alive is the alivename of the remote node.

	      node is the name of the remote node.

	      These functions return an open file descriptor on  success,  or  a  negative  value
	      indicating  that an error occurred --- in which case they will set erl_errno to one
	      of:

		EHOSTUNREACH :
		  The remote host node is unreachable

		ENOMEM :
		  No more memory available.

		EIO :
		  I/O error.

	      Additionally, errno values from socket(2) and connect(2)  system  calls  may  be
	      propagated into erl_errno .

	      #define NODE   "madonna@chivas.du.etx.ericsson.se"
	      #define ALIVE  "madonna"
	      #define IP_ADDR "150.236.14.75"

	      /*** Variant 1 ***/
	      erl_connect( NODE );

	      /*** Variant 2 ***/
	      struct in_addr addr;
	      addr = inet_addr(IP_ADDR);
	      erl_xconnect( &addr , ALIVE );

       int erl_close_connection(fd)

	      Types  int fd;

	      This function closes an open connection to an Erlang node.

	      Fd is a file descriptor obtained from erl_connect() or erl_xconnect() .

	      On success, 0 is returned. If the call fails, a non-zero value is returned, and the
	      reason for the error can be obtained with the appropriate platform-dependent call.

       int erl_receive(fd, bufp, bufsize)

	      Types  int fd;
		     char *bufp;
		     int bufsize;

	      This function receives a message consisting of a sequence of bytes  in  the  Erlang
	      external format.

	      fd is an open descriptor to an Erlang connection.

	      bufp is a buffer large enough to hold the expected message.

	      bufsize indicates the size of bufp .

	      If  a  tick  occurs,  i.e.,  the Erlang node on the other end of the connection has
	      polled this node to see if it is still alive, the function will return ERL_TICK and
	      no message will be placed in the buffer. Also, erl_errno will be set to EAGAIN .

	      On  success, the message is placed in the specified buffer and the function returns
	      the number of bytes actually read. On failure,  the  function  returns  a  negative
	      value and will set erl_errno to one of:

		EAGAIN :
		  Temporary error: Try again.

		EMSGSIZE :
		  Buffer too small.

		EIO :
		  I/O error.

       int erl_receive_msg(fd, bufp, bufsize, emsg)

	      Types  int fd;
		     unsigned char *bufp;
		     int bufsize;
		     ErlMessage *emsg;

	      This  function receives the message into the specified buffer, and decodes into the
	      (ErlMessage *) emsg .

	      fd is an open descriptor to an Erlang connection.

	      bufp is a buffer large enough to hold the expected message.

	      bufsize indicates the size of bufp .

	      emsg is a pointer to an ErlMessage  structure,  into  which  the	message  will  be
	      decoded. ErlMessage is defined as follows:

	      typedef struct {
		int type;
		ETERM *msg;
		ETERM *to;
		ETERM *from;
		char to_name[MAXREGLEN];
	      } ErlMessage;

   Note:
       The definition of ErlMessage has changed since earlier versions of Erl_Interface.

       type  identifies  the  type  of	message,  one  of  ERL_SEND  ,	ERL_REG_SEND , ERL_LINK ,
       ERL_UNLINK and ERL_EXIT .

       If type contains ERL_SEND this indicates that an ordinary send operation has taken  place,
       and  emsg->to contains the Pid of the recipient. If type contains ERL_REG_SEND then a reg-
       istered send operation took place, and emsg->from contains the Pid of the sender. In  both
       cases, the actual message will be in emsg->msg .

       If  type contains one of ERL_LINK or ERL_UNLINK , then emsg->to and emsg->from contain the
       pids of the sender and recipient of the link or unlink. emsg->msg is  not  used	in  these
       cases.

       If type contains ERL_EXIT , then this indicates that a link has been broken. In this case,
       emsg->to and emsg->from contain the pids of the linked processes, and  emsg->msg  contains
       the reason for the exit.

   Note:
       It is the caller's responsibility to release the memory pointed to by emsg->msg , emsg->to
       and emsg->from .

       If a tick occurs, i.e., the Erlang node on the other end of the connection has polled this
       node  to  see  if it is still alive, the function will return ERL_TICK indicating that the
       tick has been received and responded to, but no message will be placed in the  buffer.  In
       this case you should call erl_receive_msg() again.

       On  success,  the  function  returns  ERL_MSG  and  the Emsg struct will be initialized as
       described above, or ERL_TICK , in which case no message is returned. On failure, the func-
       tion returns ERL_ERROR and will set erl_errno to one of:

	 EMSGSIZE :
	   Buffer too small.

	 ENOMEM :
	   No more memory available.

	 EIO :
	   I/O error.

       int erl_xreceive_msg(fd, bufpp, bufsizep, emsg)

	      Types  int fd;
		     unsigned char **bufpp;
		     int *bufsizep;
		     ErlMessage *emsg;

	      This  function  is  similar  to  erl_receive_msg	. The difference is that erl_xre-
	      ceive_msg expects the buffer to have been allocated by malloc , and reallocates  it
	      if  the  received  message  does not fit into the original buffer. For that reason,
	      both buffer and buffer length are given as pointers - their values  may  change  by
	      the call.

	      On success, the function returns ERL_MSG and the Emsg struct will be initialized as
	      described above, or ERL_TICK , in which case no message is  returned.  On  failure,
	      the function returns ERL_ERROR and will set erl_errno to one of:

		EMSGSIZE :
		  Buffer too small.

		ENOMEM :
		  No more memory available.

		EIO :
		  I/O error.

       int erl_send(fd, to, msg)

	      Types  int fd;
		     ETERM *to, *msg;

	      This function sends an Erlang term to a process.

	      fd is an open descriptor to an Erlang connection.

	      to is an Erlang term containing the Pid of the intended recipient of the message.

	      msg is the Erlang term to be sent.

	      The  function  returns  1  if successful, otherwise 0 --- in which case it will set
	      erl_errno to one of:

		EINVAL :
		  Invalid argument: to is not a valid Erlang pid.

		ENOMEM :
		  No more memory available.

		EIO :
		  I/O error.

       int erl_reg_send(fd, to, msg)

	      Types  int fd;
		     char *to;
		     ETERM *msg;

	      This function sends an Erlang term to a registered process.

	      fd is an open descriptor to an Erlang connection.

	      to is a string containing the registered name of the intended recipient of the mes-
	      sage.

	      msg is the Erlang term to be sent.

	      The  function  returns  1  if successful, otherwise 0 --- in which case it will set
	      erl_errno to one of:

		ENOMEM :
		  No more memory available.

		EIO :
		  I/O error.

       ETERM * erl_rpc(fd, mod, fun, args)
       int erl_rpc_to(fd, mod, fun, args)
       int erl_rpc_from(fd, timeout, emsg)

	      Types  int fd, timeout;
		     char *mod, *fun;
		     ETERM *args;
		     ErlMessage *emsg;

	      These functions support calling Erlang  functions  on  remote  nodes.  erl_rpc_to()
	      sends  an  rpc  request to a remote node and erl_rpc_from() receives the results of
	      such a call. erl_rpc() combines the functionality of these two functions by sending
	      an rpc request and waiting for the results. See also rpc:call/4 .

	      fd is an open descriptor to an Erlang connection.

	      timeout  is the maximum time (in ms) to wait for results. Specify ERL_NO_TIMEOUT to
	      wait forever. When erl_rpc() calls erl_rpc_from(), the call will never timeout.

	      mod is the name of the module containing the function to be run on the remote node.

	      fun is the name of the function to run.

	      args is an Erlang list, containing the arguments to be passed to the function.

	      emsg is a message containing the result of the function call.

	      The actual message returned by the rpc server is a 2-tuple {rex,Reply} . If you are
	      using  erl_rpc_from() in your code then this is the message you will need to parse.
	      If you are using erl_rpc() then the tuple itself is parsed for you, and the message
	      returned	to  your program is the erlang term containing Reply only. Replies to rpc
	      requests are always ERL_SEND messages.

   Note:
       It is the caller's responsibility to free the returned ETERM structure as well as the mem-
       ory pointed to by emsg->msg and emsg->to .

       erl_rpc()  returns the remote function's return value (or NULL if it failed). erl_rpc_to()
       returns 0 on success, and a negative number on  failure.  erl_rcp_from()  returns  ERL_MSG
       when  successful  (with	Emsg  now  containing  the  reply  tuple),  and one of ERL_TICK ,
       ERL_TIMEOUT and ERL_ERROR otherwise. When failing, all three functions  set  erl_errno  to
       one of:

	 ENOMEM :
	   No more memory available.

	 EIO :
	   I/O error.

	 ETIMEDOUT :
	   Timeout expired.

	 EAGAIN :
	   Temporary error: Try again.

       int erl_publish(port)

	      Types  int port;

	      These functions are used by a server process to register with the local name server
	      epmd , thereby allowing other processes to send messages by  using  the  registered
	      name.  Before  calling  either  of  these functions, the process should have called
	      bind() and listen() on an open socket.

	      port is the local name to register, and should be the same as the port number  that
	      was previously bound to the socket.

	      To unregister with epmd, simply close the returned descriptor.

	      On  success,  the  functions  return a descriptor connecting the calling process to
	      epmd. On failure, they return -1 and set erl_errno to:

		EIO :
		  I/O error

	      Additionally, errno values from socket(2) and connect(2)  system  calls  may  be
	      propagated into erl_errno .

       int erl_accept(listensock, conp)

	      Types  int listensock;
		     ErlConnect *conp;

	      This  function  is  used	by  a server process to accept a connection from a client
	      process.

	      listensock is an open socket descriptor  on  which  listen()  has  previously  been
	      called.

	      conp is a pointer to an ErlConnect struct, described as follows:

	      typedef struct {
		char ipadr[4];
		char nodename[MAXNODELEN];
	      } ErlConnect;

	      On  success,  conp  is  filled  in with the address and node name of the connecting
	      client and a file descriptor is returned. On failure,  ERL_ERROR	is  returned  and
	      erl_errno is set to EIO .

       const char * erl_thiscookie()
       const char * erl_thisnodename()
       const char * erl_thishostname()
       const char * erl_thisalivename()
       short erl_thiscreation()

	      These  functions can be used to retrieve information about the C Node. These values
	      are initially set with erl_connect_init() or erl_connect_xinit() .

       int erl_unpublish(alive)

	      Types  char *alive;

	      This function can be called by a process to unregister a specified node  from  epmd
	      on the localhost. This is however usually not allowed, unless epmd was started with
	      the -relaxed_command_check flag, which it normally isn't.

	      To unregister a node you have published, you should instead  close  the  descriptor
	      that was returned by ei_publish() .

   Warning:
       This function is deprecated and will be removed in a future release.

       alive  is  the  name of the node to unregister, i.e., the first component of the nodename,
       without the @hostname .

       If the node was successfully unregistered from epmd, the function returns 0. Otherwise, it
       returns -1 and sets erl_errno is to EIO .

       struct hostent *erl_gethostbyname(name)
       struct hostent *erl_gethostbyaddr(addr, length, type)
       struct hostent *erl_gethostbyname_r(name, hostp, buffer, buflen, h_errnop)
       struct hostent *erl_gethostbyaddr_r(addr, length, type, hostp, buffer, buflen, h_errnop)

	      Types  const char *name;
		     const char *addr;
		     int length;
		     int type;
		     struct hostent *hostp;
		     char *buffer;
		     int buflen;
		     int *h_errnop;

	      These are convenience functions for some common name lookup functions.

DEBUG INFORMATION
       If a connection attempt fails, the following can be checked:

	 * erl_errno

	 * that the right cookie was used

	 * that epmd is running

	 * the	remote Erlang node on the other side is running the same version of Erlang as the
	   erl_interface library.

Ericsson AB			       erl_interface 3.7.3			erl_connect(3erl)


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