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ei_connect(3erl)		       C Library Functions			 ei_connect(3erl)

NAME
       ei_connect - Communicate with distributed erlang

DESCRIPTION
       This  module enables C programs to communicate with erlang nodes, using the erlang distri-
       bution over TCP/IP.

       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 .

       The environment variable ERL_EPMD_PORT can be used to indicate which logical cluster  a	C
       node belongs to.

TIMEOUT FUNCTIONS
       Most  functions	appear	in  a version with the suffix _tmo appended to the function name.
       Those function take an additional argument, a timeout in milliseconds . The  semantics  is
       this;  for  each  communication primitive involved in the operation, if the primitive does
       not complete within the time specified, the function will return an  error  and	erl_errno
       will  be  set  to  ETIMEDOUT  .	With communication primitive is meant an operation on the
       socket, like connect , accept , recv or send .

       Obviously the timeouts are for implementing fault tolerance, not  to  keep  hard  realtime
       promises.  The _tmo functions are for detecting non-responsive peers and to avoid blocking
       on socket operations.

       A timeout value of 0 (zero), means that timeouts are disabled. Calling  a  _tmo	-function
       with  the  last	argument as 0 is therefore exactly the same thing as calling the function
       without the _tmo suffix.

       As with all other ei functions, you are not expected to put the	socket	in  non  blocking
       mode  yourself in the program. Every use of non blocking mode is embedded inside the time-
       out functions. The socket will always be back in blocking mode after  the  operations  are
       completed  (regardless  of the result). To avoid problems, leave the socket options alone.
       Ei will handle any socket options that need modification.

       In all other senses, the _tmo functions inherit all the return values  and  the	semantics
       from the functions without the _tmo suffix.

EXPORTS
       int  ei_connect_init(ei_cnode*  ec,  const char* this_node_name, const char *cookie, short
       creation)
       int ei_connect_xinit(ei_cnode* ec, const char *thishostname,  const  char  *thisalivename,
       const char *thisnodename, Erl_IpAddr thisipaddr, const char *cookie, short creation)

	      These  function  initializes the ec structure, to identify the node name and cookie
	      of the server. One of them has to be called before other functions  that	works  on
	      the type ei_cnode or a file descriptor associated with a connection to another node
	      are used.

	      ec is a structure containing information about the C-node. It is used in	other  ei
	      functions for connecting and receiving data.

	      this_node_name is the registered name of the process (the name before '@').

	      cookie is the cookie for the node.

	      creation	identifies  a specific instance of a C node. It can help prevent the node
	      from receiving messages sent to an earlier process with the same registered name.

	      thishostname is the name of the machine we're running on. If long names are  to  be
	      used, it should be fully qualified (i.e. durin.erix.ericsson.se instead of durin ).

	      thisalivename is the registered name of the process.

	      thisnodename is the full name of the node, i.e. einode@durin .

	      thispaddr if the IP address of the host.

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

	      A connection is closed by simply closing the socket. Refer to system  documentation
	      to close the socket gracefully (when there are outgoing packets before close).

	      This function return a negative value indicating that an error occurred.

	      Example 1:

	      int n = 0;
	      struct in_addr addr;
	      ei_cnode ec;
	      addr.s_addr = inet_addr("150.236.14.75");
	      if (ei_connect_xinit(&ec,
				   "chivas",
				   "madonna",
				   "madonna@chivas.du.etx.ericsson.se",
				   &addr;
				   "cookie...",
				   n++) < 0) {
		  fprintf(stderr,"ERROR when initializing: %d",erl_errno);
		  exit(-1);
	      }

	      Example 2:

	      if (ei_connect_init(&ec, "madonna", "cookie...", n++) < 0) {
		  fprintf(stderr,"ERROR when initializing: %d",erl_errno);
		  exit(-1);
	      }

       int ei_connect(ei_cnode* ec, char *nodename)
       int ei_xconnect(ei_cnode* ec, Erl_IpAddr adr, char *alivename)

	      These functions set up a connection to an Erlang node.

	      ei_xconnect()  requires the IP address of the remote host and the alive name of the
	      remote node to be specified. ei_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 .

	      Example:

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

	      /*** Variant 1 ***/
	      int fd = ei_connect(&ec, NODE);

	      /*** Variant 2 ***/
	      struct in_addr addr;
	      addr.s_addr = inet_addr(IP_ADDR);
	      fd = ei_xconnect(&ec, &addr, ALIVE);

       int ei_connect_tmo(ei_cnode* ec, char *nodename, unsigned timeout_ms)
       int ei_xconnect_tmo(ei_cnode* ec, Erl_IpAddr adr, char *alivename, unsigned timeout_ms)

	      ei_connect and ei_xconnect with an optional timeout argument, see  the  description
	      at the beginning of this document.

       int ei_receive(int fd, unsigned 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. It is obtained	from  a  previous
	      ei_connect or ei_accept .

	      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  ERL_ERROR  and
	      will set erl_errno to one of:

		EAGAIN :
		  Temporary error: Try again.

		EMSGSIZE :
		  Buffer too small.

		EIO :
		  I/O error.

       int ei_receive_tmo(int fd, unsigned char* bufp, int bufsize, unsigned timeout_ms)

	      ei_receive  with an optional timeout argument, see the description at the beginning
	      of this document.

       int ei_receive_msg(int fd, erlang_msg* msg, ei_x_buff* x)
       int ei_xreceive_msg(int fd, erlang_msg* msg, ei_x_buff* x)

	      These functions receives a message to the buffer in x . ei_xreceive_msg allows  the
	      buffer  in  x  to  grow, but ei_receive_msg fails if the message is bigger than the
	      preallocated buffer in x .

	      fd is an open descriptor to an Erlang connection.

	      msg is a pointer to an erlang_msg structure and contains information on the message
	      received.

	      x is buffer obtained from ei_x_new .

	      On  success,  the  function returns ERL_MSG and the msg struct will be initialized.
	      erlang_msg is defined as follows:

	      typedef struct {
		  long msgtype;
		  erlang_pid from;
		  erlang_pid to;
		  char toname[MAXATOMLEN+1];
		  char cookie[MAXATOMLEN+1];
		  erlang_trace token;
	      } erlang_msg;

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

	      If  msgtype  is  ERL_SEND  this indicates that an ordinary send operation has taken
	      place, and msg->to contains the Pid of the  recipient  (the  C-node).  If  type  is
	      ERL_REG_SEND  then  a  registered send operation took place, and msg->from contains
	      the Pid of the sender.

	      If msgtype is ERL_LINK or ERL_UNLINK , then msg->to and msg->from contain the  pids
	      of the sender and recipient of the link or unlink.

	      If  msgtype  is ERL_EXIT , then this indicates that a link has been broken. In this
	      case, msg->to and msg->from contain the pids of the linked processes.

	      The return value is the same as for ei_receive , see above.

       int ei_receive_msg_tmo(int fd, erlang_msg* msg, ei_x_buff* x, unsigned imeout_ms)
       int ei_xreceive_msg_tmo(int fd, erlang_msg* msg, ei_x_buff* x, unsigned timeout_ms)

	      ei_receive_msg and ei_xreceive_msg with  an  optional  timeout  argument,  see  the
	      description at the beginning of this document.

       int ei_receive_encoded(int fd, char **mbufp, int *bufsz, erlang_msg *msg, int *msglen)

	      This  function  is  retained for compatibility with code generated by the interface
	      compiler and with code following examples in the same application.

	      In essence the function performs	the  same  operation  as  ei_xreceive_msg  ,  but
	      instead  of  using  an  ei_x_buff,  the  function  expects a pointer to a character
	      pointer ( mbufp ), where the character pointer should point to a memory area  allo-
	      cated  by  malloc . The argument bufsz should be a pointer to an integer containing
	      the exact size (in bytes) of the memory area. The function may reallocate the  mem-
	      ory area and will in such cases put the new size in *bufsz and update *mbufp .

	      Furthermore  the	function  returns  either  ERL_TICK  or  the msgtype field of the
	      erlang_msg *msg . The actual length of the message is put in *msglen . On error  it
	      will return a value < 0 .

	      It  is  recommended  to  use ei_xreceive_msg instead when possible, for the sake of
	      readability. The function will however be retained in the interface for compatibil-
	      ity and will not be removed not be removed in future releases without notice.

       int ei_receive_encoded_tmo(int fd, char **mbufp, int *bufsz, erlang_msg *msg, int *msglen,
       unsigned timeout_ms)

	      ei_receive_encoded with an optional timeout argument, see the  description  at  the
	      beginning of this document.

       int ei_send(int fd, erlang_pid* to, char* buf, int len)

	      This function sends an Erlang term to a process.

	      fd is an open descriptor to an Erlang connection.

	      to is the Pid of the intended recipient of the message.

	      buf is the buffer containing the term in binary format.

	      len is the length of the message in bytes.

	      The  function returns 0 if successful, otherwise -1, in the latter case it will set
	      erl_errno to EIO .

       int ei_send_tmo(int fd, erlang_pid* to, char* buf, int len, unsigned timeout_ms)

	      ei_send with an optional timeout argument, see the description at the beginning  of
	      this document.

       int ei_send_encoded(int fd, erlang_pid* to, char* buf, int len)

	      Works exactly as ei_send, the alternative name retained for backward compatibility.
	      The function will not be removed without notice.

       int ei_send_encoded_tmo(int fd, erlang_pid* to, char* buf, int len, unsigned timeout_ms)

	      ei_send_encoded with an optional timeout	argument,  see	the  description  at  the
	      beginning of this document.

       int ei_reg_send(ei_cnode* ec, int fd, char* server_name, char* buf, int len)

	      This function sends an Erlang term to a registered process.

	      This function sends an Erlang term to a process.

	      fd is an open descriptor to an Erlang connection.

	      server_name is the registered name of the intended recipient.

	      buf is the buffer containing the term in binary format.

	      len is the length of the message in bytes.

	      The  function returns 0 if successful, otherwise -1, in the latter case it will set
	      erl_errno to EIO .

	      Example, send the atom "ok" to the process "worker":

	      ei_x_buff x;
	      ei_x_new_with_version(&x);
	      ei_x_encode_atom(&x, "ok");
	      if (ei_reg_send(&ec, fd, x.buff, x.index) < 0)
		  handle_error();

       int ei_reg_send_tmo(ei_cnode* ec, int fd, char* server_name, char* buf, int len,  unsigned
       timeout_ms)

	      ei_reg_send with an optional timeout argument, see the description at the beginning
	      of this document.

       int ei_send_reg_encoded(int fd, const erlang_pid *from, const char *to, const  char  *buf,
       int len)

	      This  function  is  retained for compatibility with code generated by the interface
	      compiler and with code following examples in the same application.

	      The function works as  ei_reg_send  with	one  exception.  Instead  of  taking  the
	      ei_cnode	as  a  first  argument,  it  takes a second argument, an erlang_pid which
	      should be the process identifier of the sending process (in the erlang distribution
	      protocol).

	      A suitable erlang_pid can be constructed from the ei_cnode structure by the follow-
	      ing example code:

			ei_cnode ec;
			erlang_pid *self;
			int fd; /* the connection fd */
			...
			self = ei_self(&ec);
			self->num = fd;

       int ei_send_reg_encoded_tmo(int fd, const erlang_pid *from, const  char	*to,  const  char
       *buf, int len)

	      ei_send_reg_encoded  with  an optional timeout argument, see the description at the
	      beginning of this document.

       int ei_rpc(ei_cnode *ec, int fd, char *mod, char *fun, const char *argbuf, int  argbuflen,
       ei_x_buff *x)
       int  ei_rpc_to(ei_cnode	*ec, int fd, char *mod, char *fun, const char *argbuf, int argbu-
       flen)
       int ei_rpc_from(ei_cnode *ec, int fd, int timeout, erlang_msg *msg, ei_x_buff *x)

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

	      ec  is  the C-node structure previously initiated by a call to ei_connect_init() or
	      ei_connect_xinit()

	      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.  ei_rpc()	will  wait  infinitely for the answer, i.e. the call will
	      never time out.

	      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.

	      argbuf is a pointer to a buffer with an encoded  Erlang  list,  without  a  version
	      magic number, containing the arguments to be passed to the function.

	      argbuflen is the length of the buffer containing the encoded Erlang list.

	      msg  structure of type erlang_msg and contains information on the message received.
	      See ei_receive_msg() for a description of the erlang_msg format.

	      x points to the dynamic buffer that receives the result. For for ei_rpc() this will
	      be  the  result without the version magic number. For ei_rpc_from() the result will
	      return a version magic number and a 2-tuple {rex,Reply} .

	      ei_rpc() returns the number of bytes in the result on success and  -1  on  failure.
	      ei_rpc_from()  returns  number  of  bytes  or  one  of  ERL_TICK	, ERL_TIMEOUT and
	      ERL_ERROR otherwise. When failing, all three functions set erl_errno to one of:

		EIO :
		  I/O error.

		ETIMEDOUT :
		  Timeout expired.

		EAGAIN :
		  Temporary error: Try again.

	      Example, check to see if an erlang process is alive:

	      int index = 0, is_alive;
	      ei_x_buff args, result;

	      ei_x_new(&result);
	      ei_x_new(&args);
	      ei_x_encode_list_header(&args, 1);
	      ei_x_encode_pid(&args, &check_pid);
	      ei_x_encode_empty_list(&args);

	      if (ei_rpc(&ec, fd, "erlang", "is_process_alive",
			 args.buff, args.index, &result) < 0)
		  handle_error();

	      if (ei_decode_version(result.buff, &index) < 0
		  || ei_decode_bool(result.buff, &index, &is_alive) < 0)
		  handle_error();

       int ei_publish(ei_cnode *ec, 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.

	      ec is the C-node structure.

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

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

	      To unregister with epmd, simply close the returned descriptor. Do not use ei_unpub-
	      lish() , which is deprecated anyway.

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

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

       int ei_publish_tmo(ei_cnode *ec, int port, unsigned timeout_ms)

	      ei_publish  with an optional timeout argument, see the description at the beginning
	      of this document.

       int ei_accept(ei_cnode *ec, int listensock, ErlConnect *conp)

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

	      ec is the C-node structure.

	      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 .

       int ei_accept_tmo(ei_cnode *ec, int listensock, ErlConnect *conp, unsigned timeout_ms)

	      ei_accept with an optional timeout argument, see the description at  the	beginning
	      of this document.

       int ei_unpublish(ei_cnode *ec)

	      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 close the descriptor that was
	      returned by ei_publish() .

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

       ec is the node structure of the node to unregister.

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

       int ei_unpublish_tmo(ei_cnode *ec, unsigned timeout_ms)

	      ei_unpublish  with  an optional timeout argument, see the description at the begin-
	      ning of this document.

       const char * ei_thisnodename(ei_cnode *ec)
       const char * ei_thishostname(ei_cnode *ec)
       const char * ei_thisalivename(ei_cnode *ec)

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

	      They  simply  fetches  the  appropriate field from the ec structure. Read the field
	      directly will probably be safe for a long time, so these functions are  not  really
	      needed.

       erlang_pid * ei_self(ei_cnode *ec)

	      This function retrieves the Pid of the C-node. Every C-node has a (pseudo) pid used
	      in ei_send_reg , ei_rpc and others. This is contained in a field in the  ec  struc-
	      ture.  It  will  be  safe  for  a  long  time to fetch this field directly from the
	      ei_cnode structure.

       struct hostent *ei_gethostbyname(const char *name)
       struct hostent *ei_gethostbyaddr(const char *addr, int len, int type)
       struct hostent *ei_gethostbyname_r(const char *name, struct hostent *hostp, char  *buffer,
       int buflen, int *h_errnop)
       struct  hostent *ei_gethostbyaddr_r(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.

       int ei_get_tracelevel(void)
       void ei_set_tracelevel(int level)

	      These functions are used to set tracing on the distribution. The levels are differ-
	      ent  verbosity levels. A higher level means more information. See also Debug Infor-
	      mation and EI_TRACELEVEL below.

	      ei_set_tracelevel and ei_get_tracelevel are not thread safe.

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
	   ei library.

	 * the environment variable ERL_EPMD_PORT is set correctly.

       The   connection   attempt  can	be  traced  by	setting  a  tracelevel	by  either  using
       ei_set_tracelevel or by setting the environment variable  EI_TRACELEVEL	.  The	different
       tracelevels has the following messages:

	 * 1: Verbose error messages

	 * 2: Above messages and verbose warning messages

	 * 3: Above messages and progress reports for connection handling

	 * 4: Above messages and progress reports for communication

	 * 5: Above messages and progress reports for data conversion

Ericsson AB			       erl_interface 3.7.3			 ei_connect(3erl)
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