Provided by: erlang-manpages_16.b.3-dfsg-1ubuntu2_all bug

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_connect_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
              second 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 registered 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
              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_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_xreceive_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
              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:

                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 memory 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.