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============================================================================================
Man Page: rmr_wh_open
============================================================================================




RMR LIBRARY FUNCTIONS
=====================



NAME
----

rmr_wh_open


SYNOPSIS
--------


::

  #include <rmr/rmr.h>

  rmr_whid_t rmr_wh_open( void* vctx, char* target )



DESCRIPTION
-----------

The ``rmr_wh_open`` function creates a direct link for
sending, a wormhole, to another RMR based process. Sending
messages through a wormhole requires that the connection be
established overtly by the user application (via this
function), and that the ID returned by ``rmr_wh_open`` be
passed to the ``rmr_wh_send_msg`` function.

*Vctx* is the RMR void context pointer that was returned by
the ``rmr_init`` function. *Target* is the *name and port,*
or *IP-address and port,* combination for the process that
the wormhole should be connected to. For example,
"localhost:6123".

When invoked, this function immediately attempts to connect
to the target process. If the connection cannot be
established, an error is returned to the caller, and no
direct messages can be sent to the target. Once a wormhole is
connected, the underlying transport mechanism (e.g. NNG) will
provide reconnects should the connection be lost, however the
handling of messages sent when a connection is broken is
undetermined as each underlying transport mechanism may
handle buffering and retries differently.


RETURN VALUE
------------

The ``rmr_wh_open`` function returns a type
``rmr_whid_t`` which must be passed to the
``rmr_wh_send_msg`` function when sending a message. The id
may also be tested to determine success or failure of the
connection by using the RMR_WH_CONNECTED macro and passing
the ID as the parameter; a result of 1 indicates that the
connection was established and that the ID is valid.


ERRORS
------

The following error values are specifically set by this RMR
function. In some cases the error message of a system call is
propagated up, and thus this list might be incomplete.

    .. list-table::
      :widths: auto
      :header-rows: 0
      :class: borderless

      * - **EINVAL**
        -
          A parameter passed was not valid.

      * - **EACCESS**
        -
          The user application does not have the ability to establish a
          wormhole to the indicated target (or maybe any target).

      * - **ECONNREFUSED**
        -
          The connection was refused.




EXAMPLE
-------


::

     void*  rmc;
     rmr_whid_t wh;

     rmc = rmr_init( "43086", 4096, 0 ); // init context
     wh = rmr_wh_open( rmc, "localhost:6123" );
     if( !RMR_WH_CONNECTED( wh ) ) {
       fprintf( stderr, "unable to connect wormhole: %s\\n",
               strerror( errno ) );
     }



SEE ALSO
--------

rmr_alloc_msg(3), rmr_call(3), rmr_free_msg(3),
rmr_get_rcvfd(3), rmr_payload_size(3), rmr_send_msg(3),
rmr_rcv_msg(3), rmr_rcv_specific(3), rmr_rts_msg(3),
rmr_ready(3), rmr_fib(3), rmr_has_str(3), rmr_tokenise(3),
rmr_mk_ring(3), rmr_ring_free(3), rmr_wh_close(3),
rmr_wh_send_msg(3), rmr_wh_state(3)