NAME

       XPAGet -  retrieve data from one or more XPA servers

SYNOPSIS

         #include <xpa.h>

         int XPAGet(XPA xpa,
                    char *template, char *paramlist, char *mode,
                    char **bufs, size_t *lens, char **names, char **messages,
                    int n);

DESCRIPTION

       Retrieve data from one or more XPA servers whose class:name identifier matches the
       specified template.

       A template of the form "class1:name1" is sent to the XPA name server, which returns a list
       of at most n matching XPA servers.  A connection is established with each of these servers
       and the paramlist string is passed to the server as the data transfer request is
       initiated. If an XPA struct is passed to the call, then the persistent connections are
       updated as described above. Otherwise, temporary connections are made to the servers
       (which will be closed when the call completes).

       The XPAGet() routine then retrieves data from at most n XPA servers, places these data
       into n allocated buffers and places the buffer pointers in the bufs array. The length of
       each buffer is stored in the lens array. A string containing the class:name and ip:port is
       stored in the name array.  If a given server returned an error or the server callback
       sends a message back to the client, then the message will be stored in the associated
       element of the messages array.  NB: if specified, the name and messages arrays must be of
       size n or greater.

       The returned message string will be of the form:

         XPA$ERROR error\-message (class:name ip:port)

       or

         XPA$MESSAGE message (class:name ip:port)

       Note that when there is an error stored in an messages entry, the corresponding bufs and
       lens entry may or may not be NULL and 0 (respectively), depending on the particularities
       of the server.

       The return value will contain the actual number of servers that were processed.  This
       value thus will hold the number of valid entries in the bufs, lens, names, and messages
       arrays, and can be used to loop through these arrays.  In names and/or messages is NULL,
       no information is passed back in that array.

       The bufs, names, and messages arrays should be freed upon completion (if they are not
       NULL);

       The mode string is of the form: "key1=value1,key2=value2,..."  The following keywords are
       recognized:

         key           value           default         explanation
         ------        --------        --------        -----------
         ack           true/false      true            if false, don't wait for ack from server (after callback completes)
         doxpa         true/false      true            client processes xpa requests

       The ack keyword is not very useful, since the server completes the callback in order to
       return the data anyway.  It is here for completion (and perhaps for future usefulness).

       Normally, an XPA client will process incoming XPA server requests while awaiting the
       completion of the client request.  Setting this variable to "false" will prevent XPA
       server requests from being processed by the client.

       Example -

         #include <xpa.h>

         #define NXPA 10
         int  i, got;
         size_t  lens[NXPA];
         char *bufs[NXPA];
         char *names[NXPA];
         char *messages[NXPA];
         got = XPAGet(NULL, "ds9", "file", NULL, bufs, lens, names, messages,
         NXPA);
         for(i=0; i<got; i++){
           if( messages[i] == NULL ){
             /* process buf contents */
             ProcessImage(bufs[i], ...);
             free(bufs[i]);
           }
           else{
             /* error processing */
             fprintf(stderr, "ERROR: %s (%s)\n", messages[i], names[i]);
           }
           if( names[i] )
             free(names[i]);
           if( messages[i] )
             free(messages[i]);
         }

SEE ALSO

       See xpa(7) for a list of XPA help pages