NAME

       XPAInfo -  send short message to one or more XPA servers

SYNOPSIS

         #include <xpa.h>

         int XPAInfo(XPA xpa,
                     char *template, char *paramlist, char *mode,
                     char **names, char **messages, int n);

DESCRIPTION

       Send a short paramlist message to 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 XPAInfo() routine does not send data from a buf to the XPA servers. Only the paramlist
       is sent.  The semantics of the paramlist is not formalized, but at a minimum is should
       tell the server how to get more information.  For example, it might contain the class:name
       of the XPA access point from which the server (acting as a client) can obtain more info
       using XPAGet.

       A string containing the class:name and ip:port of each server is returned 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.  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)

       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 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 following keywords are recognized:

         key           value           default         explanation
         ------        --------        --------        -----------
         ack           true/false      true            if false, don't wait for ack from server

       When ack is false, XPAInfo() will not wait for an error return from the XPA server. This
       means, in effect, that XPAInfo will send its paramlist string to the XPA server and then
       exit: no information will be sent from the server to the client. This UDP-like behavior is
       essential to avoid race conditions in cases where XPA servers are sending info messages to
       other servers. If two servers try to send each other an info message at the same time and
       then wait for an ack, a race condition will result and one or both will time out.

       Example -

         (void)XPAInfo(NULL, "IMAGE", "ds9 image", NULL, NULL, NULL, 0);

SEE ALSO

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