xpainfo(3)							SAORD Documentation							xpainfo(3)

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

version 2.1.14							   June 7, 2012 							xpainfo(3)