NAME¶
XPAAccess - return XPA access points matching template (XPA 2.1 and above)
SYNOPSIS¶
#include <xpa.h>
int XPAAccess(XPA xpa,
char *template, char *paramlist, char *mode,
char **names, char **messages, int n);
DESCRIPTION¶
The XPAAccess routine returns the public access points that match the specified
second argument template and have the specified access type.
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
XPAAccess() routine retrieves names from at most n XPA servers that
match the specified template and that were checked for access using the
specified mode. The return string contains both the class:name and ip:port. 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$ERROR error-message (class:name ip:port)
Note that names of matching registered access points are always returned but may
not be valid; it is not sufficient to assume that the returned number of
access points is the number of valid access points. Rather, it is essential to
check the messages array for error messages. Any string in the messages array
is an error message and indicated that the associated access point is not
available.
For example, assume that a server registers a number of access points but delays
entering its event loop. If a call to
XPAAccess() is made before the
event loop is entered, the call will timeout (after waiting for the long
timeout period) and return an error of the form:
XPA$ERROR: timeout waiting for server authentication (XPA:xpa1)
The error means that the XPA access point has been registered but is not yet
available (because events are not being processed). When the server finally
enters its event loop, subsequent calls to
XPAAccess() will return
successfully.
NB: This routine only works with XPA servers built with XPA 2.1.x and later.
Servers with older versions of XPA will return the error message:
XPA$ERROR invalid xpa command in initialization string
If you get this error message, then the old server actually is ready for access,
since it got to the point of fielding the query! The xpaaccess program, for
example, ignores this message in order to work properly with older servers.
The third argument for
XPAAccess() is the type of access and can be any
combination of:
type explanation
------ -----------
g xpaget calls can be made on this access point
s xpaset calls can be made on this access point
i xpainfo calls can be made on this access point
The mode string argument 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)
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).
SEE ALSO¶
See
xpa(7) for a list of XPA help pages