[cups] Error 1282 when server has more than 200 printers and domain socket is enabled

[Alex Korobkin]

On a server with CUPS 1.7.5 (and patch for STR#4484) there is an local app
that queries a list of printers, and then reads their PPDs using CUPS API.

If I add more than 200 printers to it, local app will frequently fail to
retrieve a printer PPD or even get a list of printers, getting "1282 Transport
endpoint is not connected" from CUPS. The more printers I add, the more
often I will see error 1282. CUPS at the same time is working fine and is
able to return the list of printers normally (as tested with lpstat -a and
Web UI).

If I disable domain socket (Listen /var/run/cups/cups.sock) and restart
CUPS, the error will be gone. The app would query CUPS just fine all the
time, regardless of the number of printers.

I don't see anything helpful in debug log, unfortunately.

The only suspicious activity is frequent opening/closing of connections via
local socket:

D [03/Feb/2015:05:42:22 +0000] [Client 52] Accepted from localhost (Domain)
D [03/Feb/2015:05:42:22 +0000] [Client 52] Waiting for request.
D [03/Feb/2015:05:42:22 +0000] [Client 52] HTTP_STATE_WAITING Closing on EOF
D [03/Feb/2015:05:42:22 +0000] [Client 52] Closing connection.
D [03/Feb/2015:05:42:22 +0000] [Client 52] Accepted from localhost (Domain)
D [03/Feb/2015:05:42:22 +0000] [Client 52] Waiting for request.
D [03/Feb/2015:05:42:22 +0000] [Client 52] HTTP_STATE_WAITING Closing on EOF
D [03/Feb/2015:05:42:22 +0000] [Client 52] Closing connection.
D [03/Feb/2015:05:42:22 +0000] [Client 52] Accepted from localhost (Domain)
D [03/Feb/2015:05:42:22 +0000] [Client 52] Waiting for request.
D [03/Feb/2015:05:42:22 +0000] [Client 52] HTTP_STATE_WAITING Closing on EOF
D [03/Feb/2015:05:42:22 +0000] [Client 52] Closing connection.

-- 
Alex