(ITS#4560) [enhancement] cancel strategies for proxies

[ando@sys-net.it]

Full_Name: Pierangelo Masarati
Version: HEAD
OS: irrelevant
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (87.28.220.33)
Submitted by: ando


The proxy backends issue abandons with respect to remote server(s) whenever an
operation needs to be abandoned for internal reasons (i.e. not as a consequence
to an abandon issued to the proxy).

However, in some cases, abandoning may not be the most appropriate strategy:

- we have experienced issues with abandoning in libldap, which seem to be fixed
now, but in any case in typical use most of the times the abandon occurs while
the response is alraeady on its way, so abandoning just eats up bandwidth
without adding any value, apart from the possibility to stop serving an
operation.  In those cases, the operation may be simply ignored; the response
will eventually find its way to the proxy, and will be listed in the available
responses; in those cases, it is recommended that (persistent) connections, like
anonymous and privileged, are timed out routinely, by means of either
idle-timeout or conn-ttl.

- in some cases, one might want to be sure that cancellation occurred as
appropriate.  In those cases, using the cancel extended operation may be more
appropriate

This patch introduces the capability to ignore responses or cancel operations as
alternatives to abandoning, which is the default (basically the current
behavior). If the cancel exop is used, it can be discovered by reading the root
DSE of the remote server(s).

p.