Support for log filter policy hooks

This adds a "policy" hook into the logging framework's streams and
filters to replace the existing log filter predicates. The hook
signature is as follows:

    hook(rec: any, id: Log::ID, filter: Log::Filter);

The logging manager invokes hooks on each log record. Hooks can veto
log records via a break, and modify them if necessary. Log filters
inherit the stream-level hook, but can override or remove the hook as
needed.

The distribution's existing log streams now come with pre-defined
hooks that users can add handlers to. Their name is standardized as
"log_policy" by convention, with additional suffixes when a module
provides multiple streams. The following adds a handler to the Conn
module's default log policy hook:

    hook Conn::log_policy(rec: Conn::Info, id: Log::ID, filter: Log::Filter)
            {
            if ( some_veto_reason(rec) )
                break;
            }

By default, this handler will get invoked for any log filter
associated with the Conn::LOG stream.

The existing predicates are deprecated for removal in 4.1 but continue
to work.
This commit is contained in:
Christian Kreibich 2020-09-21 16:09:36 -07:00
parent c8545c85d8
commit 1bd658da8f
61 changed files with 289 additions and 85 deletions

View file

@ -14,6 +14,9 @@ export {
## The software logging stream identifier.
redef enum Log::ID += { LOG };
## A default logging policy hook for the stream.
global log_policy: Log::PolicyHook;
## Scripts detecting new types of software need to redef this enum to add
## their own specific software types which would then be used when they
## create :zeek:type:`Software::Info` records.
@ -123,7 +126,7 @@ export {
event zeek_init() &priority=5
{
Log::create_stream(Software::LOG, [$columns=Info, $ev=log_software, $path="software"]);
Log::create_stream(Software::LOG, [$columns=Info, $ev=log_software, $path="software", $policy=log_policy]);
}
type Description: record {