Hi.
The RewriteMap Program feature is potentially very powerful but does not appear
to be very robust. While spending some time playing with it I initially came
across the following drawbacks:
1. If the RewriteMap Program stops running for some reason, mod_rewrite does
not provide any fallback mechanism.
2. If the RewriteMap Program does not return extremely quickly it could become
a bottleneck since there is only one instance of it running.
If the RewriteMap Program fails, the code within mod_rewrite returns an empty
string rather than NULL. In my tests this caused /index.htm to be returned as
the URL which is not very useful. I think it makes more sense to handle this
situation as a NULL so that the default key is used as we could then provide a
backup method.
eg:
RewriteRule ^/proxy/(.*) ${proxymap:$1|/proxybackup/$1} [P]
RewriteRule ^/proxybackup/(.*) /proxybackup.php?url=$1 [L]
Looking at the mod_rewrite source code this appears to be a one liner change in
lookup_map_program:
if (i == 4 && !strcasecmp(buf, "NULL"))
.....
becomes:
if ((i == 0) || (i == 4 && !strcasecmp(buf, "NULL"))) {
.....
Is this minor change something that you would consider implementing?
I am also wondering if it would make sense to also try and re-launch the
program within lookup_map_program(). Does anybody have any experience or
feedback on trying to launch processes (ie: call a variation of
rewritemap_program_child) while a module is processing a request?
As for working around the potential bottleneck, I think this would be more
complicated. One solution would be to launch a pool of programs and allow
incoming requests to be handled by the first unlocked program that was still
running. Does this sound like a sensible approach and does anybody see any
potential drawbacks with this?
Thanks.Kev.
