How to log some RESTful service response informati

Question

I've a simple java RESTful service which queries database and send the response back based on the request parameter. I need to generate some simple report based on the apache access_log, for example number of queries/day, number of similar queries, etc.

One of report I need to generate is to list queries which returns zero result. I'm wondering how to achieve this. I can't rely on the response size in apache log, since the the response xml with zero result will still be returned.

I'm thinking of setting a custom cookie if the query returns no result and have it printed in apache log..

LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" \"%{Cookie}i\"" combined-cookie

Not sure if this will work or to be honest, is this is the right approach.

Any pointers will be highly appreciated.

Thanks

Answer 1

If you know for sure that the "no results" response is NNN bytes, and you know that any other response would be different (larger), then you could potentially query your access log for responses of size NNN. But that's a bit of a hack, and it's brittle if the size of an empty response changes for whatever reason.

I don't think Apache has any built-in capability to inspect the content of a response and set variables based on some property of the data. (You could potentially do something very hacky with mod_ext_filter, but it's not worth the hassle and the performance would likely suffer.)

It sounds like you already have the ability to change the server code that's producing the response. Since that's the case, I would not try to use Apache logging. Instead, I would add some additional logging capability to your server. Every response could output a line to a different log file. The lines could look like this:

2012-06-14 14:02:15.345 count=0 status=Completed
2012-06-14 14:02:15.906 count=12 status=Completed
...

Then the type of reporting you need becomes easier.

But if you absolutely have to do it with Apache, then my suggestion would be to invent a new HTTP header, something like X-Query-Result, and then tweak your server to set that header on every response. For example:

X-Query-Result: count=0 status=Completed

Then similar to what you suggested, use \"%{X-Query-Result}i\" in your log format. I'd choose this over cookies just to avoid the extra "weight" associated with cookies.