You could do this as a server intercept plugin. You could exec the helper, wire up pipes to it's standard I/O, then use TSVConnFdCreate to suck the response back into Traffic Server.
> On Feb 27, 2015, at 7:50 AM, Leif Hedstrom <firstname.lastname@example.org> wrote:
>> On Feb 27, 2015, at 12:51 AM, J David <email@example.com> wrote:
>> (Not sure if this is best for the user list or the dev list, as it's
>> development, but not of ATS per se.)
>> Squid offers a feature called url_rewrite_program that can be used to
>> change its behavior based on client IP, requested URL, and various
>> other criteria. It runs a bunch of copies of an external program and
>> passes information to and from them over pipes.
>> Overall, ATS is a much better fit for our environment, but we are
>> heavily dependent on this feature of Squid.
>> The short version of what we need to do is this:
>> Based on a (ClientIP,RequestURL) pair, either choose a backend (by
>> name or IP) to handle the request *or* issue an arbitrary redirect
>> *or* return an HTTP error.
>> According to the "squid config translation" docs, the equivalent for
>> url_rewrite_program is remap.config. Since that does not actually
>> support external programs, it appears the intent is to use the
>> built-in remapping abilities to replicate the functionality of the
>> external program. However, that is not always possible.
>> The messy part that prevents us from doing that or hacking up a module
>> is that the external program we use with squid is ridiculously
>> complicated, pulling together information from multiple sources, all
>> of them dynamic, and gets linked to all kinds of libraries like MySQL,
>> memcached, and distributed message passing stuff.
>> What is the best way to migrate this functionality to ATS? The whole
>> big ball of wax seems like a really poor candidate for a built-in ATS
>> module due to all the external dependencies, many of which run
>> asynchronously and can block. It seems really advantageous to seal
>> that off So what we probably really need is a pretty efficient way to
>> emulate squid's ability to call out to an external program.
> Dealing with external squid helpers is a bit wonky, but you probably could implement something in a plugin that does it. The fact that you are doing so much weirdness (MySql, Memcached) makes it particularly tough, I’m not sure how Squid deals with that?
> Dealing with synchronous APIs such as MySQL is tricky to say the least.
> I’m not sure we have a good answer here, other than you probably need to try to implement this as a plugin.