Async filter function (to interface with database)

[lorentzkim]

This is from tracker's point of view.

I am attempting to extend the usage of filter function by e.g. using a database to query whether the torrent has valid infoHash or not, as well as any other params that needs to be checked.

Database queries, as being network requests, are async in nature, and they don't return a value but a callback to do further processing.

Filter function requires a return value (a boolean).

Is there any way that you can think of to easily do both? As I can see it, there's no way to do this cleanly. Using async module or whatnot isn't going to cut it as it's not the order of the processing, but rather inability to return a value from a callback to original caller (which doesn't make sense anyway).

[feross]

You're correct, this isn't possible right now since filter has to be a sync function. I know that @astro was using this module to interface with a database.

@astro - any ideas about how to accomplish this?

If we must, I suppose we can make the getSwarm function asynchronous, but I'd like to avoid that if we can.

[lorentzkim]

I've in meanwhile used a module called deasync to force everything into a sync, which is a bit of a hack, but works for now. Hopefully there's a good resolution. I can totally understand not wanting to change getSwarm though.

[feross]

@lorentzkim If you really need this feature, you could send in a PR. I'm willing to consider making getSwarm async, but we'll need to bump the major version since folks may be depending on that.

I don't think getSwarm is used in that many places, so this might not be too hard of a change.

[lorentzkim]

I'll consider doing that.

Do you mind if async module gets added in as a dependency?

That said, going async is kinda infectious, especially for functions that return some result, and this might be touching quite a bit of the library. Then again, if we're bumping up a major version, might as well do it proper.

[lorentzkim]

Don't mind the async thing, looks like you're using run-series and that does about the same for this purpose.

[feross]

Yeah, run-series is equivalent to async.series without all the other cruft.

[feross]

@lorentzkim any progress? I'm happy to take a look at an in-progress PR for this and share my feedback.

[lorentzkim]

Please see my asnyc_getswarm branch. I was last changing out server.js:444.

Now I'm somewhere rewriting the tests to better fit with the async model.

[lorentzkim]

Rudimentary changes should be done now. Take a look.

[lorentzkim]

I am feeling a little iffy about the whole filters and the callback value; perhaps expand the result value to have more meaning than true/false? It already returns err for errors, if there are any. Custom filter reasons perhaps that gets passed to the server correctly?

Might also make sense to drop the infoHash+params thing to just params, since the function signatures are changing anyhow.

[feross]

Released as 5.0.0.