fix: limit concurrent HTTP requests (backport for 0.2.x)

[lidel]

This is a backport of the fix from #16 that works with 0.2.x.

The goal is to include the fix in latest js-ipfs release (without waiting for async/await changes to be propagated to js-libp2p)

cc @alanshaw @jacobheun

[alanshaw]

I don't know exactly how promisify-es6 works under the hood, does it call callback as well as return a promise? I would have thought it did one or the other.

Maybe we can make this a bit easier to understand as well as eliminate any doubt?

    this._httpQueue.add(() =>
      this.dht.findProvs(key.toString(), {
        timeout: `${options.maxTimeout}ms` // The api requires specification of the time unit (s/ms)
      })
    ).then(res => callback(null, res), callback)

[lidel]

iiuc if callback is present, promisify-es6 will call function as-is; if not, it will return a Promise that injects callback as the last argument before calling the thing

promisify-es6/index.js#L31-L32

Should work the same, so I've switched to your version in 91dcbb7

[alanshaw]

Same here!

[lidel]

That's odd: last test (provide) stop passing if I move callback call to the outside:

    this._httpQueueRefs.add(() =>
      this.refs(key.toString(), { recursive: false })
    ).then(res => callback(null, res), callback)

makes tests hang:

  6 passing (22s)
  1 failing

  1) DelegatedContentRouting
       provide
         should be able to register as a content provider to the delegate node:
     Error: Timeout of 20000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/home/lidel/project/js-libp2p-delegated-content-routing/test/index.spec.js)

Bit late on my end, so I can't tell if it is a bug somewhere, or just me being tired.
Thoughts?

[jacobheun]

Looks good, I'll get a release out for 2.x

[jacobheun]

0.2.4 is on the webs!