#246, #168: Add Kotlin Coroutines support

[lucasvsme]

This pull requests adds some suspend functions to the Request class. They were added in a new module called fuel-coroutines and are intended to allows the developers to avoid callbacks while using asynchronous calls.

[codecov]

Codecov Report

Merging #313 into master will increase coverage by 0.18%.
The diff coverage is 61.11%.

@@             Coverage Diff              @@
##             master     #313      +/-   ##
============================================
+ Coverage     77.21%   77.39%   +0.18%     
+ Complexity      193      190       -3     
============================================
  Files            32       32              
  Lines           904      898       -6     
  Branches        148      152       +4     
============================================
- Hits            698      695       -3     
+ Misses          131      122       -9     
- Partials         75       81       +6

Impacted Files	Coverage Δ	Complexity Δ
...com/github/kittinunf/fuel/coroutines/Coroutines.kt	61.11% <61.11%> (ø)	0 <0> (?)
.../kotlin/com/github/kittinunf/fuel/core/Encoding.kt	89.58% <0%> (-2.73%)	13% <0%> (-2%)
...tlin/com/github/kittinunf/fuel/core/FuelManager.kt	88.76% <0%> (-0.93%)	31% <0%> (ø)
...tlin/com/github/kittinunf/fuel/util/FuelRouting.kt	100% <0%> (ø)	0% <0%> (ø)	⬇️
.../java/com/github/kittinunf/fuel/forge/FuelForge.kt
...f/fuel/core/interceptors/RedirectionInterceptor.kt	68.75% <0%> (+6.25%)	0% <0%> (ø)	⬇️

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[yoavst]

Do we want to allow the user to select in which coroutine pool it will make the network request?
Currently it uses Executors.newCachedThreadPool.

[lucasvsme]

Do you mean wrapping the suspend function with async { } or launch { }? Something like:

fun main(args: Array<String>) = runBlocking {
    val call = async(CommonPool) { "https://httpbin.org/ip".httpGet().awaitStringResult() }
    val ipInJson = call.await()
    println(ipInJson)
}

[iNoles]

Android has own coroutine context for UI too.

[raharrison]

Doesn't Fuel already run in it's own ExecutorService? We don't want to start the coroutine on another thread which in turn calls Fuel which passes the actual request onto another thread.

[lucasvsme]

@iNoles I've added a Espresso test to covers the Android use case you've mention.

@raharrison The Request class uses a Future internally and also the ExecutorService you've mentioned. Since these fields are final and private I couldn't find a way to change them while implementing coroutines as a module apart from core.

[kittinunf]

@lucasvalenteds First of all, thanks for this!! It has been a pretty long awaited feature.

What do you think about relaxing them so that it can be modified?

[lucasvsme]

@kittinunf Your welcome. Thank you for the Fuel project!

About your question, I can't see how to make this coroutines module more flexible. I'm also failing to understand what it means in terms of implementation. Could you provide a use case to clarify how the developer can modify the module to get a better usage experience?

[raharrison]

Can this get merged as it still presents a solution to using Fuel with coroutines, even if more enhancements are needed in the future?

[kittinunf]

@lucasvalenteds would you be so generous applying the finishing touch?

[lucasvsme]

@kittinunf Sure. Tell me what you need.

[kittinunf]

I think if you can resolve conflict then this is good to go.

[kittinunf]

it looks like kotlinCoroutinesVersion is missing from the build.gradle file?

[lucasvsme]

You are right, @kittinunf. Sorry about that. I don't have the Android development environment right now, so I'll need a couple of hours to review the full code in case the CI fails again.

[kittinunf]

Sure no rush, I plan to release new version with this PR so as soon as it is ready, I will make it.

Thanks for this though. It has been long overdue. I think you deserve a lot of credit for your work here :)

[lucasvsme]

The CI has failing due to tests related to fuel module, which was not changed in this pull request. Do you have any idea why? I've run the fuel-coroutines tests and they are passing.

[kittinunf]

Let's merge this in. I will investigate from master.