Abstract over Stream type in the outbound path

[vkostyukov]

This to address #1038 as well as make it more pluggable to adopt new streaming libraries (eg FS2). The type-class name is inspired by what Sergey is doing in #1042. The new machinery allows us to reuse the same instances between ToResponse (when serving streaming content) and Input.withStream allowing users to created chunked requests for testing.

Here is how it looks and feels:

import io.finch._, io.finch.iteratee._, io.interatee.Enumerator, cats.effect.IO

val i = Input
  .post("/")
  .withStream[Text.Plain](Enumerator.enumerate[IO, String]("foo", "bar", "baz"))

Also possible to encode JSON (as you would imagine). This does the right thing and encodes ND (newline-delimited) JSON stream, reusing the same code that we use on the outbound path:

import io.finch._, io.finch.iteratee._, io.interatee.Enumerator, cats.effect.IO
import io.finch.circe._, io.circe.generic.auto._

case class Foo(s: String)

val i = Input
  .post("/")
  .withBody[Application.Json](Enumerator.enumerate[IO, Foo](Foo("foo"), Foo("bar"), Foo("baz")))

As a bonus, this addresses #1040.

[vkostyukov]

This is essentially a slam of @sergeykolbasov 's DecodeStream and FromReader as we don't really need both in the outbound path (it's way simpler).

[vkostyukov]

What I was also thinking is that streaming libraries doesn't all have to do that. We can somewhat define this "interleave new lines" logic for JSON generally in finch-core (we have access to Encode.Json there). I'll keep this in mind and maybe revisit later.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@66f15e2). Click here to learn what that means.
The diff coverage is 93.75%.

@@            Coverage Diff            @@
##             master    #1056   +/-   ##
=========================================
  Coverage          ?   84.53%           
=========================================
  Files             ?       50           
  Lines             ?      957           
  Branches          ?       61           
=========================================
  Hits              ?      809           
  Misses            ?      148           
  Partials          ?        0

Impacted Files	Coverage Δ
core/src/main/scala/io/finch/Input.scala	100% <100%> (ø)
core/src/main/scala/io/finch/ToResponse.scala	97.14% <100%> (ø)
...tee/src/main/scala/io/finch/iteratee/package.scala	88.88% <88.88%> (ø)

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[vkostyukov]

@sergeykolbasov Do you prefer this or #1042 being merged this?

[sergeykolbasov]

I like it.
Do you think it's okay if I merge this one into #1042 so we can have one PR about streaming?

[sergeykolbasov]

👍

[vkostyukov]

@sergeykolbasov I'm thinking we should probably go the opposite way - merge smaller pieces when possible. I was worried you'd need to resolve a lot of conflicts in your PR hence kept it open. If you're up for a challenge (and it sounds like you're), I'd say we merge this first and rebase your work.

I wouldn't even mind if we split your PR into couple of independent changes if possible.

[vkostyukov]

Given #1042 is blocked on a new circe-fs2 release (am I right, @sergeykolbasov ?), should we merge this first and, perhaps, cut a release?

[travisbrown]

@BenFradet Now that circe/circe-fs2#47 and circe/circe-fs2#50 are merged do you want to run a circe-fs2 release? I'm also happy to do it later this evening.

[BenFradet]

I don't think I can do so myself but I'm all for it 👍

[travisbrown]

Okay, circe-fs2 is ready: https://github.com/circe/circe-fs2/releases/tag/v0.11.0

[vkostyukov]

Thank you, Travis!

[sergeykolbasov]

@vkostyukov FYI: just merged #1042

[vkostyukov]

Awesome @sergeykolbasov! I will rebase this tonight.

[vkostyukov]

Rebased. Some pieces feel repetitive but it's workable. I think we should merge this in and keep iterating.