[Rust] Async await

[dbcfd]

Addresses #3865

Upgrade to use async/await by bringing in appropriate alpha releases for tokio, hyper, and reqwest. Also bring in async-trait to make api usage a little cleaner.

Requires beta compiler for Rust compiler. Expected to not be merged until after 1.39 is released.

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.1.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

/cc @frol @farcaller @bjgill @richardwhiuk

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[JohnDoneth]

LGTM! Exciting work. I like the use of async-trait to keep the API as a trait and still async. 👍

One small nit. It would be nice if the generated API functions were generated as follows:

async fn add_pet(&self, body: crate::models::Pet) -> Result<(), serde_json::Value>;

... instead of the lengthier but equivalent:

fn add_pet(&self, body: crate::models::Pet) -> Box<Future<Item = (), Error = Error<serde_json::Value>>>;

[dbcfd]

@JohnDoneth They will. Haven't run the bash scripts to update the examples yet.

Example from generated code

#[async_trait]
pub trait PetApi {
    async fn add_pet(&self, body: crate::models::Pet) -> Result<(), Error<serde_json::Value>>;
    async fn delete_pet(&self, pet_id: i64, api_key: Option<&str>) -> Result<(), Error<serde_json::Value>>;
    async fn find_pets_by_status(&self, status: Vec<String>) -> Result<Vec<crate::models::Pet>, Error<serde_json::Value>>;
    async fn find_pets_by_tags(&self, tags: Vec<String>) -> Result<Vec<crate::models::Pet>, Error<serde_json::Value>>;
    async fn get_pet_by_id(&self, pet_id: i64) -> Result<crate::models::Pet, Error<serde_json::Value>>;
    async fn update_pet(&self, body: crate::models::Pet) -> Result<(), Error<serde_json::Value>>;
    async fn update_pet_with_form(&self, pet_id: i64, name: Option<&str>, status: Option<&str>) -> Result<(), Error<serde_json::Value>>;
    async fn upload_file(&self, pet_id: i64, additional_metadata: Option<&str>, file: Option<std::path::PathBuf>) -> Result<crate::models::ApiResponse, Error<serde_json::Value>>;
}

[richardwhiuk]

As per Metaswitch/swagger-rs#83, we'll want to wait for Hyper 0.13 to come out of beta before merging this.

[ctaggart]

@dbcfd, I'm trying out this branch and with -library=reqwest, the first error I ran into was

error[E0599]: no method named `PUT` found for type `&reqwest::async_impl::client::Client` in the current scope

currently:

let mut req_builder = client.PUT(uri_str.as_str());

should be:

let mut req_builder = client.put(uri_str.as_str());

It is named put, not PUT for reqwest.
https://github.com/seanmonstar/reqwest/blob/master/src/async_impl/client.rs#L648

[ctaggart]

May be leave this.

[dbcfd]

There's places that require the method (e.g. .method(PUT)). Thought I had got this working, but have been working on server, so will revisit.

[dbcfd]

@ctaggart Yeah, it's still very much wip, since both hyper and reqwest are changing. Even more so, swagger-rs would take significant changes that I can't test easily, so currently just using the context portion of it to make progress. Will push up my latest work so that if people want to pitch in they can. It's a pretty signficant effort.

[ctaggart]

For our needs, these are the changes I made for the reqwest client templates ctaggart#1

• add support for custom_auth closure
• remove async_trait
• use Confguration with lifetime instead of Arc

[dbcfd]

@ctaggart can you explain the async_trait removal? Changing client from a trait to just an implementation, so not needed?

[ctaggart]

It is still early days for https://github.com/dtolnay/async-trait. I hit some lifetime issues that I didn't want to troubleshoot. Our cli app doesn't need the traits or that additional dependency. I suspect that most probably don't.

[ctaggart]

It may also be a good idea to implement std::error::Error for the custom error. ctaggart@5bd94ea

[kanekv]

What can we do to speed up this effort? Anything we can help with?

[dbcfd]

@kanekv One would be to update swagger-rs to work with latest hyper. I've temporarily forked just the changes needed for this library in https://github.com/dbcfd/openapi-context. Updating swagger-rs to latest hyper is a much larger effort, but one that will need to be done.

[kanekv]

@dbcfd Is it a blocker or we can just continue with your approach?

[dbcfd]

@kanekv it will definitely be a blocker for final merge, unless we want to roll the context stuff into this crate.

If you're looking specifically for work on this repo, the client generator needs a revisit, pulling in some of @ctaggart changes. I've also pushed up my work on the server generator code. I likely won't have time over the next week to work on that, so feel free to work on that as well.

[kanekv]

@dbcfd Not necessarily for this repo, just looking how we can coordinate the work and get it moving. Who is working on swagger-rs transition? Is there any way we can parallelize it?

[dbcfd]

I was looking at the swagger-rs transition, but realized it was fairly large on its own right, and I didn't have a great way to test the changes I would have to make. That's where the openapi-context fork came from.

The client generator and the server generator are mostly distinct from each other, so one person could finish up the client portion and split it out as its own MR.

[kanekv]

Would it be beneficial to assume we can roll context stuff in (temporarily) and make client/server based on that assumption and also get it merged until we figure out what to do with swagger-rs, at that point we can switch it back?

[dbcfd]

Yeah, we could publish openapi-context as a crate, then switch to swagger-rs when it is ready. Client/server could then be worked as publishable using openapi-context crate.

[UkonnRa]

Cool, any update?

[dbcfd]

Almost have the example generated code working. Hoping to get it finished up today. At that point it should be good for people to experiment with.

[dbcfd]

@ctaggart reqwest client should work now, in addition to hyper client and the server module.

[dbcfd]

@JohnDoneth samples have been updated with the result of this work now.

[UkonnRa]

ping~

[bcourtine]

Great job @dbcfd!

But I think replacing the current "reqwest" generator with an async version is not a good idea:
some people can prefer using a "sync" version, or can have a pre 1.39 version as requirement.

So, the two versions (sync and async) should coexist (with a generator parameter, or with a new library "reqwest-async" for example).

[dbcfd]

@bcourtine The reqwest client is by default async now, and blocking is under a different api. Leaving the default reqwest client as blocking will require a PR as well.

There's a couple of ways to move this PR forward:

• Release as is
• Release with async flagged similar to how reqwest is
• Create new generators, rust-async and rust-server-async

Release as is
Given that hyper and reqwest are both async by default and require 1.39, this is my preferred approach. The alternative is to keep openapi on older versions of tokio, hyper, reqwest, etc. One can achieve a synchronous interface to reqwest by doing what reqwest blocking is doing, where it runs the async functionality on a thread pool.

Release with async flagged
This not only suffers from maintaining a version on older crates, but complicates the generation as well.

Create new generators
This requires maintaining two generators, one which is on unsupported libraries, but works pre 1.39. And a second generator which requires 1.39 or higher and is on supported libraries. Given the usefulness of async/await, I don't see the old generator getting much use.

Thoughts?

[bcourtine]

Hi @dbcfd,

I personally like a lot async/await, and the language/crates moving forward is a good thing ;-)

But Rust 1.39 was only released 3 months ago. Even if Rust is moving fast, considering a 4 months old Rust version deprecated and not supported anymore by openapi-generator seems harsh.

@wing328 What is your opinion?

[dbcfd]

@bcourtine I meant the versions of the crates tokio, hyper, reqwest, etc. being deprecated. The current versions of those crates all require 1.39 or higher.

[bcourtine]

I agree, but theses crates still have support for a pre-1.39 version ;)

[dbcfd]

@bcourtine Although these crates have pre 1.39 versions, they are not supported. Attempting to use the currently supported crates (e.g. hyper 0.13) on a 1.38 compiler will fail.

info: default toolchain set to '1.38.0-x86_64-apple-darwin'

  1.38.0-x86_64-apple-darwin installed - rustc 1.38.0 (625451e37 2019-09-23)

$ cd code/rust/
$ cargo new --lib hyper-test
     Created library `hyper-test` package
$ cd hyper-test/
$ vi Cargo.toml
$ cargo build
   Compiling tower-service v0.3.0
error: `core::slice::<impl [T]>::len` is not yet stable as a const fn
   --> /Users/dannybrowning/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/bytes-0.5.4/src/bytes.rs:130:18
    |
130 |             len: bytes.len(),
    |                  ^^^^^^^^^^^

error: aborting due to previous error

[wing328]

@dbcfd I've added an option to support async operations for reqwest.

I wonder if you can pull the latest master to give it a try.

[wing328]

Closing as there's no update.