Wasm32-wasi target support

[rjzak]

Motivation

Getting Tokio working on WebAssembly-WASI so that web applications can be executed by a Wasi runtime, such as Wasmtime and others.

Solution

Working on supporting the wasm32-wasi target. The use of Tokio with WebAssembly should be seamless and easy to the extent possible. Companion to tokio-rs/mio#1576.

Testing

• rjzak/tokio-echo-test is a simple echo server and provides an example server running with WebAssembly.
• rjzak/axum-wasm-test is a simple web server using forks of Axum and Hyper, demonstrating Tokio-Hyper-Axum running on Wasi.

Signed-off-by: Richard Zak richard@profian.com

[carllerche]

Could you include the output you get? Ideally w/ a full backtrace?

[rjzak]

I'm not sure how to get a full stack trace, but this is the output where a connection with nc is made after "Listening" displays.

Listening.
Error: Error { kind: Unsupported, message: "operation not supported on this platform" }
Error: Exited with i32 exit status 1

[carllerche]

It looks like a specific function call is returning an error, could you identify which one it is? You can add logging even if just temporary inside your app / tokio.

[rjzak]

Two things:

1. I set the target toolchain to nightly, and further progress was made. Now the Wasm binary is able to receive connections. However, it doesn't respond.
2. I did add the print statements to track execution, as suggested.

Listening.
Tokio TcpListener::accept() /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:161
Tokio Registration::async_io() /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:250
Tokio Registration::async_io() self.readiness(READABLE) = ReadyEvent { tick: 1, ready: Ready { is_readable: true, is_writable: false, is_read_closed: true, is_write_closed: false } } returned @ /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:253
wasi::accept() /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:32
wasi::accept() listener.accept() OK /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:34
wasi::accept() stream.set_nonblocking(true) /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:36
Tokio TcpListener::accept() self.io.registration().async_io().await /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:167
Tokio TcpListener::accept() TcpStream::new() /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:169
Connection received.
Tokio TcpListener::accept() /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:161
Tokio Registration::async_io() /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:250
Tokio Registration::async_io() self.readiness(READABLE) = ReadyEvent { tick: 1, ready: Ready { is_readable: true, is_writable: false, is_read_closed: false, is_write_closed: false } } returned @ /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:253
wasi::accept() /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:32

What seems to be missing is writing the response data to the stream to send back to the client. Does work as a native Linux binary, so I'm probably just missing something...

[rjzak]

Tokio side, trying to read the contents early, I'm getting "operation not supported" when trying to peek(), and "operation would block" when trying to try_read(). What's the best way to read early on the Tokio side? The socket is already set to allow blocking I/O explicitly on the Wasi side https://github.com/tokio-rs/mio/blob/master/src/sys/wasi/mod.rs#L33.

Listening.
Tokio TcpListener::accept() /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:161
Tokio Registration::async_io() /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:250
Tokio Registration::async_io() self.readiness(READABLE) = ReadyEvent { tick: 1, ready: Ready { is_readable: true, is_writable: false, is_read_closed: true, is_write_closed: false } } returned @ /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:253
wasi::accept() /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:32
wasi::accept() listener.accept() OK /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:34
wasi::accept() stream.set_nonblocking(true) /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:36
Tokio TcpListener::accept() self.io.registration().async_io().await /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:167
Tokio TcpListener::accept() error operation not supported on this platform trying to peek() at the buffer /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:175
Tokio TcpListener::accept() error operation would block trying to TcpStream::try_read() at the buffer /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:185
Tokio TcpListener::accept() TcpStream::new() /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:188
Connection received.
Tokio TcpListener::accept() /home/rjzak/CLionProjects/tokio/tokio/src/net/tcp/listener.rs:161
Tokio Registration::async_io() /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:250
Tokio Registration::async_io() self.readiness(READABLE) = ReadyEvent { tick: 1, ready: Ready { is_readable: true, is_writable: false, is_read_closed: false, is_write_closed: false } } returned @ /home/rjzak/CLionProjects/tokio/tokio/src/io/driver/registration.rs:253
wasi::accept() /home/rjzak/CLionProjects/mio/src/sys/wasi/mod.rs:32

[rjzak]

After disabling tokio::spawn(), the echo server example works! I need to figure out the implications here. https://github.com/rjzak/tokio-echo-test/blob/main/src/main.rs#L65

[Darksonn]

I would like to have a release before I click the merge button, but I believe this PR is ready as-is.

[CryZe]

Wish I had seen this earlier. target_family = "wasm" is preferred over checking for wasm32 to be forwards compatible with wasm64.

[Darksonn]

Can you please comment that on the meta issue mentioned above? Edit: I've added it myself.

[izissise]

Hello, I'm trying to run the first example rjzak/tokio-echo-test but I'm getting this error
error: Only features sync,macros,io-util,rt are supported on wasm.

How can one uses net io with wasi?

[Darksonn]

It's unstable. You need to enable the tokio_unstable flag to use it. You can read how to do that here.

[rjzak]

@izissise Thanks for pointing this out, I updated the readme on that example project.

[AshleySetter]

@rjzak I was trying to build your example at https://github.com/rjzak/tokio-echo-test but I'm a relative beginner at rust and I was met with an error I couldn't resolve, any help would be much appreciated.

RUSTFLAGS="--cfg tokio_unstable" cargo build --target=wasm32-wasi
    Updating git repository `https://github.com/rjzak/tokio`
error: failed to get `tokio` as a dependency of package `tokio-echo-test v0.0.1 (/home/ash/Documents/Junk/tokio-echo-test)`

Caused by:
  failed to load source for dependency `tokio`

Caused by:
  Unable to update https://github.com/rjzak/tokio?branch=wasi_wip#9dfcecbd

Caused by:
  object not found - no match for id (9dfcecbdc71c8403125df1271ebdc2ea79f659e2); class=Odb (9); code=NotFound (-3)

[rjzak]

Hello! The Git branch wasi_wip was deleted when this PR was merged, so change Cargo.toml to point to tokio-rs/tokio instead of rjzak, and set branch = "master".

[AshleySetter]

@rjzak Brilliant, thanks, that works.

Is that the same for https://github.com/rjzak/axum-wasm-test as well? Which git repo and branch of axum should be used with that demo?

[rjzak]

Yes, and I'm working on fixing some things up. I noticed that the latest Tokio release don't block socket2 when compiling for Wasi, but is fixed in a later commit b2ada60. So for the time being, Tokio should be pulled in with git = "https://www.github.com/tokio-rs/tokio", rev = "b2ada60" or git = "https://www.github.com/tokio-rs/tokio", branch = "master"