Wasmtube

Wasmtube is a bridging library which allows you to communicate between Elixir and Wasm. It supports structured values and images as arguments to be passed into Wasm functions.

Installation

If available in Hex, the package can be installed by adding wasmtube to your list of dependencies in mix.exs:

def deps do
  [
    {:wasmtube, "~> 0.1.0"}
  ]
end

Usage

Use `Wasmtube` directly

Wasmtube provides simple APIs to instantiate Wasm sandbox individualized for a Wasm binary to which functions are called.

Wasmtube.from_file("hello_world.wasm")
|> Wasmtube.call_function(:hello, data: %{
  arg: "World"
})

Use `Wasmtube.Worker` to be supervised

Wasmtube.Worker is useful when you want to put the Wasmtube under supervision tree.

{:ok, worker_pid} =
  Wasmtube.Worker.start_link(
    wasm_file: "hello_world.wasm",
    name: name
  )

worker_pid
  |> Wasmtube.Worker.call_function(:echo, data: %{
    arg: "World"
  })

How `Wasmtube` works

Here's an illustration to help you intuitively understand how Wasmtube works.

Initialization process

sequenceDiagram
  autonumber

  participant Elixir App
  participant Wasmtube
  participant Linear Memory
  participant Wasm Sandbox

  Elixir App ->> Wasmtube: starts Wasmtube with <br> Wasm binary
  Wasmtube ->> Wasm Sandbox: instantiates the Wasm Sandbox <br> with the Wasm binary
  Wasm Sandbox ->> Linear Memory: prepare individualized <br> memory for <br> the Wasm module
  Wasm Sandbox -->> Wasmtube: finish init process
  Wasmtube -->> Elixir App: returns the instance <br> of `Wasm.Bridge`

Calling Wasm functions

sequenceDiagram
  autonumber

  participant Elixir App
  participant Wasmtube
  participant Linear Memory
  participant Wasm Sandbox

  Elixir App ->> Wasmtube: calls a function
  Wasmtube ->> Linear Memory: writes the data
  Wasmtube ->> Wasm Sandbox: delegates the function
  Wasm Sandbox ->> Linear Memory: reads the data
  Wasm Sandbox ->> Wasm Sandbox: process the data
  Wasm Sandbox ->> Linear Memory: writes the data
  Wasm Sandbox -->> Wasmtube: responds to the function
  Wasmtube ->> Linear Memory: reads the data
  Wasmtube -->> Elixir App: delegate the response

Update the Wasm functions

Wasmtube can handle updates of Wasm binary. It allows you to update the functions on the fly.

sequenceDiagram
  autonumber

  participant Deployer
  box White Host
    participant OS
    participant Wasmtube
    participant Wasm Sandbox
  end

  Deployer ->> OS: deploys a new <br> Wasm binary
  OS ->> Wasmtube: notifies the <br> file updated
  Wasmtube ->> OS: re-reads the file
  Wasmtube ->> Wasm Sandbox: re-instantiates <br> the sandbox <br> with the new binary
  Wasm Sandbox ->> Wasmtube: finishes init process

How to implement Wasm functions

To get to know how to implement Wasm functions to be used with Wasmtube, see wasm_test for details.

Structured values

Wasmtube writes and reads structured values by which it interacts with Wasm sandbox into Linear memory. You are supposed to read and write the data processed in Wasm function as JSON-encoded values.

Example implementation for above explanation looks like below:

#[no_mangle]
pub unsafe extern "C" fn echo(index: *const u8, length: usize) -> i32 {
    let slice = unsafe { slice::from_raw_parts(index, length) };
    let args: Args = serde_json::from_str::<Args>(str::from_utf8(slice).unwrap()).unwrap();

    store_into_memory(index, args)
}

See wasm_test/src/lib.rs for details.

Call the function implemented above as below:

Wasmtube.from_file("/path/to/wasm")
  |> Wasmtube.call_function(
    :echo,
    data: %{
      args: "Hello World!"
    }
  )

Images

Wasmtube writes and reads images by which it interacts with Wasm sandbox into Linear memory. You are supposed to read and write the data processed in Wasm function as binary-encoded values.

Example implementation for above explanation looks like below:

#[no_mangle]
pub unsafe extern "C" fn image_size(
    index: *const u8,
    _length: usize,
    width: u32,
    height: u32,
) -> i32 {
    let slice = unsafe { slice::from_raw_parts(index, (width * height * 3) as usize) };
    let img = image::RgbImage::from_raw(width, height, slice.to_vec()).unwrap();

    let image_info = ImageInfo {
        width: img.width(),
        height: img.height(),
    };

    store_into_memory(index, image_info)
}

See wasm_test/src/lib.rs for details.

Call the function implemented above as below:

Wasmtube.from_file("/path/to/wasm")
  |> Wasmtube.call_function(
    :image_size,
    image: File.read!("/path/to/image"),
      width: 256,
      height: 256
  )

Build it

You can build it using wasm-pack as below:

cd test/wasm_test
wasm-pack build

You'll see a Wasm file at test/wasm_test/target/wasm32-unknown-unknown/release/wasm_test.wasm.

Author

Kentaro Kuribayashi kentarok@gmail.com

kentaro/wasmtube