function

Calling functions

Please install the prerequisites first!

Quick start with Docker

$ docker run --rm --runtime=io.containerd.wasmedge.v1 --platform=wasi/wasm secondstate/rust-example-function:latest
Hello WasmEdge!
Howdy WasmEdge!
Hola WasmEdge!
WasmEdge 你好!

Code

The src/main.rs source code shows

• The greet() function creates a vector of Greeting struct instances. It takes an Lang as input argument to look up the matching Greeting and returns its message.
• The greet() function returns a Result struct. The struct has two fields.
  • The first field is a String. It is the return value from the function. Inside the function, we return Ok(String) to indicate success and wraps a string return value.
  • The second field is also a String. It is the error message when the function fails. We return Err(String) from inside the function to indicate failure and wraps an error message.
• When we call the greet() function from main(), we use the ? notation to unwrap the Result. The greet(Lang::English)? provides the string value of the English greeting. If the English language is not supported in the greet() function, it will unwrap into a error and cause the main() function to return the same error.

Step by step guide

Compile the Rust source code project to a Wasm bytecode file.

$ cargo build --target wasm32-wasi --release

Run the Wasm bytecode file in WasmEdge CLI.

$ wasmedge target/wasm32-wasi/release/function.wasm
Hello WasmEdge!
Howdy WasmEdge!
Hola WasmEdge!
WasmEdge 你好!

Build and publish on Docker

The Dockerfile follows the above steps to build and package a lightweight OCI-compliant container image for the Wasm app. Now, we need to publish the container image to Docker Hub. The process is slightly different depending on how you plan to use the image.

For Docker Desktop and containerd

For containerd based systems, such as the Docker Desktop and many flavors of Kubernetes, you just need to specify that the WasmEdge application image is for the wasi/wasm platform.

$ docker buildx build --provenance=false --platform wasi/wasm -t secondstate/rust-example-function .
... ...
$ docker push secondstate/rust-example-function