Develop WasmEdge Plug-in in Rust SDK with witc

By developing a plug-in, one can extend the functionality of WasmEdge and customize it to suit specific needs. WasmEdge provides a Rust-based API for registering extension modules and host functions.

备注

It is recommended that developers choose the WasmEdge C API for plug-in development because of the support, compatibility, and flexibility the WasmEdge runtime provides.

Set up the development environment

To start developing WasmEdge plug-ins, it is essential to properly set up the development environment. This section provides step-by-step instructions for WasmEdge plug-in development -

• Build WasmEdge from source: For developing the WasmEdge plug-in in C++, you must build WasmEdge from source. Follow thebuild WasmEdge from source for instructions. Once you complete the C++ plug-in code, you can use witc¹ to generate Rust Plug-in SDK.

After installing WasmEdge, you need to set up the build environment. If you're using Linux or other platforms, you can follow the instructions in the build environment setup guide.

Write the plug-in code

To develop a WasmEdge Plug-in in Rust using the witc tool, you can follow these steps:

• Generate Rust Plug-in Code: Consider you have a file named wasmedge_opencvmini.wit with the following content:

  imdecode: func(buf: list<u8>) -> u32
  imshow: func(window-name: string, mat-key: u32) -> unit
  waitkey: func(delay: u32) -> unit

  You can use the witc tool to generate Rust plug-in code for it by running the following command:

  witc plugin wasmedge_opencvmini.wit

• Create SDK Crate: You need to create an SDK crate for your plug-in. Run the following command to create a new crate named opencvmini-sdk:

  cargo new --lib opencvmini-sdk && cd opencvmini-sdk

• Create Module File: The witc tool puts the Rust code to stdout. To capture the generated code, create a new module file named src/generated.rs and run the following command:

  witc plugin wasmedge_opencvmini.wit > src/generated.rs

• Write Wrapper Functions: In the src/lib.rs file of your crate, write the following code of mod generated to access the generated code and create wrapper functions:

  mod generated;
  
  pub fn imdecode(buf: &[u8]) -> u32 {
      unsafe { generated::imdecode(buf.as_ptr(), buf.len()) }
  }
  pub fn imshow(window_name: &str, mat_key: u32) -> () {
      unsafe { generated::imshow(window_name.as_ptr(), window_name.len(), mat_key) }
  }
  pub fn waitkey(delay: u32) -> () {
      unsafe { generated::waitkey(delay) }
  }

  This code imports the generated module and provides safe wrapper functions for each generated function.

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1. https://github.com/second-state/witc↩