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WebAssembly Procedure Calls command-line interface.


WebAssembly is capable of passing and accepting simple numeric parameters between host and guests while non-trivial applications would like to leverage more complex data types like strings, structs, binary blobs, or other complex data types.


waPC is a polyglot specification and toolkit for WebAssembly that enables a bidirectional function call mechanism to enable and simplify the passing of strings, structs, binary blobs, or other complex data types between host and guests systems as native language parameter types.

Basic Overview

waPC cli is a simple and fast polyglot code generator for waPC. waPC leverages a simple workflow, robust set of templates, and user customization to generate this scaffolding code and may be further customized to your use case. It presently supports AssemblyScript, Rust, and TinyGo. You may leverage this cli to create the scaffolding and libraries necessary to build your applications. waPC internally leverages an Interactive Data Language (IDL) called WIDL, short for WebAssembly IDL, based on GraphQL, but with with many features omitted for simplicity. Complex parameters are encoded using MessagePack which is simple, performs well, and easy to use/debug.

For further information about our design choices and architecture please see our FAQ. While WIDL is used internally between the host and underlying guest, you are of course free to expose whatever IDL you would like externally via the API or other mechanisms.

waPC cli has a very simple workflow:

  1. Generate a basic project and data model scaffold with your choice of language.
  2. Customize templates.
  3. Compile your auto-generated libraries.
  4. Load your libraries in a waPC host (e.g. wapc-rust or wapc-go) and leverage them in your project. ... Profit

Getting Started

These instructions will get you a copy of the project up and running on your local machine for development and testing purposes. See deployment for notes on how to deploy the project on a live system.

QuickStart (YOLO)

Install the CLI


powershell -Command "iwr -useb | iex"


curl -fsSL | /bin/bash


wget -q -O - | /bin/bash


brew install wapc/tap/wapc

Create a waPC module


wapc new assemblyscript hello_world_as
cd hello_world_as


wapc new rust hello_world_rust
cd hello_world_rust


wapc new tinygo hello_world_tinygo
cd hello_world_tinygo
make codegen
go mod tidy
make build

The build directory will contain your .wasm file.

Note for users not using the standard NPM Registry

Set an environment variable called NPM_REG to set the registry host for the cli

NPM_REG="" wapc new ...

Basic Scaffolding

waPC cli has a very simple workflow:

  1. Generate basic project and data model scaffold.
  2. Customize templates.
  3. Compile your libraries.
  4. Load your libraries in a waPC host (e.g. wapc-rust or wapc-go) and leverage them in your project.

Generate a new application

wapc new assemblyscript hello_world

Inspect your scaffold

├── Makefile
├── assembly
│   └── tsconfig.json
├── codegen.yaml
├── package.json
└── schema.widl

About the Template Files

The scaffolding created by the wapc new step above creates a template project that you can then use 'make' to build into your custom library. You can customize this template project with your data specification, the files you would like the auto generator to build, and optionally your own custom templates.

  1. Makefile: regardless of what language you use in the generator you can simply use make to build your project.
  2. codegen.yaml is used to map generated files to their module, visitorClass and optional config settings.
  3. package.json provides instructions to npm on which templates to download for the autogeneration and further build instructions for the generated code.
  4. schema.widl is the data schema that you should customize for your application.
  5. assembly/tsconfig.json is the typescript configuration to enable AssemblyScript in your editor.

Building your module

Once you have customized your codegen.yaml and schema.widl you are ready to build your project:


npm will provide you with some feedback, download a bunch of packages, and then auto generate your library. It should look a bit like this now:

├── Makefile
├── assembly
│   ├── index.ts
│   ├── module.ts
│   └── tsconfig.json
├── build
│   └── hello_world.wasm
├── codegen.yaml
├── node_modules/*
├── package-lock.json
├── package.json
└── schema.widl

We of course have all of our node files under node_modules and our node configuration package-lock.json.

Our key autogenerated files:

  1. assembly/index.ts our AssemblyScript entry point with stubbed out functions to implement. (only generated if it does not exist)
  2. assembly/module.ts our AssemblyScript library. (generated each time with make or make codegen)
  3. build/hello_world.wasm our WebAssembly library to be loaded into a wapc guest.


A standalone guide to deploying our hello_world application is coming soon. This will describe leveraging a waPC host library (e.g. wapc-rust or wapc-go) to dynamically load hello_world.wasm in your project.



To use the waPC cli has been tested with Go 1.16. Because the CLI uses the embed package introduced in Go 1.16, previous versions of Go will have compiler errors.

Verify you have Go 1.16+ installed

go version

If Go is not installed, download and install Go 1.16+ (brew installation is not recommended because of CGO linker warnings)

Clone the project from github

git clone
cd cli
go install ./cmd/...

Compiling on Windows

In order to build a project using v8go on Windows, Go requires a gcc compiler to be installed.

To set this up:

  1. Install MSYS2 (
  2. Add the Mingw-w64 bin to your PATH environment variable (C:\msys64\mingw64\bin by default)
  3. Open MSYS2 MSYS and execute pacman -S mingw-w64-x86_64-toolchain

V8 requires 64-bit on Windows, therefore it will not work on 32-bit systems.

Confirm wapc runs (The Go installation should add ~/go/bin in your PATH)

wapc --help


Usage: wapc <command>

  -h, --help    Show context-sensitive help.

  install <location> [<release>]
    Install a module.

  generate <config>
    Generate code from a configuration file.

  new <template> <dir> [<variables> ...]
    Creates a new project from a template.

    Upgrades to the latest base modules dependencies.

Run "wapc <command> --help" for more information on a command.

WIDL and Code Generation

We are looking for help in enhancing the code generation modules to add more supported languages and plugins as well as general bug squashing. wapc will automatically download the widl-js and widl-codegen-js modules. To contribute to one of these modules, you should fork it and instruct wapc to install your fork.

wapc install<your username>/widl-codegen-js

To revert widl-codegen-js to the latest published version

wapc install @wapc/widl-codegen

You can also build independent modules and publish them to NPM.

wapc install <your optional npm org>/my-codegen-module

Your codegen modules should follow the same project structure as widl-codegen-js. See the documentation on the base code generation modules. A tutorial for writing your own code generation module is coming...

Reference projects

Let's look at a few example projects:

  • wasmCloud - A dynamic, elastically scalable WebAssembly host runtime for securely connecting actors and capability providers
  • Mandelbrot Example - an adaptation of AssemblyScript mandelbrot for waPC.
  • Rule Demo - a simple rules engine for waPC
  • IBM Hyperledger - Smart Contracts, running in Wasm. waPC Go Host is leveraged to execute the Wasm chaincode.

Built With

  • waPC - The WebAssembly Procedure Calls GitHub organization that contains host and guest libraries, this CLI, and all the supporting modules.
  • widl-js - Parser, AST, and Visitor pattern for the waPC Interface Definition Language (WIDL).
  • widl-codegen-js - Code generation library using waPC Interface Definition Language (WIDL). Making your life, a wittle bit easier.
  • esbuild - An extremely fast JavaScript bundler written in Go that is used to compile the code generation TypeScript modules into JavaScript that can run natively in V8.
  • v8go and V8 - Execute JavaScript from Go
  • kong - A very simple and easy to use command-line parser for Go
  • The Go 1.16 embed package - Finally embedding files is built into the Go toolchain!


Please read for details on our code of conduct, and the process for submitting pull requests to us.


We use SemVer for versioning. For the versions available, see the tags on this repository.



This project is licensed under the Apache License 2.0 - see the LICENSE.txt file for details