C++ for WebAssembly: Emscripten, WASI and wasmtime

Getting started

Install Boost, b2 and a C++20 compiler, at the versions the README gives. Then clone the superproject with its libraries, and run every library's tests:

git clone --recursive https://github.com/webcpporg/webcpp
cd webcpp
b2 test

A b2 project uses a library through /webcpp/<name>//<name>. CMake or a plain compiler uses the headers that b2 install --prefix=<dir> copies to <dir>/include/webcpp/.

Building for each target

Native. b2 builds with your own compiler, as for any C++ library, for programs that integrate closely with an operating system.

b2 test example

WASI, for servers. Two clang toolsets of wasi-sdk build for wasm32-wasip2 and wasm32-wasip3. wasmtime runs each test, and serves a component the way a cloud runs a WebAssembly container, lighter than Docker.

b2 toolset=clang-wasip2 testing.launcher=wasmtime test example
b2 toolset=clang-wasip3 testing.launcher=wasmtime test example

Emscripten, for the browser. The emscripten toolset builds a library that declares that target, and node runs its tests. A program for a page is linked, and runs in the browser.

b2 toolset=emscripten libs/<name>/test libs/<name>/example

b2 declared-targets -d0 lists the targets each library declares.

The libraries' pages

Each library's page teaches it: its guide, its guarantees, its API reference and how it is tested.

• asio

  Boost.Asio for native, browser and WASIp2/P3 targets, with explicit platform capabilities and shipped Wasm implementations.

• beast

  Beast-compatible HTTP and WebSocket interfaces for WebAssembly and native applications.

• cobalt

  Boost.Cobalt coroutine applications on native, browser and WASI targets.

• config

  webcpp's configuration, which every webcpp library includes first: the target a program is built for, whether webcpp has exceptions, and webcpp's version.

• document

  A JSON document for C++20 that behaves as JavaScript does, in one relocatable image.

• idna

  IDNA2008 and UTS 46 for C++20: Punycode, ToASCII and ToUnicode, and label validity, over generated Unicode 17.0 tables.

• lexical

  Validators and Boost.URL grammar rules for the string formats of JSON Schema, for C++20.

• pratt

  A generic Pratt parser engine for C++20, with a decimal calculator built on it.

• trystero

  Serverless WebRTC rooms for C++20, wire compatible with Trystero.

• wasi

  Header-only helpers for C++ built as WebAssembly components: the HTTP handler a component exports on wasip2 and wasip3, and the macros a program writes its main between.

• xactor

  A header-only, deterministic actor system: actors that handle one message at a time, with fuel per execution, timers and a lifecycle.

• xstate

  A header-only port of XState's state machines and actors: machines read from XState's JSON config, stepped by XState's pure functions or run as actors on xactor.