wasmer-embedding

Demonstrates three approaches to embedding a WebAssembly module in a C program using the Wasmer C API. The module is a trivial sum(i32, i32) → i32 function defined in add.wat.

Approaches

Source file	How the module is loaded
main.c	Reads add.wasm from disk, compiles it, and serializes the result to add.cwasm for fast reuse on subsequent runs.
main_embed.c	The WAT source is embedded as a C string literal. No external files are needed at runtime.
main_wat_external.c	Reads add.wat from disk and converts it to binary via wat2wasm() at runtime.

Prerequisites

• clang
• Wasmer — install with the official script (Linux/macOS) or winget (Windows):

# Linux / macOS
curl https://get.wasmer.io -sSfL | sh

# Windows
winget install Wasmer.Wasmer

Building

Linux / macOS

export WASMER_DIR="$HOME/.wasmer"
make

This builds a.out (the main.c example). add.wasm is generated from add.wat as part of the build.

Windows

make

Wasmer is located automatically via the ProgramFiles(x86) environment variable. The build produces main.exe and copies wasmer.dll into the project directory.

Building a specific example

make main_embed        # builds main_embed   (Linux) / main_embed.exe   (Windows)
make main_wat_external # builds main_wat_external (Linux) / main_wat_external.exe (Windows)
make all               # builds all three examples

Running

# Linux
./a.out

# Windows
./main.exe

Expected output (all three examples produce the same result):

Creating the store...
Compiling module...
Creating imports...
Instantiating module...
Retrieving exports...
Retrieving the `sum` function...
Calling `sum` function...
Results of `sum`: 7

Testing

make test

Builds and runs test_sum against add.wasm with six input cases covering normal values, negative addends, and 32-bit integer boundaries.

PASS: sum(3, 4) == 7
PASS: sum(0, 0) == 0
PASS: sum(-1, 1) == 0
PASS: sum(10, -3) == 7
PASS: sum(INT32_MAX, 0) == INT32_MAX
PASS: sum(INT32_MIN, 0) == INT32_MIN

6/6 tests passed

Project structure

add.wat              # WebAssembly Text source for the sum module
main.c               # Example 1: load .wasm binary with .cwasm caching
main_embed.c         # Example 2: WAT embedded as a C string literal
main_wat_external.c  # Example 3: load .wat file and convert at runtime
wat2wasm_tool.c      # Build utility: converts .wat → .wasm via the Wasmer C API
test_sum.c           # Unit tests for the sum function
Makefile

CI

Tests run automatically on every push and pull request via GitHub Actions (ubuntu-latest, clang, Wasmer installed from the official script).