Wasm-C FFI
==========
main.c:
.. code-block:: c
// Example function
int add(int a, int b)
{
return a + b;
}
// This function is defined in javascript
extern void print(const char* str);
int main(void)
{
print("Hello, World!");
return 0;
}
Compilation:
.. code-block:: bash
clang --target=wasm32 -nodefaultlibs -nostdlib -Wl,--no-entry -Wl,--export-all -Wl,--allow-undefined -Wl,--initial-memory=131072 -o main.wasm main.c
index.js:
.. code-block:: c
// Helper function to get a string from a pointer in memory
function getString(ptr, memory) {
const bytes = new Uint8Array(memory.buffer, ptr);
let len = 0;
while (bytes[len] !== 0) len++;
return new TextDecoder().decode(bytes.slice(0, len));
}
const importObject = {
env: {
// Provide functions that can be called from C
print: (ptr) => {
const str = getString(ptr, wasmInstance.exports.memory);
console.log("From C: ", str);
},
},
}
let wasmInstance;
WebAssembly.instantiateStreaming(fetch("main.wasm"), importObject).then(
(obj) => {
wasmInstance = obj.instance;
// Call a C function
const res = wasmInstance.exports.add(1, 2);
console.log("1 + 2 = ", res);
// Call main
wasmInstance.exports.main();
}
);
index.html:
.. code-block:: c
My Website
Welcome to My Website
Run a server:
.. code-block:: bash
python3 -m http.server