wasm-c-string

Library for passing JavaScript strings in and out of WebAssembly modules written in C.

API

WebAssembly module compatibility

In order to use this library, the WebAssembly module must export two memory management functions:

• void* allocate(size_t size): Allocator
• void deallocate(void* allocation): Deallocator

These functions could simply wrap malloc and free from malloc.h.

createCString(module, str, runCallback)

Copies a string from the JavaScript host into a UTF-8 C string within a WebAssembly module instance's memory and manages the string's lifetime.

runCallback is a callback during which the allocated C string must remain alive (the string will be deallocated when this callback returns or throws).

The result of runCallback is returned.

readStaticCString(module, address)

Reads a C string from a WebAssembly module instance. Returns a new (JavaScript) string that is a copy of the source C string.

Note: This is only for reading statically allocated strings that require no memory management. See the next function for dynamically allocated strings where the exported C function is passing ownership of the allocation to the caller (e.g. strdup).

receiveCString(module, createCallback)

Receives a newly-allocated C string (created using the supplied callback), copies the string into a JavaScript string, and frees the underlying C string allocation. Returns the (JavaScript) string.

createCallback is a callback that allocates the new C string and returns its address (generally, this calls one of the module's exports that returns a newly allocated string, e.g. strdup).