D language bindings for wasmtime

• Dynamic library loading (static loading coming later).
• Full binding to the C API.
• A class-based API with automatic memory management.
• Templates generating automatic binding to D functions.

The DLL/SO file can be loaded with the following function call:

loadWasmtime();

Optionally it can accept an argument of type of null-terminated string, that specifies the path to the dynamic library, and a boolean argument of which is true then it loads the minimalistic version of the library. It returns an error code if something haven't gone right.

Files can be loaded as such:

File file = File("pathtofile/file.wat", "r");
ulong size = file.size();
WasmByteVec wat = new WasmByteVec(cast(size_t)size);
file.rawRead(wat.backend.data[0..wat.backend.size]);

Textual files can be compiled into WASM with the following function:

WasmByteVec wasm = new WasmByteVec();
WasmtimeError error = wat2wasm(cast(const(char)[])source, wasm);

First, you need to initialize the WASM engine, the Wasmtime storage, and a context:

WasmEngine engine = new WasmEngine();
WasmtimeStore store = new WasmtimeStore(engine, null, null);
WasmtimeContext context = store.context();

You can create a module as from a compiled file with the following function:

WasmtimeModule mod;
WasmtimeError error = WasmtimeModule.create(engine, cast(ubyte[])wasm.backend.data[0..wasm.backend.size], mod);

Use the following factory function template to create an automatic binding to a D function, which can be called as an import function from the WASM script:

WasmtimeFunc dFunc = WasmtimeFunc.createFuncBinding!(myDFunc)(context);
WasmtimeExtern dFuncAsExtern;
dFuncAsExtern.kind = WasmExternkind.Func;
dFuncAsExtern.of.func = dFunc.backend;

Creating a Wasmtime instance follows as:

WasmtimeInstance instance = new WasmtimeInstance(context, mod, imports);

Extracting an export function, then executing it is as easy as:

WasmtimeExtern run = instance.exportGet("run");
WasmtimeFunc wasmentrypoint = new WasmtimeFunc(context, run.of.func);
//Number is the expected return arguments, after that the function can accept any number of arguments as long as the variadic function is built to deal with it.
auto funcResult = wasmentrypoint(0);

(Manual binding is still available if needed.)

• Basic functionality works as of now.
• Handling of classes, interfaces, and structs as arguments are untested.
• Automatic function binding generation template factory works, untested for function arguments.

• Shared memory handling.
• Member function binding generation.
• Asynchronous functions.