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/*
Example of instantiating of the WebAssembly module and invoking its exported
function.
You can compile and run this example on Linux with:
cargo build --release -p wasmtime-c-api
cc examples/hello.c \
-I crates/c-api/include \
target/release/libwasmtime.a \
-lpthread -ldl -lm \
-o hello
./hello
Note that on Windows and macOS the command will be similar, but you'll need
to tweak the `-lpthread` and such annotations as well as the name of the
`libwasmtime.a` file on Windows.
You can also build using cmake:
mkdir build && cd build && cmake .. && \
cmake --build . --target wasmtime-serialize
*/
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <wasm.h>
#include <wasmtime.h>
static void exit_with_error(const char *message, wasmtime_error_t *error,
wasm_trap_t *trap);
static wasm_trap_t *hello_callback(void *env, wasmtime_caller_t *caller,
const wasmtime_val_t *args, size_t nargs,
wasmtime_val_t *results, size_t nresults) {
printf("Calling back...\n");
printf("> Hello World!\n");
return NULL;
}
int serialize(wasm_byte_vec_t *buffer) {
// Set up our compilation context. Note that we could also work with a
// `wasm_config_t` here to configure what feature are enabled and various
// compilation settings.
printf("Initializing...\n");
wasm_engine_t *engine = wasm_engine_new();
assert(engine != NULL);
// Read our input file, which in this case is a wasm text file.
FILE *file = fopen("examples/hello.wat", "r");
assert(file != NULL);
fseek(file, 0L, SEEK_END);
size_t file_size = ftell(file);
fseek(file, 0L, SEEK_SET);
wasm_byte_vec_t wat;
wasm_byte_vec_new_uninitialized(&wat, file_size);
if (fread(wat.data, file_size, 1, file) != 1) {
printf("> Error loading module!\n");
return 1;
}
fclose(file);
// Parse the wat into the binary wasm format
wasm_byte_vec_t wasm;
wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &wasm);
if (error != NULL)
exit_with_error("failed to parse wat", error, NULL);
wasm_byte_vec_delete(&wat);
// Now that we've got our binary webassembly we can compile our module
// and serialize into buffer.
printf("Compiling and serializing module...\n");
wasmtime_module_t *module = NULL;
error = wasmtime_module_new(engine, (uint8_t *)wasm.data, wasm.size, &module);
wasm_byte_vec_delete(&wasm);
if (error != NULL)
exit_with_error("failed to compile module", error, NULL);
error = wasmtime_module_serialize(module, buffer);
wasmtime_module_delete(module);
if (error != NULL)
exit_with_error("failed to serialize module", error, NULL);
printf("Serialized.\n");
wasm_engine_delete(engine);
return 0;
}
int deserialize(wasm_byte_vec_t *buffer) {
// Set up our compilation context. Note that we could also work with a
// `wasm_config_t` here to configure what feature are enabled and various
// compilation settings.
printf("Initializing...\n");
wasm_engine_t *engine = wasm_engine_new();
assert(engine != NULL);
// With an engine we can create a *store* which is a long-lived group of wasm
// modules.
wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL);
assert(store != NULL);
wasmtime_context_t *context = wasmtime_store_context(store);
// Deserialize compiled module.
printf("Deserialize module...\n");
wasmtime_module_t *module = NULL;
wasmtime_error_t *error = wasmtime_module_deserialize(
engine, (uint8_t *)buffer->data, buffer->size, &module);
if (error != NULL)
exit_with_error("failed to compile module", error, NULL);
// Next up we need to create the function that the wasm module imports. Here
// we'll be hooking up a thunk function to the `hello_callback` native
// function above.
printf("Creating callback...\n");
wasm_functype_t *hello_ty = wasm_functype_new_0_0();
wasmtime_func_t hello;
wasmtime_func_new(context, hello_ty, hello_callback, NULL, NULL, &hello);
// With our callback function we can now instantiate the compiled module,
// giving us an instance we can then execute exports from. Note that
// instantiation can trap due to execution of the `start` function, so we need
// to handle that here too.
printf("Instantiating module...\n");
wasm_trap_t *trap = NULL;
wasmtime_instance_t instance;
wasmtime_extern_t imports[1];
imports[0].kind = WASMTIME_EXTERN_FUNC;
imports[0].of.func = hello;
error = wasmtime_instance_new(context, module, imports, 1, &instance, &trap);
if (error != NULL || trap != NULL)
exit_with_error("failed to instantiate", error, trap);
wasmtime_module_delete(module);
// Lookup our `run` export function
wasmtime_extern_t run;
bool ok = wasmtime_instance_export_get(context, &instance, "run", 3, &run);
assert(ok);
assert(run.kind == WASMTIME_EXTERN_FUNC);
// And call it!
printf("Calling export...\n");
error = wasmtime_func_call(context, &run.of.func, NULL, 0, NULL, 0, &trap);
if (error != NULL || trap != NULL)
exit_with_error("failed to call function", error, trap);
// Clean up after ourselves at this point
printf("All finished!\n");
wasmtime_store_delete(store);
wasm_engine_delete(engine);
return 0;
}
int main() {
wasm_byte_vec_t buffer;
if (serialize(&buffer)) {
return 1;
}
if (deserialize(&buffer)) {
return 1;
}
wasm_byte_vec_delete(&buffer);
return 0;
}
static void exit_with_error(const char *message, wasmtime_error_t *error,
wasm_trap_t *trap) {
fprintf(stderr, "error: %s\n", message);
wasm_byte_vec_t error_message;
if (error != NULL) {
wasmtime_error_message(error, &error_message);
wasmtime_error_delete(error);
} else {
wasm_trap_message(trap, &error_message);
wasm_trap_delete(trap);
}
fprintf(stderr, "%.*s\n", (int)error_message.size, error_message.data);
wasm_byte_vec_delete(&error_message);
exit(1);
}
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