1 /* 2 Example of instantiating of the WebAssembly module and invoking its exported 3 function. 4 5 You can compile and run this example on Linux with: 6 7 cargo build --release -p wasmtime-c-api 8 cc examples/hello.c \ 9 -I crates/c-api/include \ 10 -I crates/c-api/wasm-c-api/include \ 11 target/release/libwasmtime.a \ 12 -lpthread -ldl -lm \ 13 -o hello 14 ./hello 15 16 Note that on Windows and macOS the command will be similar, but you'll need 17 to tweak the `-lpthread` and such annotations as well as the name of the 18 `libwasmtime.a` file on Windows. 19 */ 20 21 #include <assert.h> 22 #include <stdio.h> 23 #include <stdlib.h> 24 #include <wasm.h> 25 #include <wasmtime.h> 26 27 static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap); 28 29 static wasm_trap_t* hello_callback(const wasm_val_t args[], wasm_val_t results[]) { 30 printf("Calling back...\n"); 31 printf("> Hello World!\n"); 32 return NULL; 33 } 34 35 int main() { 36 int ret = 0; 37 // Set up our compilation context. Note that we could also work with a 38 // `wasm_config_t` here to configure what feature are enabled and various 39 // compilation settings. 40 printf("Initializing...\n"); 41 wasm_engine_t *engine = wasm_engine_new(); 42 assert(engine != NULL); 43 44 // With an engine we can create a *store* which is a long-lived group of wasm 45 // modules. 46 wasm_store_t *store = wasm_store_new(engine); 47 assert(store != NULL); 48 49 // Read our input file, which in this case is a wasm text file. 50 FILE* file = fopen("examples/hello.wat", "r"); 51 assert(file != NULL); 52 fseek(file, 0L, SEEK_END); 53 size_t file_size = ftell(file); 54 fseek(file, 0L, SEEK_SET); 55 wasm_byte_vec_t wat; 56 wasm_byte_vec_new_uninitialized(&wat, file_size); 57 assert(fread(wat.data, file_size, 1, file) == 1); 58 fclose(file); 59 60 // Parse the wat into the binary wasm format 61 wasm_byte_vec_t wasm; 62 wasmtime_error_t *error = wasmtime_wat2wasm(&wat, &wasm); 63 if (error != NULL) 64 exit_with_error("failed to parse wat", error, NULL); 65 wasm_byte_vec_delete(&wat); 66 67 // Now that we've got our binary webassembly we can compile our module. 68 printf("Compiling module...\n"); 69 wasm_module_t *module = NULL; 70 error = wasmtime_module_new(engine, &wasm, &module); 71 wasm_byte_vec_delete(&wasm); 72 if (error != NULL) 73 exit_with_error("failed to compile module", error, NULL); 74 75 // Next up we need to create the function that the wasm module imports. Here 76 // we'll be hooking up a thunk function to the `hello_callback` native 77 // function above. 78 printf("Creating callback...\n"); 79 wasm_functype_t *hello_ty = wasm_functype_new_0_0(); 80 wasm_func_t *hello = wasm_func_new(store, hello_ty, hello_callback); 81 82 // With our callback function we can now instantiate the compiled module, 83 // giving us an instance we can then execute exports from. Note that 84 // instantiation can trap due to execution of the `start` function, so we need 85 // to handle that here too. 86 printf("Instantiating module...\n"); 87 wasm_trap_t *trap = NULL; 88 wasm_instance_t *instance = NULL; 89 const wasm_extern_t *imports[] = { wasm_func_as_extern(hello) }; 90 error = wasmtime_instance_new(store, module, imports, 1, &instance, &trap); 91 if (instance == NULL) 92 exit_with_error("failed to instantiate", error, trap); 93 94 // Lookup our `run` export function 95 printf("Extracting export...\n"); 96 wasm_extern_vec_t externs; 97 wasm_instance_exports(instance, &externs); 98 assert(externs.size == 1); 99 wasm_func_t *run = wasm_extern_as_func(externs.data[0]); 100 assert(run != NULL); 101 102 // And call it! 103 printf("Calling export...\n"); 104 error = wasmtime_func_call(run, NULL, 0, NULL, 0, &trap); 105 if (error != NULL || trap != NULL) 106 exit_with_error("failed to call function", error, trap); 107 108 // Clean up after ourselves at this point 109 printf("All finished!\n"); 110 ret = 0; 111 112 wasm_extern_vec_delete(&externs); 113 wasm_instance_delete(instance); 114 wasm_module_delete(module); 115 wasm_store_delete(store); 116 wasm_engine_delete(engine); 117 return ret; 118 } 119 120 static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap) { 121 fprintf(stderr, "error: %s\n", message); 122 wasm_byte_vec_t error_message; 123 if (error != NULL) { 124 wasmtime_error_message(error, &error_message); 125 wasmtime_error_delete(error); 126 } else { 127 wasm_trap_message(trap, &error_message); 128 wasm_trap_delete(trap); 129 } 130 fprintf(stderr, "%.*s\n", (int) error_message.size, error_message.data); 131 wasm_byte_vec_delete(&error_message); 132 exit(1); 133 } 134