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( 30 void *env, 31 wasmtime_caller_t *caller, 32 const wasmtime_val_t *args, 33 size_t nargs, 34 wasmtime_val_t *results, 35 size_t nresults 36 ) { 37 printf("Calling back...\n"); 38 printf("> Hello World!\n"); 39 return NULL; 40 } 41 42 int main() { 43 int ret = 0; 44 // Set up our compilation context. Note that we could also work with a 45 // `wasm_config_t` here to configure what feature are enabled and various 46 // compilation settings. 47 printf("Initializing...\n"); 48 wasm_engine_t *engine = wasm_engine_new(); 49 assert(engine != NULL); 50 51 // With an engine we can create a *store* which is a long-lived group of wasm 52 // modules. Note that we allocate some custom data here to live in the store, 53 // but here we skip that and specify NULL. 54 wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL); 55 assert(store != NULL); 56 wasmtime_context_t *context = wasmtime_store_context(store); 57 58 // Read our input file, which in this case is a wasm text file. 59 FILE* file = fopen("examples/hello.wat", "r"); 60 assert(file != NULL); 61 fseek(file, 0L, SEEK_END); 62 size_t file_size = ftell(file); 63 fseek(file, 0L, SEEK_SET); 64 wasm_byte_vec_t wat; 65 wasm_byte_vec_new_uninitialized(&wat, file_size); 66 assert(fread(wat.data, file_size, 1, file) == 1); 67 fclose(file); 68 69 // Parse the wat into the binary wasm format 70 wasm_byte_vec_t wasm; 71 wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &wasm); 72 if (error != NULL) 73 exit_with_error("failed to parse wat", error, NULL); 74 wasm_byte_vec_delete(&wat); 75 76 // Now that we've got our binary webassembly we can compile our module. 77 printf("Compiling module...\n"); 78 wasmtime_module_t *module = NULL; 79 error = wasmtime_module_new(engine, (uint8_t*) wasm.data, wasm.size, &module); 80 wasm_byte_vec_delete(&wasm); 81 if (error != NULL) 82 exit_with_error("failed to compile module", error, NULL); 83 84 // Next up we need to create the function that the wasm module imports. Here 85 // we'll be hooking up a thunk function to the `hello_callback` native 86 // function above. Note that we can assign custom data, but we just use NULL 87 // for now). 88 printf("Creating callback...\n"); 89 wasm_functype_t *hello_ty = wasm_functype_new_0_0(); 90 wasmtime_func_t hello; 91 wasmtime_func_new(context, hello_ty, hello_callback, NULL, NULL, &hello); 92 93 // With our callback function we can now instantiate the compiled module, 94 // giving us an instance we can then execute exports from. Note that 95 // instantiation can trap due to execution of the `start` function, so we need 96 // to handle that here too. 97 printf("Instantiating module...\n"); 98 wasm_trap_t *trap = NULL; 99 wasmtime_instance_t instance; 100 wasmtime_extern_t import; 101 import.kind = WASMTIME_EXTERN_FUNC; 102 import.of.func = hello; 103 error = wasmtime_instance_new(context, module, &import, 1, &instance, &trap); 104 if (error != NULL || trap != NULL) 105 exit_with_error("failed to instantiate", error, trap); 106 107 // Lookup our `run` export function 108 printf("Extracting export...\n"); 109 wasmtime_extern_t run; 110 bool ok = wasmtime_instance_export_get(context, &instance, "run", 3, &run); 111 assert(ok); 112 assert(run.kind == WASMTIME_EXTERN_FUNC); 113 114 // And call it! 115 printf("Calling export...\n"); 116 error = wasmtime_func_call(context, &run.of.func, NULL, 0, NULL, 0, &trap); 117 if (error != NULL || trap != NULL) 118 exit_with_error("failed to call function", error, trap); 119 120 // Clean up after ourselves at this point 121 printf("All finished!\n"); 122 ret = 0; 123 124 wasmtime_module_delete(module); 125 wasmtime_store_delete(store); 126 wasm_engine_delete(engine); 127 return ret; 128 } 129 130 static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap) { 131 fprintf(stderr, "error: %s\n", message); 132 wasm_byte_vec_t error_message; 133 if (error != NULL) { 134 wasmtime_error_message(error, &error_message); 135 wasmtime_error_delete(error); 136 } else { 137 wasm_trap_message(trap, &error_message); 138 wasm_trap_delete(trap); 139 } 140 fprintf(stderr, "%.*s\n", (int) error_message.size, error_message.data); 141 wasm_byte_vec_delete(&error_message); 142 exit(1); 143 } 144