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 You can also build using cmake: 21 22 mkdir build && cd build && cmake .. && cmake --build . --target wasmtime-hello 23 */ 24 25 #include <assert.h> 26 #include <stdio.h> 27 #include <stdlib.h> 28 #include <wasm.h> 29 #include <wasmtime.h> 30 31 static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap); 32 33 static wasm_trap_t* hello_callback( 34 void *env, 35 wasmtime_caller_t *caller, 36 const wasmtime_val_t *args, 37 size_t nargs, 38 wasmtime_val_t *results, 39 size_t nresults 40 ) { 41 printf("Calling back...\n"); 42 printf("> Hello World!\n"); 43 return NULL; 44 } 45 46 int main() { 47 int ret = 0; 48 // Set up our compilation context. Note that we could also work with a 49 // `wasm_config_t` here to configure what feature are enabled and various 50 // compilation settings. 51 printf("Initializing...\n"); 52 wasm_engine_t *engine = wasm_engine_new(); 53 assert(engine != NULL); 54 55 // With an engine we can create a *store* which is a long-lived group of wasm 56 // modules. Note that we allocate some custom data here to live in the store, 57 // but here we skip that and specify NULL. 58 wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL); 59 assert(store != NULL); 60 wasmtime_context_t *context = wasmtime_store_context(store); 61 62 // Read our input file, which in this case is a wasm text file. 63 FILE* file = fopen("examples/hello.wat", "r"); 64 assert(file != NULL); 65 fseek(file, 0L, SEEK_END); 66 size_t file_size = ftell(file); 67 fseek(file, 0L, SEEK_SET); 68 wasm_byte_vec_t wat; 69 wasm_byte_vec_new_uninitialized(&wat, file_size); 70 assert(fread(wat.data, file_size, 1, file) == 1); 71 fclose(file); 72 73 // Parse the wat into the binary wasm format 74 wasm_byte_vec_t wasm; 75 wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &wasm); 76 if (error != NULL) 77 exit_with_error("failed to parse wat", error, NULL); 78 wasm_byte_vec_delete(&wat); 79 80 // Now that we've got our binary webassembly we can compile our module. 81 printf("Compiling module...\n"); 82 wasmtime_module_t *module = NULL; 83 error = wasmtime_module_new(engine, (uint8_t*) wasm.data, wasm.size, &module); 84 wasm_byte_vec_delete(&wasm); 85 if (error != NULL) 86 exit_with_error("failed to compile module", error, NULL); 87 88 // Next up we need to create the function that the wasm module imports. Here 89 // we'll be hooking up a thunk function to the `hello_callback` native 90 // function above. Note that we can assign custom data, but we just use NULL 91 // for now). 92 printf("Creating callback...\n"); 93 wasm_functype_t *hello_ty = wasm_functype_new_0_0(); 94 wasmtime_func_t hello; 95 wasmtime_func_new(context, hello_ty, hello_callback, NULL, NULL, &hello); 96 97 // With our callback function we can now instantiate the compiled module, 98 // giving us an instance we can then execute exports from. Note that 99 // instantiation can trap due to execution of the `start` function, so we need 100 // to handle that here too. 101 printf("Instantiating module...\n"); 102 wasm_trap_t *trap = NULL; 103 wasmtime_instance_t instance; 104 wasmtime_extern_t import; 105 import.kind = WASMTIME_EXTERN_FUNC; 106 import.of.func = hello; 107 error = wasmtime_instance_new(context, module, &import, 1, &instance, &trap); 108 if (error != NULL || trap != NULL) 109 exit_with_error("failed to instantiate", error, trap); 110 111 // Lookup our `run` export function 112 printf("Extracting export...\n"); 113 wasmtime_extern_t run; 114 bool ok = wasmtime_instance_export_get(context, &instance, "run", 3, &run); 115 assert(ok); 116 assert(run.kind == WASMTIME_EXTERN_FUNC); 117 118 // And call it! 119 printf("Calling export...\n"); 120 error = wasmtime_func_call(context, &run.of.func, NULL, 0, NULL, 0, &trap); 121 if (error != NULL || trap != NULL) 122 exit_with_error("failed to call function", error, trap); 123 124 // Clean up after ourselves at this point 125 printf("All finished!\n"); 126 ret = 0; 127 128 wasmtime_module_delete(module); 129 wasmtime_store_delete(store); 130 wasm_engine_delete(engine); 131 return ret; 132 } 133 134 static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap) { 135 fprintf(stderr, "error: %s\n", message); 136 wasm_byte_vec_t error_message; 137 if (error != NULL) { 138 wasmtime_error_message(error, &error_message); 139 wasmtime_error_delete(error); 140 } else { 141 wasm_trap_message(trap, &error_message); 142 wasm_trap_delete(trap); 143 } 144 fprintf(stderr, "%.*s\n", (int) error_message.size, error_message.data); 145 wasm_byte_vec_delete(&error_message); 146 exit(1); 147 } 148