Using multi-value
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This example shows off how to interact with a wasm module that uses multi-value exports and imports.
Wasm Source
(module (func $f (import "" "f") (param i32 i64) (result i64 i32)) (func $g (export "g") (param i32 i64) (result i64 i32) (call $f (local.get 0) (local.get 1)) ) (func $round_trip_many (export "round_trip_many") (param i64 i64 i64 i64 i64 i64 i64 i64 i64 i64) (result i64 i64 i64 i64 i64 i64 i64 i64 i64 i64) local.get 0 local.get 1 local.get 2 local.get 3 local.get 4 local.get 5 local.get 6 local.get 7 local.get 8 local.get 9) ) Host Source
//! This is an example of working with multi-value modules and dealing with //! multi-value functions. //! //! Note that the `Func::wrap*` interfaces cannot be used to return multiple //! values just yet, so we need to use the more dynamic `Func::new` and //! `Func::call` methods. // You can execute this example with `cargo run --example multi` use wasmtime::Result; fn main() -> Result<()> { use wasmtime::*; println!("Initializing..."); let engine = Engine::default(); let mut store = Store::new(&engine, ()); // Compile. println!("Compiling module..."); let module = Module::from_file(&engine, "examples/multi.wat")?; // Create a host function which takes multiple parameters and returns // multiple results. println!("Creating callback..."); let callback_func = Func::wrap(&mut store, |a: i32, b: i64| -> (i64, i32) { (b + 1, a + 1) }); // Instantiate. println!("Instantiating module..."); let instance = Instance::new(&mut store, &module, &[callback_func.into()])?; // Extract exports. println!("Extracting export..."); let g = instance.get_typed_func::<(i32, i64), (i64, i32)>(&mut store, "g")?; // Call `$g`. println!("Calling export \"g\"..."); let (a, b) = g.call(&mut store, (1, 3))?; println!("Printing result..."); println!("> {a} {b}"); assert_eq!(a, 4); assert_eq!(b, 2); // Call `$round_trip_many`. println!("Calling export \"round_trip_many\"..."); let round_trip_many = instance .get_typed_func::< (i64, i64, i64, i64, i64, i64, i64, i64, i64, i64), (i64, i64, i64, i64, i64, i64, i64, i64, i64, i64), > (&mut store, "round_trip_many")?; let results = round_trip_many.call(&mut store, (0, 1, 2, 3, 4, 5, 6, 7, 8, 9))?; println!("Printing result..."); println!("> {results:?}"); assert_eq!(results, (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)); Ok(()) }
/* Example of instantiating of the WebAssembly module and invoking its exported function. You can build using cmake: mkdir build && cd build && cmake .. && cmake --build . --target wasmtime-multi Also note that this example was taken from https://github.com/WebAssembly/wasm-c-api/blob/master/example/multi.c originally */ #include <inttypes.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <wasm.h> #include <wasmtime.h> static void exit_with_error(const char *message, wasmtime_error_t *error, wasm_trap_t *trap); // A function to be called from Wasm code. wasm_trap_t *callback(void *env, wasmtime_caller_t *caller, const wasmtime_val_t *args, size_t nargs, wasmtime_val_t *results, size_t nresults) { (void)env; (void)caller; (void)nargs; (void)nresults; printf("Calling back...\n"); printf("> %" PRIu32 " %" PRIu64 "\n", args[0].of.i32, args[1].of.i64); printf("\n"); results[0] = args[1]; results[1] = args[0]; return NULL; } // A function closure. wasm_trap_t *closure_callback(void *env, wasmtime_caller_t *caller, const wasmtime_val_t *args, size_t nargs, wasmtime_val_t *results, size_t nresults) { (void)caller; (void)args; (void)nargs; (void)nresults; int i = *(int *)env; printf("Calling back closure...\n"); printf("> %d\n", i); results[0].kind = WASMTIME_I32; results[0].of.i32 = (int32_t)i; return NULL; } int main() { // Initialize. printf("Initializing...\n"); wasm_engine_t *engine = wasm_engine_new(); wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL); wasmtime_context_t *context = wasmtime_store_context(store); // Load our input file to parse it next FILE *file = fopen("examples/multi.wat", "r"); if (!file) { printf("> Error loading file!\n"); return 1; } 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 binary; wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &binary); if (error != NULL) exit_with_error("failed to parse wat", error, NULL); wasm_byte_vec_delete(&wat); // Compile. printf("Compiling module...\n"); wasmtime_module_t *module = NULL; error = wasmtime_module_new(engine, (uint8_t *)binary.data, binary.size, &module); if (error) exit_with_error("failed to compile module", error, NULL); wasm_byte_vec_delete(&binary); // Create external print functions. printf("Creating callback...\n"); wasm_functype_t *callback_type = wasm_functype_new_2_2(wasm_valtype_new_i32(), wasm_valtype_new_i64(), wasm_valtype_new_i64(), wasm_valtype_new_i32()); wasmtime_func_t callback_func; wasmtime_func_new(context, callback_type, callback, NULL, NULL, &callback_func); wasm_functype_delete(callback_type); // Instantiate. printf("Instantiating module...\n"); wasmtime_extern_t imports[1]; imports[0].kind = WASMTIME_EXTERN_FUNC; imports[0].of.func = callback_func; wasmtime_instance_t instance; wasm_trap_t *trap = NULL; 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); // Extract export. printf("Extracting export...\n"); wasmtime_extern_t run; bool ok = wasmtime_instance_export_get(context, &instance, "g", 1, &run); assert(ok); assert(run.kind == WASMTIME_EXTERN_FUNC); // Call. printf("Calling export...\n"); wasmtime_val_t args[2]; args[0].kind = WASMTIME_I32; args[0].of.i32 = 1; args[1].kind = WASMTIME_I64; args[1].of.i64 = 2; wasmtime_val_t results[2]; error = wasmtime_func_call(context, &run.of.func, args, 2, results, 2, &trap); if (error != NULL || trap != NULL) exit_with_error("failed to call run", error, trap); // Print result. printf("Printing result...\n"); printf("> %" PRIu64 " %" PRIu32 "\n", results[0].of.i64, results[1].of.i32); assert(results[0].kind == WASMTIME_I64); assert(results[0].of.i64 == 2); assert(results[1].kind == WASMTIME_I32); assert(results[1].of.i32 == 1); // Shut down. printf("Shutting down...\n"); wasmtime_store_delete(store); wasm_engine_delete(engine); // All done. printf("Done.\n"); 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); } /* Example of instantiating of the WebAssembly module and invoking its exported function. You can build the example using CMake: mkdir build && (cd build && cmake .. && \ cmake --build . --target wasmtime-multi-cpp) And then run it: build/wasmtime-multi-cpp */ #include <fstream> #include <iostream> #include <sstream> #include <wasmtime.hh> using namespace wasmtime; std::string readFile(const char *name) { std::ifstream watFile; watFile.open(name); std::stringstream strStream; strStream << watFile.rdbuf(); return strStream.str(); } int main() { std::cout << "Initializing...\n"; Engine engine; Store store(engine); std::cout << "Compiling module...\n"; auto wat = readFile("examples/multi.wat"); Module module = Module::compile(engine, wat).unwrap(); std::cout << "Creating callback...\n"; Func callback_func = Func::wrap( store, [](int32_t a, int64_t b) -> std::tuple<int64_t, int32_t> { // Rust example adds 1 to each argument but flips order. return std::make_tuple(b + 1, a + 1); }); std::cout << "Instantiating module...\n"; Instance instance = Instance::create(store, module, {callback_func}).unwrap(); std::cout << "Extracting export...\n"; Func g = std::get<Func>(*instance.get(store, "g")); std::cout << "Calling export \"g\"...\n"; // Provide (i32=1, i64=3) like the Rust example auto results = g.call(store, {Val(int32_t(1)), Val(int64_t(3))}).unwrap(); std::cout << "Printing result...\n"; std::cout << "> " << results[0].i64() << " " << results[1].i32() << "\n"; std::cout << "Calling export \"round_trip_many\"...\n"; Func round_trip_many = std::get<Func>(*instance.get(store, "round_trip_many")); auto many_results = round_trip_many .call(store, {Val(int64_t(0)), Val(int64_t(1)), Val(int64_t(2)), Val(int64_t(3)), Val(int64_t(4)), Val(int64_t(5)), Val(int64_t(6)), Val(int64_t(7)), Val(int64_t(8)), Val(int64_t(9))}) .unwrap(); std::cout << "Printing result...\n"; std::cout << "> ("; for (size_t i = 0; i < many_results.size(); i++) { if (i) std::cout << ", "; std::cout << many_results[i].i64(); } std::cout << ")\n"; return 0; }