Add example of execution limits using fuel consumption

examples/fuel.c

@@ -0,0 +1,132 @@
+/*
+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/fuel.c \
+ -I crates/c-api/include \
+ -I crates/c-api/wasm-c-api/include \
+ target/release/libwasmtime.a \
+ -lpthread -ldl -lm \
+ -o fuel
+ ./fuel
+
+Note that on Windows and macOS the command will be similar, but you'll need
+to tweak the `-lpthread` and such annotations.
+*/
+
+#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);
+
+int main() {
+ wasmtime_error_t *error = NULL;
+
+ wasm_config_t *config = wasm_config_new();
+ assert(config != NULL);
+ wasmtime_config_consume_fuel_set(config, true);
+
+ // Create an *engine*, which is a compilation context, with our configured options.
+ wasm_engine_t *engine = wasm_engine_new_with_config(config);
+ assert(engine != NULL);
+ wasm_store_t *store = wasm_store_new(engine);
+ assert(store != NULL);
+ error = wasmtime_store_add_fuel(store, 10000);
+ if (error != NULL)
+ exit_with_error("failed to add fuel", error, NULL);
+
+ // Load our input file to parse it next
+ FILE* file = fopen("examples/fuel.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 wasm;
+ error = wasmtime_wat2wasm(&wat, &wasm);
+ if (error != NULL)
+ exit_with_error("failed to parse wat", error, NULL);
+ wasm_byte_vec_delete(&wat);
+
+ // Compile and instantiate our module
+ wasm_module_t *module = NULL;
+ error = wasmtime_module_new(engine, &wasm, &module);
+ if (module == NULL)
+ exit_with_error("failed to compile module", error, NULL);
+ wasm_byte_vec_delete(&wasm);
+ wasm_trap_t *trap = NULL;
+ wasm_instance_t *instance = NULL;
+ wasm_extern_vec_t imports = WASM_EMPTY_VEC;
+ error = wasmtime_instance_new(store, module, &imports, &instance, &trap);
+ if (instance == NULL)
+ exit_with_error("failed to instantiate", error, trap);
+
+ // Lookup our `fibonacci` export function
+ wasm_extern_vec_t externs;
+ wasm_instance_exports(instance, &externs);
+ assert(externs.size == 1);
+ wasm_func_t *fibonacci = wasm_extern_as_func(externs.data[0]);
+ assert(fibonacci != NULL);
+
+ // Call it repeatedly until it fails
+ for (int n = 1; ; n++) {
+ uint64_t fuel_before;
+ wasmtime_store_fuel_consumed(store, &fuel_before);
+ wasm_val_t params[1] = { WASM_I32_VAL(n) };
+ wasm_val_t results[1];
+ wasm_val_vec_t params_vec = WASM_ARRAY_VEC(params);
+ wasm_val_vec_t results_vec = WASM_ARRAY_VEC(results);
+ error = wasmtime_func_call(fibonacci, &params_vec, &results_vec, &trap);
+ if (error != NULL || trap != NULL) {
+ printf("Exhausted fuel computing fib(%d)\n", n);
+ break;
+ }
+
+ uint64_t fuel_after;
+ wasmtime_store_fuel_consumed(store, &fuel_after);
+ assert(results[0].kind == WASM_I32);
+ printf("fib(%d) = %d [consumed %lld fuel]\n", n, results[0].of.i32, fuel_after - fuel_before);
+
+ error = wasmtime_store_add_fuel(store, fuel_after - fuel_before);
+ if (error != NULL)
+ exit_with_error("failed to add fuel", error, NULL);
+ }
+
+ // Clean up after ourselves at this point
+ wasm_extern_vec_delete(&externs);
+ wasm_instance_delete(instance);
+ wasm_module_delete(module);
+ wasm_store_delete(store);
+ wasm_engine_delete(engine);
+ 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);
+ } else {
+ wasm_trap_message(trap, &error_message);
+ }
+ fprintf(stderr, "%.*s\n", (int) error_message.size, error_message.data);
+ wasm_byte_vec_delete(&error_message);
+ exit(1);
+}

examples/fuel.rs

@@ -0,0 +1,33 @@
+//! Example of limiting a WebAssembly function's runtime using "fuel consumption".
+
+// You can execute this example with `cargo run --example fuel`
+
+use anyhow::Result;
+use wasmtime::*;
+
+fn main() -> Result<()> {
+ let mut config = Config::new();
+ config.consume_fuel(true);
+ let engine = Engine::new(&config)?;
+ let store = Store::new(&engine);
+ store.add_fuel(10_000)?;
+ let module = Module::from_file(store.engine(), "examples/fuel.wat")?;
+ let instance = Instance::new(&store, &module, &[])?;
+
+ // Invoke `fibonacci` export with higher and higher numbers until we exhaust our fuel.
+ let fibonacci = instance.get_typed_func::<i32, i32>("fibonacci")?;
+ for n in 1.. {
+ let fuel_before = store.fuel_consumed().unwrap();
+ let output = match fibonacci.call(n) {
+ Ok(v) => v,
+ Err(_) => {
+ println!("Exhausted fuel computing fib({})", n);
+ break;
+ }
+ };
+ let fuel_consumed = store.fuel_consumed().unwrap() - fuel_before;
+ println!("fib({}) = {} [consumed {} fuel]", n, output, fuel_consumed);
+ store.add_fuel(fuel_consumed)?;
+ }
+ Ok(())
+}

examples/fuel.wat

@@ -0,0 +1,13 @@
+(module
+ (func $fibonacci (param $n i32) (result i32)
+ (if
+ (i32.lt_s (local.get $n) (i32.const 2))
+ (return (local.get $n))
+ )
+ (i32.add
+ (call $fibonacci (i32.sub (local.get $n) (i32.const 1)))
+ (call $fibonacci (i32.sub (local.get $n) (i32.const 2)))
+ )
+ )
+ (export "fibonacci" (func $fibonacci))
+)