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Wasmer C API Example
#include <stdio.h>
#include "rust-build/src/wasmer-runtime-c-api/lib/runtime-c-api/wasmer.h"
#include <assert.h>
#include <stdint.h>
static print_str_called = false;
// Host function that will be imported into the Web Assembly Instance
void print_str(wasmer_instance_context_t *ctx, int32_t ptr, int32_t len)
{
print_str_called = true;
wasmer_memory_t *memory = wasmer_instance_context_memory(ctx, 0);
uint32_t mem_len = wasmer_memory_length(memory);
uint8_t *mem_bytes = wasmer_memory_data(memory);
printf("%.*s", len, mem_bytes + ptr);
}
// Use the last_error API to retrieve error messages
void print_wasmer_error()
{
int error_len = wasmer_last_error_length();
printf("Error len: `%d`\n", error_len);
char *error_str = malloc(error_len);
wasmer_last_error_message(error_str, error_len);
printf("Error str: `%s`\n", error_str);
}
int main()
{
// Create a new func to hold the parameter and signature
// of our `print_str` host function
wasmer_value_tag params_sig[] = {WASM_I32, WASM_I32};
wasmer_value_tag returns_sig[] = {};
wasmer_import_func_t *func = wasmer_import_func_new(print_str, params_sig, 2, returns_sig, 0);
// Create module name for our imports
// represented in bytes for UTF-8 compatability
char *module_name = "env";
wasmer_byte_array module_name_bytes;
module_name_bytes.bytes = module_name;
module_name_bytes.bytes_len = strlen(module_name);
// Define a function import
char *import_name = "_print_str";
wasmer_byte_array import_name_bytes;
import_name_bytes.bytes = import_name;
import_name_bytes.bytes_len = strlen(import_name);
wasmer_import_t func_import;
func_import.module_name = module_name_bytes;
func_import.import_name = import_name_bytes;
func_import.tag = WASM_FUNCTION;
func_import.value.func = func;
// Define a memory import
char *import_memory_name = "memory";
wasmer_byte_array import_memory_name_bytes;
import_memory_name_bytes.bytes = import_memory_name;
import_memory_name_bytes.bytes_len = strlen(import_memory_name);
wasmer_import_t memory_import;
memory_import.module_name = module_name_bytes;
memory_import.import_name = import_memory_name_bytes;
memory_import.tag = WASM_MEMORY;
wasmer_memory_t *memory = NULL;
wasmer_limits_t descriptor;
descriptor.min = 256;
wasmer_limit_option_t max;
max.has_some = true;
max.some = 256;
descriptor.max = max;
wasmer_result_t memory_result = wasmer_memory_new(&memory, descriptor);
if (memory_result != WASMER_OK)
{
print_wasmer_error();
}
memory_import.value.memory = memory;
// Define a global import
char *import_global_name = "__memory_base";
wasmer_byte_array import_global_name_bytes;
import_global_name_bytes.bytes = import_global_name;
import_global_name_bytes.bytes_len = strlen(import_global_name);
wasmer_import_t global_import;
global_import.module_name = module_name_bytes;
global_import.import_name = import_global_name_bytes;
global_import.tag = WASM_GLOBAL;
wasmer_value_t val;
val.tag = WASM_I32;
val.value.I32 = 1024;
wasmer_global_t *global = wasmer_global_new(val, false);
global_import.value.global = global;
// Define an array containing our imports
wasmer_import_t imports[] = {func_import, global_import, memory_import};
// Read the wasm file bytes
FILE *file = fopen("wasm-sample-app/target.wasm", "r");
fseek(file, 0, SEEK_END);
long len = ftell(file);
uint8_t *bytes = malloc(len);
fseek(file, 0, SEEK_SET);
fread(bytes, 1, len, file);
fclose(file);
// Creates a WebAssembly Instance from wasm bytes and imports
wasmer_instance_t *instance = NULL;
wasmer_result_t compile_result = wasmer_instantiate(&instance, bytes, len, imports, 3);
printf("Compile result: %d\n", compile_result);
if (compile_result != WASMER_OK)
{
print_wasmer_error();
}
assert(compile_result == WASMER_OK);
// Call the exported "hello_wasm" function of our instance
wasmer_value_t params[] = {};
wasmer_value_t result_one;
wasmer_value_t results[] = {result_one};
wasmer_result_t call_result = wasmer_instance_call(instance, "_hello_wasm", params, 0, results, 1);
printf("Call result: %d\n", call_result);
assert(call_result == WASMER_OK);
assert(print_str_called);
// Use *_destroy methods to cleanup as specified in the header documentation
wasmer_import_func_destroy(func);
wasmer_global_destroy(global);
wasmer_memory_destroy(memory);
wasmer_instance_destroy(instance);
return 0;
}
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