This is how we’re able to produce just one Wasm binary that the Candid can be extracted from and that can be deployed to the IC:
Essentially we do this in the canister:
candid::export_service!();
// Heavily inspired by https://stackoverflow.com/a/47676844
#[no_mangle]
pub fn get_candid_pointer() -> *mut std::os::raw::c_char {
let c_string = std::ffi::CString::new(__export_service()).unwrap();
c_string.into_raw()
}
And we do this in Node.js during the build step:
import { readFileSync, writeFileSync } from 'fs';
export function generateCandidFile(candidPath: string, wasmFilePath: string) {
const wasmBuffer = readFileSync(wasmFilePath);
const wasmModule = new WebAssembly.Module(wasmBuffer);
const wasmInstance = new WebAssembly.Instance(wasmModule, {
ic0: {
accept_message: () => {},
call_cycles_add: () => {},
call_cycles_add128: () => {},
call_data_append: () => {},
call_new: () => {},
call_on_cleanup: () => {},
call_perform: () => {},
canister_cycle_balance: () => {},
canister_cycle_balance128: () => {},
canister_self_copy: () => {},
canister_self_size: () => {},
canister_version: () => {},
certified_data_set: () => {},
data_certificate_copy: () => {},
data_certificate_present: () => {},
data_certificate_size: () => {},
debug_print: () => {},
global_timer_set: () => {},
instruction_counter: () => {},
is_controller: () => {},
msg_arg_data_copy: () => {},
msg_arg_data_size: () => {},
msg_caller_copy: () => {},
msg_caller_size: () => {},
msg_cycles_accept: () => {},
msg_cycles_accept128: () => {},
msg_cycles_available: () => {},
msg_cycles_refunded: () => {},
msg_cycles_refunded128: () => {},
msg_method_name_copy: () => {},
msg_method_name_size: () => {},
msg_reject_code: () => {},
msg_reject_msg_copy: () => {},
msg_reject_msg_size: () => {},
msg_reject: () => {},
msg_reply_data_append: () => {},
msg_reply: () => {},
performance_counter: () => {},
stable_grow: () => {},
stable_read: () => {},
stable_size: () => {},
stable_write: () => {},
stable64_grow: () => {},
stable64_read: () => {},
stable64_size: () => {},
stable64_write: () => {},
time: () => {},
trap: () => {}
}
});
const candidPointer = (wasmInstance.exports as any).get_candid_pointer();
const memory = new Uint8Array((wasmInstance.exports.memory as any).buffer);
let candidBytes = [];
let i = candidPointer;
while (memory[i] !== 0) {
candidBytes.push(memory[i]);
i += 1;
}
writeFileSync(candidPath, Buffer.from(candidBytes));
}
.