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import { fileURLToPath } from 'node:url';
import type { Logger } from '../../logger/definition.ts';
import { withLogger } from '../../logger/off-logger.ts';
import { withPrefix } from '../../logger/prefixed-logger.ts';
import type { Closer, SyncClosable } from '../common/closable.ts';
import { asClosable, createCloser, safeClose } from '../common/closable.ts';
import { exhaustiveCheck } from '../common/exhaustive-check.ts';
/**
* Indicates whether the current module is the main entry point of the running process.
*
* The first argument `moduleReference` is used to detect if the module invoking this method is the entry point of the
* process. The possible values are:
*
* - `import.meta.url` in ESM
* - `__filename` or `module.filename` in CommonJS
* - `undefined` if the application bundles the dependencies (or, at least, emitnlog)
*
* If it is not possible to know during development time how the code is distributed, use the following approach to
* determine the value of the argument:
*
* ```ts
* const moduleReference =
* typeof __filename === 'string'
* ? __filename
* : typeof import.meta === 'object' && import.meta.url
* ? import.meta.url
* : undefined;
* ```
*
* @example
*
* ```ts
* if (isProcessMain(import.meta.url)) {
* void main();
* }
* ```
*
* @param moduleReference `import.meta.url`, `__filename`, `module.filename`, or `undefined` as described above.
* @returns `true` when the current file started the process, otherwise `false`.
*/
export const isProcessMain = (moduleReference: string | URL | undefined) => {
if (testScope.processMain === true) {
return true;
}
const scriptPath = toPath(process.argv[1]);
Iif (!scriptPath) {
return false;
}
Iif (toPath(moduleReference) === scriptPath) {
return true;
}
Iif (typeof __filename === 'string' && toPath(__filename) === scriptPath) {
return true;
}
Iif (typeof import.meta === 'object' && toPath(import.meta.url) === scriptPath) {
return true;
}
return false;
};
const toPath = (value: string | URL | undefined): string | undefined => {
if (!value) {
return undefined;
}
Iif (typeof value !== 'string') {
value = value.toString();
}
if (value.includes('://')) {
value = fileURLToPath(value);
}
return resolve(value);
};
/**
* The input object passed to the `main` function of {@link runProcessMain}.
*/
export type ProcessMainInput = {
/**
* The start of the process.
*/
readonly start: Date;
/**
* A `Closer` instance that can be used to register cleanup operations.
*/
readonly closer: Closer;
/**
* A logger instance, either the one passed via the `options` parameter or the `OFF_LOGGER`.
*
* This logger is closed when the process ends.
*/
readonly logger: Logger;
};
/**
* Wraps the main entry point of a NodeJS process with automatic lifecycle management.
*
* This helper checks if the current module is the process entry point (via {@link isProcessMain}), and if so, executes
* the provided async function. Moreover,
*
* - If the function "fails" (throws or rejects), the process exits with code `1`.
* - If a logger is provided via the `options` parameter, it will be used to log the start and end of the process
* lifecycle, with the duration of the operation. This logger is closed when the applications exists.
*
* If the current module is not the main entry point, this function does nothing. This allows the same module to be
* safely imported elsewhere without side effects.
*
* The specified main method is invoked with an input object with the following properties:
*
* - `start`: The start `Date` of the process.
* - `closer`: A `Closer` instance that can be used to register cleanup operations, immediately before the process exits.
* - `logger`: A logger instance, either the one passed via the `options` parameter or the `OFF_LOGGER`.
*
* The first argument `moduleReference` is used to detect if the module invoking this method is the entry point of the
* process. The possible values are:
*
* - `import.meta.url` in ESM
* - `__filename` or `module.filename` in CommonJS
* - `undefined` if the application bundles the dependencies (or, at least, emitnlog)
*
* If it is not possible to know during development time how the code is distributed, use the following approach to
* determine the value of the argument:
*
* ```ts
* const moduleReference =
* typeof __filename === 'string'
* ? __filename
* : typeof import.meta === 'object' && import.meta.url
* ? import.meta.url
* : undefined;
* ```
*
* @example Simple usage (ESM):
*
* ```ts
* import { runProcessMain } from 'emitnlog/utils';
*
* runProcessMain(import.meta.url, async ({ start }) => {
* const args = process.argv.slice(2);
* console.log(`CLI started at ${start}`);
* // ... your application logic
* });
* ```
*
* @example Simple usage (CommonJS):
*
* ```ts
* import { runProcessMain } from 'emitnlog/utils';
*
* runProcessMain(__filename, async ({ start }) => {
* // ... your application logic
* });
* ```
*
* @example With a logger factory for startup logging:
*
* ```ts
* import { createConsoleErrorLogger, withPrefix } from 'emitnlog/logger';
* import { runProcessMain } from 'emitnlog/utils';
*
* runProcessMain(
* undefined,
* async ({ start, closer, logger }) => {
* logger.i`starting HTTP bridge...`;
* // ... your application logic
* },
* { logger: (start) => withPrefix(createConsoleErrorLogger(), `backend-${start.valueOf()}`) },
* );
* ```
*
* @param moduleReference `import.meta.url`, `__filename`, `module.filename`, or `undefined` as described above.
* @param main The async function to execute as the process entry point. Receives an input object as argument as
* described above.
* @param options Optional configuration.
*/
export const runProcessMain = (
moduleReference: string | URL | undefined,
main: (input: ProcessMainInput) => Promise<void>,
options?: {
/**
* A logger or a factory function that creates one. If a factory is provided, it receives the same start `Date`
* passed to the `main` method, to enable timestamp-based logger configuration.
*/
readonly logger?: Logger | ((start: Date) => Logger);
},
): void => {
if (isProcessMain(moduleReference)) {
const start = new Date();
const logger = withLogger(typeof options?.logger === 'function' ? options.logger(start) : options?.logger);
const closer = createCloser(logger);
logger.i`starting the process main operation at ${start}`;
void Promise.resolve()
.then(() => main({ start, closer, logger }))
.then(async () => {
const end = new Date();
logger.i`the process has closed at ${end} after ${end.valueOf() - start.valueOf()}ms`;
await safeClose(closer);
})
.catch(async (error: unknown) => {
const end = new Date();
logger.args(error)
.e`an error occurred and the process has closed at ${end} after ${end.valueOf() - start.valueOf()}ms`;
await safeClose(closer);
process.exit(1);
});
}
};
// Do not add 'exit':
// - Fires on every normal shutdown
// - Runs after the event loop is drained and Node forbids asynchronous work at that point.
export type ProcessExitSignal = 'SIGINT' | 'SIGTERM' | 'disconnect' | 'uncaughtException' | 'unhandledRejection';
export type ProcessExitEvent<S extends ProcessExitSignal = ProcessExitSignal> = S extends
| 'SIGINT'
| 'SIGTERM'
| 'disconnect'
? { readonly signal: S; readonly error?: undefined }
: { readonly signal: S; readonly error: unknown };
export type ProcessExitListener<S extends ProcessExitSignal = ProcessExitSignal> = (event: ProcessExitEvent<S>) => void;
/**
* Registers a listener that fires once when the process receives one of the `ProcessExitSignal` signals.
*
* All process signal handlers are cleared upon exit. Clients may close the returned closable to proactively unregister
* then.
*
* @example
*
* ```ts
* const subscribe = onProcessExit((event) => application.close(event.error), { logger });
*
* // if there is no need to monitor the process signals anymore...
* subscribe.close();
* ```
*
* @param listener Callback invoked with the exit event when the first configured signal fires.
* @param options
* @returns A synchronous closable to proactively unregister the listeners.
*/
export const onProcessExit = (
listener: ProcessExitListener,
options?: {
/**
* Alternative notifier implementing {@link ProcessNotifier} to replace the `process` instance.
*
* @default `process`
*/
readonly notifier?: ProcessNotifier;
readonly logger?: Logger;
},
): SyncClosable => {
const logger = withPrefix(withLogger(options?.logger), '', { fallbackPrefix: 'process-exit' });
const notificationProcess = options?.notifier ?? process;
let closable: SyncClosable | undefined = undefined;
const closeAndListen: ProcessExitListener = (event) => {
closable?.close();
listener(event);
};
closable = asClosable(
onProcessExitSignal('SIGINT', closeAndListen, notificationProcess, logger),
onProcessExitSignal('SIGTERM', closeAndListen, notificationProcess, logger),
onProcessExitSignal('disconnect', closeAndListen, notificationProcess, logger),
onProcessExitSignal('uncaughtException', closeAndListen, notificationProcess, logger),
onProcessExitSignal('unhandledRejection', closeAndListen, notificationProcess, logger),
);
return closable;
};
/**
* The subset of the NodeJS `process` interface required by {@link onProcessExit}.
*
* Provide a custom implementation (for example, a fake emitter in unit tests) via `options.notifier`.
*/
export type ProcessNotifier = {
once(eventName: ProcessExitSignal, listener: (...args: unknown[]) => void): void;
off(eventName: ProcessExitSignal, listener: (...args: unknown[]) => void): void;
};
const onProcessExitSignal = (
signal: ProcessExitSignal,
listener: ProcessExitListener,
notifier: ProcessNotifier,
logger: Logger,
): SyncClosable => {
const handler = (error: unknown) => {
switch (signal) {
case 'SIGINT':
case 'SIGTERM':
case 'disconnect':
logger.d`process exited with signal '${signal}'`;
listener({ signal });
break;
case 'uncaughtException':
case 'unhandledRejection':
logger.args(error).e`process exited with signal '${signal}' and error '${error}'`;
listener({ signal, error });
break;
default:
exhaustiveCheck(signal);
}
};
notifier.once(signal, handler);
return asClosable(() => {
logger.t`removing process signal handler for '${signal}'`;
notifier.off(signal, handler);
});
};
const testScope: {
/**
* Forces the value to be returned by {@link isProcessMain}, which is used by {@link runProcessMain}.
*/
processMain?: boolean | undefined;
} = {};
/**
* Internal export to be used on tests only.
*
* @example
*
* ```ts
* import inner from '../src/utils/node/process-lifecycle.ts';
*
* beforeEach(() => {
* inner[Symbol.for('@emitnlog:test')].processMain = true;
* });
*
* afterEach(() => {
* inner[Symbol.for('@emitnlog:test')].processMain = undefined;
* });
* ```
*
* @internal
*/
export default { [Symbol.for('@emitnlog:test')]: testScope } as const;
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