Nodejs shutdown handler

shutdown.ts

'use strict';
/* This module handles shutdown procedures to ensure a graceful shutdown

   - Function to register a shutdown callbacks
   - Call shutdown callbacks on uncaught promise rejections and signals
   - Call the exported setup() at the top of the bootup, usually in main.ts
 */

// import your logging code here
const log = (level, message) => {
    // This is a log shim. Adapt it to your logger
};

const error_types = ['unhandledRejection', 'uncaughtException']; // as NodeJS.UncaughtExceptionOrigin[];
const signal_traps = ['SIGTERM', 'SIGINT', 'SIGUSR2'] as NodeJS.Signals[];
const shutdown_handlers = [];

// This is called to register a shutdown handler. Call this from elsewhere so that
// cleanup code can be executed
export const registerShutdownHandler = (f: () => Promise<void>): void => {
    shutdown_handlers.push(f);
};

const triggerShutdownHandlers = async (): Promise<void> => {
    await Promise.all.forEach((x) => x() ));
    log("info", "All shutdown handlers have completed. Resuming exit");
};

export const shutdownNow = (reason: string, exit_code: number): Promise<void> => {
    try {
        log("info", `Receiving shutdown (reason: ${reason}). Starting shutdown.`);

        triggerShutdownHandlers().
            then(() => { process.exit(exit_code) }).
            catch((err) => {
                log("error", `Error during shutdown: ${err}`);
                process.exit(127);
            });
        } catch (_) {
            process.exit(128);
        }
    process.exit(exit_code);
};

// Custom error handler, because this also works with unhandled rejections
const handleErrors  = (...args) => {
    const err = args[0];
    try {
        log("warn", `Uncaught exception of unhandled rejection. Error (${err}) received. Starting graceful shutdown.`);
        triggerShutdownHandlers().
            then(() => { process.exit(1) }).
            catch((err) => {
                log("error", `Error during shutdown: ${err}`);
                process.exit(2);
            })
                } catch (_) {
                    process.exit(1);
                }
};

// Call this once during bootup, at the top of the bootup
export const setup = () => {
    log("info", "Setting up shutdown handlers");

    process.on("unhandledRejection", handleErrors);
    process.on("uncaughtException", handleErrors);

    signal_traps.forEach(type => {
        log("info", `Setting up signal trap ${type}`)
        process.once(type, (_signal) => {
            try {
                log("warn", `Signal ${type} received. Starting graceful shutdown`);
                triggerShutdownHandlers().
                    catch((err) => {
                        log("error", `Error during shutdown: ${err}`);
                    }).
                    finally(() => { process.kill(process.pid, type) }) // fire off the OS signal again

            } catch (err) {
                log("error", `Error during shutdown: ${err}`);
                process.exit(2); // Return a different exit code to indicate an error during graceful shutdown
            }
        })
    });
};