From 7dad00523ff53a9ad49730c3421b880bdaecc979 Mon Sep 17 00:00:00 2001
From: Mononaut <github@monospace.live>
Date: Mon, 28 Aug 2023 19:20:58 +0900
Subject: [PATCH] Implement pid file & checks

---
 backend/mempool-config.sample.json   |  3 ++-
 backend/src/__tests__/config.test.ts |  1 +
 backend/src/config.ts                |  2 ++
 backend/src/database.ts              | 29 ++++++++++++++++++++++++++++
 backend/src/index.ts                 | 14 ++++++++++++++
 docker/backend/mempool-config.json   |  3 ++-
 docker/backend/start.sh              |  2 ++
 7 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/backend/mempool-config.sample.json b/backend/mempool-config.sample.json
index 00fe95cc5..4bbf6cfad 100644
--- a/backend/mempool-config.sample.json
+++ b/backend/mempool-config.sample.json
@@ -68,7 +68,8 @@
     "DATABASE": "mempool",
     "USERNAME": "mempool",
     "PASSWORD": "mempool",
-    "TIMEOUT": 180000
+    "TIMEOUT": 180000,
+    "PID_DIR": ""
   },
   "SYSLOG": {
     "ENABLED": true,
diff --git a/backend/src/__tests__/config.test.ts b/backend/src/__tests__/config.test.ts
index 8097a2465..1a21cd99b 100644
--- a/backend/src/__tests__/config.test.ts
+++ b/backend/src/__tests__/config.test.ts
@@ -84,6 +84,7 @@ describe('Mempool Backend Config', () => {
         USERNAME: 'mempool',
         PASSWORD: 'mempool',
         TIMEOUT: 180000,
+        PID_DIR: ''
       });
 
       expect(config.SYSLOG).toStrictEqual({
diff --git a/backend/src/config.ts b/backend/src/config.ts
index ed320d957..9ded762fa 100644
--- a/backend/src/config.ts
+++ b/backend/src/config.ts
@@ -93,6 +93,7 @@ interface IConfig {
     USERNAME: string;
     PASSWORD: string;
     TIMEOUT: number;
+    PID_DIR: string;
   };
   SYSLOG: {
     ENABLED: boolean;
@@ -219,6 +220,7 @@ const defaults: IConfig = {
     'USERNAME': 'mempool',
     'PASSWORD': 'mempool',
     'TIMEOUT': 180000,
+    'PID_DIR': '',
   },
   'SYSLOG': {
     'ENABLED': true,
diff --git a/backend/src/database.ts b/backend/src/database.ts
index 6ad545fda..c27f28d23 100644
--- a/backend/src/database.ts
+++ b/backend/src/database.ts
@@ -1,3 +1,5 @@
+import * as fs from 'fs';
+import path from 'path';
 import config from './config';
 import { createPool, Pool, PoolConnection } from 'mysql2/promise';
 import logger from './logger';
@@ -101,6 +103,33 @@ import { FieldPacket, OkPacket, PoolOptions, ResultSetHeader, RowDataPacket } fr
     }
   }
 
+  public getPidLock(): boolean {
+    const filePath = path.join(config.DATABASE.PID_DIR || __dirname, `/mempool-${config.DATABASE.DATABASE}.pid`);
+    if (fs.existsSync(filePath)) {
+      const pid = fs.readFileSync(filePath).toString();
+      if (pid !== `${process.pid}`) {
+        const msg = `Already running on PID ${pid} (or pid file '${filePath}' is stale)`;
+        logger.err(msg);
+        throw new Error(msg);
+      } else {
+        return true;
+      }
+    } else {
+      fs.writeFileSync(filePath, `${process.pid}`);
+      return true;
+    }
+  }
+
+  public releasePidLock(): void {
+    const filePath = path.join(config.DATABASE.PID_DIR || __dirname, `/mempool-${config.DATABASE.DATABASE}.pid`);
+    if (fs.existsSync(filePath)) {
+      const pid = fs.readFileSync(filePath).toString();
+      if (pid === `${process.pid}`) {
+        fs.unlinkSync(filePath);
+      }
+    }
+  }
+
   private async getPool(): Promise<Pool> {
     if (this.pool === null) {
       this.pool = createPool(this.poolConfig);
diff --git a/backend/src/index.ts b/backend/src/index.ts
index 9d0fa07f5..a8af35d1c 100644
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -91,11 +91,18 @@ class Server {
   async startServer(worker = false): Promise<void> {
     logger.notice(`Starting Mempool Server${worker ? ' (worker)' : ''}... (${backendInfo.getShortCommitHash()})`);
 
+    // Register cleanup listeners for exit events
+    ['exit', 'SIGINT', 'SIGTERM', 'SIGUSR1', 'SIGUSR2', 'uncaughtException', 'unhandledRejection'].forEach(event => {
+      process.on(event, () => { this.onExit(event); });
+    });
+
     if (config.MEMPOOL.BACKEND === 'esplora') {
       bitcoinApi.startHealthChecks();
     }
 
     if (config.DATABASE.ENABLED) {
+      DB.getPidLock();
+
       await DB.checkDbConnection();
       try {
         if (process.env.npm_config_reindex_blocks === 'true') { // Re-index requests
@@ -306,6 +313,13 @@ class Server {
       this.lastHeapLogTime = now;
     }
   }
+
+  onExit(exitEvent): void {
+    DB.releasePidLock();
+    process.exit(0);
+  }
 }
 
+
+
 ((): Server => new Server())();
diff --git a/docker/backend/mempool-config.json b/docker/backend/mempool-config.json
index aa084133f..5642b36d3 100644
--- a/docker/backend/mempool-config.json
+++ b/docker/backend/mempool-config.json
@@ -69,7 +69,8 @@
     "DATABASE": "__DATABASE_DATABASE__",
     "USERNAME": "__DATABASE_USERNAME__",
     "PASSWORD": "__DATABASE_PASSWORD__",
-    "TIMEOUT": __DATABASE_TIMEOUT__
+    "TIMEOUT": __DATABASE_TIMEOUT__,
+    "PID_DIR": "__PID_DIR__",
   },
   "SYSLOG": {
     "ENABLED": __SYSLOG_ENABLED__,
diff --git a/docker/backend/start.sh b/docker/backend/start.sh
index 1bfb06c24..938a5c26f 100755
--- a/docker/backend/start.sh
+++ b/docker/backend/start.sh
@@ -71,6 +71,7 @@ __DATABASE_DATABASE__=${DATABASE_DATABASE:=mempool}
 __DATABASE_USERNAME__=${DATABASE_USERNAME:=mempool}
 __DATABASE_PASSWORD__=${DATABASE_PASSWORD:=mempool}
 __DATABASE_TIMEOUT__=${DATABASE_TIMEOUT:=180000}
+__DATABASE_PID_DIR__=${DATABASE_PID_DIR:=""}
 
 # SYSLOG
 __SYSLOG_ENABLED__=${SYSLOG_ENABLED:=false}
@@ -209,6 +210,7 @@ sed -i "s!__DATABASE_DATABASE__!${__DATABASE_DATABASE__}!g" mempool-config.json
 sed -i "s!__DATABASE_USERNAME__!${__DATABASE_USERNAME__}!g" mempool-config.json
 sed -i "s!__DATABASE_PASSWORD__!${__DATABASE_PASSWORD__}!g" mempool-config.json
 sed -i "s!__DATABASE_TIMEOUT__!${__DATABASE_TIMEOUT__}!g" mempool-config.json
+sed -i "s!__DATABASE_PID_DIR__!${__DATABASE_PID_DIR__}!g" mempool-config.json
 
 sed -i "s!__SYSLOG_ENABLED__!${__SYSLOG_ENABLED__}!g" mempool-config.json
 sed -i "s!__SYSLOG_HOST__!${__SYSLOG_HOST__}!g" mempool-config.json