Fix: Connection terminated unexpectedly error not caught in on error listener

lib/postgresql.js

@@ -103,11 +103,19 @@ function PostgreSQL(postgresql, settings) {
 function attachErrorHandler(settings, pg) {
   if (settings.onError) {
     if (settings.onError === 'ignore') {
-      pg.on('error', function(err) {
-        debug(err);
-      });
+      // Check if the error handler is already attached
+      // to avoid possible memory leak
+      if (!pg.listenerCount('error')) {
+        pg.on('error', function(err) {
+          debug(err);
+        });
+      }
     } else {
-      pg.on('error', settings.onError);
+      // Check if the error handler is already attached
+      // to avoid possible memory leak
+      if (!pg.listenerCount('error')) {
+        pg.on('error', settings.onError);
+      }
     }
   }
 }
@@ -165,8 +173,6 @@ PostgreSQL.prototype.executeSQL = function(sql, params, options, callback) {
       // Release the connection back to the pool.
       if (releaseCb) {
         releaseCb(err);
-        // Remove error event listener to avoid possible memory leak
-        connection.removeAllListeners('error');
       }
       let result = null;
       if (data) {

package.json

@@ -19,7 +19,8 @@
     "pretest": "node pretest.js",
     "test": "mocha test/*.test.js",
     "posttest": "npm run lint",
-    "lint": "eslint ."
+    "lint": "eslint .",
+    "lint-fix": "eslint . --fix"
   },
   "files": [
     "intl",
@@ -47,6 +48,7 @@
     "loopback-datasource-juggler": "^5.1.5",
     "mocha": "^11.0.0",
     "rc": "^1.0.0",
+    "rewire": "^8.0.0",
     "should": "^13.2.3",
     "sinon": "^21.0.0"
   }

test/postgresql.attachErrorHandler.test.js

@@ -0,0 +1,42 @@
+// Copyright IBM Corp. 2013,2025. All Rights Reserved.
+// Node module: loopback-connector-postgresql
+// This file is licensed under the Artistic License 2.0.
+// License text available at https://opensource.org/licenses/Artistic-2.0
+
+'use strict';
+const sinon = require('sinon');
+const assert = require('assert');
+const rewire = require('rewire');
+const postgresqlModule = rewire('../lib/postgresql');
+const attachErrorHandler = postgresqlModule.__get__('attachErrorHandler');
+
+describe('attachErrorHandler', function() {
+  let pg;
+  beforeEach(function() {
+    pg = {
+      on: sinon.spy(),
+      listenerCount: sinon.stub().returns(0),
+    };
+  });
+
+  it('should attach custom handler if onError is a function', function() {
+    const handler = sinon.spy();
+    const settings = {onError: handler};
+    attachErrorHandler(settings, pg);
+    assert(pg.on.calledOnce, 'pg.on should be called once');
+    assert(pg.on.firstCall.args[1] === handler, 'should attach the custom handler');
+  });
+
+  it('should not attach handler if already attached', function() {
+    pg.listenerCount.returns(1);
+    const settings = {onError: 'ignore'};
+    attachErrorHandler(settings, pg);
+    assert(pg.on.notCalled, 'pg.on should not be called if already attached');
+  });
+
+  it('should do nothing if onError is not set', function() {
+    const settings = {};
+    attachErrorHandler(settings, pg);
+    assert(pg.on.notCalled, 'pg.on should not be called if onError is not set');
+  });
+});