fix: add missing connection error handler in pool, resolving process crash

pg-pool requires attaching an error handler to each item checked out off the pool, which will
handle connection-level errors. Without it, the application straight-up crashes whenever the
connection is interrupted (e.g. database failover).

See brianc/node-postgres#1324

Signed-off-by: Quentin Machu <quentin@bitmex.com>

Author: Quentin-M

lib/postgresql.js

@@ -80,16 +80,7 @@ function PostgreSQL(postgresql, settings) {
   }
   this.clientConfig.Promise = Promise;
   this.pg = new postgresql.Pool(this.clientConfig);
-
-  if (settings.onError) {
-    if (settings.onError === 'ignore') {
-      this.pg.on('error', function(err) {
-        debug(err);
-      });
-    } else {
-      this.pg.on('error', settings.onError);
-    }
-  }
+  attachErrorHandler(settings, this.pg);
 
   this.settings = settings;
   debug('Settings %j', {
@@ -109,6 +100,18 @@ function PostgreSQL(postgresql, settings) {
   });
 }
 
+function attachErrorHandler(settings, pg) {
+  if (settings.onError) {
+    if (settings.onError === 'ignore') {
+      pg.on('error', function(err) {
+        debug(err);
+      });
+    } else {
+      pg.on('error', settings.onError);
+    }
+  }
+}
+
 // Inherit from loopback-datasource-juggler BaseSQL
 util.inherits(PostgreSQL, SqlConnector);
 
@@ -125,6 +128,10 @@ PostgreSQL.prototype.multiInsertSupported = true;
 PostgreSQL.prototype.connect = function(callback) {
   const self = this;
   self.pg.connect(function(err, client, releaseCb) {
+    // pg-pool requires attaching an error handler to each item checked out off the pool,
+    // which will handle connection-level errors.
+    // See https://github.com/brianc/node-postgres/issues/1324
+    attachErrorHandler(self.settings, client);
     self.client = client;
     process.nextTick(releaseCb);
     callback && callback(err, client);
@@ -194,6 +201,10 @@ PostgreSQL.prototype.executeSQL = function(sql, params, options, callback) {
   } else {
     self.pg.connect(function(err, connection, releaseCb) {
       if (err) return callback(err);
+      // pg-pool requires attaching an error handler to each item checked out off the pool,
+      // which will handle connection-level errors.
+      // See https://github.com/brianc/node-postgres/issues/1324
+      attachErrorHandler(self.settings, connection);
       executeWithConnection(connection, releaseCb);
     });
   }