fix: connection string seed list parsing

closes: loopbackio#663

lib/mongodb.js

@@ -332,15 +332,12 @@ MongoDB.prototype.connect = function(callback) {
       if (callback) callback(err);
     }
 
-    const urlObj = new URL(self.settings.url);
-
-    if ((urlObj.pathname === '' ||
-        urlObj.pathname.split('/')[1] === '') &&
-        typeof self.settings.database === 'string') {
-      urlObj.pathname = self.settings.database;
-      self.settings.url = urlObj.toString();
+    // This is special processing if database is not part of url, but is in settings
+    if (self.settings.url && self.settings.database) {
+      if (self.settings.url.indexOf('/' + self.settings.database) === -1) {
+        self.settings.url = processMongoDBURL(self.settings.database, self.settings.url);
+      }
     }
-
     new mongodb.MongoClient(self.settings.url, validOptions).connect(function(
       err,
       client,
@@ -2120,6 +2117,105 @@ MongoDB.prototype.rollback = function(tx, cb) {
   });
 };
 
+exports.processMongoDBURL = processMongoDBURL;
+/**
+ * This method parses a Mongo connection url string and refers the formats
+ * specified at: https://www.mongodb.com/docs/manual/reference/connection-string/.
+ * Since there are cases where database is not specified in the url, but as a settings property,
+ * the code has to reflect that in the url otherwise the MongoDB driver defaults to 'admin' db.
+ * @param {string} settingsDatabase - the database that will be added if url doesn't have a db specified
+ * @param {string} mongoUrl - the url to be processed for database manipulation
+ */
+function processMongoDBURL(settingsDatabase, mongoUrl) {
+  // Reference: https://www.mongodb.com/docs/manual/reference/connection-string/
+  // Standard format:::  mongodb://[username:password@]host1[:port1][,...hostN[:portN]][/[defaultauthdb][?options]]
+  // DNS SeedList format::: mongodb+srv://server.example.com/?connectTimeoutMS=300000&authSource=aDifferentAuthDB
+  // Actual replicaset example::: mongodb://mongodb1.example.com:27317,mongodb2.example.com:27017/?connectTimeoutMS=300000&replicaSet=mySet&authSource=aDifferentAuthDB
+
+  if (mongoUrl) {
+    // 1. Know the protocol
+    let baseUrl = '';
+    if (mongoUrl.startsWith('mongodb:'))
+      baseUrl = 'mongodb://';
+    else if (mongoUrl.startsWith('mongodb+srv:'))
+      baseUrl = 'mongodb+srv://';
+    else if (mongoUrl.startsWith('loopback-connector-mongodb:'))
+      baseUrl = 'loopback-connector-mongodb://';
+    else if (mongoUrl.startsWith('loopback-connector-mongodb+srv:'))
+      baseUrl = 'loopback-connector-mongodb+srv://';
+    else
+      return mongoUrl; // Not a MongoURL that we can process
+
+    let remainderUrl = mongoUrl.substring(baseUrl.length);
+    // 2. Check if userId/password is present
+    let uidPassword = '';
+    if (remainderUrl.indexOf('@') !== -1) {
+      const parts = remainderUrl.split('@');
+      uidPassword = parts[0];
+      if (parts.length === 2)
+        remainderUrl = parts[1];
+      else
+        remainderUrl = '';
+    }
+    let hosts = '';
+    let dbName = '';
+    let options = '';
+    let hostsArray = [];
+    // 3. Check if comma separated replicas are specified
+    if (remainderUrl.indexOf(',') !== -1) {
+      hostsArray = remainderUrl.split(',');
+      remainderUrl = hostsArray[hostsArray.length - 1];
+    }
+
+    // 4. Check if authDB is specified in the URL
+    const slashIndex = remainderUrl.indexOf('/');
+    if ((slashIndex !== -1)) {
+      if (slashIndex !== (remainderUrl.length - 1)) {
+        const optionsIndex = remainderUrl.indexOf('?');
+        if (optionsIndex !== -1) {
+          options = remainderUrl.substring(optionsIndex + 1);
+          dbName = remainderUrl.substring(slashIndex + 1, optionsIndex);
+        } else {
+          // No DB options specified
+          dbName = remainderUrl.substring(slashIndex + 1);
+        }
+      }
+
+      if (hostsArray.length > 1) {
+        const newHosts = hostsArray;
+        newHosts.pop();
+        newHosts.push(remainderUrl.substring(0, slashIndex));
+        hosts = newHosts.join(',');
+      } else {
+        hosts = remainderUrl.substring(0, slashIndex);
+      }
+    } else {
+      // No database specified
+      if (hostsArray.length > 1)
+        hosts = hostsArray.join(',');
+      else
+        hosts = remainderUrl;
+    }
+
+    // 5. Reconstruct url, but this time add database from settings if URL didn't have it
+    // The below code has an overlap with generateMongoDBURL()
+    let modifiedUrl = baseUrl;
+
+    if (uidPassword)
+      modifiedUrl += uidPassword + '@';
+    if (hosts)
+      modifiedUrl += hosts;
+
+    modifiedUrl += '/' + (dbName ? dbName : settingsDatabase);
+
+    if (options)
+      modifiedUrl += '?' + options;
+
+    return modifiedUrl;
+  }
+  return mongoUrl;
+}
+
 function isInTransation(options) {
   const ops = {};
   if (options && options.transaction && options.transaction.isInTransation)