fix: keep error messages for loose validation same as for strict validation (#22)

Author: addaleax

src/index.ts

@@ -174,7 +174,23 @@ export class ConnectionString extends URLWithoutHost {
     if (typeof password === 'string') authString += `:${password}`;
     if (authString) authString += '@';
 
-    super(`${protocol.toLowerCase()}://${authString}${DUMMY_HOSTNAME}${rest}`);
+    try {
+      super(`${protocol.toLowerCase()}://${authString}${DUMMY_HOSTNAME}${rest}`);
+    } catch (err: any) {
+      if (looseValidation) {
+        // Call the constructor again, this time with loose validation off,
+        // for a better error message
+        // eslint-disable-next-line no-new
+        new ConnectionString(uri, {
+          ...options,
+          looseValidation: false
+        });
+      }
+      if (typeof err.message === 'string') {
+        err.message = err.message.replace(DUMMY_HOSTNAME, hosts);
+      }
+      throw err;
+    }
     this._hosts = hosts.split(',');
 
     if (!looseValidation) {

test/index.ts

@@ -191,6 +191,16 @@ describe('ConnectionString', () => {
       expect(cs.port).to.equal('');
       expect(cs.href).to.equal('mongodb://:password@x/');
     });
+
+    it('throws good error messages for invalid URLs', () => {
+      try {
+        // eslint-disable-next-line no-new
+        new ConnectionString('-://:password@x', { looseValidation: true });
+        expect.fail('missed exception');
+      } catch (err: any) {
+        expect(err.message).to.equal('Invalid scheme, expected connection string to start with "mongodb://" or "mongodb+srv://"');
+      }
+    });
   });
 });