Bug Report: Cannot Set Property Query Of #<IncomingMessage> Error When Using Express-mongo-sanitize

May 2, 2025 by ADMIN 100 views

Introduction

When working with Express.js applications, ensuring the security of user input is crucial to prevent common web vulnerabilities such as SQL injection and cross-site scripting (XSS). One effective way to achieve this is by using middleware that sanitizes user input. In this article, we will explore the issue of using the express-mongo-sanitize middleware in an Express.js application, which results in the error "Cannot set property query of # which has only a getter."

Problem Description

The express-mongo-sanitize middleware is designed to sanitize user input by removing any special characters that could be used to inject malicious code into a MongoDB database. However, when this middleware is added to an Express.js application, it throws an error on every request. The error message indicates that the query property of the IncomingMessage object cannot be set, as it has only a getter.

Installation and Setup

To reproduce this issue, you can install the express-mongo-sanitize middleware using npm:

npm install express-mongo-sanitize

Then, add the middleware to your Express.js application:

import express from 'express';
import mongoSanitize from 'express-mongo-sanitize';

const app = express();
app.use(mongoSanitize());

Expected Behavior

The expected behavior of the express-mongo-sanitize middleware is to sanitize the req.body, req.query, and req.params objects without throwing any errors. This ensures that user input is secure and cannot be used to inject malicious code into the database.

Current Behavior

However, when the middleware is added to the Express.js application, it throws the error "Cannot set property query of # which has only a getter" on every request. This error prevents the application from functioning correctly and requires immediate attention to resolve.

Debugging and Resolution

To resolve this issue, we need to understand the root cause of the problem. The error message indicates that the query property of the IncomingMessage object has only a getter, which means it cannot be set. This is because the express-mongo-sanitize middleware is trying to modify the query object, which is not allowed.

To fix this issue, we need to modify the middleware to use the req.query object instead of trying to set the query property of the IncomingMessage object. We can do this by creating a custom middleware function that sanitizes the req.query object:

import express from 'express';
import mongoSanitize from 'express-mongo-sanitize';

const app = express();

const sanitizeQuery = (req, res, next) => {
  req.query = mongoSanitize(req.query);
  next();
};

app.use(sanitizeQuery);

By creating a custom middleware function, we can sanitize the req.query object without trying to set the query property of the IncomingMessage object. This resolves the issue and allows the application to function correctly.

Conclusion

In conclusion, the express-mongo-sanitize can throw an error when used in an Express.js application, resulting in the "Cannot set property query of # which has only a getter" error. To resolve this issue, we need to create a custom middleware function that sanitizes the req.query object instead of trying to set the query property of the IncomingMessage object. By following the steps outlined in this article, we can ensure that our Express.js application is secure and functions correctly.

Troubleshooting Tips

Make sure to install the express-mongo-sanitize middleware using npm.
Add the middleware to your Express.js application using the app.use() method.
Create a custom middleware function to sanitize the req.query object.
Use the req.query object instead of trying to set the query property of the IncomingMessage object.

Related Issues

Example Use Cases

Sanitizing user input in an Express.js application to prevent SQL injection and XSS attacks.
Using the express-mongo-sanitize middleware to sanitize user input in a MongoDB database.
Creating a custom middleware function to sanitize user input in an Express.js application.

Code Snippets

Installing the express-mongo-sanitize middleware using npm:

npm install express-mongo-sanitize

Adding the middleware to the Express.js application:

import express from 'express';
import mongoSanitize from 'express-mongo-sanitize';

const app = express();
app.use(mongoSanitize());

Creating a custom middleware function to sanitize the req.query object:

const sanitizeQuery = (req, res, next) => {
  req.query = mongoSanitize(req.query);
  next();
};

app.use(sanitizeQuery);
```<br/>
**Q&A: Bug Report: Cannot set property query of #<IncomingMessage> error when using express-mongo-sanitize**
===========================================================

**Q: What is the express-mongo-sanitize middleware and why is it used?**
----------------------------------------------------------------

A: The `express-mongo-sanitize` middleware is a security tool used in Express.js applications to sanitize user input and prevent common web vulnerabilities such as SQL injection and cross-site scripting (XSS). It removes any special characters that could be used to inject malicious code into a MongoDB database.

**Q: What is the error "Cannot set property query of #<IncomingMessage> which has only a getter" and how is it related to express-mongo-sanitize?**
---------------------------------------------------------

A: The error "Cannot set property query of #<IncomingMessage> which has only a getter" is thrown when the `express-mongo-sanitize` middleware tries to set the `query` property of the `IncomingMessage` object. This is because the `query` property has only a getter, which means it cannot be set.

**Q: How can I resolve the error "Cannot set property query of #<IncomingMessage> which has only a getter" when using express-mongo-sanitize?**
---------------------------------------------------------

A: To resolve this issue, you need to create a custom middleware function that sanitizes the `req.query` object instead of trying to set the `query` property of the `IncomingMessage` object. You can do this by using the `mongoSanitize` function to sanitize the `req.query` object and then setting it as the `req.query` property.

**Q: What is the difference between the original express-mongo-sanitize middleware and the custom middleware function created to resolve the error?**
---------------------------------------------------------

A: The original `express-mongo-sanitize` middleware tries to set the `query` property of the `IncomingMessage` object, which has only a getter. The custom middleware function created to resolve the error sanitizes the `req.query` object and then sets it as the `req.query` property, which is allowed.

**Q: How can I ensure that my Express.js application is secure and functions correctly after resolving the error?**
---------------------------------------------------------

A: To ensure that your Express.js application is secure and functions correctly, you need to:

* Install the `express-mongo-sanitize` middleware using npm.
* Add the middleware to your Express.js application using the `app.use()` method.
* Create a custom middleware function to sanitize the `req.query` object.
* Use the `req.query` object instead of trying to set the `query` property of the `IncomingMessage` object.

**Q: What are some common use cases for the express-mongo-sanitize middleware?**
----------------------------------------------------------------

A: Some common use cases for the `express-mongo-sanitize` middleware include:

* Sanitizing user input in an Express.js application to prevent SQL injection and XSS attacks.
* Using the `express-mongo-sanitize` middleware to sanitize user input in a MongoDB database.
* Creating a custom middleware function to sanitize user input in an Express.js application.

**Q: What are some related issues that I should be aware of when using express-mongo-sanitize?**
----------------------------------------------------------------

A: Some related issues that you should be aware of when using `-mongo-sanitize` include:

* The `express-mongo-sanitize` middleware is not compatible with older versions of Express.js.
* The `express-mongo-sanitize` middleware may not work correctly with certain types of user input.
* The `express-mongo-sanitize` middleware may require additional configuration to work correctly.

**Q: Where can I find more information about express-mongo-sanitize and how to use it?**
----------------------------------------------------------------

A: You can find more information about `express-mongo-sanitize` and how to use it in the following resources:

* The official `express-mongo-sanitize` documentation.
* The Express.js documentation.
* The MongoDB documentation.

**Q: What are some code snippets that I can use to resolve the error and ensure that my Express.js application is secure?**
----------------------------------------------------------------

A: Here are some code snippets that you can use to resolve the error and ensure that your Express.js application is secure:

* Installing the `express-mongo-sanitize` middleware using npm:
```bash
npm install express-mongo-sanitize

Adding the middleware to the Express.js application:

import express from 'express';
import mongoSanitize from 'express-mongo-sanitize';

const app = express();
app.use(mongoSanitize());

Creating a custom middleware function to sanitize the req.query object:

const sanitizeQuery = (req, res, next) => {
  req.query = mongoSanitize(req.query);
  next();
};

app.use(sanitizeQuery);