In this blog post, we will explore how to develop a custom middleware for the requests-html library in Python.

Introduction to requests-html

requests-html is a Python library that provides a convenient and powerful way to interact with websites, make HTTP requests, and parse HTML responses. It is built on top of the popular requests library and uses the pyppeteer library for HTML rendering.

By default, requests-html provides a set of middleware that allows modifying requests and responses. However, there may be situations where you need to implement custom functionality for handling requests or responses.

Setting up the Development Environment

Before we begin, make sure you have Python installed on your system. You can install requests-html using pip:

pip install requests-html

We also need to install the requests library:

pip install requests

Implementing a Custom Middleware

To implement a custom middleware for requests-html, we need to create a class that inherits from the BaseMiddleware class provided by the library. This class contains various methods that we can override to customize the behavior of the middleware.

Here’s an example of a custom middleware that adds a custom header to each request:

from requests_html import BaseMiddleware

class CustomMiddleware(BaseMiddleware):
    def __init__(self, header):
        super().__init__()
        self.header = header

    async def __call__(self, request):
        request.headers.update(self.header)
        response = await self.next_middleware(request)
        return response

In the example above, we define a CustomMiddleware class that takes a header dictionary as a parameter. In the __call__ method, we update the request headers with the custom header and then call the next_middleware method to pass the modified request to the next middleware in the chain.

Using the Custom Middleware

To use our custom middleware, we have to create an instance of it and add it to the requests-html session. Here’s an example:

from requests_html import HTMLSession

url = "https://example.com"
header = {"User-Agent": "Custom User-Agent"}

session = HTMLSession()
session.mount("https://", CustomMiddleware(header))
response = session.get(url)

In the example above, we create an instance of the HTMLSession class from requests-html. Then, we create an instance of our CustomMiddleware class and pass it the custom header. Finally, we mount the middleware to the session by calling the mount method.

Now, when we make requests using the session, our custom middleware will add the custom header to each request.

Conclusion

In this blog post, we learned how to develop a custom middleware for the requests-html library in Python. Custom middlewares allow us to modify requests and responses, enabling us to tailor the behavior of the library to our specific needs.

By implementing a custom middleware, we can extend the functionality of requests-html and customize its behavior to suit our use cases.