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Asked: 2024-09-25T13:32:28+05:30

How can I alter the request bodies of network calls using a Chrome extension? I’m looking for guidance or examples on how to achieve this effectively.

I’ve been diving into Chrome extensions lately, and I’m super intrigued by the idea of altering the request bodies of network calls. I’ve seen some extensions do some really cool stuff, but I’m struggling to wrap my head around how I can make that happen for my own project.

Here’s what I’m trying to achieve: I want to create an extension that modifies the outgoing API requests from a website I use frequently. For instance, let’s say I’m interacting with a web app where I frequently submit forms. It would be amazing if my extension could automatically tweak some JSON data in the request body to include additional parameters, or even change existing ones. I could see this being useful for various use cases, like testing how the application responds to different inputs without needing to manually adjust everything each time.

I’ve done a bit of digging and found out about the `webRequest` API in Chrome, which seems to be the key to intercepting and modifying requests. However, I’m not entirely sure how to implement this effectively. Plus, I’m dealing with CORS issues; some requests I want to modify might get blocked due to that.

Has anyone here done something similar or can provide some insight? It would be awesome to get some pointers or examples to get me on the right track. What are the best practices for using the `webRequest` API? Are there any potential pitfalls I should be aware of? Also, any tips on handling CORS so I can actually intercept those requests without running into roadblocks would be super helpful.

I can already envision how powerful this could be, so I’m pretty eager to hear your thoughts and experiences. If you’ve built an extension that alters request bodies, how did you approach it? Any snippets or specific functions you found particularly useful would be a great addition! Thanks in advance, looking forward to your replies!

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    2 Answers



    1. Chrome Extension Help

      Modifying Request Bodies in Chrome Extensions

      So, you’re diving into Chrome extensions and want to modify the request bodies? That’s awesome! Using the `webRequest` API is definitely the way to go. 😄

      Here’s a quick rundown:

      • First, make sure to declare the necessary permissions in your manifest.json. You’ll need something like:
        • {
    "manifest_version": 3,
    "name": "Your Extension Name",
    "version": "1.0",
    "permissions": [
        "webRequest",
        "webRequestBlocking",
        "storage",
        "*://your-target-site.com/*"
    ],
    "background": {
        "service_worker": "background.js"
    }
}
      • Next, you’ll want to set up your background.js file to listen for requests and modify them. Here’s a simple example that shows how to intercept a specific request:
        • chrome.webRequest.onBeforeRequest.addListener(
    function(details) {
        // Modify the request body here
        let newData = JSON.stringify({
            ...JSON.parse(details.requestBody),
            newParam: 'newValue'
        });
        return {requestBody: newData};
    },
    {urls: ["*://your-target-site.com/api/*"]},
    ["blocking", "requestBody"]
);

      CORS Issues

      Dealing with CORS can be tricky! Make sure the website you’re targeting allows your extension to send those requests. You might need to add the URL in your permissions as shown above. If the server has CORS enabled, it should handle requests from your extension just fine.

      Best Practices

      • Always test your changes thoroughly. This is especially important when working with requests that could alter data on the server.
      • Be careful with the data you’re sending around. Sensitive data should be handled securely.
      • Check the Chrome extension documentation for updates, as things can change!

      Resources

      Check out the Chrome WebRequest API documentation for more details. It can be super helpful. 🛠️

      Hope that gives you a good start! Happy coding and don’t hesitate to reach out if you have more questions!


    2. To create a Chrome extension that modifies the outgoing API requests, you’ll want to leverage the `webRequest` API effectively. First, make sure to request the necessary permissions in your `manifest.json` file. You’ll need the “webRequest” and “webRequestBlocking” permissions to intercept and modify requests. You can listen for requests matching certain criteria using the `chrome.webRequest.onBeforeSendHeaders` event. Within your listener function, you can manipulate the request body by intercepting the `onBeforeRequest` event. This is where you can alter the `requestBody` property if it is specified, adding or modifying JSON parameters as needed for your use case. Here is a simple example of how to listen for such requests: 

          
      chrome.webRequest.onBeforeRequest.addListener(
        function(details) {
          if (details.method === "POST" && details.url.includes("your-api-endpoint")) {
            let modifiedBody = JSON.stringify({
              ...JSON.parse(details.requestBody.raw[0].bytes), // Spread the existing body
              newParam: "value" // Add new parameter
            });
            return {requestBody: {raw: [new Blob([modifiedBody])]}};
          }
        },
        {urls: [""]},
        ["blocking", "requestBody"]
      );

      Regarding CORS, you might encounter challenges when trying to make cross-origin requests, but you can handle it by correctly setting the `permissions` in your extension manifest and using a background script to manage the requests. Ensure your manifest file includes “host_permissions” for the URLs you intend to modify. If you find requests blocked due to CORS, it might be necessary to configure the external server to allow your extension by including necessary headers (like `Access-Control-Allow-Origin`). Additionally, consider using a proxy setup if modifying server responses becomes essential, as this can sidestep some of the restrictions imposed by CORS. Remember to test thoroughly, as excessive modifications or incorrectly implemented logic could lead to unexpected behaviors.