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Learn how to handle and download chunked files in Node.js using Axios. This guide breaks down the step-by-step approach for successfully saving binary data to a file without corruption.
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How to Download Chunked Files with Node.js POST Requests

Downloading files using Node.js can sometimes present challenges, especially when dealing with chunked responses from an API. If you've ever tried saving a binary file and found that it just won't open, you're not alone. In this guide, we'll tackle a common issue related to downloading chunked files in Node.js using the Axios library and guide you through the solution step-by-step.

Understanding the Problem

You may receive binary files—like images—through an API. However, if the API sends data with the headers indicating chunked transfer-encoding, simply saving the body may lead to a corrupted file that cannot be opened. Here’s a brief rundown of what happens:

The API responds with headers indicating Transfer-Encoding: chunked, which means the data is sent in parts (or chunks).

You're trying to write this binary data to a file, but it results in a corrupted file that your image viewer cannot read, despite the file size appearing correct.

Key Headers to Note

Content-Type: Specifies the type of file (e.g., image/png).

Transfer-Encoding : Indicates that the response is sent in chunks.

Let’s Break Down the Solution

To download chunked files properly, you need to adjust how you're handling the response:

Step 1: Set the Correct Response Type

When you make your POST request using Axios, you need to specify the responseType in your request parameters. Setting this to 'stream' is crucial when dealing with chunked file transfers.

Here’s how to modify your code accordingly:

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Step 2: Save the Stream to a File

Instead of attempting to directly write the raw response data, you will utilize the .pipe() method to stream the data into a file. This method handles the incoming data effectively, ensuring that it is written correctly as it arrives.

[[See Video to Reveal this Text or Code Snippet]]

Key Takeaways from the Solution

Setting the response type to 'stream' allows Axios to handle the data correctly.

Using .pipe() ensures data is streamed and written to the file safely, preserving the file integrity.

Check for the finish event to know when the file has been completely written.

Conclusion

By following the above steps, you can effectively download chunked files using Node.js and Axios without the risk of file corruption. This method is essential for handling binary data correctly, especially when dealing with large files or when API responses come in chunks.

If you have further questions or need assistance, feel free to reach out. Happy coding!