Solving the NextResponse.json Corruption Issue in Next.js API Routes

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The Problem

You fetch a response from an external service.

You modify one or more fields in the response data (in this case, changing an integer ID to a string).

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

Analyzing the Code

Let’s take a closer look at the key parts of the route handler that may contribute to this issue.

Example Route Handler

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

Investigating the Issue

Upon further testing and examination, it was found that the issue stems from reusing the original response headers, particularly the Content-Length header. Here’s why this is problematic:

When you modify the response body (by changing the ID), the length of the new body is different from the original.

By keeping the original headers, the Content-Length header remains unchanged, causing a mismatch that leads to the JSON parsing error.

The Solution

To address this, the solution is relatively straightforward:

Copy the Headers: Copy the response headers to a new Headers object.

Delete the Content-Length Header: This step is crucial because removing the Content-Length header allows the browser to recalculate the header based on the modified response body.

Here’s how you can implement the solution:

Updated Route Handler Code

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

What This Accomplishes

By making these changes:

The Content-Length header is removed, preventing mismatch errors.

The new response will now correctly reflect the modified body, allowing it to be parsed by the client without encountering errors.

Conclusion

Remember, always ensure that when you're modifying the response data in an API route, you handle the headers appropriately to maintain communication integrity with the client.

Feel free to share your thoughts or further questions in the comments below!