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karlkras's avatar

Getting "Unexpected non-whitespace character... " in Lumen response.

Have an endpoint in a Lumen based rest service. Calls to this are occasionally resulting in a 31082:2 Uncaught (in promise) SyntaxError: Unexpected non-whitespace character after JSON at position 2

from the client's fetch call. How best to debug this? I suspect that the lumen code is somehow including garbage on the end of the json transmission, but it's not consistent... the call itself is working, but the data that it's returning is somehow and sometimes including garbage... since these aren't "printable" I can't "see" them. Any rule of thumb how best to figure out what the problem is?

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LaryAI's avatar
Level 58

The error message "Unexpected non-whitespace character after JSON at position 2" suggests that there is some non-JSON content being returned along with the JSON response. This could be caused by whitespace characters, HTML tags, or any other non-JSON content that is being output by the Lumen application.

To debug this issue, you can try the following steps:

  1. Check the response headers: Make sure that the response headers are correctly set to indicate that the response is JSON. You can do this by checking the "Content-Type" header in the response. It should be set to "application/json".

  2. Check the response body: Inspect the response body to see if there is any non-JSON content being returned along with the JSON response. You can do this by logging the response body to the console or using a tool like Postman to inspect the response.

  3. Check the Lumen code: Review the Lumen code that is generating the response to see if there are any issues with how the JSON response is being generated. Make sure that there are no stray echo statements or other output that could be causing the issue.

Here's an example of how to set the "Content-Type" header in a Lumen response:

return response()->json($data)->header('Content-Type', 'application/json');

If you're still having trouble identifying the issue, you can try using a tool like Xdebug to step through the code and see exactly what is being output at each step.

karlkras's avatar

@LaryAI Thanks, but if I hadn't had tried this already I wouldn't have posted this.

karlkras's avatar

Figured it out... there was a conditional echo statement in a very obscure function that was getting appended onto the response payload occasionally. Spent most of the day hunting this down.

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