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adrelanos
Asked: 2022-12-16 09:32:51 +0800 CST

nginx: How to backup / duplicate nginx Cache-Control header?

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The backend server sets the Cache-Control HTTP header but the frontend might manipulate it. For debugging it would be useful to see the Cache-Control HTTP header as the backend had set it. Hence wondering, it it possible on the backend server to set custom (X-) header that contains the same value as Cache-Control?

I tried the following already:

more_set_headers "X-Backend-Cache-Control: $http_cache_control";

But that didn't work. No header has been added.

It's not an issue with more_set_headers. The following worked:

more_set_headers "X-Backend-Cache-Control: test";

A header was added. But that was just a simple test to see headers can be set at all and not useful obviously.

nginx

2 Answers

  1. Best Answer

    You're looking for the $sent_http_cache_control variable. This will contain the response's Cache-Control value, so:

    more_set_headers "X-Backend-Cache-Control: $sent_http_cache_control";
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  2. The $http_ variables contain HTTP headers from the HTTP request, as shown in nginx documentation.

    I don't know if there is a way to refer to HTTP response headers in nginx.

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