Hello!

On Thu, Apr 22, 2021 at 04:51:59AM -0400, kkobylyanskiy wrote:

> I'm using Nginx as a reverse-proxy to cache my POST request and wrote the
> following config:

[...]

> proxy_cache_key "$request_uri|$request_body";

[...]

> client_body_buffer_size 512k;

[...]

> I'm getting the following error when trying so send a request for the second
> time after the first on is cached:
>
> [crit] 20#20: *2 cache file
> "/var/cache/nginx/6/fb/bee5677b8b46add7cfef279105773fb6" is too small
> I logged in to the container and verified that this file contains cached
> content.

This is not going to work, since cache header is limited to 64k
due to the unsigned short type being used in the on-disk format
for header_start and body_start offsets. The cache header
includes the cache key, which in you case can be up to 512k or
even larger.

Thanks for reporting this. This probably needs some explicit
checks to fail in an obvious way instead of silently producing
corrupted files and complaining later.

To make this work, consider either limiting the request body to
something less than 64k, or using a request body hash in the cache
key instead of the full request body. The latter can be done
using embedded perl or njs, see here:

http://nginx.org/r/perl_set
http://nginx.org/r/js_set

--
Maxim Dounin
http://mdounin.ru/
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