What to use for SSI/ESI like feature?

Hello,

I am working on a project where I need an SSI/ESI like feature. For full page cache I am now using the srcache-nginx-module with Redis and a PHP backend. There will be at least 3 blocks per page which I need whole-punched with something like SSI/ESI and these will also be cached.

SSI does not play well with Lua, on the other hand if I am using SSI with srcache_fetch only then it won't work on my sub-requests.

What would be a good (elegant and also performance wise) approach to replace SSI/ESI tags in both the backend and srcache_fetch responses? Liked replace-filter-nginx-module, but it does not support Lua replacements which I need.

I've done some research and testing, but none worked so far:

• Use a template engine - no buffer and how to process cached responses
• use body_filter_by_lua would fail when chunk ends in the middle of a placeholder

Thank you in advance!

Start by reviewing the issue's constraints around srcache_fetch, Redis-cached responses, SSI/ESI, and body_filter_by_lua, then compare them with replace-filter-nginx-module. The work is not scoped to a file or test; done would mean identifying or implementing an approach that replaces placeholders across backend and cached subrequest responses while supporting Lua replacements.