Lua, memc and image_filter, image not resized via lua

[agentzh]

Hello!

On Fri, Sep 14, 2012 at 3:22 PM, agentzh <agentzh at gmail.com> wrote:
>
> This is because the standard ngx_image_filter module's output filter
> always runs *after* ngx_lua's subrequest capturing filter and there's
> no easy way to change this order. The response body of your subrequest
> is captured by ngx_lua *before* the ngx_image_filter's filter gets a
> chance to run.
>

BTW, I've also just written a command-line utility named
ngx-body-filters that can dump out all the output body filters of any
running Nginx worker processes (on Linux) in the order they actually
run.

This tool is part of my Nginx SystemTap Toolkit:

    https://github.com/agentzh/nginx-systemtap-toolkit#ngx-body-filters

For example, on my side, the nginx configured with both the ngx_lua
and ngx_image_filter modules will give me the following result:

    $ ./ngx-body-filters -p 30132
    Tracing 30132 (.../nginx/sbin/nginx)...

    ngx_http_range_body_filter
    ngx_http_copy_filter
    ngx_output_chain
    ngx_http_lua_capture_body_filter
    ngx_http_image_body_filter
    ngx_http_charset_body_filter
    ngx_http_ssi_body_filter
    ngx_http_postpone_filter
    ngx_http_gzip_body_filter
    ngx_http_chunked_body_filter
    ngx_http_write_filter

    113 microseconds elapsed in the probe handler.

where my nginx worker process pid is 30132.

>From this output, we can see clearly that
ngx_http_lua_capture_body_filter indeed runs before
ngx_http_image_body_filter.

So this tool is really handy in determining if there is an issue with
the nginx output filter running order, which is often not so obvious
for many users.

Best regards,
-agentzh