$slice_range variable does not work in set directive.

[ptcong@…]

Hello,

I want to set proxy_cache_key dynamically with $cache_key variable.
It works fine with another variables, but with $slice_range this config does not work and give incorrect range from upstream.

set $cache_key "$another_var $blahblah $slice_range";
if ($something) {
set $cache_key "$cache_key new";
}

slice                   1m;
proxy_set_header        Range $slice_range;
proxy_cache_key $cache_key;

$slice_range only works when it's placed directly to proxy_cache_key as this:

slice                   1m;
proxy_set_header        Range $slice_range;
proxy_cache_key $old_cache_key$slice_range;

Is this a bug ?

[Roman Arutyunyan]

It is true $slice_range does not work with the rewrite module directives such as if and set. To fetch a slice, nginx creates a subrequest and sets the value of $slice_range accordingly. This subrequest does not go through normal request phases, but skips to the content phase. This means that if and set are ignored and your cache key remains the same for all slices.

You can still modify the cache key, but you need to escape using rewrite module directives. As an alternative, use volatile maps:

​http://nginx.org/en/docs/http/ngx_http_map_module.html#map

Example:

map $something $cache_key {                                                      
    volatile;                                                                
    1       'foo$uri$slice_range';                                           
    default 'bar$uri$slice_range';                                           
}

[maxim]

Ticket retargeted after milestone closed

[Maxim Dounin]

As explained in comment:1, the $slice_range is not expected to work in the rewrite module directives, including set.