Module ngx_http_sub_module

The ngx_http_sub_module module is a filter that modifies a response by replacing one specified string by another.

This module is not built by default, it should be enabled with the --with-http_sub_module configuration parameter.

location / {
    sub_filter '<a href="/404.html'  '<a href="/404.html';
    sub_filter '<img src="http://127.0.0.1:8080/' '<img src="https://$host/';
    sub_filter_once on;
}

Sets a string to replace and a replacement string. The string to replace is matched ignoring the case. The string to replace (1.9.4) and replacement string can contain variables. Several sub_filter directives can be specified on the same configuration level (1.9.4). These directives are inherited from the previous configuration level if and only if there are no sub_filter directives defined on the current level.

sub_filter_last_modified off;

Allows preserving the “Last-Modified” header field from the original response during replacement to facilitate response caching.

By default, the header field is removed as contents of the response are modified during processing.

sub_filter_once on;

Indicates whether to look for each string to replace once or repeatedly.

sub_filter_types text/html;

Enables string replacement in responses with the specified MIME types in addition to “text/html”. The special value “*” matches any MIME type (0.8.29).