[BUG] ngx_http_sub_module fails to process single-char patterns

[Yichun Zhang (agentzh)]

Hello!

I've noted a bug in nginx 1.7.4's standard ngx_http_sub_module that
single-char patterns are never handled properly but longer patterns
work. Consider the following minimal example:

    location = /t {
        default_type text/html;
        return 200 "hello world";
        sub_filter 'h' '';
    }

Accessing /t gives the response body

    hello world

instead of the expected output

    ello world

The 'h' pattern is essentially ignored. Using longer patterns like
'he' in the example above works as expected though.

Best regards,
-agentzh