Since 4611:2b6cb7528409 responses from the gzip static, flv, and mp4 modules can be used with subrequests, though empty files were not properly handled. Empty gzipped, flv, and mp4 files thus resulted in "zero size buf in output" alerts. While valid corresponding files are not expected to be empty, such files shouldn't result in alerts. Fix is to set b->sync on such empty subrequest responses, similarly to what ngx_http_send_special() does. Additionally, the static module, the ngx_http_send_response() function, and file cache are modified to do the same instead of not sending the response body at all in such cases, since not sending the response body at all is believed to be at least questionable, and might break various filters which do not expect such behaviour.
With introduction of open_file_cache in 1454:f497ed7682a7, opening a file with ngx_open_cached_file() automatically adds a cleanup handler to close the file. As such, calling ngx_close_file() directly for non-regular files is no longer needed and will result in duplicate close() call. In 1454:f497ed7682a7 ngx_close_file() call for non-regular files was removed in the static module, but wasn't in the flv module. And the resulting incorrect code was later copied to the mp4 module. Fix is to remove the ngx_close_file() call from both modules. Reported by Chris Newton.
ngx_open_file_info_t moved to a separate function. This is preparation for the "from=" parameter implementation of the "disable_symlinks" directive.
Used "\x5" in 5th byte to claim presence of both audio and video. Used previous tag size 0 in the beginning of the flv body (bytes 10 .. 13) as required by specification (see http://www.adobe.com/devnet/f4v.html). Patch by Piotr Sikora.