[vlc-devel] [PATCH] Add HLS output option to write index revisions as different files

[Chris Smowton]

Hi,

I attach a simple patch adding an option to the HTTP live streaming 
output module, setting it to record successive revisions of the playlist 
like:

/some/path/playlist.m3u8.00000000
/some/path/playlist.m3u8.00000001
etc.

As opposed to the existing (and still default) behaviour of overwriting 
a single file.

I made this change for my own use when writing HLS streams under Win32. 
This is because of two weaknesses of Win32's filesystem semantics:

1. vlc_rename is not atomic under Win32. Atomic replacement of a file is 
possible under Windows Vista and 7 using MoveFileTransacted, but not 
under earlier versions and possibly not under later versions (Microsoft 
are deprecating transactional NTFS for being too difficult to maintain). 
This non-atomic replacement of the m3u8 means that the file so produced 
is not suitable for serving directly with a web server on Win32, as 
users will occasionally fall into the gap between versions and get a 
404. Many clients will call that a fatal error.

Therefore my first plan was to serve the m3u8 under Win32 using a simple 
server-side wrapper script, which would retry reading as necessary to 
work around the lack of atomicity. However, this too causes problems 
because:

2. Under Win32, a file which still has open handles may not be deleted 
immediately after DeleteFile (or vlc_unlink here) is called. This means 
that if the webserver has an open handle against the m3u8 file (as it 
will if it's popular), the file will not disappear immediately and a 
subsequent rename operation will fail.

Therefore I wrote the attached patch; I have my server watch the 
directory for newer versions of the m3u8 file and serve the most recent 
version. No risk of a client 404, and each name is fresh so there's no 
risk of VLC stumbling over its own previous version of the playlist.

--Chris
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