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How to safely get the file extension from a URL?

Consider the following URLs

http://m3u.com/tunein.m3u
http://asxsomeurl.com/listen.asx:8024
http://www.plssomeotherurl.com/station.pls?id=111
http://22.198.133.16:8024

Whats the proper way to determine the file extensions (.m3u/.asx/.pls)? Obviously the last one doesn't have a file extension.

EDIT: I forgot to mention that m3u/asx/pls are playlists (textfiles) for audio streams and must be parsed differently. The goal determine the extension and then send the url to the proper parsing-function. E.g. 


url = argv[1]
ext = GetExtension(url)
if ext == "pls":
  realurl = ParsePLS(url)
elif ext == "asx":
  realurl = ParseASX(url)
(etc.)
else:
  realurl = url
Play(realurl)
GetExtension() should return the file extension (if any), preferrably without connecting to the URL.

Solution

  • The real proper way is to not use file extensions at all. Do a GET (or HEAD) request to the URL in question, and use the returned "Content-type" HTTP header to get the content type. File extensions are unreliable.

    See MIME types (IANA media types) for more information and a list of useful MIME types.