This function is orignally used for determining file extensions of DASH
formats. Now in DASH, ext is determined by mime_type. See #8766 for more
information.
This is much more robust than just using regexps, and handles all
the common scenarios, such as empty/no values, repeated attributes,
entity decoding, mixed case names, and the different possible value
quoting schemes.
1. Renamed to encode_base_n()
2. Allow tables longer than 62 characters
3. Raise ValueError instead of AssertionError for invalid input data
4. Return the first character in the table instead of '0' for number 0
5. Add tests
With cn_verification_proxy, our http_response() is called twice, one from
PerRequestProxyHandler.proxy_open() and another from normal
YoutubeDL.urlopen(). As a result, for proxies honoring Accept-Encoding, the
following bug occurs:
$ youtube-dl -vs --cn-verification-proxy https://secure.uku.im:993 "test:letv"
[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['-vs', '--cn-verification-proxy', 'https://secure.uku.im:993', 'test:letv']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2015.12.23
[debug] Git HEAD: 97f18fa
[debug] Python version 3.5.1 - Linux-4.3.3-1-ARCH-x86_64-with-arch-Arch-Linux
[debug] exe versions: ffmpeg 2.8.4, ffprobe 2.8.4, rtmpdump 2.4
[debug] Proxy map: {}
[TestURL] Test URL: http://www.letv.com/ptv/vplay/22005890.html
[Letv] 22005890: Downloading webpage
[Letv] 22005890: Downloading playJson data
ERROR: Unable to download JSON metadata: Not a gzipped file (b'{"') (caused by OSError('Not a gzipped file (b\'{"\')',)); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see https://yt-dl.org/update on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
File "/home/yen/Executables/Multimedia/youtube-dl/youtube_dl/extractor/common.py", line 330, in _request_webpage
return self._downloader.urlopen(url_or_request)
File "/home/yen/Executables/Multimedia/youtube-dl/youtube_dl/YoutubeDL.py", line 1886, in urlopen
return self._opener.open(req, timeout=self._socket_timeout)
File "/usr/lib/python3.5/urllib/request.py", line 471, in open
response = meth(req, response)
File "/home/yen/Executables/Multimedia/youtube-dl/youtube_dl/utils.py", line 773, in http_response
raise original_ioerror
File "/home/yen/Executables/Multimedia/youtube-dl/youtube_dl/utils.py", line 761, in http_response
uncompressed = io.BytesIO(gz.read())
File "/usr/lib/python3.5/gzip.py", line 274, in read
return self._buffer.read(size)
File "/usr/lib/python3.5/gzip.py", line 461, in read
if not self._read_gzip_header():
File "/usr/lib/python3.5/gzip.py", line 409, in _read_gzip_header
raise OSError('Not a gzipped file (%r)' % magic)
