JSON-LD with "@context": "https://schema.org" not parsed by `_json_ld` function

[aeph6Ee0]

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The Problem

The way the @context property of a JSON-LD string is checked it too strict. Currently @context has to be exactly the string http://schema.org in order to be parsed by the _json_ld function in common.py. However, some websites have http changed to https. I also saw websites adding a / to the end like so: http://schema.org/.
This leads to the problem, that JSON-LD strings of those websites do not get parsed, which cause video extraction errors, since _json_ld then returns an empty dictionary. (See below for an example.)

Suggested Fix

In order to solve the problem, I suggest to make the check for the @context property more resiliant. Instead of checking against a static string...

https://github.com/rg3/youtube-dl/blob/5d60b9971784289acd4325a8ed7b5afd7bea05ca/youtube_dl/extractor/common.py#L1028

we should use a regex that allows the above mentioned modification of the string:

if re.match(r'^https?://schema.org/?$', e.get('@context')):

This small change already fixes the currently broken gamestar.py extractor. Additionally, no existing extractor can be affected in a negative way, e.g, no extractor will get broken through this change.

Please let me know, if I should open a pull request myself.

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Example

An example of an extractor that fails because of not parsed JSON-LD is gamestar.py. Please note, that 'KeyError' occurs only because the info_dict is empty, since the self._json_ld function didn't parse anything. Here, there is a https instead of http used in the @context property.

# python -m youtube_dl -v http://www.gamestar.de/videos/trailer,3/hobbit-3-die-schlacht-der-fuenf-heere,76110.html
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', 'http://www.gamestar.de/videos/trailer,3/hobbit-3-die-schlacht-der-fuenf-heere,76110.html']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2018.03.26.1
[debug] Git HEAD: 5d60b9971
[debug] Python version 3.6.4 (CPython) - Linux-4.15.7-1-ARCH-x86_64-with-arch
[debug] exe versions: ffmpeg 3.4.2, ffprobe 3.4.2
[debug] Proxy map: {}
[GameStar] 76110: Downloading webpage
ERROR: An extractor error has occurred. (caused by KeyError('title',)); 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.
Traceback (most recent call last):
  File "/home/user/youtube-dl/youtube_dl/extractor/common.py", line 440, in extract
    ie_result = self._real_extract(url)
  File "/home/user/youtube-dl/youtube_dl/extractor/gamestar.py", line 50, in _real_extract
    info_dict['title'], ' - Game%s' % site.title())
KeyError: 'title'
Traceback (most recent call last):
  File "/home/user/youtube-dl/youtube_dl/extractor/common.py", line 440, in extract
    ie_result = self._real_extract(url)
  File "/home/user/youtube-dl/youtube_dl/extractor/gamestar.py", line 50, in _real_extract
    info_dict['title'], ' - Game%s' % site.title())
KeyError: 'title'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/user/youtube-dl/youtube_dl/YoutubeDL.py", line 785, in extract_info
    ie_result = ie.extract(url)
  File "/home/user/youtube-dl/youtube_dl/extractor/common.py", line 453, in extract
    raise ExtractorError('An extractor error has occurred.', cause=e)
youtube_dl.utils.ExtractorError: An extractor error has occurred. (caused by KeyError('title',)); 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.