prerelease artifact generator, for youtube sig

.gitignore

@@ -15,6 +15,7 @@ haruhi-dl.1
 haruhi-dl.bash-completion
 haruhi-dl.fish
 haruhi_dl/extractor/lazy_extractors.py
+haruhi_dl/extractor_artifacts/
 haruhi-dl
 haruhi-dl.exe
 haruhi-dl.tar.gz

devscripts/prerelease_codegen.py

@@ -0,0 +1,31 @@
+# this is intended to speed-up some extractors,
+# which sometimes need to extract some data that doesn't change very much often,
+# but it does on random times, like youtube's signature "crypto" or soundcloud's client id
+
+import os
+from os.path import dirname as dirn
+import sys
+sys.path.insert(0, dirn(dirn((os.path.abspath(__file__)))))
+
+from haruhi_dl import HaruhiDL
+from haruhi_dl.utils import (
+    ExtractorError,
+)
+
+hdl = HaruhiDL(params={
+    'quiet': True,
+})
+artifact_dir = os.path.join(dirn(dirn((os.path.abspath(__file__)))), 'haruhi_dl', 'extractor_artifacts')
+if not os.path.exists(artifact_dir):
+    os.mkdir(artifact_dir)
+
+for ie_name in (
+    'Youtube',
+):
+    ie = hdl.get_info_extractor(ie_name)
+    try:
+        file_contents = ie._generate_prerelease_file()
+        with open(os.path.join(artifact_dir, ie_name.lower() + '.py'), 'w') as file:
+            file.write(file_contents)
+    except ExtractorError as err:
+        print(err)

haruhi_dl/extractor/youtube.py

@@ -4,6 +4,7 @@ from __future__ import unicode_literals
 from datetime import datetime
 import json
 import hashlib
+from inspect import getsource
 import random
 import re
 import time
@@ -45,6 +46,10 @@ from ..utils import (
     urlencode_postdata,
     GeoRestrictedError,
 )
+try:
+    from ..extractor_artifacts.youtube import _decrypt_signature_protected
+except ImportError:
+    _decrypt_signature_protected = None
 
 
 class YoutubeBaseInfoExtractor(InfoExtractor):
@@ -901,7 +906,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             raise ExtractorError('Cannot identify player %r' % player_url)
         return id_m.group('id')
 
-    def _extract_signature_function(self, video_id, player_url, example_sig):
+    def _extract_signature_function(self, video_id, player_url):
         player_id = self._extract_player_info(player_url)
 
         # Read from filesystem cache
@@ -1012,31 +1017,44 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                 '    return %s\n') % (signature_id_tuple, expr_code)
         self.to_screen('Extracted signature function:\n' + code)
 
-    def mess(self, a, b):
+    @staticmethod
+    def mess(a, b):
         c = a[0]
         a[0] = a[b % len(a)]
         a[b % len(a)] = c
         return a
 
-    def _decrypt_signature_protected(self, s):
-        a = list(s)
-        a = self.mess(a, 49)
-        a = self.mess(a, 26)
-        a.reverse()
-        a = self.mess(a, 62)
-        a.reverse()
-        a = a[2:]
-        return "".join(a)
-
     def _full_signature_handling(self, sig, player_url, video_id):
-        signature = self._decrypt_signature_protected(sig)
+        signature = _decrypt_signature_protected(sig)
         if re.match(self._VALID_SIG_VALUE_RE, signature):
             return signature
         if self._downloader.params.get('verbose'):
             self.to_screen("Built-in signature decryption failed, trying dynamic")
-        sig_decrypt_stack = self._extract_signature_function(video_id, player_url, sig)
+        sig_decrypt_stack = self._extract_signature_function(video_id, player_url)
         return self._do_decrypt_signature(sig, sig_decrypt_stack)
 
+    def _generate_prerelease_file(self):
+        # It's Monday, so I'm in a bad mood, but at least my sailor uniform is super cute!
+        video_id = 'ieQ1rAIjzXc'
+        self._set_consent()
+        webpage = self._download_webpage('https://www.youtube.com/watch?v=%s' % video_id, video_id)
+        player_url = self._search_regex(r'"jsUrl":"(/s/player/.*?/player_ias.vflset/.*?/base.js)', webpage, 'player url')
+        sig_decrypt_stack = self._extract_signature_function(video_id, player_url)
+        func = re.sub(r'(?m)^    ', '', getsource(self.mess).replace('@staticmethod', ''))
+        func += '\n\ndef _decrypt_signature_protected(sig):\n'
+        stack = ['a = list(sig)']
+        for fun in sig_decrypt_stack:
+            if fun[0] == 'splice':
+                stack.append(f'a = a[{fun[1]}:]')
+            elif fun[0] == 'reverse':
+                stack.append('a.reverse()')
+            elif fun[0] == 'mess':
+                stack.append(f'a = mess(a, {fun[1]})')
+            else:
+                raise ExtractorError('Unknown stack action: %s' % (fun[0]))
+        stack.append("return ''.join(a)")
+        return func + '\n'.join(map(lambda x: ' ' * 4 + x, stack)) + '\n'
+
     def _get_subtitles(self, video_id, webpage):
         try:
             subs_doc = self._download_xml(