feat: videoplayback proxying

adds support for proxying videos through the instance
the support is configurable, and disabled by default

views.py

@@ -1,8 +1,8 @@
 #!/usr/bin/python3
-from flask import render_template, Response
+from flask import render_template, request, Response
 from flask_sqlalchemy import SQLAlchemy
 from markupsafe import escape
-import requests, json
+import json, re, requests
 import ythdd_globals
 
 def homepage():
@@ -78,4 +78,64 @@ def imgProxy(received_request):
 	thumbnail.raw.decode_content = True
 	response = Response(thumbnail.raw, mimetype=thumbnail.headers['content-type'], status=thumbnail.status_code)
 
-	return response
+	return response
+
+def videoplaybackProxy():
+	# inspired by Yotter's video proxy
+	# https://github.com/ytorg/Yotter/blob/b43a72ab7bfa5a59916fa3259cbc39165717c6bb/app/routes.py#L527
+
+	if not ythdd_globals.config['proxy']['allow_proxying_videos']:
+		return Response(json.dumps({"error": "Administrator has disabled this endpoint"}), mimetype="application/json", status=403)
+
+	headers = dict(request.headers)
+	proxy_headers = ythdd_globals.getHeaders(caller='proxy')
+	if "Range" in headers:
+		proxy_headers["Range"] = headers["Range"]
+
+	params = dict(request.args)
+
+	# reconstruct the url
+	# first attempt: from host param
+	host = params.get('host')
+	# failed? then try to get it from the rest of the params
+	if host is None:
+		# second attempt: reconstruct url from mn and mvi?
+		# the host schema seems to be as follows:
+		# rr{mvi[any]/fvip[any]?}---{mn[any]}.googlevideo.com
+		# regarding mvi/fvip, it seems that any value smaller than 5 passes
+		try:
+			mvi = params.get('mvi').split(',')[-1]
+			mn  = params.get('mn').split(',')[-1]
+			if int(mvi) > 5:
+				mvi = 3 # invidious uses this as fallback
+			host = f"rr{mvi}---{mn}.googlevideo.com"
+		except (AttributeError, ValueError):
+			return Response(json.dumps({"error": "Couldn't extract crucial parameters for hostname reconstruction"}, mimetype="application/json", status=400))
+	else:
+		# don't echo host "hint" back to the googlevideo server
+		del params['host']
+	# run a regex sanity check
+	if re.fullmatch(r"[\w-]+\.googlevideo\.com", host) is None:
+		# fallback behavior for unexpected hostnames
+		return Response(json.dumps({"error": "Please either pass a valid host, or don't pass any"}), mimetype="application/json", status=400)
+
+	try:
+		# request the proxied data
+		remote_response = requests.get(f"https://{host}/videoplayback", headers=proxy_headers, params=params, stream=True)
+	except:
+		return Response(json.dumps({"error": "Couldn't connect to googlevideo host"}), mimetype="application/json", status=500)
+
+	# determine the chunk size
+	chunk_size = 10 * 1024 # by default it's 10 MB (as this is the most youtube is willing to send without ratelimiting)
+	# or the one in initcwndbps (if user enabled the config flag to match chunk_size with initcwndbps)
+	if ythdd_globals.config['proxy']['match_initcwndbps']:
+		try:
+			chunk_size = int(params.get('initcwndbps')) / 1024
+		except:
+			pass
+	# return a chunked response
+	resp = Response(remote_response.iter_content(chunk_size=chunk_size), content_type=remote_response.headers['Content-Type'], status=remote_response.status_code, headers=remote_response.headers, direct_passthrough=True)
+	resp.cache_control.public = True
+	resp.cache_control.max_age = int(60_000)
+
+	return resp