We introduced HTTP/2 support by default in #3506. This lead to two problems:

1. Connection to a local bot api instance without proxy leads to a broken connection, since the local api only supports HTTP/1.0 or HTTP/1.1. While this can be fixed by the user if they run a proxy in front of it which is capable of resolving HTTP/2 requests, this is an unnecessary strain to the end user. I propose the following:

   • whenever local_mode or http_version is called, check if the http is set to 2/local mode is set to true. If yes, raise a PTBUserWarning that this will probably not work out.
     • (maybe also when changing the URLs?)
   • when building, reset http to 1.1 if we still decide it should be 2 by default and if local mode is true. Don't do that if http is explicitly set to 2.
   • add a big note to the docs about all this to the http_version command

2. For two users in our report chat, the long polling getUpdates process broke. For now, we do not know why. I will try to see if I can get it to fail with curl or a different back-end over the coming days, but if I can't find the reason why/reproduce it reliable enough to report it to the api developer, we should consider changing our default to 1.1.

   Related traceback, courtesy of @Trifase https://nekobin.com/fuluyanoja.py

Workaround

If you're getting connection errors, such as the one in the traceback, add this to your builder:

builder.get_updates_http_version('1.1').http_version('1.1').build()