HS Extension Length = 0

[kierank]

libsrt doesn't seem to like it too much if you set HS Extension Length = 0 (e.g for stream ID). The spec should clarify this is not allowed.

[maxsharabayko]

I would say, given (until) there is no HS extension assuming or allowing its length to be zero, having the HS Extension Length = 0 means the handshake is invalid (as of now).
In case of further protocol evolution, the spec should probably allow zero HS extension length for certain extension types.
The tricky question is what to do with extension type not known to a certain protocol version: treat as invalid and reject or ignore?