obfs2: Corrupted magic value '0xb312f1ad': Closing circuit

obfs2: Corrupted magic value '0xb312f1ad': Closing circuit

I've been getting a couple of messages like the above in my pyobfsproxy bridge. It seems that some obfs2 clients don't handle their encryption correctly. The bug seems to occur rarely, but it's a bug that must be solved.

The problem is that I haven't figured out whether it's a bug in pyobfsproxy or in obfsproxy yet. I've tried to reproduce the problem by firing up thousands of obfs2 clients (both pyobfsproxy and obfsproxy) but it doesn't happen.

(Bridges running obfsproxy won't throw such a warning, because they just silently close the circuit: https://gitweb.torproject.org/obfsproxy.git/blob/HEAD:/src/protocols/obfs2.c#l635 )

(Flagging this as an obfsproxy bug for now.)

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