HTTP headers causing exception in debug

KeyError exception experienced using asyncio, with txaio logging level at debug, when performing WAMP handshake.

A debug logging statement in asyncio.websocket.protocol.WebSocketServerProtocol.processHandshake receives the HTTP header dict cast to a string. This seems to be read as part of the formatting, causing a KeyError to be raised from the logger during interpolation, as the tokens visible between the braces are not present in kwargs.

Example output:

2016-03-01T15:17:02 Exception in callback WebSocketAdapterProtocol._consume.<locals>.process(<Future finished result=None>) at /usr/local/lib/python3.4/dist-packages/autobahn/asyncio/websocket.py:105

I tried to see where this had come in, but it seems to happen in master, and is not obvious following git blame back (at least to me!) - can bisect if desired. Also, not sure whether the preferred solution is to have the braces escaped or a dict passed.

Start at autobahn/websocket/protocol.py, in asyncio.websocket.protocol.WebSocketServerProtocol.processHandshake around line 3484, and inspect the debug logging statement that formats the HTTP header dictionary. Reproduce a WAMP handshake with txaio logging at debug level. Done means the handshake no longer raises KeyError while interpolating the logged headers.