Undocumented circuit purpose: MEASURE_TIMEOUT
The CIRC event's Purpose spec is reused for CIRC_MINOR events...
https://gitweb.torproject.org/torspec.git/blob/HEAD:/control-spec.txt#l1291
Looks like the later can emit a MEASURE_TIMEOUT purpose which is undocumented (newlines added by me)...
650 CIRC_MINOR 7 PURPOSE_CHANGED
$67B2BDA4264D8A189D9270E28B1D30A262838243~europa1
BUILD_FLAGS=IS_INTERNAL,NEED_CAPACITY
PURPOSE=MEASURE_TIMEOUT
TIME_CREATED=2012-12-03T16:45:33.409602
OLD_PURPOSE=TESTING
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