ExceptionSourceFilter does not properly attribute CancelledRequestExceptions

[jcohen]

ExceptionSourceFilter does not properly attribute CancelledRequestExceptions

Expected behavior

The source should be attributed to the client (or at least not to the downstream service)

Actual behavior

When a future is cancelled by a client, the source is still attributed to the downstream service. This leads to confusion when the error message is along the lines of:

com.twitter.finagle.CancelledRequestException: request cancelled. Remote Info: Upstream Address: Not Available, Upstream id: Not Available, Downstream Address: my.downstream.host/X.X.X.X:443, Downstream label: my.downstream.host:443, Trace Id: efdec7e41b7c30fa.d535d24f770f3fa8<:efdec7e41b7c30fa

even though the downstream was not involved in the request at all.

Steps to reproduce the behavior

Cancel a future and observe the attribution from ExceptionSourceFilter.

[mosesn]

To elaborate on @jcohen's problem, his topology looks like A => B => C, and sees the exception on B. This is when A cuts the connection to B, but the exception says that the downstream was C. It should instead report that the downstream was B.