A DESCRIPTION OF THE PROBLEM :
The current partial support for 100 Continue is that if an Expect: 100-Continue header was sent in the request we automatically prepend the final response with the 100 Continue before the filters/handlers are called. This is obviously not helpful for code that really wants to do 100 continue the way it was intended. The sequence would normally be (for example):

Request. ---------------------------------->
      Content-Length: 10000000
      Expect: 100 Continue
Interim response <---------------------- 100 Continue
Request body ----------------------------->
FInal response headers <-----------------------
Response body <---------------------------

This can be resolved by moving the logic of autosending 100 to when the inputstream is actually read by the handler/filters