Hi Commoncpp developer,

 

Playing around commoncpp 1.6.3 code, I met some behavior under following
scenario, which I believe as buggy:

 

1.       Peer A and peer B enter a tcp session

2.       A sends some contents to B; if no error is reported (tcp
subsystem agree to take over whatever needs to be done to deliver), A
closes and exit

3.       meanwhile, in a loop, peer B receive byte streams through the
TCPStream::read, after which follows a call of TCPStream::gcount() to
know how many bytes the previous read() has read in - a exit condition
for the loop is gcound() returns 0, indicating tcp stream has nothing to
read and should be closed to release this tcp resource.

 

Here comes the bug: the last TCPStrteam::read() actually reads some
bytes before its underlying (socket) read returns 0. The 0 return value
would immediately call clear(ios::failbit | rdstate() ) (line 2911,
src/csocket.cpp, commoncpp-1.6.3), which in turn resets gcount internal
data structure _M_gcount to 0, causing the subsequent
TCPStream::gcount() returns the incorrect 0.

 

For a socket read to return 0 is quite normal and legitimate when the
peer send FIN and enters the so-called half-close state.
TCPStream::read() actually reads correctly all the byte stream that
might be queued, but the TCPStream::gcount returning 0 subsequently is
definitely conflicting what is expected from a read/gcound with an
istream object.

 

Hope this description serves its purpose well.

 

Regards,

 

Howell Chen



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