secur32: Handle incomplete schannel records on decryption.

secur32: Handle incomplete schannel records on decryption.

I pulled myself away from the richedit controls for a bit to track this down.

I found that the problem was with DencryptMessage being called with a data
buffer that contains incomplete records.  This will happen when a lot of data
is received at a time.  The schannel code in wine was handling this by letting
the partial record be pulled by libgnutls, so no decrypted data will be
returned for the partial record, but will be included in the data returned from
the following call to DecryptMessage.  This seems alright so far, but the
amount of data that can be returned for a call to DecryptMessage is limited to
the size of the buffer holding the encrypted data.  Once the buffer was filled
on a call to DecryptMessage, it would ignore the rest of the encrypted data
without notifying the caller in any way.  So the next DecryptMessage will try
to read the next record header, but will read from the wrong place, causing
errors that cause the disconnection.

The patch I submitted deals with this by not letting the pull function give
libgnutls a partial record for DecryptMessage, and then notifying the caller
about the unprocessed data by changing an empty buffer to a buffer fo type
SECBUFFER_EXTRA with a size field that gives the size of the unprocessed data.
This is documented on MSDN at
http://msdn.microsoft.com/en-us/library/aa375412(VS.85).aspx

Currently the test suites for schannel don't cover EncryptMessage or
DecryptMessage.  These tests should probably be implemented in order to make
sure this is implemented properly, but my patch at least seems to make Google
Talk happy.  Let me know if you still experience connection problems with this
patch applied.

http://bugs.winehq.org/attachment.cgi?id=23392
from
http://bugs.winehq.org/show_bug.cgi?id=3254