The ssync Receiver performs some checks on request parameters
in initialize_request() before starting the exchange of missing
hashes and updates e.g. the destination device must be available;
the policy must be valid. Currently if any of these checks fails
then the receiver just closes the connection, so the Sender gets
no useful response code and noise is generated in logs by httplib
and wsgi Exceptions.
This change moves the request parameter checks to the Receiver
constructor so that the HTTPExceptions raised are actually sent
as responses. (The 'connection close' exception handling still
applies once the 'missing_check' and 'updates' handshakes are in
progress.)
Moving initialize_request() revealed the following lurking bug:
* initialize_request() sets
req.environ['eventlet.minimum_write_chunk_size'] = 0
* this was previously ineffective because the Response environ
had already been copied from Request environ before this value
was set, so the Response never used the value :/
* Now that it is effective (a good thing) it causes the empty string
yielded by the receiver when there are no missing hashes in
missing_checks() to be sent to the sender immediately. This makes
the Sender.readline() think there has been an early disconnect
and raise an Exception (a bad thing), as revealed by
test/unit/obj/test_ssync_sender.py:TestSsync.test_nothing_to_sync
The fix for this is to simply make the receiver skip sending the empty
string if there are no missing object_hashes.
Change-Id: I036a6919fead6e970505dccbb0da7bfbdf8cecc3
3aa06f185a