On Wed, 2011-02-09 at 14:31 +0200, Frank Millman wrote: > I am dabbling with writing an ajax-style app. On occasion, I want to send > more than one message from the client to the server. It is important that > the server processes the messages in the same order that they are generated. > I have found that the Safari browser does not always send them in the > correct sequence. > I found an article on the subject - > http://www.sitepen.com/blog/2009/02/27/deterministic-clientserver-interaction/ > It explains that you can never guarantee that the messages will arrive in > the same order, with *any* browser.
Correct. > Maybe I was lucky with the other ones. > It goes on to say that, if the order is important, you must include a header > with a sequential counter, and the server must check the sequence. Yep. This is similar to the If-Match headers used by HTTP (and especially WebDAV). > So the question is, how can I achieve this with wsgi? If I detect that I > have received a request out of sequence, I can queue the request, and send > an empty response. When I receive the correct request, I can process it, > call start_response(), and return the response body, but I cannot figure out > how to get back to process the queued request. I'd simply notify the client that the request could not be processed and have the client resend; this generally works much better than trying to "hold" the request on the server [what if the next one you expect never comes? what if you hit a different server due to DNS round-robin / clustering / etc...] If order is *very* important the client should perform each operation sequentially only sending the next-step when it has confirmation the previous ones have completed. This is really a client-side issue IMO. -- http://mail.python.org/mailman/listinfo/python-list
