[Twisted-Python] Streaming File Transfer Protocol?

Darren Govoni darren at ontrenet.com
Wed Feb 10 18:34:09 EST 2010

Thanks for that explanation David. Makes sense! 

On Wed, 2010-02-10 at 16:01 -0500, David Bolen wrote:

> Darren Govoni <darren at ontrenet.com> writes:
> >>From what I learned in other posts, the dataReceived(self, data): in the
> > Echo server
> > will get called with out-of-order data/bytes from the client. Of course,
> > I could be misinformed,
> > but what I understood before was that in this type of Protocol, I would
> > have to re-order
> > and re-assemble the bytes.  And I'm trying to avoid that, since of
> > course, TCP already does it.
> Data being received out of order can't happen, as long as the Protocol
> is layered on top of TCP, since as you say, TCP already provides that
> guarantee.  The dataReceived() method is really just how the data
> being received from TCP is handed to the Protocol object.
> UDP can be out of order, as it provides very few guarantees above and
> beyond IP itself.  But I'm not sure you can layer an IProtocol over
> UDP with Twisted.
> There is a general issue where you may receive the data in differently
> sized chunks in dataReceived() than it might have been transmitted
> originally, which is a common source of confusion to people new to
> stream protocols, so perhaps you were thinking of that issue?
> The stream nature (and possibility for early disconnect from the
> client) is why having some internal length information for bulk
> transfers is sensible.  For your original question, I was going to
> suggest an older posting of mine for a similar situation where I needed
> a bulk upload to augment a PB-based server, but it appears that you've
> located it in the archives yourself.
> > But like I said, I could have been misinformed because it seems pretty
> > basic to write 1,2,3
> > to a server and have it received 1,2,3, guaranteed.
> Yes - TCP guarantees that what you transmit at one end will be
> received in order at the other end or not at all (e.g., outages,
> disconnects, etc...).  It has a weaker guarantee in terms of no
> corruption, but one that is, in combination with typical link layer
> protections, generally more than sufficient for the vast majority of
> connections using it each day.
> -- David
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