[opensource-dev] ParcelAccessListReply packets have no reliable end of list indication?
josh at lindenlab.com
Mon Apr 19 17:42:32 PDT 2010
On Mon, Apr 19, 2010 at 5:07 PM, Argent Stonecutter
<secret.argent at gmail.com> wrote:
> Would that explain why the viewer sometimes appears to lose data (for
> example, spurious missing inventory), because it's got no way of
> knowing if some of the packets from the server were lost unless there
> were later packets? If so, that doesn't seem like a really good design
> for the viewer itself.
That's a completely different issue. The lower level transport
protocol guarantees reliable delivery of certain types of messages -
packets are ack'd and resent if missed. It's possible that there are
bugs in reliable message delivery (it is a non-standard protocol),
bugs in how they are handled if received out of order, and/or that the
messages you are referring to are not flagged for "reliable" delivery;
I'm not sure.
You can use the analogy of certified mail as the low level transport.
If you snail-mail me to ask a question (say, ask me for the draft of
my latest novel), and I snail-mail my my answer back in multiple
letters via certified mail (say, one chapter at a time), we can both
be certain they arrived (assuming we trust the postal service...), but
you have no idea how many to expect, so you can never be sure you got
them all... unless the last page says "The End".
(We're talking about old and - bluntly - crufty parts of the protocol
here. In general, new additions to the Second Life protocol are done
using HTTP(S) as a transport and RESTful semantics where they make
sense, which uses the operating system provided implementation of TCP
for reliable transport, optional TLS encryption, transport metadata
like content length, and overall structure of the message content in
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