Accessing DataSocket Server with Python

[Grant Edwards]

On 2015-05-29, William Ray Wing <wrw at mac.com> wrote:

> While that’s certainly possible in a routed network (and even then
> can be overridden with the “do not fragment” bit), it won’t happen in
> a LAN or self-contained instrument set-up.

You don't know that.

> These days, even routed networks tend to deliver anything less than a
> 1500 byte packet as a single entity.

Doesn't matter.

It can still happen in the network stack on either end.  If you
quickly call send() which small amounts of data, it's quite possible
that the network stack will combine them into a single packet.  Under
some conditions this is done intentionally to reduce the overall
network overhead.

On the receiving end, if several small packets are received between
calls to recv(), then a single call to recv() will return data from
multiple packets.

> With fiber backbones and high-speed LANs, it is more work for a
> router to fragment a packet then to simply pass it on.  The days of
> 480 byte packets pretty much went away with dial-up modems.

But modern TCP/IP stacks will still combine packets to save on network
overhead.

If you assume TCP read/write operations are atomic and "message"
boundaries are preserved, your code is wrong.  It will eventually
fail.  Period.

-- 
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