[dcc2] Other comments

[codemastr]

> I don't think UDP is needed but it is available so I use it in
> examples. It wouldn't be hard to number all the UDP packets, assemble
> them in the file out-of-order, and check a hash or something I
> suppose. In a file transfer getting the packets in order is NOT a
> concern.
Well that depends on what you're doing. For example, say I'm transfering a
picture. In a web browser, the picture is displayed as it is downloaded (e.g
png files in IE). Well, if the packets are sent out of order, you can't do
that. However, if the packets are sent in order, having the image displayed
while it downloads would work just fine. And, based on some things I've
read, there are IRC clients that display images as they are downloaded
(though I've never found one that actually does it).

Additionally, this makes it inefficient. Since the packets are stored out of
order, this means you need to do one of three things. Either store the
unordered contents in memory,  store the unordered contents in a temporary
file, or treat the file as memory and reorder within the file. Then, when
the file is done, you can arrange it all, and in cases 1 and 2, either copy
from memory, or from the tmp file, to the actual file. Now for a 1KB file,
no big deal. But, what if I'm d/ling a 4GB file? Well, I don't have 4GB of
RAM for the program to store the unordered packets in memory. I don't want
to dedicate 8GB of disk space to receive a 4GB file, and I don't want the
tremendous speed decrease that reordering the packets within a 4GB file
would cause (Imagine the unlikely scenario where packet 45782 goes in
location 2). If the packets did not coincide with sector sizes, reordering
within the existing file could cause a great deal of overhead.

I agree, for some applications, UDP is useful. But, the way the draft is set
up, it can be used for ANY application. It doesn't mention anywhere in the
file send draft that "this Application requires TCP." So I don't think
saying other applications might need UDP is valid. That explains why UDP
should be supported by certain applications, not by all of them.

-- codemastr