Bug #4184


Issues/observations related to DCC

Added by Paul Janson over 5 years ago. Updated over 4 years ago.

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making sure there's no download file and create dummy file:
//remove downloads\test2.txt | btrunc test2.txt 0 | bwrite test2.txt 4095 1 t | echo -a size $file(test2.txt).size

Create an event to monitor what's happening with the DCC:

CTCP :*::echo s ctcp from $nick : $1

Bug1: The menu says "ON CTCP" even though there's no 'ON'. Ditto with "ON RAW".

Send to self:
//dcc send $me test2.txt

DCC Send of test2.txt to self complete (00:00:00 24.69KB/Sec)
DCC Get of test2.txt from self complete (00:00:00 249.99KB/Sec)

Bug2: DCC send/resume should trigger the CTCP event, but did not.
Bug3: I'm having trouble replicating the cause, but I ended up with a test1.txt which didn't allow writing to it nor could Windows Explorer delete it. Once this happened, of course /bwrite fails to write to it, and /btrunc can't change the filesize either. However there is no error message, and there's nothing that halts the next next command from executing. There is an error when /write /remove or /rename try to mess with it.

change dummy size smaller:
//bwrite -c test2.txt 2047 1 33 | echo -a size $file(test2.txt).size

fix: add -c switch to the TODO list, filesize still 4096

Other related issues with handling of DCC protocol.

1. If incoming file is same filesize as the file you already have, should it really do a DCC RESUME so it can ask for the last 8kb of the file? Best case scenario is that you receive data identical to the last 8192 bytes of the existing image.jpg of the same filesize, and the file is not changed other than updating the timestamp. The alternative is that the incoming file is coincidentally the same filename/filesize as a file you already have but a different image, so a valid image gets the final 8kb replaced with the content of a different image.

To avoid having the sender think you were rejecting the file, or had problems accepting files, instead of resuming an identical filesize, it could 'lie' to the sender and say it received the DCC ok but really does nothing. Like it does when the incoming file is larger than the existing file.

2. If the file in the download folder has filesize 0-8192, it requests a dcc-resume at offset zero. Would it be reasonable for the client to just do a normal ACCEPT, then if the transfer begins successfully, just replace the content beginning at the start of the file. It's even doing a dcc-resume at offset zero if the existing file is size zero. My prior ISP caused a problem where sometimes the port changed somewhere outside the client, which meant normal DCC worked fine, but which caused all dcc-resume to fail because the port was unknown. In the case of size 8192 or smaller, this seems wasted handshaking when the successful DCC does the same thing as if the DCC overwrites the existing filename entirely.

I know DCC's not supposed to truncate the file unless the transfer actually begins, otherwise someone could delete your small file or else snip 8kb from the tail end just by starting a DCC then failing.

3. I'm assuming the reason for resuming the last 8192 of a file was in case the last packet of the transfer was corrupted, to either to make sure to repeat the last full packet when packet size was 4096, or because 8192 used to be the max valid packetsize. However now that packet sizes of up to 64k are allowed, should this 8192 also be configurable too? Either allowing it to be zero to not repeat anything, or to have it be 100% or 200% of whatever your configured dcc-get packetsize is? i.e. if I change my packet size to 65536, resuming at 8192 below the existing filesize doesn't make sense, since that's retrieving only 1/8th of a packet. Related to #1 above, I'm not sure if packets being corrupted would happen when a transfer reports to both sides that it was successful at 100% of filesize.


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