Got Cancel Unrequested

[5618]

After enabling "log errors" in the Logger tab, I see this message showing up. I realize it's not a real/bad error, but I'm wondering what it and all suffixed info means.

[HH:nn:ss] peer.ip :[peer.client]: Got Cancel Unrequested: xxx:yyyyyy->zzzzz

So what does it mean and what do X, Y and Z indicate? Is this a peer canceling a (duplicate) request? No much of a clue regarding Y, Y and Z though.

[Saribro]

xx is the number of the piece

yy is the starting byte(?) in the requested piece

zz is the end byte in the requested piece

[5618]

That's strange because Z is always the same number (for the same torrent?) whereas X and Y are always different and Y can be much bigger than Z. E.g.:

X being the piece number would make sense.

[Stone]

z is requested block length in bytes.

[Saribro]

Ah yes, was too lazy to recheck my logs, my memory apparently sucks .

[5618]

So if we have X = piece number and Z = requested block length... that still leaves Y, since it obviously can't be the starting byte, because a) piece number and starting byte would be linearly correlated (not?) and the numbers just don't add up (compare 17:09:16a with 17:09:18; both are 0).

Plus the explanation of what the message as a whole means is still lacking.

[Saribro]

If you start from 0 on each piece (so relative adressing per piece as it were), Y as starting byte could still make sense, also note that all those Ys are integer multiples of Z.

[funchords]

So what does it mean [...] Is this a peer canceling a (duplicate) request?

It means that uTorrent got a CANCEL message that it cannot act on because it is not holding a REQUEST like that.

uTorrent UNCHOKES peers (allows them to make and receive requests) for a limited time, but the peers do not know what that time interval will be. When the time is up, uTorrent sends a CHOKE message.

When the CHOKE message is received, the peer will often send a CANCEL message for any REQUESTS that have not yet been filled.

Sometimes, uTorrent will send the CHOKE message at the same time that the peer sends a REQUEST message. And this is when things get interesting.

When uTorrent receives that REQUEST, it is ignored because uTorrent considers the peer as choked and is not allowed to make requests.

When the peer receives the CHOKE message, it sends a CANCEL message for outstanding requests (including the last one that crossed on the wire).

It is on those late messages that you see "Got Cancel Unrequested: xxx:yyyyyy->zzzzz." Since uTorrent did not process the REQUEST, it has no request in memory that corresponds with the peer's CANCEL message.

[Saribro]

Ah, thanks, good info.