Disable the ability to create torrents with a piece size of 256MiB

[stalkerok]

Disabling will reduce the number of users experiencing this issue.

• Crash when checking torrent with piece size of 256.0 MiB #21011

[Chocobo1]

Please add description of "why" is it done.

[stalkerok]

Done.

[xavier2k6]

What needs to be done really IMO is for libtorrent 1.2.x to reject those torrents from actually being loaded.

[stalkerok]

What will happen to the torrents already added? And like I said, 2.0 also has an issue (at least with creating torrents, but I think with rehash too) with the 512MB and 1GB piece size. Maybe for 2.0 this has already been fixed, I don't know.

[stalkerok]

Can this be merged and added to the backport to 5.0?

[xavier2k6]

What will happen to the torrents already added?

• Will load/re-check fine with libtorrent 2.x based builds (currently)
• Will load fine but will crash when re-checked with libtorrent 1.x based builds (currently)
• Advise users to migrate to libtorrent 2.x based builds

And like I said, 2.0 also has an issue (at least with creating torrents, but I think with rehash too) with the 512MB and 1GB piece size.

Creation of torrents >256MiB in qBittorrent (LT20) was blocked/limited intentionally.

#21011 & other tickets showed that even if we reduced the ability in qBittorrent to create torrents with a piece size of 256MiB, there are programs/options to force creation of such large piece size.

---

py3createtorrent was used to create & indeed highlight the issue experienced in previously mentioned crash reports.

Plan should be:

• libtorrent 1.2.x to reject unsupported torrents from actually being loaded. ie it can create MAX 128MiB, so should limit to loading <=128MiB
• libtorrent 2.x to reject unsupported torrents from actually being loaded. ie it can create MAX 256MiB, so should limit to loading <=256MiB

[stalkerok]

Wouldn't it be better to just temporarily limit torrent creation to 256MiB torrents in 2.0 until lt 1.2 is fixed?

[glassez]

1. I agree with @xavier2k6. It doesn't make much sense to only prevent the creation of such torrents without preventing such torrents from being added to session.
2. Since libtorrent-2.0 works correctly with 256MB piece size we can safely allow qBittorrent to create v2 torrents of this piece size because they won't be used by libtorrent-1.2 anyway.

[stalkerok]

1. It doesn't make much sense to only prevent the creation of such torrents without preventing such torrents from being added to session.

In any case, users are already using torrents with a 256MiB piece size for lt1.2 and won't be happy with that.

2. Since libtorrent-2.0 works correctly with 256MB piece size we can safely allow qBittorrent to create v2 torrents of this piece size because they won't be used by libtorrent-1.2 anyway.

py3createtorrent is a little known torrent creation tool. Allowing lt2.0 to create torrents V1 and hybrids will cause a really big wave of users who will face this issue on lt1.2.

But these restrictive measures still won't fix the issue for lt1.2...

[stalkerok]

As I said, it can be used as a temporary solution for 5.0, which won't break anything for sure. Anyway, I don't have the skills to make something bigger.

[stalkerok]

As far as I understand this PR is no longer relevant since a fix has been submitted to libtorrent, what if I make it possible to create 256MiB torrents for lt1.2 as well?

[xavier2k6]

I believe the limit is now 128MiB in libtorrent 2.x too, haven't tested any new patches..

@glassez Did you?

[glassez]

I believe the limit is now 128MiB in libtorrent 2.x too

Yes, it is.

[xavier2k6]

I believe the limit is now 128MiB in libtorrent 2.x too

Yes, it is.

@stalkerok pre-approved, will do some testing tomorrow (Saturday)

[xavier2k6]

Have tested, latest libtorrent RC_1_2 commit now rejects loading & removes any previous torrent with a invalid piece size of 256MiB.

RC_2_0 is now on par with RC_1_2 with the torrent creation limit of 128MiB piece size.

However, RC_2_0 needs to have a patch rejecting the invalid piece size torrents as it still allows adding new torrents of 256MiB piece size/loading previously added to session......

Outside of that...I approve of this PR.

[Chocobo1]

@stalkerok
Thank you!

[qBittUser]

Can this be backported to v5_0_x?

[glassez]

Can this be backported to v5_0_x?

I believe Yes.