Fixed in DC++ 0.880
** Changed in: dcplusplus
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1979900
Title:
Outgoing connections are attempted on IPv6 on some cases when there's
no v6 connectivity
Status in DC++:
Fix Released
Bug description:
[2022-06-17 17:13] <eMTee> Recently I was surprised seeing "::" in the IP
column in the hubframe userlist for all other DC++ users in each LuaDCH hubs
I'm in. I've never seen such thing before.
[2022-06-17 17:14] <eMTee> Actually the hub sends I6:: in BINF for all DC++
users but not for users of some other clients.
[2022-06-17 17:16] <eMTee> LuaDCH devs confirmed that it is a known issue and
they're working on it.
[2022-06-17 17:18] <eMTee> They did not tell the cause but I'm guessing it is
because DC++ doesn't support HBRI, an unofficial ADC extension developed by
maksis in AirDC++ and what they're using for managing hybrid v4/v6 connetions.
[2022-06-17 17:20] <eMTee> I checked why this zero IP value is displayed
instead of the usual v4 address in DC++. Turned out it's
User::Identity::getIp() which prefers returning IPv6 when both IP adresses are
available.
[2022-06-17 17:22] <eMTee> This a hub bug and since I see we accept whatever
the hub send in an ADC command param without checking for format/value so it
causes a visual disruption.
[2022-06-17 17:24] <eMTee> But. I checked where User::Identity::getIp() used
elsewhere. Actually it is used for getting the IP for outgoing connections in
ConnectionManager and ClientManager.
[2022-06-17 17:26] <eMTee> In this buggy case it would return the IPv6 value
for all outgoing connection attempts, even if you have IPv4 connectivity only.
That obviously breaks outgoing connections to those users for whom the hub
supplies a wrong I6 value. Still, this isn't much of a problem as it caused by
getting some nonsense from a buggy hub.
[2022-06-17 17:28] <eMTee> Sending zero IP value from a hub is indeed
nonsense but if the hub sends the valid IPv6 address of the user in I6 then
this will actually break your outgoing connections the same way in case you
have v4 connectivity only.
[2022-06-17 17:29] <eMTee> It breaks uploads, CCPM and sending udp search
responds.
[2022-06-17 17:34] <eMTee> Looks like getting IPv6 addresses in BINF from the
hub seems to be nonexistent thing even from hubs running in dual IP mode.
[2022-06-17 17:39] <eMTee> Relevant parts of the code are
https://sourceforge.net/p/dcplusplus/code/ci/93a0986b55c5b07038451fd336a30149076a21d1/tree/dcpp/User.cpp#l86
,
https://sourceforge.net/p/dcplusplus/code/ci/93a0986b55c5b07038451fd336a30149076a21d1/tree/dcpp/ConnectionManager.cpp#l410
,
https://sourceforge.net/p/dcplusplus/code/ci/93a0986b55c5b07038451fd336a30149076a21d1/tree/dcpp/ClientManager.cpp#l455
[2022-06-17 17:41] <eMTee> tl;dr is that we should not attempt to estabilish
an outgoing connection using a v6 IP address when we have only v4 connectivity.
[2022-06-18 08:49] <eMTee> Possible fix is to check for the current
connectivity status and choose the right IP before attempting the connection.
[2022-06-18 08:56] <eMTee> As we see IPv4 is still the go to connection
around the network I guess we must make sure such connections work properly.
This bug can be clearly triggered by receiving a valid ADC command parameter
from a hub.
See also https://bugs.launchpad.net/adchpp/+bug/309402 regarding all
the ipv6 issues. The above linked parts of the code suggest that plans
in https://bugs.launchpad.net/adchpp/+bug/309402/comments/23 has not
been implemented yet in DC++.
The attached patch fixes this issue by using info from
ConnectivityManager and forces IPv4 address/connection when there's no
IPv6 connectivity set/detected. Otherwise it does the same as before,
allowing User::Identity::getIp() to decide what protocol to be
used/preferred.
But the question is do we need to care of this at all or just rely on
what the hub sends... in other words is this kind of safeguard worth
or needed at all? Or it's useful for a temporary fix until one of the
few maintained ADC hubs fixes its bug?
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