SAM: can't connect to self

[anikey-from-i2p]

Steps to reproduce:

Open three terminals, all with netcat to SAM port.

Terminal 1 (input only):

HELLO VERSION
SESSION CREATE STYLE=STREAM ID=testing DESTINATION=TRANSIENT SIGNATURE_TYPE=7 i2cp.leaseSetEncType=4,0 inbound.length=2 outbound.length=2 inbound.quantity=2 outbound.quantity=2
NAMING LOOKUP NAME=ME

Copy the VALUE of NAMING LOOKUP.

Terminal 2 (input only):

HELLO VERSION
STREAM ACCEPT ID=testing

Terminal 3 (input only):

HELLO VERSION
STREAM CONNECT ID=testing DESTINATION=<paste the VALUE from NAMING LOOKUP>

Then try communicating with terminal 2 and 3.

In java i2p, it works fine: messages from one side appear on the other with a slight delay (because of tunnels i guess).

In i2pd it does not work:

• in the terminal with STREAM ACCEPT it prints the destination, but the messages sent from the other one do not appear
• in logs it keeps saying about missing / not finding remote leaseset
• in webconsole streams list there are 2 streams: one with received=0, another with sent=0

practical consideration

qbittorrent seems to like to connect to itself.

[Vort]

I confirm this behaviour, with 2.50.1-8-g5cf1961f.

[Vort]

Check for self address was added intentionally, with this commit: d81ca5f.

However, no one remember why it was needed to be done this way.

I tried to disable check here:

i2pd/libi2pd/Destination.cpp

Lines 446 to 452 in dfe8b25

	if (leaseSet->GetIdentHash () != GetIdentHash ())
	{
	LogPrint (eLogDebug, "Destination: New remote LeaseSet added");
	m_RemoteLeaseSets[key] = leaseSet;
	}
	else
	LogPrint (eLogDebug, "Destination: Own remote LeaseSet dropped");

Connection established correctly, nothing exploded.

But I can't be sure that it is safe to make such change of course.

[orignal]

I don't see a reason why a destination should be able to connect to itself. For testing purposes, just create two session. Hence this check was added to avoid some potential security breaches.

[Vort]

Probably related:
qbittorrent/qBittorrent#10791
arvidn/libtorrent#7479

[orignal]

I would prefer to return CANT_REACH_PEER error in this case

[zzzi2p]

after discussion, Java I2P agrees with orignal that we should send CANT_REACH_PEER, and propose to make that change in our code unless somebody can come up with a good reason why we should support loopback

[orignal]

cd08756

[anikey-from-i2p]

I just thought i should report it because it also causes log spam with messages like "Remote LeaseSet not found" and "Can't send packets, missing remote LeaseSet, sSID=..."

[zzzi2p]

https://i2pgit.org/i2p-hackers/i2p.i2p/-/merge_requests/173