Peer.readLoop will only terminate if the connection is closed. Fix the
hang by closing the connection before waiting for readLoop to terminate.
This also removes the british disconnect procedure where we're waiting
for the remote end to close the connection. I have confirmed with
@subtly that cpp-ethereum doesn't adhere to it either.
This is supposed to apply some back pressure so Server is not accepting
more connections than it can actually handle. The current limit is 50.
This doesn't really need to be configurable, but we'll see how it
behaves in our test nodes and adjust accordingly.
As of this commit, p2p will disconnect nodes directly after the
encryption handshake if too many peer connections are active.
Errors in the protocol handshake packet are now handled more politely
by sending a disconnect packet before closing the connection.
There were multiple synchronization issues in the disconnect handling,
all caused by the odd special-casing of Peer.readLoop errors. Remove the
special handling of read errors and make readLoop part of the Peer
WaitGroup.
Thanks to @Gustav-Simonsson for pointing at arrows in a diagram
and playing rubber-duck.
This a fix for an attack vector where the discovery protocol could be
used to amplify traffic in a DDOS attack. A malicious actor would send a
findnode request with the IP address and UDP port of the target as the
source address. The recipient of the findnode packet would then send a
neighbors packet (which is 16x the size of findnode) to the victim.
Our solution is to require a 'bond' with the sender of findnode. If no
bond exists, the findnode packet is not processed. A bond between nodes
α and β is created when α replies to a ping from β.
This (initial) version of the bonding implementation might still be
vulnerable against replay attacks during the expiration time window.
We will add stricter source address validation later.
This is better because protocols might not actually read the payload for
some errors (msg too big, etc.) which can be a pain to test with the old
behaviour.
