Convert ipv4-mapped ipv6 when accepting peer

[quentinlesceller]

Linked to #3221.
Maybe a bit naive. This will attempt to convert ipv4-mapped ipv6 when accepting peer, so we don't accept twice the same IP (ipv4 and ipv4-mapped ipv6).

[quentinlesceller]

I'm not even sure TcpListener accept() will give us an ipv4 mapped ipv6.

[antiochp]

I'm not even sure TcpListener accept() will give us an ipv4 mapped ipv6.

My understanding is it will if the local node is listening on :: (rather than 0.0.0.0).
i.e. If we are listening for both ipv4 and ipv6 connections then any ipv4 connections will themselves be mapped as we need a common way of representing them internally.

Which is making me think about why we are suddenly seeing a large number of these mapped addresses on the network.

• single node on the network listening on ::
• every ipv4 address connecting to it will be seen as a mapped address by this node
• it will then send out a peer addrs msg containing many mapped addresses to its peers
• these then propagate through the network via peer addrs msgs

[antiochp]

👍