Breaking change 50576: Fix the behavior of Socket.address

[Brian Quinlan]

See discussion on breaking change: https://github.com/dart-lang/sdk/issues/50576

Change

Socket.address currently returns the same InternetAddress as Socket.remoteAddress. Instead, it should return the local address that the Socket was bound to.

The original bug is: dart:io, address getter of Socket returns wrong address.

Rationale

The current behavior is not useful. Instead, two connected sockets should have a relationship like:

Expect.equals(clientSocket.address, serverSocket.remoteAddress);
Expect.equals(clientSocket.remoteAddress, serverSocket.address);

There is a work-in-progress change in Gerrit.

Impact

It is hard to know how much existing code this will break. It does not break any Google tests and I would guess that it does not break much existing code.

Mitigation

Users can switch their code to use Socket.remoteAddress instead of Socket.address if they want the remote socket binding.