[anandghegde]

Fixes #3634.

Both hs.socket and hs.socket.udp server sockets currently bind to every interface, with no way to narrow that down. As @cmsj noted on the issue, CocoaAsyncSocket already exposes the APIs for this:

CocoaAsyncSocket supports binding to either interface or address, and I agree we should do this.

What changed

listen() on both extensions takes an optional interface string:

-- only reachable from this machine
server = hs.socket.server(9001, "loopback", callback)

-- only on the bridge interface to a VM
hs.socket.udp.new(callback):listen(9001, "bridge100")

The interface can be a name ("en1", "lo0"), the corresponding IP address ("192.168.4.34"), or the special strings "localhost"/"loopback" — whatever GCDAsyncSocket accepts.

• socket_listen() now calls -acceptOnInterface:port:error: instead of -acceptOnPort:error:
• socketudp_listen() now calls -bindToPort:interface:error: instead of -bindToPort:error:
• hs.socket.server() / hs.socket.udp.server() take the same optional argument between the port and the callback

Backwards compatibility

Passing no interface is unchanged. In CocoaAsyncSocket, -acceptOnPort:error: is literally return [self acceptOnInterface:nil port:port error:errPtr];, and -bindToPort:error: is return [self bindToPort:port interface:nil error:errPtr];, so the nil path is the same code as before.

The server() constructors shuffle their arguments when the second one is a function, so hs.socket.server(port, fn) keeps working.

Unix domain sockets aren't bound to an interface, so hs.socket:listen(path, interface) logs a warning and ignores the interface rather than failing.

Tests

Five new tests in test_socket.lua / test_udpsocket.lua, registered in Hammerspoon Tests/HSsocket.m:

• testTcpListenerSocketInterfaceAttributes / testUdpListenerSocketInterfaceAttributes — a listener bound to "loopback" reports localHost == "127.0.0.1" rather than "0.0.0.0"
• testTcpListenerSocketInterfaceConnect — a client can still connect to a loopback-bound server and the server reads what it wrote
• testTcpListenerSocketBadInterface / testUdpListenerSocketBadInterface — an unknown interface returns nil and leaves the socket unbound; a Unix domain socket ignores the interface

Local run of the HSsocket suite: 46 passed, 1 failed. The failure is testUdpReusePort, which also fails on an unmodified master here — it broadcasts to 255.255.255.255, which this machine doesn't allow.

[github-actions]

This pull request does not contain a valid label. Please add one of the following labels: ['pr-fix', 'pr-change', 'pr-feature', 'pr-maintenance']

[anandghegde]

CI is asking for one of the pr-fix / pr-change / pr-feature / pr-maintenance labels, and I can't set labels as an outside contributor. This one is pr-feature — could a maintainer add it so the check goes green? Happy to rebase if anything has moved in the meantime.

[anandghegde]

The required pr-feature label is still missing. I attempted to add it, but GitHub denied label-management permission for this fork PR. Could a maintainer add pr-feature so the automated check can pass?