daemon: distinguish inetd from local stdin sockets

[steadytao]

May fix #1068

Summary

Require stdin to be a connected IPv4 or IPv6 stream socket before selecting inetd mode.

ADB shell without a PTY presents stdin as a local socket. The existing is_a_socket(STDIN_FILENO) check therefore mistakes the ADB process channel for an accepted rsync connection. Rsync then attempts client-address lookup and SO_KEEPALIVE on that socket before writing the rsync daemon greeting.

Local sockets are now treated as ordinary process I/O, allowing --daemon --no-detach to enter its normal listening loop. Genuine inetd connections remain detected through their connected IP stream and --no-detach retains its documented no-op behaviour in inetd mode.

[steadytao]

@schuelermine not absolute but I do think this is likely the issue, could you test please?

[schuelermine]

@steadytao I’ve been trying to test this. Unfortunately, I don’t have a non-Nix cross compilation environment set up, and the Nixpkgs code refuses to work with the bare repository instead of the distribution tarballs.
How can I make a distribution tarball from the repository?

[schuelermine]

(More specifically, it fails due to missing aclocal if I build from a tarball made from my own repository)

[steadytao]

@steadytao I’ve been trying to test this. Unfortunately, I don’t have a non-Nix cross compilation environment set up, and the Nixpkgs code refuses to work with the bare repository instead of the distribution tarballs. How can I make a distribution tarball from the repository?

aclocal is provided by Automake. For a Nix environment, nix shell nixpkgs#autoconf nixpkgs#automake nixpkgs#gawk nixpkgs#gnumake -c ./prepare-source should generate the files required to build from the checkout. Please note to re-pull as well.