SC-14: IPv4/IPv6 dual-stack support - #14
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--ipv4/-4, --ipv6/-6, --address flags. tcpNetwork/resolveLocalAddr helpers threaded through the two real call sites needing them: daemon listener (cli/daemon.go) and daemon-client dial (cli/rsync_url.go). internal/daemon needed zero changes - it only operates on an already-built net.Listener/net.Conn handed to it. SSH transport: -4/-6 forwarded to the spawned ssh process, verified against real rsync's main.c - only when the resolved remote-shell basename is exactly 'ssh', matching the man page's guidance that other --rsh overrides need the flag passed manually. --address has two real, documented scopes (daemon listen address, client outbound source address) - never SSH, verified rather than assumed. Self-review caught a real typed-nil bug before shipping: assigning a possibly-nil *net.TCPAddr directly into net.Dialer.LocalAddr (a net.Addr interface field) would wrap a nil pointer in a non-nil interface, corrupting every dial when no --address was given. Fixed. --ipv4+--ipv6 together is an explicit error - real rsync's own popt silently lets whichever is parsed last win, an artifact of shared C storage, not a designed behavior worth replicating. Address validation is eager and uniform even for local syncs, a disclosed departure from real rsync's lazy/unchecked-if-unused behavior. Real loopback tests for 127.0.0.1 and ::1, a real address-family constraint proof (--ipv4 against an IPv6-only daemon fails with an actual dial tcp4 refused), SSH argv-forwarding tests including the non-ssh-shell case. IPv6 tests skip gracefully via requireIPv6Loopback. Manual smoke test confirmed a live IPv6-only daemon syncing correctly and --ipv4 genuinely failing against it. Clean on native Windows and cross-compiled Linux.
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--ipv4/-4, --ipv6/-6, --address flags. tcpNetwork/resolveLocalAddr helpers threaded through the two real call sites needing them: daemon listener (cli/daemon.go) and daemon-client dial (cli/rsync_url.go). internal/daemon needed zero changes - it only operates on an already-built net.Listener/net.Conn handed to it.
SSH transport: -4/-6 forwarded to the spawned ssh process, verified against real rsync's main.c - only when the resolved remote-shell basename is exactly 'ssh', matching the man page's guidance that other --rsh overrides need the flag passed manually. --address has two real, documented scopes (daemon listen address, client outbound source address) - never SSH, verified rather than assumed.
Self-review caught a real typed-nil bug before shipping: assigning a possibly-nil *net.TCPAddr directly into net.Dialer.LocalAddr (a net.Addr interface field) would wrap a nil pointer in a non-nil interface, corrupting every dial when no --address was given. Fixed.
--ipv4+--ipv6 together is an explicit error - real rsync's own popt silently lets whichever is parsed last win, an artifact of shared C storage, not a designed behavior worth replicating. Address validation is eager and uniform even for local syncs, a disclosed departure from real rsync's lazy/unchecked-if-unused behavior.
Real loopback tests for 127.0.0.1 and ::1, a real address-family constraint proof (--ipv4 against an IPv6-only daemon fails with an actual dial tcp4 refused), SSH argv-forwarding tests including the non-ssh-shell case. IPv6 tests skip gracefully via requireIPv6Loopback. Manual smoke test confirmed a live IPv6-only daemon syncing correctly and --ipv4 genuinely failing against it.
Clean on native Windows and cross-compiled Linux.