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Johnathan Corgan
674c7fe1ff
Three related UDP transport changes that together close a real gap in the v0.2.x "this transport accepts inbound" assumption: - outbound_only (default false). When true, the transport binds a kernel-assigned ephemeral port (0.0.0.0:0) regardless of the configured bind_addr, refuses inbound handshakes (Transport trait's accept_connections() returns false), and is never advertised on Nostr regardless of advertise_on_nostr. Lets a node participate in the mesh as a pure client — initiate outbound links without exposing an inbound listener on a known port. Also closes the "loopback bind as outbound-only workaround" trap: a UDP socket bound to 127.0.0.1 pins 127.0.0.1 as the source IP on outbound packets, and Linux refuses to deliver such packets out an external interface — the daemon happily reports "transport started" while no flow ever reaches an external peer. - accept_connections (default true). Mirrors the existing Ethernet/BLE knob. Lets operators run UDP in a "client" posture (initiate outbound, refuse inbound msg1 from new addresses) without switching transport. The Node-level handshake gate already carves out msg1 from peers established on the transport so rekey works on existing sessions. - Startup validation: reject `transports.udp[*].bind_addr` set to a loopback address (127.x.x.x, ::1, localhost) when at least one peer has a non-loopback UDP address. Replaces the silent "peer link won't establish" failure mode with a clear error pointing at the bind misconfiguration. outbound_only is exempt (it overrides bind_addr to 0.0.0.0:0). The is_punch_packet-based filter from the previous commit, the Node-level admission gate landed earlier on master, and these new config fields together cover the three distinct ways the v0.2.x "this transport accepts inbound" assumption could break. Tests: validation truth table (loopback+external rejected, loopback+loopback ok, outbound_only exempt), is_loopback_addr_str helper, accept_connections wiring (default, explicit-false, outbound_only-forces-false), end-to-end ephemeral-bind in the runtime. 1082 tests pass with --features nostr-discovery.