util: do not bind outbound dials to a loopback -ip.bind (#12198)

`weed server -ip.bind=127.0.0.1` keeps every listener local, but the
same address became the source of outbound connections, so the filer
dialled its remote mount from 127.0.0.1 and failed with "connect:
invalid argument". A loopback source cannot reach off the host; leave
the source to the OS, as for a wildcard bind.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/util/outbound_dial.go

@@ -20,8 +20,10 @@ var (
 )
 
 // SetOutboundLocalIP records ip as the source address for outbound TCP
-// connections. An empty, wildcard (0.0.0.0 / ::), or unparseable value leaves
-// the source address to the OS.
+// connections. An empty, wildcard (0.0.0.0 / ::), loopback, or unparseable
+// value leaves the source address to the OS: a loopback source cannot reach
+// anything off the host, so `-ip.bind=127.0.0.1` (listen locally only) would
+// otherwise break every dial to a remote S3 endpoint or peer.
 //
 // The first call wins. `weed server` applies the top-level -ip.bind before its
 // embedded master/volume/filer/s3/... start, so a component's own (possibly
@@ -32,7 +34,7 @@ func SetOutboundLocalIP(ip string) {
 		return
 	}
 	parsed := net.ParseIP(ip)
-	if parsed == nil || parsed.IsUnspecified() {
+	if parsed == nil || parsed.IsUnspecified() || parsed.IsLoopback() {
 		return
 	}
 	outboundLocalAddr.Store(&net.TCPAddr{IP: parsed})

weed/util/outbound_dial_test.go

@@ -24,6 +24,10 @@ func TestSetOutboundLocalIP(t *testing.T) {
 		{"empty", "", ""},
 		{"wildcard v4", "0.0.0.0", ""},
 		{"wildcard v6", "::", ""},
+		// A loopback source cannot reach anything off the host, so binding to
+		// one would break every dial to a remote endpoint (S3, peers).
+		{"loopback v4", "127.0.0.1", ""},
+		{"loopback v6", "::1", ""},
 		{"garbage", "not-an-ip", ""},
 	}
 	for _, tc := range cases {