Proposal: Compact port range mode for port-restricted NAT environments (MAP-E / RFC 7597)

[sweetfish329]

Hi team,

Currently Sunshine uses ports spread across a ~27-port range (from base - 5 to base + 21), but only around 7–8 ports are actively used:

• Web UI & Discovery: 47984, 47989, 47990 (TCP)
• RTSP: 48010 (TCP)
• Video / Audio / Control: 47998, 47999, 48000 (UDP)

In Japan and some other regions, many ISPs deploy MAP-E (RFC 7597, e.g. v6 Plus / OCN Virtual Connect). Under MAP-E, subscribers share a public IPv4 address and are each allocated discontinuous blocks of 16 ports (e.g. 6272–6287, 10368–10383, 47232–47247, etc.).

Because Sunshine's current port footprint is 27 ports wide, it cannot fit into any single 16-port block. This makes direct WAN port-forwarding impossible, even though we have router control over our assigned 16 ports.

While mesh VPNs like Tailscale work as a workaround, direct port-forwarding is still preferable for lower latency and connecting without third-party overlays.

Would it be possible to consider an optional "compact port" mode?

• Pack the internal offsets into a tighter span (e.g. within 8 or 16 consecutive ports, like base+0 through base+6).
• If needed for Moonlight compatibility, advertise the assigned ports dynamically through Sunshine's pairing/serverinfo API so clients know where to connect.

I know single-port multiplexing / QUIC has been brought up before (#4830, #4832), but a compact port offset profile feels like a much smaller and more realistic stepping stone.

Any thoughts on whether this could be feasible?