DERP is Tailscale's TCP relay protocol for peers that can't establish a
direct UDP path. Add the standalone client:
- derp/framing: 5-byte frame codec (1-byte type + 4-byte BE length)
- derp/client: HTTP /derp upgrade, Tailscale's NaCl SealedBox handshake
(ServerKey → ClientInfo → ServerInfo → NotePreferred), and
send_packet/recv_packet for forwarding WireGuard datagrams
Includes the 8-byte DERP\xf0\x9f\x94\x91 magic prefix in the ServerKey
payload and reads the HTTP upgrade response one byte at a time so the
inline first frame isn't swallowed by a buffered reader.
Sienna Meridian Satterwhite
76ab2c1a8e
