Add two small APIs to support out-of-tree projects to exchange custom
signaling messages over DERP without requiring disco protocol
extensions:
- OnDERPRecv callback on magicsock.Options / wgengine.Config: called for
every non-disco DERP packet before the peer map lookup, allowing callers
to intercept packets from unknown peers that would otherwise be dropped.
- SendDERPPacketTo method on magicsock.Conn: sends arbitrary bytes to a
node key via a DERP region, creating the connection if needed. Thin
wrapper around the existing internal sendAddr.
Also allow netstack.Start to accept a nil LocalBackend for use cases
that wire up TCP/UDP handlers directly without a full LocalBackend.
Updates tailscale/corp#24454
Change-Id: I99a523ef281625b8c0024a963f5f5bf5d8792c17
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad Fitzpatrick
073a9a8c9e