Struct Server

tailcat.go:277–350

Server listens for clients over a WireGuard tunnel relayed through DERP. Incoming TCP connections are dispatched via [Server.OnTCP] (for connections addressed to the server itself) and [Server.OnTCPForward] (for connections the server relays to other addresses, acting as an exit node). The zero val

// configuration fields, then call [Server.Start], which picks
// defaults for anything unset.
type Server struct {
	// Key is the server's node identity.
	// If zero, Start generates a new ephemeral key.
	Key key.NodePrivate

	// Logf is the logger used for debug messages.
	// If nil, log.Printf is used.
	Logf logger.Logf

	// Region, if non-nil, is the DERP region to use as the bootstrap
	// relay, without fetching any DERP map.
	Region *tailcfg.DERPRegion

	// RegionID, if non-zero and Region is nil, is the ID of the DERP
	// map region to use. If zero, the nearest region is picked based
	// on latency at Start.
	RegionID int

	// DERPMapURL, if non-empty, is an alternate URL to fetch the DERP
	// map from when Region is nil. If empty, [DefaultDERPMapURL] is
	// used.
	DERPMapURL string

	// DERPMapCache, if non-nil, caches fetched DERP maps. If nil, a
	// process-wide in-memory cache is used.
	DERPMapCache DERPMapCache

	// AllowedClients, if non-empty, restricts which client node keys
	// may connect; all others are silently ignored. If empty, all
	// clients are allowed. See [Server.AddAllowedClient] to add more
	// at runtime.
	AllowedClients []key.NodePublic

	lb *locoBackend // non-nil once Start has been called

	// AllowProxy, if non-nil, reports whether
	// a TCP or UDP proxy is allowed for that target.
	AllowProxy func(netip.AddrPort) bool

	// OnTCP, if non-nil, specifies a func that returns a handler to handle
	// incoming connections to the provided port. If nil or if it returns nil,
	// then a RST is sent.
	//
	// This only applies to connections directly to the server node and not
	// when being a subnet router. See OnTCPForward for relayed connections.
	//
	// It must be set before calling Start.
	OnTCP func(port uint16) (handler func(net.Conn))

	// OnTCPForward, if non-nil, specifies a func that returns a handler to handle
	// incoming connections to the provided IP:port. If nil or if it returns nil,
	// then a RST is sent.
	//
	// This only applies to connections relayed through the server and not to the server
	// itself. See OnTCP for direct connections to the server.
	//
	// It must be set before calling Start. Setting it also widens the
	// packet filter installed at Start to admit traffic to any