Update dependencies

vendor/tailscale.com/derp/README.md

@@ -0,0 +1,61 @@
+# DERP
+
+This directory (and subdirectories) contain the DERP code. The server itself is
+in `../cmd/derper`.
+
+DERP is a packet relay system (client and servers) where peers are addressed
+using WireGuard public keys instead of IP addresses.
+
+It relays two types of packets:
+
+* "Disco" discovery messages (see `../disco`) as the a side channel during [NAT
+  traversal](https://tailscale.com/blog/how-nat-traversal-works/).
+
+* Encrypted WireGuard packets as the fallback of last resort when UDP is blocked
+  or NAT traversal fails.
+
+## DERP Map
+
+Each client receives a "[DERP
+Map](https://pkg.go.dev/tailscale.com/tailcfg#DERPMap)" from the coordination
+server describing the DERP servers the client should try to use.
+
+The client picks its home "DERP home" based on latency. This is done to keep
+costs low by avoid using cloud load balancers (pricey) or anycast, which would
+necessarily require server-side routing between DERP regions.
+
+Clients pick their DERP home and report it to the coordination server which
+shares it to all the peers in the tailnet. When a peer wants to send a packet
+and it doesn't already have a WireGuard session open, it sends disco messages
+(some direct, and some over DERP), trying to do the NAT traversal. The client
+will make connections to multiple DERP regions as needed. Only the DERP home
+region connection needs to be alive forever.
+
+## DERP Regions
+
+Tailscale runs 1 or more DERP nodes (instances of `cmd/derper`) in various
+geographic regions to make sure users have low latency to their DERP home.
+
+Regions generally have multiple nodes per region "meshed" (routing to each
+other) together for redundancy: it allows for cloud failures or upgrades without
+kicking users out to a higher latency region. Instead, clients will reconnect to
+the next node in the region. Each node in the region is required to to be meshed
+with every other node in the region and forward packets to the other nodes in
+the region. Packets are forwarded only one hop within the region. There is no
+routing between regions. The assumption is that the mesh TCP connections are
+over a VPC that's very fast, low latency, and not charged per byte. The
+coordination server assigns the list of nodes in a region as a function of the
+tailnet, so all nodes within a tailnet should generally be on the same node and
+not require forwarding. Only after a failure do clients of a particular tailnet
+get split between nodes in a region and require inter-node forwarding. But over
+time it balances back out. There's also an admin-only DERP frame type to force
+close the TCP connection of a particular client to force them to reconnect to
+their primary if the operator wants to force things to balance out sooner.
+(Using the `(*derphttp.Client).ClosePeer` method, as used by Tailscale's
+internal rarely-used `cmd/derpprune` maintenance tool)
+
+We generally run a minimum of three nodes in a region not for quorum reasons
+(there's no voting) but just because two is too uncomfortably few for cascading
+failure reasons: if you're running two nodes at 51% load (CPU, memory, etc) and
+then one fails, that makes the second one fail. With three or more nodes, you
+can run each node a bit hotter.

vendor/tailscale.com/derp/derp.go

@@ -0,0 +1,256 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package derp implements the Designated Encrypted Relay for Packets (DERP)
+// protocol.
+//
+// DERP routes packets to clients using curve25519 keys as addresses.
+//
+// DERP is used by Tailscale nodes to proxy encrypted WireGuard
+// packets through the Tailscale cloud servers when a direct path
+// cannot be found or opened. DERP is a last resort. Both sides
+// between very aggressive NATs, firewalls, no IPv6, etc? Well, DERP.
+package derp
+
+import (
+	"bufio"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"time"
+)
+
+// MaxPacketSize is the maximum size of a packet sent over DERP.
+// (This only includes the data bytes visible to magicsock, not
+// including its on-wire framing overhead)
+const MaxPacketSize = 64 << 10
+
+// magic is the DERP magic number, sent in the frameServerKey frame
+// upon initial connection.
+const magic = "DERP🔑" // 8 bytes: 0x44 45 52 50 f0 9f 94 91
+
+const (
+	nonceLen       = 24
+	frameHeaderLen = 1 + 4 // frameType byte + 4 byte length
+	keyLen         = 32
+	maxInfoLen     = 1 << 20
+	keepAlive      = 60 * time.Second
+)
+
+// ProtocolVersion is bumped whenever there's a wire-incompatible change.
+//   - version 1 (zero on wire): consistent box headers, in use by employee dev nodes a bit
+//   - version 2: received packets have src addrs in frameRecvPacket at beginning
+const ProtocolVersion = 2
+
+// frameType is the one byte frame type at the beginning of the frame
+// header.  The second field is a big-endian uint32 describing the
+// length of the remaining frame (not including the initial 5 bytes).
+type frameType byte
+
+/*
+Protocol flow:
+
+Login:
+* client connects
+* server sends frameServerKey
+* client sends frameClientInfo
+* server sends frameServerInfo
+
+Steady state:
+* server occasionally sends frameKeepAlive (or framePing)
+* client responds to any framePing with a framePong
+* client sends frameSendPacket
+* server then sends frameRecvPacket to recipient
+*/
+const (
+	frameServerKey     = frameType(0x01) // 8B magic + 32B public key + (0+ bytes future use)
+	frameClientInfo    = frameType(0x02) // 32B pub key + 24B nonce + naclbox(json)
+	frameServerInfo    = frameType(0x03) // 24B nonce + naclbox(json)
+	frameSendPacket    = frameType(0x04) // 32B dest pub key + packet bytes
+	frameForwardPacket = frameType(0x0a) // 32B src pub key + 32B dst pub key + packet bytes
+	frameRecvPacket    = frameType(0x05) // v0/1: packet bytes, v2: 32B src pub key + packet bytes
+	frameKeepAlive     = frameType(0x06) // no payload, no-op (to be replaced with ping/pong)
+	frameNotePreferred = frameType(0x07) // 1 byte payload: 0x01 or 0x00 for whether this is client's home node
+
+	// framePeerGone is sent from server to client to signal that
+	// a previous sender is no longer connected. That is, if A
+	// sent to B, and then if A disconnects, the server sends
+	// framePeerGone to B so B can forget that a reverse path
+	// exists on that connection to get back to A. It is also sent
+	// if A tries to send a CallMeMaybe to B and the server has no
+	// record of B (which currently would only happen if there was
+	// a bug).
+	framePeerGone = frameType(0x08) // 32B pub key of peer that's gone + 1 byte reason
+
+	// framePeerPresent is like framePeerGone, but for other members of the DERP
+	// region when they're meshed up together.
+	//
+	// The message is at least 32 bytes (the public key of the peer that's
+	// connected). If there are at least 18 bytes remaining after that, it's the
+	// 16 byte IP + 2 byte BE uint16 port of the client. If there's another byte
+	// remaining after that, it's a PeerPresentFlags byte.
+	// While current servers send 41 bytes, old servers will send fewer, and newer
+	// servers might send more.
+	framePeerPresent = frameType(0x09)
+
+	// frameWatchConns is how one DERP node in a regional mesh
+	// subscribes to the others in the region.
+	// There's no payload. If the sender doesn't have permission, the connection
+	// is closed. Otherwise, the client is initially flooded with
+	// framePeerPresent for all connected nodes, and then a stream of
+	// framePeerPresent & framePeerGone has peers connect and disconnect.
+	frameWatchConns = frameType(0x10)
+
+	// frameClosePeer is a privileged frame type (requires the
+	// mesh key for now) that closes the provided peer's
+	// connection. (To be used for cluster load balancing
+	// purposes, when clients end up on a non-ideal node)
+	frameClosePeer = frameType(0x11) // 32B pub key of peer to close.
+
+	framePing = frameType(0x12) // 8 byte ping payload, to be echoed back in framePong
+	framePong = frameType(0x13) // 8 byte payload, the contents of the ping being replied to
+
+	// frameHealth is sent from server to client to tell the client
+	// if their connection is unhealthy somehow. Currently the only unhealthy state
+	// is whether the connection is detected as a duplicate.
+	// The entire frame body is the text of the error message. An empty message
+	// clears the error state.
+	frameHealth = frameType(0x14)
+
+	// frameRestarting is sent from server to client for the
+	// server to declare that it's restarting. Payload is two big
+	// endian uint32 durations in milliseconds: when to reconnect,
+	// and how long to try total. See ServerRestartingMessage docs for
+	// more details on how the client should interpret them.
+	frameRestarting = frameType(0x15)
+)
+
+// PeerGoneReasonType is a one byte reason code explaining why a
+// server does not have a path to the requested destination.
+type PeerGoneReasonType byte
+
+const (
+	PeerGoneReasonDisconnected  = PeerGoneReasonType(0x00) // peer disconnected from this server
+	PeerGoneReasonNotHere       = PeerGoneReasonType(0x01) // server doesn't know about this peer, unexpected
+	PeerGoneReasonMeshConnBroke = PeerGoneReasonType(0xf0) // invented by Client.RunWatchConnectionLoop on disconnect; not sent on the wire
+)
+
+// PeerPresentFlags is an optional byte of bit flags sent after a framePeerPresent message.
+//
+// For a modern server, the value should always be non-zero. If the value is zero,
+// that means the server doesn't support this field.
+type PeerPresentFlags byte
+
+// PeerPresentFlags bits.
+const (
+	PeerPresentIsRegular  = 1 << 0
+	PeerPresentIsMeshPeer = 1 << 1
+	PeerPresentIsProber   = 1 << 2
+)
+
+var bin = binary.BigEndian
+
+func writeUint32(bw *bufio.Writer, v uint32) error {
+	var b [4]byte
+	bin.PutUint32(b[:], v)
+	// Writing a byte at a time is a bit silly,
+	// but it causes b not to escape,
+	// which more than pays for the silliness.
+	for _, c := range &b {
+		err := bw.WriteByte(c)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func readUint32(br *bufio.Reader) (uint32, error) {
+	var b [4]byte
+	// Reading a byte at a time is a bit silly,
+	// but it causes b not to escape,
+	// which more than pays for the silliness.
+	for i := range &b {
+		c, err := br.ReadByte()
+		if err != nil {
+			return 0, err
+		}
+		b[i] = c
+	}
+	return bin.Uint32(b[:]), nil
+}
+
+func readFrameTypeHeader(br *bufio.Reader, wantType frameType) (frameLen uint32, err error) {
+	gotType, frameLen, err := readFrameHeader(br)
+	if err == nil && wantType != gotType {
+		err = fmt.Errorf("bad frame type 0x%X, want 0x%X", gotType, wantType)
+	}
+	return frameLen, err
+}
+
+func readFrameHeader(br *bufio.Reader) (t frameType, frameLen uint32, err error) {
+	tb, err := br.ReadByte()
+	if err != nil {
+		return 0, 0, err
+	}
+	frameLen, err = readUint32(br)
+	if err != nil {
+		return 0, 0, err
+	}
+	return frameType(tb), frameLen, nil
+}
+
+// readFrame reads a frame header and then reads its payload into
+// b[:frameLen].
+//
+// If the frame header length is greater than maxSize, readFrame returns
+// an error after reading the frame header.
+//
+// If the frame is less than maxSize but greater than len(b), len(b)
+// bytes are read, err will be io.ErrShortBuffer, and frameLen and t
+// will both be set. That is, callers need to explicitly handle when
+// they get more data than expected.
+func readFrame(br *bufio.Reader, maxSize uint32, b []byte) (t frameType, frameLen uint32, err error) {
+	t, frameLen, err = readFrameHeader(br)
+	if err != nil {
+		return 0, 0, err
+	}
+	if frameLen > maxSize {
+		return 0, 0, fmt.Errorf("frame header size %d exceeds reader limit of %d", frameLen, maxSize)
+	}
+
+	n, err := io.ReadFull(br, b[:min(frameLen, uint32(len(b)))])
+	if err != nil {
+		return 0, 0, err
+	}
+	remain := frameLen - uint32(n)
+	if remain > 0 {
+		if _, err := io.CopyN(io.Discard, br, int64(remain)); err != nil {
+			return 0, 0, err
+		}
+		err = io.ErrShortBuffer
+	}
+	return t, frameLen, err
+}
+
+func writeFrameHeader(bw *bufio.Writer, t frameType, frameLen uint32) error {
+	if err := bw.WriteByte(byte(t)); err != nil {
+		return err
+	}
+	return writeUint32(bw, frameLen)
+}
+
+// writeFrame writes a complete frame & flushes it.
+func writeFrame(bw *bufio.Writer, t frameType, b []byte) error {
+	if len(b) > 10<<20 {
+		return errors.New("unreasonably large frame write")
+	}
+	if err := writeFrameHeader(bw, t, uint32(len(b))); err != nil {
+		return err
+	}
+	if _, err := bw.Write(b); err != nil {
+		return err
+	}
+	return bw.Flush()
+}

vendor/tailscale.com/derp/derp_client.go

@@ -0,0 +1,673 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package derp
+
+import (
+	"bufio"
+	"encoding/binary"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/netip"
+	"sync"
+	"time"
+
+	"go4.org/mem"
+	"golang.org/x/time/rate"
+	"tailscale.com/syncs"
+	"tailscale.com/tstime"
+	"tailscale.com/types/key"
+	"tailscale.com/types/logger"
+)
+
+// Client is a DERP client.
+type Client struct {
+	serverKey   key.NodePublic // of the DERP server; not a machine or node key
+	privateKey  key.NodePrivate
+	publicKey   key.NodePublic // of privateKey
+	logf        logger.Logf
+	nc          Conn
+	br          *bufio.Reader
+	meshKey     string
+	canAckPings bool
+	isProber    bool
+
+	wmu  sync.Mutex // hold while writing to bw
+	bw   *bufio.Writer
+	rate *rate.Limiter // if non-nil, rate limiter to use
+
+	// Owned by Recv:
+	peeked  int                      // bytes to discard on next Recv
+	readErr syncs.AtomicValue[error] // sticky (set by Recv)
+
+	clock tstime.Clock
+}
+
+// ClientOpt is an option passed to NewClient.
+type ClientOpt interface {
+	update(*clientOpt)
+}
+
+type clientOptFunc func(*clientOpt)
+
+func (f clientOptFunc) update(o *clientOpt) { f(o) }
+
+// clientOpt are the options passed to newClient.
+type clientOpt struct {
+	MeshKey     string
+	ServerPub   key.NodePublic
+	CanAckPings bool
+	IsProber    bool
+}
+
+// MeshKey returns a ClientOpt to pass to the DERP server during connect to get
+// access to join the mesh.
+//
+// An empty key means to not use a mesh key.
+func MeshKey(key string) ClientOpt { return clientOptFunc(func(o *clientOpt) { o.MeshKey = key }) }
+
+// IsProber returns a ClientOpt to pass to the DERP server during connect to
+// declare that this client is a a prober.
+func IsProber(v bool) ClientOpt { return clientOptFunc(func(o *clientOpt) { o.IsProber = v }) }
+
+// ServerPublicKey returns a ClientOpt to declare that the server's DERP public key is known.
+// If key is the zero value, the returned ClientOpt is a no-op.
+func ServerPublicKey(key key.NodePublic) ClientOpt {
+	return clientOptFunc(func(o *clientOpt) { o.ServerPub = key })
+}
+
+// CanAckPings returns a ClientOpt to set whether it advertises to the
+// server that it's capable of acknowledging ping requests.
+func CanAckPings(v bool) ClientOpt {
+	return clientOptFunc(func(o *clientOpt) { o.CanAckPings = v })
+}
+
+func NewClient(privateKey key.NodePrivate, nc Conn, brw *bufio.ReadWriter, logf logger.Logf, opts ...ClientOpt) (*Client, error) {
+	var opt clientOpt
+	for _, o := range opts {
+		if o == nil {
+			return nil, errors.New("nil ClientOpt")
+		}
+		o.update(&opt)
+	}
+	return newClient(privateKey, nc, brw, logf, opt)
+}
+
+func newClient(privateKey key.NodePrivate, nc Conn, brw *bufio.ReadWriter, logf logger.Logf, opt clientOpt) (*Client, error) {
+	c := &Client{
+		privateKey:  privateKey,
+		publicKey:   privateKey.Public(),
+		logf:        logf,
+		nc:          nc,
+		br:          brw.Reader,
+		bw:          brw.Writer,
+		meshKey:     opt.MeshKey,
+		canAckPings: opt.CanAckPings,
+		isProber:    opt.IsProber,
+		clock:       tstime.StdClock{},
+	}
+	if opt.ServerPub.IsZero() {
+		if err := c.recvServerKey(); err != nil {
+			return nil, fmt.Errorf("derp.Client: failed to receive server key: %v", err)
+		}
+	} else {
+		c.serverKey = opt.ServerPub
+	}
+	if err := c.sendClientKey(); err != nil {
+		return nil, fmt.Errorf("derp.Client: failed to send client key: %v", err)
+	}
+	return c, nil
+}
+
+func (c *Client) PublicKey() key.NodePublic { return c.publicKey }
+
+func (c *Client) recvServerKey() error {
+	var buf [40]byte
+	t, flen, err := readFrame(c.br, 1<<10, buf[:])
+	if err == io.ErrShortBuffer {
+		// For future-proofing, allow server to send more in its greeting.
+		err = nil
+	}
+	if err != nil {
+		return err
+	}
+	if flen < uint32(len(buf)) || t != frameServerKey || string(buf[:len(magic)]) != magic {
+		return errors.New("invalid server greeting")
+	}
+	c.serverKey = key.NodePublicFromRaw32(mem.B(buf[len(magic):]))
+	return nil
+}
+
+func (c *Client) parseServerInfo(b []byte) (*serverInfo, error) {
+	const maxLength = nonceLen + maxInfoLen
+	fl := len(b)
+	if fl < nonceLen {
+		return nil, fmt.Errorf("short serverInfo frame")
+	}
+	if fl > maxLength {
+		return nil, fmt.Errorf("long serverInfo frame")
+	}
+	msg, ok := c.privateKey.OpenFrom(c.serverKey, b)
+	if !ok {
+		return nil, fmt.Errorf("failed to open naclbox from server key %s", c.serverKey)
+	}
+	info := new(serverInfo)
+	if err := json.Unmarshal(msg, info); err != nil {
+		return nil, fmt.Errorf("invalid JSON: %v", err)
+	}
+	return info, nil
+}
+
+type clientInfo struct {
+	// MeshKey optionally specifies a pre-shared key used by
+	// trusted clients.  It's required to subscribe to the
+	// connection list & forward packets. It's empty for regular
+	// users.
+	MeshKey string `json:"meshKey,omitempty"`
+
+	// Version is the DERP protocol version that the client was built with.
+	// See the ProtocolVersion const.
+	Version int `json:"version,omitempty"`
+
+	// CanAckPings is whether the client declares it's able to ack
+	// pings.
+	CanAckPings bool
+
+	// IsProber is whether this client is a prober.
+	IsProber bool `json:",omitempty"`
+}
+
+func (c *Client) sendClientKey() error {
+	msg, err := json.Marshal(clientInfo{
+		Version:     ProtocolVersion,
+		MeshKey:     c.meshKey,
+		CanAckPings: c.canAckPings,
+		IsProber:    c.isProber,
+	})
+	if err != nil {
+		return err
+	}
+	msgbox := c.privateKey.SealTo(c.serverKey, msg)
+
+	buf := make([]byte, 0, keyLen+len(msgbox))
+	buf = c.publicKey.AppendTo(buf)
+	buf = append(buf, msgbox...)
+	return writeFrame(c.bw, frameClientInfo, buf)
+}
+
+// ServerPublicKey returns the server's public key.
+func (c *Client) ServerPublicKey() key.NodePublic { return c.serverKey }
+
+// Send sends a packet to the Tailscale node identified by dstKey.
+//
+// It is an error if the packet is larger than 64KB.
+func (c *Client) Send(dstKey key.NodePublic, pkt []byte) error { return c.send(dstKey, pkt) }
+
+func (c *Client) send(dstKey key.NodePublic, pkt []byte) (ret error) {
+	defer func() {
+		if ret != nil {
+			ret = fmt.Errorf("derp.Send: %w", ret)
+		}
+	}()
+
+	if len(pkt) > MaxPacketSize {
+		return fmt.Errorf("packet too big: %d", len(pkt))
+	}
+
+	c.wmu.Lock()
+	defer c.wmu.Unlock()
+	if c.rate != nil {
+		pktLen := frameHeaderLen + key.NodePublicRawLen + len(pkt)
+		if !c.rate.AllowN(c.clock.Now(), pktLen) {
+			return nil // drop
+		}
+	}
+	if err := writeFrameHeader(c.bw, frameSendPacket, uint32(key.NodePublicRawLen+len(pkt))); err != nil {
+		return err
+	}
+	if _, err := c.bw.Write(dstKey.AppendTo(nil)); err != nil {
+		return err
+	}
+	if _, err := c.bw.Write(pkt); err != nil {
+		return err
+	}
+	return c.bw.Flush()
+}
+
+func (c *Client) ForwardPacket(srcKey, dstKey key.NodePublic, pkt []byte) (err error) {
+	defer func() {
+		if err != nil {
+			err = fmt.Errorf("derp.ForwardPacket: %w", err)
+		}
+	}()
+
+	if len(pkt) > MaxPacketSize {
+		return fmt.Errorf("packet too big: %d", len(pkt))
+	}
+
+	c.wmu.Lock()
+	defer c.wmu.Unlock()
+
+	timer := c.clock.AfterFunc(5*time.Second, c.writeTimeoutFired)
+	defer timer.Stop()
+
+	if err := writeFrameHeader(c.bw, frameForwardPacket, uint32(keyLen*2+len(pkt))); err != nil {
+		return err
+	}
+	if _, err := c.bw.Write(srcKey.AppendTo(nil)); err != nil {
+		return err
+	}
+	if _, err := c.bw.Write(dstKey.AppendTo(nil)); err != nil {
+		return err
+	}
+	if _, err := c.bw.Write(pkt); err != nil {
+		return err
+	}
+	return c.bw.Flush()
+}
+
+func (c *Client) writeTimeoutFired() { c.nc.Close() }
+
+func (c *Client) SendPing(data [8]byte) error {
+	return c.sendPingOrPong(framePing, data)
+}
+
+func (c *Client) SendPong(data [8]byte) error {
+	return c.sendPingOrPong(framePong, data)
+}
+
+func (c *Client) sendPingOrPong(typ frameType, data [8]byte) error {
+	c.wmu.Lock()
+	defer c.wmu.Unlock()
+	if err := writeFrameHeader(c.bw, typ, 8); err != nil {
+		return err
+	}
+	if _, err := c.bw.Write(data[:]); err != nil {
+		return err
+	}
+	return c.bw.Flush()
+}
+
+// NotePreferred sends a packet that tells the server whether this
+// client is the user's preferred server. This is only used in the
+// server for stats.
+func (c *Client) NotePreferred(preferred bool) (err error) {
+	defer func() {
+		if err != nil {
+			err = fmt.Errorf("derp.NotePreferred: %v", err)
+		}
+	}()
+
+	c.wmu.Lock()
+	defer c.wmu.Unlock()
+
+	if err := writeFrameHeader(c.bw, frameNotePreferred, 1); err != nil {
+		return err
+	}
+	var b byte = 0x00
+	if preferred {
+		b = 0x01
+	}
+	if err := c.bw.WriteByte(b); err != nil {
+		return err
+	}
+	return c.bw.Flush()
+}
+
+// WatchConnectionChanges sends a request to subscribe to the peer's connection list.
+// It's a fatal error if the client wasn't created using MeshKey.
+func (c *Client) WatchConnectionChanges() error {
+	c.wmu.Lock()
+	defer c.wmu.Unlock()
+	if err := writeFrameHeader(c.bw, frameWatchConns, 0); err != nil {
+		return err
+	}
+	return c.bw.Flush()
+}
+
+// ClosePeer asks the server to close target's TCP connection.
+// It's a fatal error if the client wasn't created using MeshKey.
+func (c *Client) ClosePeer(target key.NodePublic) error {
+	c.wmu.Lock()
+	defer c.wmu.Unlock()
+	return writeFrame(c.bw, frameClosePeer, target.AppendTo(nil))
+}
+
+// ReceivedMessage represents a type returned by Client.Recv. Unless
+// otherwise documented, the returned message aliases the byte slice
+// provided to Recv and thus the message is only as good as that
+// buffer, which is up to the caller.
+type ReceivedMessage interface {
+	msg()
+}
+
+// ReceivedPacket is a ReceivedMessage representing an incoming packet.
+type ReceivedPacket struct {
+	Source key.NodePublic
+	// Data is the received packet bytes. It aliases the memory
+	// passed to Client.Recv.
+	Data []byte
+}
+
+func (ReceivedPacket) msg() {}
+
+// PeerGoneMessage is a ReceivedMessage that indicates that the client
+// identified by the underlying public key is not connected to this
+// server.
+//
+// It has only historically been sent by the server when the client
+// connection count decremented from 1 to 0 and not from e.g. 2 to 1.
+// See https://github.com/tailscale/tailscale/issues/13566 for details.
+type PeerGoneMessage struct {
+	Peer   key.NodePublic
+	Reason PeerGoneReasonType
+}
+
+func (PeerGoneMessage) msg() {}
+
+// PeerPresentMessage is a ReceivedMessage that indicates that the client is
+// connected to the server. (Only used by trusted mesh clients)
+//
+// It will be sent to client watchers for every new connection from a client,
+// even if the client's already connected with that public key.
+// See https://github.com/tailscale/tailscale/issues/13566 for PeerPresentMessage
+// and PeerGoneMessage not being 1:1.
+type PeerPresentMessage struct {
+	// Key is the public key of the client.
+	Key key.NodePublic
+	// IPPort is the remote IP and port of the client.
+	IPPort netip.AddrPort
+	// Flags is a bitmask of info about the client.
+	Flags PeerPresentFlags
+}
+
+func (PeerPresentMessage) msg() {}
+
+// ServerInfoMessage is sent by the server upon first connect.
+type ServerInfoMessage struct {
+	// TokenBucketBytesPerSecond is how many bytes per second the
+	// server says it will accept, including all framing bytes.
+	//
+	// Zero means unspecified. There might be a limit, but the
+	// client need not try to respect it.
+	TokenBucketBytesPerSecond int
+
+	// TokenBucketBytesBurst is how many bytes the server will
+	// allow to burst, temporarily violating
+	// TokenBucketBytesPerSecond.
+	//
+	// Zero means unspecified. There might be a limit, but the
+	// client need not try to respect it.
+	TokenBucketBytesBurst int
+}
+
+func (ServerInfoMessage) msg() {}
+
+// PingMessage is a request from a client or server to reply to the
+// other side with a PongMessage with the given payload.
+type PingMessage [8]byte
+
+func (PingMessage) msg() {}
+
+// PongMessage is a reply to a PingMessage from a client or server
+// with the payload sent previously in a PingMessage.
+type PongMessage [8]byte
+
+func (PongMessage) msg() {}
+
+// KeepAliveMessage is a one-way empty message from server to client, just to
+// keep the connection alive. It's like a PingMessage, but doesn't solicit
+// a reply from the client.
+type KeepAliveMessage struct{}
+
+func (KeepAliveMessage) msg() {}
+
+// HealthMessage is a one-way message from server to client, declaring the
+// connection health state.
+type HealthMessage struct {
+	// Problem, if non-empty, is a description of why the connection
+	// is unhealthy.
+	//
+	// The empty string means the connection is healthy again.
+	//
+	// The default condition is healthy, so the server doesn't
+	// broadcast a HealthMessage until a problem exists.
+	Problem string
+}
+
+func (HealthMessage) msg() {}
+
+// ServerRestartingMessage is a one-way message from server to client,
+// advertising that the server is restarting.
+type ServerRestartingMessage struct {
+	// ReconnectIn is an advisory duration that the client should wait
+	// before attempting to reconnect. It might be zero.
+	// It exists for the server to smear out the reconnects.
+	ReconnectIn time.Duration
+
+	// TryFor is an advisory duration for how long the client
+	// should attempt to reconnect before giving up and proceeding
+	// with its normal connection failure logic. The interval
+	// between retries is undefined for now.
+	// A server should not send a TryFor duration more than a few
+	// seconds.
+	TryFor time.Duration
+}
+
+func (ServerRestartingMessage) msg() {}
+
+// Recv reads a message from the DERP server.
+//
+// The returned message may alias memory owned by the Client; it
+// should only be accessed until the next call to Client.
+//
+// Once Recv returns an error, the Client is dead forever.
+func (c *Client) Recv() (m ReceivedMessage, err error) {
+	return c.recvTimeout(120 * time.Second)
+}
+
+func (c *Client) recvTimeout(timeout time.Duration) (m ReceivedMessage, err error) {
+	readErr := c.readErr.Load()
+	if readErr != nil {
+		return nil, readErr
+	}
+	defer func() {
+		if err != nil {
+			err = fmt.Errorf("derp.Recv: %w", err)
+			c.readErr.Store(err)
+		}
+	}()
+	for {
+		c.nc.SetReadDeadline(time.Now().Add(timeout))
+
+		// Discard any peeked bytes from a previous Recv call.
+		if c.peeked != 0 {
+			if n, err := c.br.Discard(c.peeked); err != nil || n != c.peeked {
+				// Documented to never fail, but might as well check.
+				return nil, fmt.Errorf("bufio.Reader.Discard(%d bytes): got %v, %v", c.peeked, n, err)
+			}
+			c.peeked = 0
+		}
+
+		t, n, err := readFrameHeader(c.br)
+		if err != nil {
+			return nil, err
+		}
+		if n > 1<<20 {
+			return nil, fmt.Errorf("unexpectedly large frame of %d bytes returned", n)
+		}
+
+		var b []byte // frame payload (past the 5 byte header)
+
+		// If the frame fits in our bufio.Reader buffer, just use it.
+		// In practice it's 4KB (from derphttp.Client's bufio.NewReader(httpConn)) and
+		// in practive, WireGuard packets (and thus DERP frames) are under 1.5KB.
+		// So this is the common path.
+		if int(n) <= c.br.Size() {
+			b, err = c.br.Peek(int(n))
+			c.peeked = int(n)
+		} else {
+			// But if for some reason we read a large DERP message (which isn't necessarily
+			// a WireGuard packet), then just allocate memory for it.
+			// TODO(bradfitz): use a pool if large frames ever happen in practice.
+			b = make([]byte, n)
+			_, err = io.ReadFull(c.br, b)
+		}
+		if err != nil {
+			return nil, err
+		}
+
+		switch t {
+		default:
+			continue
+		case frameServerInfo:
+			// Server sends this at start-up. Currently unused.
+			// Just has a JSON message saying "version: 2",
+			// but the protocol seems extensible enough as-is without
+			// needing to wait an RTT to discover the version at startup.
+			// We'd prefer to give the connection to the client (magicsock)
+			// to start writing as soon as possible.
+			si, err := c.parseServerInfo(b)
+			if err != nil {
+				return nil, fmt.Errorf("invalid server info frame: %v", err)
+			}
+			sm := ServerInfoMessage{
+				TokenBucketBytesPerSecond: si.TokenBucketBytesPerSecond,
+				TokenBucketBytesBurst:     si.TokenBucketBytesBurst,
+			}
+			c.setSendRateLimiter(sm)
+			return sm, nil
+		case frameKeepAlive:
+			// A one-way keep-alive message that doesn't require an acknowledgement.
+			// This predated framePing/framePong.
+			return KeepAliveMessage{}, nil
+		case framePeerGone:
+			if n < keyLen {
+				c.logf("[unexpected] dropping short peerGone frame from DERP server")
+				continue
+			}
+			// Backward compatibility for the older peerGone without reason byte
+			reason := PeerGoneReasonDisconnected
+			if n > keyLen {
+				reason = PeerGoneReasonType(b[keyLen])
+			}
+			pg := PeerGoneMessage{
+				Peer:   key.NodePublicFromRaw32(mem.B(b[:keyLen])),
+				Reason: reason,
+			}
+			return pg, nil
+
+		case framePeerPresent:
+			remain := b
+			chunk, remain, ok := cutLeadingN(remain, keyLen)
+			if !ok {
+				c.logf("[unexpected] dropping short peerPresent frame from DERP server")
+				continue
+			}
+			var msg PeerPresentMessage
+			msg.Key = key.NodePublicFromRaw32(mem.B(chunk))
+
+			const ipLen = 16
+			const portLen = 2
+			chunk, remain, ok = cutLeadingN(remain, ipLen+portLen)
+			if !ok {
+				// Older server which didn't send the IP.
+				return msg, nil
+			}
+			msg.IPPort = netip.AddrPortFrom(
+				netip.AddrFrom16([16]byte(chunk[:ipLen])).Unmap(),
+				binary.BigEndian.Uint16(chunk[ipLen:]),
+			)
+
+			chunk, _, ok = cutLeadingN(remain, 1)
+			if !ok {
+				// Older server which doesn't send PeerPresentFlags.
+				return msg, nil
+			}
+			msg.Flags = PeerPresentFlags(chunk[0])
+			return msg, nil
+
+		case frameRecvPacket:
+			var rp ReceivedPacket
+			if n < keyLen {
+				c.logf("[unexpected] dropping short packet from DERP server")
+				continue
+			}
+			rp.Source = key.NodePublicFromRaw32(mem.B(b[:keyLen]))
+			rp.Data = b[keyLen:n]
+			return rp, nil
+
+		case framePing:
+			var pm PingMessage
+			if n < 8 {
+				c.logf("[unexpected] dropping short ping frame")
+				continue
+			}
+			copy(pm[:], b[:])
+			return pm, nil
+
+		case framePong:
+			var pm PongMessage
+			if n < 8 {
+				c.logf("[unexpected] dropping short ping frame")
+				continue
+			}
+			copy(pm[:], b[:])
+			return pm, nil
+
+		case frameHealth:
+			return HealthMessage{Problem: string(b[:])}, nil
+
+		case frameRestarting:
+			var m ServerRestartingMessage
+			if n < 8 {
+				c.logf("[unexpected] dropping short server restarting frame")
+				continue
+			}
+			m.ReconnectIn = time.Duration(binary.BigEndian.Uint32(b[0:4])) * time.Millisecond
+			m.TryFor = time.Duration(binary.BigEndian.Uint32(b[4:8])) * time.Millisecond
+			return m, nil
+		}
+	}
+}
+
+func (c *Client) setSendRateLimiter(sm ServerInfoMessage) {
+	c.wmu.Lock()
+	defer c.wmu.Unlock()
+
+	if sm.TokenBucketBytesPerSecond == 0 {
+		c.rate = nil
+	} else {
+		c.rate = rate.NewLimiter(
+			rate.Limit(sm.TokenBucketBytesPerSecond),
+			sm.TokenBucketBytesBurst)
+	}
+}
+
+// LocalAddr returns the TCP connection's local address.
+//
+// If the client is broken in some previously detectable way, it
+// returns an error.
+func (c *Client) LocalAddr() (netip.AddrPort, error) {
+	readErr, _ := c.readErr.Load().(error)
+	if readErr != nil {
+		return netip.AddrPort{}, readErr
+	}
+	if c.nc == nil {
+		return netip.AddrPort{}, errors.New("nil conn")
+	}
+	a := c.nc.LocalAddr()
+	if a == nil {
+		return netip.AddrPort{}, errors.New("nil addr")
+	}
+	return netip.ParseAddrPort(a.String())
+}
+
+func cutLeadingN(b []byte, n int) (chunk, remain []byte, ok bool) {
+	if len(b) >= n {
+		return b[:n], b[n:], true
+	}
+	return nil, b, false
+}

vendor/tailscale.com/derp/derp_server_default.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !linux
+
+package derp
+
+import "context"
+
+func (c *sclient) startStatsLoop(ctx context.Context) {
+	// Nothing to do
+	return
+}

vendor/tailscale.com/derp/derp_server_linux.go

@@ -0,0 +1,89 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package derp
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+	"time"
+
+	"tailscale.com/net/tcpinfo"
+)
+
+func (c *sclient) startStatsLoop(ctx context.Context) {
+	// Get the RTT initially to verify it's supported.
+	conn := c.tcpConn()
+	if conn == nil {
+		c.s.tcpRtt.Add("non-tcp", 1)
+		return
+	}
+	if _, err := tcpinfo.RTT(conn); err != nil {
+		c.logf("error fetching initial RTT: %v", err)
+		c.s.tcpRtt.Add("error", 1)
+		return
+	}
+
+	const statsInterval = 10 * time.Second
+
+	// Don't launch a goroutine; use a timer instead.
+	var gatherStats func()
+	gatherStats = func() {
+		// Do nothing if the context is finished.
+		if ctx.Err() != nil {
+			return
+		}
+
+		// Reschedule ourselves when this stats gathering is finished.
+		defer c.s.clock.AfterFunc(statsInterval, gatherStats)
+
+		// Gather TCP RTT information.
+		rtt, err := tcpinfo.RTT(conn)
+		if err == nil {
+			c.s.tcpRtt.Add(durationToLabel(rtt), 1)
+		}
+
+		// TODO(andrew): more metrics?
+	}
+
+	// Kick off the initial timer.
+	c.s.clock.AfterFunc(statsInterval, gatherStats)
+}
+
+// tcpConn attempts to get the underlying *net.TCPConn from this client's
+// Conn; if it cannot, then it will return nil.
+func (c *sclient) tcpConn() *net.TCPConn {
+	nc := c.nc
+	for {
+		switch v := nc.(type) {
+		case *net.TCPConn:
+			return v
+		case *tls.Conn:
+			nc = v.NetConn()
+		default:
+			return nil
+		}
+	}
+}
+
+func durationToLabel(dur time.Duration) string {
+	switch {
+	case dur <= 10*time.Millisecond:
+		return "10ms"
+	case dur <= 20*time.Millisecond:
+		return "20ms"
+	case dur <= 50*time.Millisecond:
+		return "50ms"
+	case dur <= 100*time.Millisecond:
+		return "100ms"
+	case dur <= 150*time.Millisecond:
+		return "150ms"
+	case dur <= 250*time.Millisecond:
+		return "250ms"
+	case dur <= 500*time.Millisecond:
+		return "500ms"
+	default:
+		return "inf"
+	}
+}

vendor/tailscale.com/derp/derphttp/derphttp_server.go

@@ -0,0 +1,108 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package derphttp
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+
+	"tailscale.com/derp"
+)
+
+// fastStartHeader is the header (with value "1") that signals to the HTTP
+// server that the DERP HTTP client does not want the HTTP 101 response
+// headers and it will begin writing & reading the DERP protocol immediately
+// following its HTTP request.
+const fastStartHeader = "Derp-Fast-Start"
+
+// Handler returns an http.Handler to be mounted at /derp, serving s.
+func Handler(s *derp.Server) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// These are installed both here and in cmd/derper. The check here
+		// catches both cmd/derper run with DERP disabled (STUN only mode) as
+		// well as DERP being run in tests with derphttp.Handler directly,
+		// as netcheck still assumes this replies.
+		switch r.URL.Path {
+		case "/derp/probe", "/derp/latency-check":
+			ProbeHandler(w, r)
+			return
+		}
+
+		up := strings.ToLower(r.Header.Get("Upgrade"))
+		if up != "websocket" && up != "derp" {
+			if up != "" {
+				log.Printf("Weird upgrade: %q", up)
+			}
+			http.Error(w, "DERP requires connection upgrade", http.StatusUpgradeRequired)
+			return
+		}
+
+		fastStart := r.Header.Get(fastStartHeader) == "1"
+
+		h, ok := w.(http.Hijacker)
+		if !ok {
+			http.Error(w, "HTTP does not support general TCP support", 500)
+			return
+		}
+
+		netConn, conn, err := h.Hijack()
+		if err != nil {
+			log.Printf("Hijack failed: %v", err)
+			http.Error(w, "HTTP does not support general TCP support", 500)
+			return
+		}
+
+		if !fastStart {
+			pubKey := s.PublicKey()
+			fmt.Fprintf(conn, "HTTP/1.1 101 Switching Protocols\r\n"+
+				"Upgrade: DERP\r\n"+
+				"Connection: Upgrade\r\n"+
+				"Derp-Version: %v\r\n"+
+				"Derp-Public-Key: %s\r\n\r\n",
+				derp.ProtocolVersion,
+				pubKey.UntypedHexString())
+		}
+
+		s.Accept(r.Context(), netConn, conn, netConn.RemoteAddr().String())
+	})
+}
+
+// ProbeHandler is the endpoint that clients without UDP access (including js/wasm) hit to measure
+// DERP latency, as a replacement for UDP STUN queries.
+func ProbeHandler(w http.ResponseWriter, r *http.Request) {
+	switch r.Method {
+	case "HEAD", "GET":
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+	default:
+		http.Error(w, "bogus probe method", http.StatusMethodNotAllowed)
+	}
+}
+
+// ServeNoContent generates the /generate_204 response used by Tailscale's
+// captive portal detection.
+func ServeNoContent(w http.ResponseWriter, r *http.Request) {
+	if challenge := r.Header.Get(NoContentChallengeHeader); challenge != "" {
+		badChar := strings.IndexFunc(challenge, func(r rune) bool {
+			return !isChallengeChar(r)
+		}) != -1
+		if len(challenge) <= 64 && !badChar {
+			w.Header().Set(NoContentResponseHeader, "response "+challenge)
+		}
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func isChallengeChar(c rune) bool {
+	// Semi-randomly chosen as a limited set of valid characters
+	return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') ||
+		('0' <= c && c <= '9') ||
+		c == '.' || c == '-' || c == '_'
+}
+
+const (
+	NoContentChallengeHeader = "X-Tailscale-Challenge"
+	NoContentResponseHeader  = "X-Tailscale-Response"
+)

vendor/tailscale.com/derp/derphttp/mesh_client.go

@@ -0,0 +1,177 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package derphttp
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"tailscale.com/derp"
+	"tailscale.com/types/key"
+	"tailscale.com/types/logger"
+)
+
+var retryInterval = 5 * time.Second
+
+// testHookWatchLookConnectResult, if non-nil for tests, is called by RunWatchConnectionLoop
+// with the connect result. If it returns false, the loop ends.
+var testHookWatchLookConnectResult func(connectError error, wasSelfConnect bool) (keepRunning bool)
+
+// RunWatchConnectionLoop loops until ctx is done, sending
+// WatchConnectionChanges and subscribing to connection changes.
+//
+// If the server's public key is ignoreServerKey, RunWatchConnectionLoop
+// returns.
+//
+// Otherwise, the add and remove funcs are called as clients come & go.
+// Note that add is called for every new connection and remove is only
+// called for the final disconnection. See https://github.com/tailscale/tailscale/issues/13566.
+// This behavior will likely change. Callers should do their own accounting
+// and dup suppression as needed.
+//
+// infoLogf, if non-nil, is the logger to write periodic status updates about
+// how many peers are on the server. Error log output is set to the c's logger,
+// regardless of infoLogf's value.
+//
+// To force RunWatchConnectionLoop to return quickly, its ctx needs to be
+// closed, and c itself needs to be closed.
+//
+// It is a fatal error to call this on an already-started Client without having
+// initialized Client.WatchConnectionChanges to true.
+//
+// If the DERP connection breaks and reconnects, remove will be called for all
+// previously seen peers, with Reason type PeerGoneReasonSynthetic. Those
+// clients are likely still connected and their add message will appear after
+// reconnect.
+func (c *Client) RunWatchConnectionLoop(ctx context.Context, ignoreServerKey key.NodePublic, infoLogf logger.Logf, add func(derp.PeerPresentMessage), remove func(derp.PeerGoneMessage)) {
+	if !c.WatchConnectionChanges {
+		if c.isStarted() {
+			panic("invalid use of RunWatchConnectionLoop on already-started Client without setting Client.RunWatchConnectionLoop")
+		}
+		c.WatchConnectionChanges = true
+	}
+	if infoLogf == nil {
+		infoLogf = logger.Discard
+	}
+	logf := c.logf
+	const statusInterval = 10 * time.Second
+	var (
+		mu              sync.Mutex
+		present         = map[key.NodePublic]bool{}
+		loggedConnected = false
+	)
+	clear := func() {
+		mu.Lock()
+		defer mu.Unlock()
+		if len(present) == 0 {
+			return
+		}
+		logf("reconnected; clearing %d forwarding mappings", len(present))
+		for k := range present {
+			remove(derp.PeerGoneMessage{Peer: k, Reason: derp.PeerGoneReasonMeshConnBroke})
+		}
+		present = map[key.NodePublic]bool{}
+	}
+	lastConnGen := 0
+	lastStatus := c.clock.Now()
+	logConnectedLocked := func() {
+		if loggedConnected {
+			return
+		}
+		infoLogf("connected; %d peers", len(present))
+		loggedConnected = true
+	}
+
+	const logConnectedDelay = 200 * time.Millisecond
+	timer := c.clock.AfterFunc(2*time.Second, func() {
+		mu.Lock()
+		defer mu.Unlock()
+		logConnectedLocked()
+	})
+	defer timer.Stop()
+
+	updatePeer := func(k key.NodePublic, isPresent bool) {
+		mu.Lock()
+		defer mu.Unlock()
+		if isPresent {
+			present[k] = true
+			if !loggedConnected {
+				timer.Reset(logConnectedDelay)
+			}
+		} else {
+			// If we got a peerGone message, that means the initial connection's
+			// flood of peerPresent messages is done, so we can log already:
+			logConnectedLocked()
+			delete(present, k)
+		}
+	}
+
+	sleep := func(d time.Duration) {
+		t, tChannel := c.clock.NewTimer(d)
+		select {
+		case <-ctx.Done():
+			t.Stop()
+		case <-tChannel:
+		}
+	}
+
+	for ctx.Err() == nil {
+		// Make sure we're connected before calling s.ServerPublicKey.
+		_, _, err := c.connect(ctx, "RunWatchConnectionLoop")
+		if err != nil {
+			if f := testHookWatchLookConnectResult; f != nil && !f(err, false) {
+				return
+			}
+			logf("mesh connect: %v", err)
+			sleep(retryInterval)
+			continue
+		}
+		selfConnect := c.ServerPublicKey() == ignoreServerKey
+		if f := testHookWatchLookConnectResult; f != nil && !f(err, selfConnect) {
+			return
+		}
+		if selfConnect {
+			logf("detected self-connect; ignoring host")
+			return
+		}
+		for {
+			m, connGen, err := c.RecvDetail()
+			if err != nil {
+				clear()
+				logf("Recv: %v", err)
+				sleep(retryInterval)
+				break
+			}
+			if connGen != lastConnGen {
+				lastConnGen = connGen
+				clear()
+			}
+			switch m := m.(type) {
+			case derp.PeerPresentMessage:
+				add(m)
+				updatePeer(m.Key, true)
+			case derp.PeerGoneMessage:
+				switch m.Reason {
+				case derp.PeerGoneReasonDisconnected:
+					// Normal case, log nothing
+				case derp.PeerGoneReasonNotHere:
+					logf("Recv: peer %s not connected to %s",
+						key.NodePublic(m.Peer).ShortString(), c.ServerPublicKey().ShortString())
+				default:
+					logf("Recv: peer %s not at server %s for unknown reason %v",
+						key.NodePublic(m.Peer).ShortString(), c.ServerPublicKey().ShortString(), m.Reason)
+				}
+				remove(m)
+				updatePeer(m.Peer, false)
+			default:
+				continue
+			}
+			if now := c.clock.Now(); now.Sub(lastStatus) > statusInterval {
+				lastStatus = now
+				infoLogf("%d peers", len(present))
+			}
+		}
+	}
+}

vendor/tailscale.com/derp/derphttp/websocket.go

@@ -0,0 +1,32 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build linux || js
+
+package derphttp
+
+import (
+	"context"
+	"log"
+	"net"
+
+	"github.com/coder/websocket"
+	"tailscale.com/net/wsconn"
+)
+
+func init() {
+	dialWebsocketFunc = dialWebsocket
+}
+
+func dialWebsocket(ctx context.Context, urlStr string) (net.Conn, error) {
+	c, res, err := websocket.Dial(ctx, urlStr, &websocket.DialOptions{
+		Subprotocols: []string{"derp"},
+	})
+	if err != nil {
+		log.Printf("websocket Dial: %v, %+v", err, res)
+		return nil, err
+	}
+	log.Printf("websocket: connected to %v", urlStr)
+	netConn := wsconn.NetConn(context.Background(), c, websocket.MessageBinary, urlStr)
+	return netConn, nil
+}

vendor/tailscale.com/derp/dropreason_string.go

@@ -0,0 +1,33 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by "stringer -type=dropReason -trimprefix=dropReason"; DO NOT EDIT.
+
+package derp
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[dropReasonUnknownDest-0]
+	_ = x[dropReasonUnknownDestOnFwd-1]
+	_ = x[dropReasonGoneDisconnected-2]
+	_ = x[dropReasonQueueHead-3]
+	_ = x[dropReasonQueueTail-4]
+	_ = x[dropReasonWriteError-5]
+	_ = x[dropReasonDupClient-6]
+	_ = x[numDropReasons-7]
+}
+
+const _dropReason_name = "UnknownDestUnknownDestOnFwdGoneDisconnectedQueueHeadQueueTailWriteErrorDupClientnumDropReasons"
+
+var _dropReason_index = [...]uint8{0, 11, 27, 43, 52, 61, 71, 80, 94}
+
+func (i dropReason) String() string {
+	if i < 0 || i >= dropReason(len(_dropReason_index)-1) {
+		return "dropReason(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _dropReason_name[_dropReason_index[i]:_dropReason_index[i+1]]
+}