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tailscale/derp/derphttp/derphttp_client.go

1062 lines
29 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package derphttp implements DERP-over-HTTP.
//
// This makes DERP look exactly like WebSockets.
// A server can implement DERP over HTTPS and even if the TLS connection
// intercepted using a fake root CA, unless the interceptor knows how to
// detect DERP packets, it will look like a web socket.
package derphttp
import (
"bufio"
"context"
"crypto/rand"
"crypto/tls"
"crypto/x509"
"errors"
"fmt"
"io"
"net"
"net/http"
"net/netip"
"net/url"
"runtime"
"strings"
"sync"
"time"
"go4.org/mem"
"tailscale.com/derp"
"tailscale.com/envknob"
"tailscale.com/net/dnscache"
"tailscale.com/net/netmon"
"tailscale.com/net/netns"
"tailscale.com/net/sockstats"
"tailscale.com/net/tlsdial"
"tailscale.com/net/tshttpproxy"
"tailscale.com/syncs"
"tailscale.com/tailcfg"
"tailscale.com/types/key"
"tailscale.com/types/logger"
"tailscale.com/util/cmpx"
)
// Client is a DERP-over-HTTP client.
//
// It automatically reconnects on error retry. That is, a failed Send or
// Recv will report the error and not retry, but subsequent calls to
// Send/Recv will completely re-establish the connection (unless Close
// has been called).
type Client struct {
TLSConfig *tls.Config // optional; nil means default
DNSCache *dnscache.Resolver // optional; nil means no caching
MeshKey string // optional; for trusted clients
IsProber bool // optional; for probers to optional declare themselves as such
privateKey key.NodePrivate
logf logger.Logf
netMon *netmon.Monitor // optional; nil means interfaces will be looked up on-demand
dialer func(ctx context.Context, network, addr string) (net.Conn, error)
// Either url or getRegion is non-nil:
url *url.URL
getRegion func() *tailcfg.DERPRegion
ctx context.Context // closed via cancelCtx in Client.Close
cancelCtx context.CancelFunc
// addrFamSelAtomic is the last AddressFamilySelector set
// by SetAddressFamilySelector. It's an atomic because it needs
// to be accessed by multiple racing routines started while
// Client.conn holds mu.
addrFamSelAtomic syncs.AtomicValue[AddressFamilySelector]
mu sync.Mutex
preferred bool
canAckPings bool
closed bool
netConn io.Closer
client *derp.Client
connGen int // incremented once per new connection; valid values are >0
serverPubKey key.NodePublic
tlsState *tls.ConnectionState
pingOut map[derp.PingMessage]chan<- bool // chan to send to on pong
}
func (c *Client) String() string {
return fmt.Sprintf("<derphttp_client.Client %s url=%s>", c.serverPubKey.ShortString(), c.url)
}
// NewRegionClient returns a new DERP-over-HTTP client. It connects lazily.
// To trigger a connection, use Connect.
// The netMon parameter is optional; if non-nil it's used to do faster interface lookups.
func NewRegionClient(privateKey key.NodePrivate, logf logger.Logf, netMon *netmon.Monitor, getRegion func() *tailcfg.DERPRegion) *Client {
ctx, cancel := context.WithCancel(context.Background())
c := &Client{
privateKey: privateKey,
logf: logf,
netMon: netMon,
getRegion: getRegion,
ctx: ctx,
cancelCtx: cancel,
}
return c
}
// NewNetcheckClient returns a Client that's only able to have its DialRegionTLS method called.
// It's used by the netcheck package.
func NewNetcheckClient(logf logger.Logf) *Client {
return &Client{logf: logf}
}
// NewClient returns a new DERP-over-HTTP client. It connects lazily.
// To trigger a connection, use Connect.
func NewClient(privateKey key.NodePrivate, serverURL string, logf logger.Logf) (*Client, error) {
u, err := url.Parse(serverURL)
if err != nil {
return nil, fmt.Errorf("derphttp.NewClient: %v", err)
}
if urlPort(u) == "" {
return nil, fmt.Errorf("derphttp.NewClient: invalid URL scheme %q", u.Scheme)
}
ctx, cancel := context.WithCancel(context.Background())
c := &Client{
privateKey: privateKey,
logf: logf,
url: u,
ctx: ctx,
cancelCtx: cancel,
}
return c, nil
}
// Connect connects or reconnects to the server, unless already connected.
// It returns nil if there was already a good connection, or if one was made.
func (c *Client) Connect(ctx context.Context) error {
_, _, err := c.connect(ctx, "derphttp.Client.Connect")
return err
}
// TLSConnectionState returns the last TLS connection state, if any.
// The client must already be connected.
func (c *Client) TLSConnectionState() (_ *tls.ConnectionState, ok bool) {
c.mu.Lock()
defer c.mu.Unlock()
if c.closed || c.client == nil {
return nil, false
}
return c.tlsState, c.tlsState != nil
}
// ServerPublicKey returns the server's public key.
//
// It only returns a non-zero value once a connection has succeeded
// from an earlier call.
func (c *Client) ServerPublicKey() key.NodePublic {
c.mu.Lock()
defer c.mu.Unlock()
return c.serverPubKey
}
// SelfPublicKey returns our own public key.
func (c *Client) SelfPublicKey() key.NodePublic {
return c.privateKey.Public()
}
func urlPort(u *url.URL) string {
if p := u.Port(); p != "" {
return p
}
switch u.Scheme {
case "https":
return "443"
case "http":
return "80"
}
return ""
}
// debugDERPUseHTTP tells clients to connect to DERP via HTTP on port
// 3340 instead of HTTPS on 443.
var debugUseDERPHTTP = envknob.RegisterBool("TS_DEBUG_USE_DERP_HTTP")
func (c *Client) targetString(reg *tailcfg.DERPRegion) string {
if c.url != nil {
return c.url.String()
}
return fmt.Sprintf("region %d (%v)", reg.RegionID, reg.RegionCode)
}
func (c *Client) useHTTPS() bool {
if c.url != nil && c.url.Scheme == "http" {
return false
}
if debugUseDERPHTTP() {
return false
}
return true
}
// tlsServerName returns the tls.Config.ServerName value (for the TLS ClientHello).
func (c *Client) tlsServerName(node *tailcfg.DERPNode) string {
if c.url != nil {
return c.url.Host
}
return node.HostName
}
func (c *Client) urlString(node *tailcfg.DERPNode) string {
if c.url != nil {
return c.url.String()
}
proto := "https"
if debugUseDERPHTTP() {
proto = "http"
}
return fmt.Sprintf("%s://%s/derp", proto, node.HostName)
}
// AddressFamilySelector decides whether IPv6 is preferred for
// outbound dials.
type AddressFamilySelector interface {
// PreferIPv6 reports whether IPv4 dials should be slightly
// delayed to give IPv6 a better chance of winning dial races.
// Implementations should only return true if IPv6 is expected
// to succeed. (otherwise delaying IPv4 will delay the
// connection overall)
PreferIPv6() bool
}
// SetAddressFamilySelector sets the AddressFamilySelector that this
// connection will use. It should be called before any dials.
// The value must not be nil. If called more than once, s must
// be the same concrete type as any prior calls.
func (c *Client) SetAddressFamilySelector(s AddressFamilySelector) {
c.addrFamSelAtomic.Store(s)
}
func (c *Client) preferIPv6() bool {
if s, ok := c.addrFamSelAtomic.Load().(AddressFamilySelector); ok {
return s.PreferIPv6()
}
return false
}
// dialWebsocketFunc is non-nil (set by websocket.go's init) when compiled in.
var dialWebsocketFunc func(ctx context.Context, urlStr string) (net.Conn, error)
func useWebsockets() bool {
if runtime.GOOS == "js" {
return true
}
if dialWebsocketFunc != nil {
return envknob.Bool("TS_DEBUG_DERP_WS_CLIENT")
}
return false
}
func (c *Client) connect(ctx context.Context, caller string) (client *derp.Client, connGen int, err error) {
c.mu.Lock()
defer c.mu.Unlock()
if c.closed {
return nil, 0, ErrClientClosed
}
if c.client != nil {
return c.client, c.connGen, nil
}
// timeout is the fallback maximum time (if ctx doesn't limit
// it further) to do all of: DNS + TCP + TLS + HTTP Upgrade +
// DERP upgrade.
const timeout = 10 * time.Second
ctx, cancel := context.WithTimeout(ctx, timeout)
go func() {
select {
case <-ctx.Done():
// Either timeout fired (handled below), or
// we're returning via the defer cancel()
// below.
case <-c.ctx.Done():
// Propagate a Client.Close call into
// cancelling this context.
cancel()
}
}()
defer cancel()
var reg *tailcfg.DERPRegion // nil when using c.url to dial
if c.getRegion != nil {
reg = c.getRegion()
if reg == nil {
return nil, 0, errors.New("DERP region not available")
}
}
var tcpConn net.Conn
defer func() {
if err != nil {
if ctx.Err() != nil {
err = fmt.Errorf("%v: %v", ctx.Err(), err)
}
err = fmt.Errorf("%s connect to %v: %v", caller, c.targetString(reg), err)
if tcpConn != nil {
go tcpConn.Close()
}
}
}()
var node *tailcfg.DERPNode // nil when using c.url to dial
switch {
case useWebsockets():
var urlStr string
if c.url != nil {
urlStr = c.url.String()
} else {
urlStr = c.urlString(reg.Nodes[0])
}
c.logf("%s: connecting websocket to %v", caller, urlStr)
conn, err := dialWebsocketFunc(ctx, urlStr)
if err != nil {
c.logf("%s: websocket to %v error: %v", caller, urlStr, err)
return nil, 0, err
}
brw := bufio.NewReadWriter(bufio.NewReader(conn), bufio.NewWriter(conn))
derpClient, err := derp.NewClient(c.privateKey, conn, brw, c.logf,
derp.MeshKey(c.MeshKey),
derp.CanAckPings(c.canAckPings),
derp.IsProber(c.IsProber),
)
if err != nil {
return nil, 0, err
}
if c.preferred {
if err := derpClient.NotePreferred(true); err != nil {
go conn.Close()
return nil, 0, err
}
}
c.serverPubKey = derpClient.ServerPublicKey()
c.client = derpClient
c.netConn = conn
c.connGen++
return c.client, c.connGen, nil
case c.url != nil:
c.logf("%s: connecting to %v", caller, c.url)
tcpConn, err = c.dialURL(ctx)
default:
c.logf("%s: connecting to derp-%d (%v)", caller, reg.RegionID, reg.RegionCode)
tcpConn, node, err = c.dialRegion(ctx, reg)
}
if err != nil {
return nil, 0, err
}
// Now that we have a TCP connection, force close it if the
// TLS handshake + DERP setup takes too long.
done := make(chan struct{})
defer close(done)
go func() {
select {
case <-done:
// Normal path. Upgrade occurred in time.
case <-ctx.Done():
select {
case <-done:
// Normal path. Upgrade occurred in time.
// But the ctx.Done() is also done because
// the "defer cancel()" above scheduled
// before this goroutine.
default:
// The TLS or HTTP or DERP exchanges didn't complete
// in time. Force close the TCP connection to force
// them to fail quickly.
tcpConn.Close()
}
}
}()
var httpConn net.Conn // a TCP conn or a TLS conn; what we speak HTTP to
var serverPub key.NodePublic // or zero if unknown (if not using TLS or TLS middlebox eats it)
var serverProtoVersion int
var tlsState *tls.ConnectionState
if c.useHTTPS() {
tlsConn := c.tlsClient(tcpConn, node)
httpConn = tlsConn
// Force a handshake now (instead of waiting for it to
// be done implicitly on read/write) so we can check
// the ConnectionState.
if err := tlsConn.Handshake(); err != nil {
return nil, 0, err
}
// We expect to be using TLS 1.3 to our own servers, and only
// starting at TLS 1.3 are the server's returned certificates
// encrypted, so only look for and use our "meta cert" if we're
// using TLS 1.3. If we're not using TLS 1.3, it might be a user
// running cmd/derper themselves with a different configuration,
// in which case we can avoid this fast-start optimization.
// (If a corporate proxy is MITM'ing TLS 1.3 connections with
// corp-mandated TLS root certs than all bets are off anyway.)
// Note that we're not specifically concerned about TLS downgrade
// attacks. TLS handles that fine:
// https://blog.gypsyengineer.com/en/security/how-does-tls-1-3-protect-against-downgrade-attacks.html
cs := tlsConn.ConnectionState()
tlsState = &cs
if cs.Version >= tls.VersionTLS13 {
serverPub, serverProtoVersion = parseMetaCert(cs.PeerCertificates)
}
} else {
httpConn = tcpConn
}
brw := bufio.NewReadWriter(bufio.NewReader(httpConn), bufio.NewWriter(httpConn))
var derpClient *derp.Client
req, err := http.NewRequest("GET", c.urlString(node), nil)
if err != nil {
return nil, 0, err
}
req.Header.Set("Upgrade", "DERP")
req.Header.Set("Connection", "Upgrade")
if !serverPub.IsZero() && serverProtoVersion != 0 {
// parseMetaCert found the server's public key (no TLS
// middlebox was in the way), so skip the HTTP upgrade
// exchange. See https://github.com/tailscale/tailscale/issues/693
// for an overview. We still send the HTTP request
// just to get routed into the server's HTTP Handler so it
// can Hijack the request, but we signal with a special header
// that we don't want to deal with its HTTP response.
req.Header.Set(fastStartHeader, "1") // suppresses the server's HTTP response
if err := req.Write(brw); err != nil {
return nil, 0, err
}
// No need to flush the HTTP request. the derp.Client's initial
// client auth frame will flush it.
} else {
if err := req.Write(brw); err != nil {
return nil, 0, err
}
if err := brw.Flush(); err != nil {
return nil, 0, err
}
resp, err := http.ReadResponse(brw.Reader, req)
if err != nil {
return nil, 0, err
}
if resp.StatusCode != http.StatusSwitchingProtocols {
b, _ := io.ReadAll(resp.Body)
resp.Body.Close()
return nil, 0, fmt.Errorf("GET failed: %v: %s", err, b)
}
}
derpClient, err = derp.NewClient(c.privateKey, httpConn, brw, c.logf,
derp.MeshKey(c.MeshKey),
derp.ServerPublicKey(serverPub),
derp.CanAckPings(c.canAckPings),
derp.IsProber(c.IsProber),
)
if err != nil {
return nil, 0, err
}
if c.preferred {
if err := derpClient.NotePreferred(true); err != nil {
go httpConn.Close()
return nil, 0, err
}
}
c.serverPubKey = derpClient.ServerPublicKey()
c.client = derpClient
c.netConn = tcpConn
c.tlsState = tlsState
c.connGen++
return c.client, c.connGen, nil
}
// SetURLDialer sets the dialer to use for dialing URLs.
// This dialer is only use for clients created with NewClient, not NewRegionClient.
// If unset or nil, the default dialer is used.
//
// The primary use for this is the derper mesh mode to connect to each
// other over a VPC network.
func (c *Client) SetURLDialer(dialer func(ctx context.Context, network, addr string) (net.Conn, error)) {
c.dialer = dialer
}
func (c *Client) dialURL(ctx context.Context) (net.Conn, error) {
host := c.url.Hostname()
if c.dialer != nil {
return c.dialer(ctx, "tcp", net.JoinHostPort(host, urlPort(c.url)))
}
hostOrIP := host
dialer := netns.NewDialer(c.logf, c.netMon)
if c.DNSCache != nil {
ip, _, _, err := c.DNSCache.LookupIP(ctx, host)
if err == nil {
hostOrIP = ip.String()
}
if err != nil && netns.IsSOCKSDialer(dialer) {
// Return an error if we're not using a dial
// proxy that can do DNS lookups for us.
return nil, err
}
}
tcpConn, err := dialer.DialContext(ctx, "tcp", net.JoinHostPort(hostOrIP, urlPort(c.url)))
if err != nil {
return nil, fmt.Errorf("dial of %v: %v", host, err)
}
return tcpConn, nil
}
// dialRegion returns a TCP connection to the provided region, trying
// each node in order (with dialNode) until one connects or ctx is
// done.
func (c *Client) dialRegion(ctx context.Context, reg *tailcfg.DERPRegion) (net.Conn, *tailcfg.DERPNode, error) {
if len(reg.Nodes) == 0 {
return nil, nil, fmt.Errorf("no nodes for %s", c.targetString(reg))
}
var firstErr error
for _, n := range reg.Nodes {
if n.STUNOnly {
if firstErr == nil {
firstErr = fmt.Errorf("no non-STUNOnly nodes for %s", c.targetString(reg))
}
continue
}
c, err := c.dialNode(ctx, n)
if err == nil {
return c, n, nil
}
if firstErr == nil {
firstErr = err
}
}
return nil, nil, firstErr
}
func (c *Client) tlsClient(nc net.Conn, node *tailcfg.DERPNode) *tls.Conn {
tlsConf := tlsdial.Config(c.tlsServerName(node), c.TLSConfig)
if node != nil {
if node.InsecureForTests {
tlsConf.InsecureSkipVerify = true
tlsConf.VerifyConnection = nil
}
if node.CertName != "" {
tlsdial.SetConfigExpectedCert(tlsConf, node.CertName)
}
}
return tls.Client(nc, tlsConf)
}
// DialRegionTLS returns a TLS connection to a DERP node in the given region.
//
// DERP nodes for a region are tried in sequence according to their order
// in the DERP map. TLS is initiated on the first node where a socket is
// established.
func (c *Client) DialRegionTLS(ctx context.Context, reg *tailcfg.DERPRegion) (tlsConn *tls.Conn, connClose io.Closer, node *tailcfg.DERPNode, err error) {
tcpConn, node, err := c.dialRegion(ctx, reg)
if err != nil {
return nil, nil, nil, err
}
done := make(chan bool) // unbuffered
defer close(done)
tlsConn = c.tlsClient(tcpConn, node)
go func() {
select {
case <-done:
case <-ctx.Done():
tcpConn.Close()
}
}()
err = tlsConn.Handshake()
if err != nil {
return nil, nil, nil, err
}
select {
case done <- true:
return tlsConn, tcpConn, node, nil
case <-ctx.Done():
return nil, nil, nil, ctx.Err()
}
}
func (c *Client) dialContext(ctx context.Context, proto, addr string) (net.Conn, error) {
return netns.NewDialer(c.logf, c.netMon).DialContext(ctx, proto, addr)
}
// shouldDialProto reports whether an explicitly provided IPv4 or IPv6
// address (given in s) is valid. An empty value means to dial, but to
// use DNS. The predicate function reports whether the non-empty
// string s contained a valid IP address of the right family.
func shouldDialProto(s string, pred func(netip.Addr) bool) bool {
if s == "" {
return true
}
ip, _ := netip.ParseAddr(s)
return pred(ip)
}
const dialNodeTimeout = 1500 * time.Millisecond
// dialNode returns a TCP connection to node n, racing IPv4 and IPv6
// (both as applicable) against each other.
// A node is only given dialNodeTimeout to connect.
//
// TODO(bradfitz): longer if no options remain perhaps? ... Or longer
// overall but have dialRegion start overlapping races?
func (c *Client) dialNode(ctx context.Context, n *tailcfg.DERPNode) (net.Conn, error) {
// First see if we need to use an HTTP proxy.
proxyReq := &http.Request{
Method: "GET", // doesn't really matter
URL: &url.URL{
Scheme: "https",
Host: c.tlsServerName(n),
Path: "/", // unused
},
}
if proxyURL, err := tshttpproxy.ProxyFromEnvironment(proxyReq); err == nil && proxyURL != nil {
return c.dialNodeUsingProxy(ctx, n, proxyURL)
}
type res struct {
c net.Conn
err error
}
resc := make(chan res) // must be unbuffered
ctx, cancel := context.WithTimeout(ctx, dialNodeTimeout)
defer cancel()
ctx = sockstats.WithSockStats(ctx, sockstats.LabelDERPHTTPClient, c.logf)
nwait := 0
startDial := func(dstPrimary, proto string) {
nwait++
go func() {
if proto == "tcp4" && c.preferIPv6() {
t := time.NewTimer(200 * time.Millisecond)
select {
case <-ctx.Done():
// Either user canceled original context,
// it timed out, or the v6 dial succeeded.
t.Stop()
return
case <-t.C:
// Start v4 dial
}
}
dst := cmpx.Or(dstPrimary, n.HostName)
port := "443"
if n.DERPPort != 0 {
port = fmt.Sprint(n.DERPPort)
}
c, err := c.dialContext(ctx, proto, net.JoinHostPort(dst, port))
select {
case resc <- res{c, err}:
case <-ctx.Done():
if c != nil {
c.Close()
}
}
}()
}
if shouldDialProto(n.IPv4, netip.Addr.Is4) {
startDial(n.IPv4, "tcp4")
}
if shouldDialProto(n.IPv6, netip.Addr.Is6) {
startDial(n.IPv6, "tcp6")
}
if nwait == 0 {
return nil, errors.New("both IPv4 and IPv6 are explicitly disabled for node")
}
var firstErr error
for {
select {
case res := <-resc:
nwait--
if res.err == nil {
return res.c, nil
}
if firstErr == nil {
firstErr = res.err
}
if nwait == 0 {
return nil, firstErr
}
case <-ctx.Done():
return nil, ctx.Err()
}
}
}
func firstStr(a, b string) string {
if a != "" {
return a
}
return b
}
// dialNodeUsingProxy connects to n using a CONNECT to the HTTP(s) proxy in proxyURL.
func (c *Client) dialNodeUsingProxy(ctx context.Context, n *tailcfg.DERPNode, proxyURL *url.URL) (proxyConn net.Conn, err error) {
pu := proxyURL
if pu.Scheme == "https" {
var d tls.Dialer
proxyConn, err = d.DialContext(ctx, "tcp", net.JoinHostPort(pu.Hostname(), firstStr(pu.Port(), "443")))
} else {
var d net.Dialer
proxyConn, err = d.DialContext(ctx, "tcp", net.JoinHostPort(pu.Hostname(), firstStr(pu.Port(), "80")))
}
defer func() {
if err != nil && proxyConn != nil {
// In a goroutine in case it's a *tls.Conn (that can block on Close)
// TODO(bradfitz): track the underlying tcp.Conn and just close that instead.
go proxyConn.Close()
}
}()
if err != nil {
return nil, err
}
done := make(chan struct{})
defer close(done)
go func() {
select {
case <-done:
return
case <-ctx.Done():
proxyConn.Close()
}
}()
target := net.JoinHostPort(n.HostName, "443")
var authHeader string
if v, err := tshttpproxy.GetAuthHeader(pu); err != nil {
c.logf("derphttp: error getting proxy auth header for %v: %v", proxyURL, err)
} else if v != "" {
authHeader = fmt.Sprintf("Proxy-Authorization: %s\r\n", v)
}
if _, err := fmt.Fprintf(proxyConn, "CONNECT %s HTTP/1.1\r\nHost: %s\r\n%s\r\n", target, pu.Hostname(), authHeader); err != nil {
if ctx.Err() != nil {
return nil, ctx.Err()
}
return nil, err
}
br := bufio.NewReader(proxyConn)
res, err := http.ReadResponse(br, nil)
if err != nil {
if ctx.Err() != nil {
return nil, ctx.Err()
}
c.logf("derphttp: CONNECT dial to %s: %v", target, err)
return nil, err
}
c.logf("derphttp: CONNECT dial to %s: %v", target, res.Status)
if res.StatusCode != 200 {
return nil, fmt.Errorf("invalid response status from HTTP proxy %s on CONNECT to %s: %v", pu, target, res.Status)
}
return proxyConn, nil
}
func (c *Client) Send(dstKey key.NodePublic, b []byte) error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.Send")
if err != nil {
return err
}
if err := client.Send(dstKey, b); err != nil {
c.closeForReconnect(client)
}
return err
}
func (c *Client) registerPing(m derp.PingMessage, ch chan<- bool) {
c.mu.Lock()
defer c.mu.Unlock()
if c.pingOut == nil {
c.pingOut = map[derp.PingMessage]chan<- bool{}
}
c.pingOut[m] = ch
}
func (c *Client) unregisterPing(m derp.PingMessage) {
c.mu.Lock()
defer c.mu.Unlock()
delete(c.pingOut, m)
}
func (c *Client) handledPong(m derp.PongMessage) bool {
c.mu.Lock()
defer c.mu.Unlock()
k := derp.PingMessage(m)
if ch, ok := c.pingOut[k]; ok {
ch <- true
delete(c.pingOut, k)
return true
}
return false
}
// Ping sends a ping to the peer and waits for it either to be
// acknowledged (in which case Ping returns nil) or waits for ctx to
// be over and returns an error. It will wait at most 5 seconds
// before returning an error.
//
// Another goroutine must be in a loop calling Recv or
// RecvDetail or ping responses won't be handled.
func (c *Client) Ping(ctx context.Context) error {
maxDL := time.Now().Add(5 * time.Second)
if dl, ok := ctx.Deadline(); !ok || dl.After(maxDL) {
var cancel context.CancelFunc
ctx, cancel = context.WithDeadline(ctx, maxDL)
defer cancel()
}
var data derp.PingMessage
rand.Read(data[:])
gotPing := make(chan bool, 1)
c.registerPing(data, gotPing)
defer c.unregisterPing(data)
if err := c.SendPing(data); err != nil {
return err
}
select {
case <-gotPing:
return nil
case <-ctx.Done():
return ctx.Err()
}
}
// SendPing writes a ping message, without any implicit connect or
// reconnect. This is a lower-level interface that writes a frame
// without any implicit handling of the response pong, if any. For a
// higher-level interface, use Ping.
func (c *Client) SendPing(data [8]byte) error {
c.mu.Lock()
closed, client := c.closed, c.client
c.mu.Unlock()
if closed {
return ErrClientClosed
}
if client == nil {
return errors.New("client not connected")
}
return client.SendPing(data)
}
// LocalAddr reports c's local TCP address, without any implicit
// connect or reconnect.
func (c *Client) LocalAddr() (netip.AddrPort, error) {
c.mu.Lock()
closed, client := c.closed, c.client
c.mu.Unlock()
if closed {
return netip.AddrPort{}, ErrClientClosed
}
if client == nil {
return netip.AddrPort{}, errors.New("client not connected")
}
return client.LocalAddr()
}
func (c *Client) ForwardPacket(from, to key.NodePublic, b []byte) error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.ForwardPacket")
if err != nil {
return err
}
if err := client.ForwardPacket(from, to, b); err != nil {
c.closeForReconnect(client)
}
return err
}
// SendPong sends a reply to a ping, with the ping's provided
// challenge/identifier data.
//
// Unlike other send methods, SendPong makes no attempt to connect or
// reconnect to the peer. It's best effort. If there's a connection
// problem, the server will choose to hang up on us if we're not
// replying.
func (c *Client) SendPong(data [8]byte) error {
c.mu.Lock()
if c.closed {
c.mu.Unlock()
return ErrClientClosed
}
if c.client == nil {
c.mu.Unlock()
return errors.New("not connected")
}
dc := c.client
c.mu.Unlock()
return dc.SendPong(data)
}
// SetCanAckPings sets whether this client will reply to ping requests from the server.
//
// This only affects future connections.
func (c *Client) SetCanAckPings(v bool) {
c.mu.Lock()
defer c.mu.Unlock()
c.canAckPings = v
}
// NotePreferred notes whether this Client is the caller's preferred
// (home) DERP node. It's only used for stats.
func (c *Client) NotePreferred(v bool) {
c.mu.Lock()
if c.preferred == v {
c.mu.Unlock()
return
}
c.preferred = v
client := c.client
c.mu.Unlock()
if client != nil {
if err := client.NotePreferred(v); err != nil {
c.closeForReconnect(client)
}
}
}
// WatchConnectionChanges sends a request to subscribe to
// notifications about clients connecting & disconnecting.
//
// Only trusted connections (using MeshKey) are allowed to use this.
func (c *Client) WatchConnectionChanges() error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.WatchConnectionChanges")
if err != nil {
return err
}
err = client.WatchConnectionChanges()
if err != nil {
c.closeForReconnect(client)
}
return err
}
// ClosePeer asks the server to close target's TCP connection.
//
// Only trusted connections (using MeshKey) are allowed to use this.
func (c *Client) ClosePeer(target key.NodePublic) error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.ClosePeer")
if err != nil {
return err
}
err = client.ClosePeer(target)
if err != nil {
c.closeForReconnect(client)
}
return err
}
// Recv reads a message from c. The returned message may alias memory from Client.
// The message should only be used until the next Client call.
func (c *Client) Recv() (derp.ReceivedMessage, error) {
m, _, err := c.RecvDetail()
return m, err
}
// RecvDetail is like Recv, but additional returns the connection generation on each message.
// The connGen value is incremented every time the derphttp.Client reconnects to the server.
func (c *Client) RecvDetail() (m derp.ReceivedMessage, connGen int, err error) {
client, connGen, err := c.connect(context.TODO(), "derphttp.Client.Recv")
if err != nil {
return nil, 0, err
}
for {
m, err = client.Recv()
switch m := m.(type) {
case derp.PongMessage:
if c.handledPong(m) {
continue
}
}
if err != nil {
c.closeForReconnect(client)
if c.isClosed() {
err = ErrClientClosed
}
}
return m, connGen, err
}
}
func (c *Client) isClosed() bool {
c.mu.Lock()
defer c.mu.Unlock()
return c.closed
}
// Close closes the client. It will not automatically reconnect after
// being closed.
func (c *Client) Close() error {
if c.cancelCtx != nil {
c.cancelCtx() // not in lock, so it can cancel Connect, which holds mu
}
c.mu.Lock()
defer c.mu.Unlock()
if c.closed {
return ErrClientClosed
}
c.closed = true
if c.netConn != nil {
c.netConn.Close()
}
return nil
}
// closeForReconnect closes the underlying network connection and
// zeros out the client field so future calls to Connect will
// reconnect.
//
// The provided brokenClient is the client to forget. If current
// client is not brokenClient, closeForReconnect does nothing. (This
// prevents a send and receive goroutine from failing at the ~same
// time and both calling closeForReconnect and the caller goroutines
// forever calling closeForReconnect in lockstep endlessly;
// https://github.com/tailscale/tailscale/pull/264)
func (c *Client) closeForReconnect(brokenClient *derp.Client) {
c.mu.Lock()
defer c.mu.Unlock()
if c.client != brokenClient {
return
}
if c.netConn != nil {
c.netConn.Close()
c.netConn = nil
}
c.client = nil
}
var ErrClientClosed = errors.New("derphttp.Client closed")
func parseMetaCert(certs []*x509.Certificate) (serverPub key.NodePublic, serverProtoVersion int) {
for _, cert := range certs {
// Look for derpkey prefix added by initMetacert() on the server side.
if pubHex, ok := strings.CutPrefix(cert.Subject.CommonName, "derpkey"); ok {
var err error
serverPub, err = key.ParseNodePublicUntyped(mem.S(pubHex))
if err == nil && cert.SerialNumber.BitLen() <= 8 { // supports up to version 255
return serverPub, int(cert.SerialNumber.Int64())
}
}
}
return key.NodePublic{}, 0
}