headscale/derp_server.go
2022-03-08 12:11:51 +01:00

234 lines
6.2 KiB
Go

package headscale
import (
"context"
"fmt"
"net"
"net/http"
"net/url"
"strconv"
"strings"
"time"
"github.com/gin-gonic/gin"
"github.com/rs/zerolog/log"
"tailscale.com/derp"
"tailscale.com/net/stun"
"tailscale.com/tailcfg"
"tailscale.com/types/key"
)
// 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"
type DERPServer struct {
tailscaleDERP *derp.Server
region tailcfg.DERPRegion
}
func (h *Headscale) NewDERPServer() (*DERPServer, error) {
server := derp.NewServer(key.NodePrivate(*h.privateKey), log.Info().Msgf)
region, err := h.generateRegionLocalDERP()
if err != nil {
return nil, err
}
return &DERPServer{server, region}, nil
}
func (h *Headscale) generateRegionLocalDERP() (tailcfg.DERPRegion, error) {
serverURL, err := url.Parse(h.cfg.ServerURL)
if err != nil {
return tailcfg.DERPRegion{}, err
}
var host string
var port int
host, portStr, err := net.SplitHostPort(serverURL.Host)
if err != nil {
if serverURL.Scheme == "https" {
host = serverURL.Host
port = 443
} else {
host = serverURL.Host
port = 80
}
} else {
port, err = strconv.Atoi(portStr)
if err != nil {
return tailcfg.DERPRegion{}, err
}
}
localDERPregion := tailcfg.DERPRegion{
RegionID: h.cfg.DERP.ServerRegionID,
RegionCode: h.cfg.DERP.ServerRegionCode,
RegionName: h.cfg.DERP.ServerRegionName,
Avoid: false,
Nodes: []*tailcfg.DERPNode{
{
Name: fmt.Sprintf("%d", h.cfg.DERP.ServerRegionID),
RegionID: h.cfg.DERP.ServerRegionID,
HostName: host,
DERPPort: port,
},
},
}
if h.cfg.DERP.STUNEnabled {
_, portStr, err := net.SplitHostPort(h.cfg.DERP.STUNAddr)
if err != nil {
return tailcfg.DERPRegion{}, err
}
port, err := strconv.Atoi(portStr)
if err != nil {
return tailcfg.DERPRegion{}, err
}
localDERPregion.Nodes[0].STUNPort = port
}
return localDERPregion, nil
}
func (h *Headscale) DERPHandler(ctx *gin.Context) {
log.Trace().Caller().Msgf("/derp request from %v", ctx.ClientIP())
up := strings.ToLower(ctx.Request.Header.Get("Upgrade"))
if up != "websocket" && up != "derp" {
if up != "" {
log.Warn().Caller().Msgf("Weird websockets connection upgrade: %q", up)
}
ctx.String(http.StatusUpgradeRequired, "DERP requires connection upgrade")
return
}
fastStart := ctx.Request.Header.Get(fastStartHeader) == "1"
hijacker, ok := ctx.Writer.(http.Hijacker)
if !ok {
log.Error().Caller().Msg("DERP requires Hijacker interface from Gin")
ctx.String(http.StatusInternalServerError, "HTTP does not support general TCP support")
return
}
netConn, conn, err := hijacker.Hijack()
if err != nil {
log.Error().Caller().Err(err).Msgf("Hijack failed")
ctx.String(http.StatusInternalServerError, "HTTP does not support general TCP support")
return
}
if !fastStart {
pubKey := h.privateKey.Public()
pubKeyStr := pubKey.UntypedHexString() // nolint
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,
pubKeyStr)
}
h.DERPServer.tailscaleDERP.Accept(netConn, conn, netConn.RemoteAddr().String())
}
// DERPProbeHandler is the endpoint that js/wasm clients hit to measure
// DERP latency, since they can't do UDP STUN queries.
func (h *Headscale) DERPProbeHandler(ctx *gin.Context) {
switch ctx.Request.Method {
case "HEAD", "GET":
ctx.Writer.Header().Set("Access-Control-Allow-Origin", "*")
default:
ctx.String(http.StatusMethodNotAllowed, "bogus probe method")
}
}
// DERPBootstrapDNSHandler implements the /bootsrap-dns endpoint
// Described in https://github.com/tailscale/tailscale/issues/1405,
// this endpoint provides a way to help a client when it fails to start up
// because its DNS are broken.
// The initial implementation is here https://github.com/tailscale/tailscale/pull/1406
// They have a cache, but not clear if that is really necessary at Headscale, uh, scale.
// An example implementation is found here https://derp.tailscale.com/bootstrap-dns
func (h *Headscale) DERPBootstrapDNSHandler(ctx *gin.Context) {
dnsEntries := make(map[string][]net.IP)
resolvCtx, cancel := context.WithTimeout(context.Background(), time.Minute)
defer cancel()
var r net.Resolver
for _, region := range h.DERPMap.Regions {
for _, node := range region.Nodes { // we don't care if we override some nodes
addrs, err := r.LookupIP(resolvCtx, "ip", node.HostName)
if err != nil {
log.Trace().Caller().Err(err).Msgf("bootstrap DNS lookup failed %q", node.HostName)
continue
}
dnsEntries[node.HostName] = addrs
}
}
ctx.JSON(http.StatusOK, dnsEntries)
}
// ServeSTUN starts a STUN server on the configured addr.
func (h *Headscale) ServeSTUN() {
packetConn, err := net.ListenPacket("udp", h.cfg.DERP.STUNAddr)
if err != nil {
log.Fatal().Msgf("failed to open STUN listener: %v", err)
}
log.Info().Msgf("STUN server started at %s", packetConn.LocalAddr())
udpConn, ok := packetConn.(*net.UDPConn)
if !ok {
log.Fatal().Msg("STUN listener is not a UDP listener")
}
serverSTUNListener(context.Background(), udpConn)
}
func serverSTUNListener(ctx context.Context, packetConn *net.UDPConn) {
var buf [64 << 10]byte
var (
bytesRead int
udpAddr *net.UDPAddr
err error
)
for {
bytesRead, udpAddr, err = packetConn.ReadFromUDP(buf[:])
if err != nil {
if ctx.Err() != nil {
return
}
log.Error().Caller().Err(err).Msgf("STUN ReadFrom")
time.Sleep(time.Second)
continue
}
log.Trace().Caller().Msgf("STUN request from %v", udpAddr)
pkt := buf[:bytesRead]
if !stun.Is(pkt) {
log.Trace().Caller().Msgf("UDP packet is not STUN")
continue
}
txid, err := stun.ParseBindingRequest(pkt)
if err != nil {
log.Trace().Caller().Err(err).Msgf("STUN parse error")
continue
}
res := stun.Response(txid, udpAddr.IP, uint16(udpAddr.Port))
_, err = packetConn.WriteTo(res, udpAddr)
if err != nil {
log.Trace().Caller().Err(err).Msgf("Issue writing to UDP")
continue
}
}
}