tsweb, cmd/derper: move common web/debug stuff from derper to new tsweb

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/derper/derper.go

@@ -8,27 +8,22 @@
 import (
 	"encoding/json"
 	"expvar"
-	_ "expvar"
 	"flag"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"log"
-	"net"
 	"net/http"
-	_ "net/http/pprof"
 	"os"
 	"path/filepath"
-	"strings"
-	"time"
 
 	"github.com/tailscale/wireguard-go/wgcfg"
 	"golang.org/x/crypto/acme/autocert"
 	"tailscale.com/atomicfile"
 	"tailscale.com/derp"
 	"tailscale.com/derp/derphttp"
-	"tailscale.com/interfaces"
 	"tailscale.com/logpolicy"
+	"tailscale.com/tsweb"
 	"tailscale.com/types/key"
 )
 
@@ -36,20 +31,12 @@
 	dev           = flag.Bool("dev", false, "run in localhost development mode")
 	addr          = flag.String("a", ":443", "server address")
 	configPath    = flag.String("c", "", "config file path")
-	certDir       = flag.String("certdir", defaultCertDir(), "directory to store LetsEncrypt certs, if addr's port is :443")
+	certDir       = flag.String("certdir", tsweb.DefaultCertDir("derper-certs"), "directory to store LetsEncrypt certs, if addr's port is :443")
 	hostname      = flag.String("hostname", "derp.tailscale.com", "LetsEncrypt host name, if addr's port is :443")
 	mbps          = flag.Int("mbps", 5, "Mbps (mebibit/s) per-client rate limit; 0 means unlimited")
 	logCollection = flag.String("logcollection", "", "If non-empty, logtail collection to log to")
 )
 
-func defaultCertDir() string {
-	cacheDir, err := os.UserCacheDir()
-	if err == nil {
-		return filepath.Join(cacheDir, "tailscale", "derper-certs")
-	}
-	return ""
-}
-
 type config struct {
 	PrivateKey wgcfg.PrivateKey
 }
@@ -120,24 +107,17 @@ func main() {
 
 	cfg := loadConfig()
 
-	letsEncrypt := false
-	if _, port, _ := net.SplitHostPort(*addr); port == "443" {
-		letsEncrypt = true
-	}
+	letsEncrypt := tsweb.IsProd443(*addr)
 
 	s := derp.NewServer(key.Private(cfg.PrivateKey), log.Printf)
 	if *mbps != 0 {
 		s.BytesPerSecond = (*mbps << 20) / 8
 	}
 	expvar.Publish("derp", s.ExpVar())
-	expvar.Publish("uptime", uptimeVar{})
 
 	// Create our own mux so we don't expose /debug/ stuff to the world.
-	mux := http.NewServeMux()
+	mux := tsweb.NewMux(debugHandler(s))
 	mux.Handle("/derp", derphttp.Handler(s))
-	mux.Handle("/debug/", protected(debugHandler(s)))
-	mux.Handle("/debug/pprof/", protected(http.DefaultServeMux)) // to net/http/pprof
-	mux.Handle("/debug/vars", protected(http.DefaultServeMux))   // to expvar
 	mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 		w.WriteHeader(200)
@@ -150,7 +130,7 @@ func main() {
   server.
 </p>
 `)
-		if allowDebugAccess(r) {
+		if tsweb.AllowDebugAccess(r) {
 			io.WriteString(w, "<p>Debug info at <a href='/debug/'>/debug/</a>.</p>\n")
 		}
 	}))
@@ -173,7 +153,7 @@ func main() {
 		}
 		httpsrv.TLSConfig = certManager.TLSConfig()
 		go func() {
-			err := http.ListenAndServe(":80", certManager.HTTPHandler(port80Handler{mux}))
+			err := http.ListenAndServe(":80", certManager.HTTPHandler(tsweb.Port80Handler{mux}))
 			if err != nil {
 				if err != http.ErrServerClosed {
 					log.Fatal(err)
@@ -190,57 +170,6 @@ func main() {
 	}
 }
 
-func protected(h http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if !allowDebugAccess(r) {
-			http.Error(w, "debug access denied", http.StatusForbidden)
-			return
-		}
-		h.ServeHTTP(w, r)
-	})
-}
-
-func allowDebugAccess(r *http.Request) bool {
-	if r.Header.Get("X-Forwarded-For") != "" {
-		// TODO if/when needed. For now, conservative:
-		return false
-	}
-	ipStr, _, err := net.SplitHostPort(r.RemoteAddr)
-	if err != nil {
-		return false
-	}
-	ip := net.ParseIP(ipStr)
-	return interfaces.IsTailscaleIP(ip) || ip.IsLoopback() || ipStr == os.Getenv("ALLOW_DEBUG_IP")
-}
-
-type port80Handler struct{ tlsHandler http.Handler }
-
-func (h port80Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	path := r.RequestURI
-	if path == "/debug" || strings.HasPrefix(path, "/debug") {
-		h.tlsHandler.ServeHTTP(w, r)
-		return
-	}
-	if r.Method != "GET" && r.Method != "HEAD" {
-		http.Error(w, "Use HTTPS", http.StatusBadRequest)
-		return
-	}
-	if path == "/" && allowDebugAccess(r) {
-		// Redirect authorized user to the debug handler.
-		path = "/debug/"
-	}
-	target := "https://" + stripPort(r.Host) + path
-	http.Redirect(w, r, target, http.StatusFound)
-}
-
-func stripPort(hostport string) string {
-	host, _, err := net.SplitHostPort(hostport)
-	if err != nil {
-		return hostport
-	}
-	return net.JoinHostPort(host, "443")
-}
-
 func debugHandler(s *derp.Server) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		f := func(format string, args ...interface{}) { fmt.Fprintf(w, format, args...) }
@@ -250,7 +179,7 @@ func debugHandler(s *derp.Server) http.Handler {
 `)
 		f("<li><b>Hostname:</b> %v</li>\n", *hostname)
 		f("<li><b>Rate Limit:</b> %v Mbps</li>\n", *mbps)
-		f("<li><b>Uptime:</b> %v</li>\n", uptime().Round(time.Second))
+		f("<li><b>Uptime:</b> %v</li>\n", tsweb.Uptime())
 
 		f(`<li><a href="/debug/vars">/debug/vars</a></li>
    <li><a href="/debug/pprof/">/debug/pprof/</a></li>
@@ -261,11 +190,3 @@ func debugHandler(s *derp.Server) http.Handler {
 `)
 	})
 }
-
-var timeStart = time.Now()
-
-func uptime() time.Duration { return time.Since(timeStart) }
-
-type uptimeVar struct{}
-
-func (uptimeVar) String() string { return fmt.Sprint(int64(uptime().Seconds())) }

tsweb/tsweb.go

@@ -0,0 +1,116 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package tsweb contains code between various Tailscale webservers.
+package tsweb
+
+import (
+	"expvar"
+	_ "expvar"
+	"fmt"
+	"net"
+	"net/http"
+	_ "net/http/pprof"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"tailscale.com/interfaces"
+)
+
+// NewMux returns a new ServeMux with debugHandler registered (and protected) at /debug/.
+func NewMux(debugHandler http.Handler) *http.ServeMux {
+	mux := http.NewServeMux()
+	RegisterCommonDebug(mux)
+	mux.Handle("/debug/", Protected(debugHandler))
+	return mux
+}
+
+func RegisterCommonDebug(mux *http.ServeMux) {
+	expvar.Publish("uptime", uptimeVar{})
+	mux.Handle("/debug/pprof/", Protected(http.DefaultServeMux)) // to net/http/pprof
+	mux.Handle("/debug/vars", Protected(http.DefaultServeMux))   // to expvar
+}
+
+func DefaultCertDir(leafDir string) string {
+	cacheDir, err := os.UserCacheDir()
+	if err == nil {
+		return filepath.Join(cacheDir, "tailscale", leafDir)
+	}
+	return ""
+}
+
+// IsProd443 reports whether addr is a Go listen address for port 443.
+func IsProd443(addr string) bool {
+	_, port, _ := net.SplitHostPort(addr)
+	return port == "443" || port == "https"
+}
+
+// AllowDebugAccess reports whether r should be permitted to access
+// various debug endpoints.
+func AllowDebugAccess(r *http.Request) bool {
+	if r.Header.Get("X-Forwarded-For") != "" {
+		// TODO if/when needed. For now, conservative:
+		return false
+	}
+	ipStr, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return false
+	}
+	ip := net.ParseIP(ipStr)
+	return interfaces.IsTailscaleIP(ip) || ip.IsLoopback() || ipStr == os.Getenv("ALLOW_DEBUG_IP")
+}
+
+// Protected wraps a provided debug handler, h, returning a Handler
+// that enforces AllowDebugAccess and returns forbiden replies for
+// unauthorized requests.
+func Protected(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !AllowDebugAccess(r) {
+			http.Error(w, "debug access denied", http.StatusForbidden)
+			return
+		}
+		h.ServeHTTP(w, r)
+	})
+}
+
+var timeStart = time.Now()
+
+func Uptime() time.Duration { return time.Since(timeStart).Round(time.Second) }
+
+type uptimeVar struct{}
+
+func (uptimeVar) String() string { return fmt.Sprint(int64(Uptime().Seconds())) }
+
+// Port80Handler is the handler to be given to
+// autocert.Manager.HTTPHandler.  The inner handler is the mux
+// returned by NewMux containing registered /debug handlers.
+type Port80Handler struct{ Main http.Handler }
+
+func (h Port80Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	path := r.RequestURI
+	if path == "/debug" || strings.HasPrefix(path, "/debug") {
+		h.Main.ServeHTTP(w, r)
+		return
+	}
+	if r.Method != "GET" && r.Method != "HEAD" {
+		http.Error(w, "Use HTTPS", http.StatusBadRequest)
+		return
+	}
+	if path == "/" && AllowDebugAccess(r) {
+		// Redirect authorized user to the debug handler.
+		path = "/debug/"
+	}
+	target := "https://" + stripPort(r.Host) + path
+	http.Redirect(w, r, target, http.StatusFound)
+}
+
+func stripPort(hostport string) string {
+	host, _, err := net.SplitHostPort(hostport)
+	if err != nil {
+		return hostport
+	}
+	return net.JoinHostPort(host, "443")
+}