Console: redirect plain HTTP to HTTPS on a TLS port

README.md

@@ -102,7 +102,8 @@ LAN access is off by default. To turn it on, set your own password first
 - start it with `-lan`.
 
 The console restarts on every network interface, on the same port, over
-HTTPS with a self-signed certificate (browsers warn about it once). The
+HTTPS with a self-signed certificate (browsers warn about it once). Typing
+the address without `https://` works too; you're sent to the HTTPS page. The
 address to use, such as `https://192.168.1.50:8787`, is shown under
 Settings, in the sidebar's Network card and in the terminal. The choice is
 remembered across restarts; untick the box or run with `-lan=false` to go

internal/app/app_test.go

@@ -188,6 +188,28 @@ func TestSelfSignedTLS(t *testing.T) {
 	if !strings.HasPrefix(url, "https://") {
 		t.Fatalf("url %s", url)
 	}
+
+	// Plain http:// on the same port is sent to https://, not refused.
+	c := &http.Client{Timeout: 5 * time.Second, CheckRedirect: func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }}
+	resp, err := c.Get("http://" + strings.TrimPrefix(url, "https://") + "devices?x=1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusFound || resp.Header.Get("Location") != url+"devices?x=1" {
+		t.Fatalf("plain HTTP: %d, Location %q", resp.StatusCode, resp.Header.Get("Location"))
+	}
+
+	// HTTPS still works.
+	c.Transport = &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}}
+	resp, err = c.Get(url)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Fatalf("HTTPS: %d", resp.StatusCode)
+	}
 }
 
 // lanConfig is testConfig on a free port, which -lan keeps; -addr can't be

internal/app/console.go

@@ -44,6 +44,7 @@ type console struct {
 	lan    bool
 	ln     net.Listener
 	srv    *http.Server
+	plain  *http.Server // redirects http:// to https:// on a TLS port
 	tlsCfg *tls.Config
 	moving bool
 	closed bool
@@ -83,6 +84,16 @@ func (c *console) bind(lan bool, port int, fallback bool) error {
 // serve serves the console on the bound listener in the background.
 func (c *console) serve() {
 	ln, tlsCfg := c.ln, c.tlsCfg
+	if tlsCfg != nil {
+		var plainLn net.Listener
+		ln, plainLn = splitTLS(ln)
+		c.plain = &http.Server{
+			Handler:           redirectHTTPS,
+			ReadHeaderTimeout: 10 * time.Second,
+			ErrorLog:          slog.NewLogLogger(c.log.Handler(), slog.LevelWarn),
+		}
+		go c.plain.Serve(plainLn) // ends when the console's listener closes
+	}
 	srv := &http.Server{
 		Handler:           c.handler(ln.Addr().(*net.TCPAddr).IP.IsLoopback(), tlsCfg),
 		ReadHeaderTimeout: 10 * time.Second,
@@ -176,6 +187,7 @@ func (c *console) move(st *store.Store, on bool) {
 	}
 	port := c.ln.Addr().(*net.TCPAddr).Port
 	c.srv.Close()
+	c.closePlain()
 	if err := c.bind(on, port, false); err != nil {
 		c.log.Error("couldn't move the console", "lan", on, "err", err)
 		fmt.Fprintf(c.stderr, "Couldn't move the console: %v\n", err)
@@ -198,6 +210,14 @@ func (c *console) stop(ctx context.Context) {
 	} else {
 		c.ln.Close()
 	}
+	c.closePlain()
+}
+
+func (c *console) closePlain() {
+	if c.plain != nil {
+		c.plain.Close()
+		c.plain = nil
+	}
 }
 
 // consoleInfo is what the dashboard and the terminal are told about the

internal/app/split.go

@@ -0,0 +1,113 @@
+package app
+
+import (
+	"bufio"
+	"errors"
+	"net"
+	"net/http"
+	"sync"
+	"time"
+)
+
+// splitTLS lets an HTTPS port answer plain HTTP too. Phones try http://
+// first when you type 192.168.1.50:8787, and Go's TLS server would answer
+// that with "Client sent an HTTP request to an HTTPS server". Connections
+// that start with a TLS handshake go to tlsLn, everything else to plainLn,
+// where redirectHTTPS sends the browser to the https:// address.
+func splitTLS(ln net.Listener) (tlsLn, plainLn net.Listener) {
+	s := &split{inner: ln, done: make(chan struct{})}
+	s.tls = &chanListener{s: s, conns: make(chan net.Conn)}
+	s.plain = &chanListener{s: s, conns: make(chan net.Conn)}
+	go s.run()
+	return s.tls, s.plain
+}
+
+type split struct {
+	inner      net.Listener
+	tls, plain *chanListener
+	done       chan struct{}
+	once       sync.Once
+}
+
+func (s *split) close() error {
+	var err error
+	s.once.Do(func() {
+		close(s.done)
+		err = s.inner.Close()
+	})
+	return err
+}
+
+func (s *split) run() {
+	for {
+		c, err := s.inner.Accept()
+		if err != nil {
+			if errors.Is(err, net.ErrClosed) {
+				s.close()
+				return
+			}
+			time.Sleep(50 * time.Millisecond) // e.g. out of file descriptors
+			continue
+		}
+		go s.route(c)
+	}
+}
+
+// tlsHandshake is the first byte of every TLS connection.
+const tlsHandshake = 0x16
+
+func (s *split) route(c net.Conn) {
+	c.SetReadDeadline(time.Now().Add(10 * time.Second))
+	br := bufio.NewReader(c)
+	b, err := br.Peek(1)
+	if err != nil {
+		c.Close()
+		return
+	}
+	c.SetReadDeadline(time.Time{})
+	dest := s.plain
+	if b[0] == tlsHandshake {
+		dest = s.tls
+	}
+	select {
+	case dest.conns <- &peekedConn{Conn: c, r: br}:
+	case <-s.done:
+		c.Close()
+	}
+}
+
+type chanListener struct {
+	s     *split
+	conns chan net.Conn
+}
+
+func (l *chanListener) Accept() (net.Conn, error) {
+	select {
+	case c := <-l.conns:
+		return c, nil
+	case <-l.s.done:
+		return nil, net.ErrClosed
+	}
+}
+
+func (l *chanListener) Close() error   { return l.s.close() }
+func (l *chanListener) Addr() net.Addr { return l.s.inner.Addr() }
+
+// peekedConn reads the bytes route looked at before the rest.
+type peekedConn struct {
+	net.Conn
+	r *bufio.Reader
+}
+
+func (c *peekedConn) Read(p []byte) (int, error) { return c.r.Read(p) }
+
+// redirectHTTPS sends plain HTTP requests to the same address over HTTPS.
+// It's temporary, so a browser doesn't remember it if the console goes
+// back to plain HTTP on this machine.
+var redirectHTTPS = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	if r.Host == "" {
+		http.Error(w, "this console only speaks HTTPS", http.StatusBadRequest)
+		return
+	}
+	http.Redirect(w, r, "https://"+r.Host+r.URL.RequestURI(), http.StatusFound)
+})