client/web: show features based on platform support

Hiding/disabling UI features when not available on the running
client.

Updates #10261

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

envknob/features.go

@@ -0,0 +1,39 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package envknob
+
+import (
+	"errors"
+	"runtime"
+
+	"tailscale.com/version"
+	"tailscale.com/version/distro"
+)
+
+// CanRunTailscaleSSH reports whether serving a Tailscale SSH server is
+// supported for the current os/distro.
+func CanRunTailscaleSSH() error {
+	switch runtime.GOOS {
+	case "linux":
+		if distro.Get() == distro.Synology && !UseWIPCode() {
+			return errors.New("The Tailscale SSH server does not run on Synology.")
+		}
+		if distro.Get() == distro.QNAP && !UseWIPCode() {
+			return errors.New("The Tailscale SSH server does not run on QNAP.")
+		}
+		// otherwise okay
+	case "darwin":
+		// okay only in tailscaled mode for now.
+		if version.IsSandboxedMacOS() {
+			return errors.New("The Tailscale SSH server does not run in sandboxed Tailscale GUI builds.")
+		}
+	case "freebsd", "openbsd":
+	default:
+		return errors.New("The Tailscale SSH server is not supported on " + runtime.GOOS)
+	}
+	if !CanSSHD() {
+		return errors.New("The Tailscale SSH server has been administratively disabled.")
+	}
+	return nil
+}