tails-documentation: rewrite in Python + use WebKit for display.

... instead of using the Tor Browser: since version 7.0.8 it fails to
render local pages (like our docs) due to #14962.

Refs: #14962

config/chroot_local-includes/usr/local/bin/tails-documentation

-#! /bin/sh
-
-if [ $# -ge 1 ]; then
-   PAGE="$1"
-else
-   PAGE='index'
-fi
-
-WIKI_ROOT='/usr/share/doc/tails/website'
-LANG_CODE="`echo ${LANG} | head -c 2`"
-
-if [ -r "${WIKI_ROOT}/${PAGE}.${LANG_CODE}.html" ]; then
-   FILE="${PAGE}.${LANG_CODE}.html"
-elif  [ -r "${WIKI_ROOT}/${PAGE}.en.html" ]; then
-   FILE="${PAGE}.en.html"
-else
-   FILE="${PAGE}.html"
-fi
-
-if [ -n "${2}" ]; then
-   FILE="${FILE}#${2}"
-fi
-
-export TOR_BROWSER_SKIP_OFFLINE_WARNING=yes
-exec /usr/local/bin/tor-browser "file://${WIKI_ROOT}/${FILE}"
+#!/usr/bin/env python3
+
+import gettext
+import gi
+import locale
+import os
+import os.path
+import sys
+import tailsgreeter.gui
+
+gi.require_version('Gtk', '3.0')
+from gi.repository import Gtk                                   # NOQA: E402
+gi.require_version('WebKit2', '4.0')
+from gi.repository import WebKit2                               # NOQA: E402
+
+# We'll only use a single translation, "Tails documentation", which
+# already is translated for the launcher. For this reason, this script
+# is not managed by `refresh-translations`.
+gettext.textdomain('tails')
+
+# The browser from the Greeter is good as-is, but a button for
+# navigating backwards in the history would be nice.
+class DocumentationWindow(tailsgreeter.gui.GreeterHelpWindow):
+    def _build_ui(self):
+        super(DocumentationWindow, self)._build_ui()
+        # The super class' headerbar is not exposed as an instance
+        # variable, but we need it!
+        headerbar = next(child for child in self.get_children() \
+                         if isinstance(child, Gtk.HeaderBar))
+        back_button = Gtk.Button('←')
+        back_button.connect("clicked", lambda x: self.webview.go_back())
+        headerbar.pack_start(back_button)
+        back_button.show()
+        self.webview.connect(
+            "load-changed",
+            lambda webview, e: back_button.set_visible(webview.can_go_back())
+        )
+
+
+# Main
+
+try:
+    page = sys.argv[1]
+except IndexError:
+    page = 'getting_started'
+wiki_path = '/usr/share/doc/tails/website'
+lang_code = os.getenv('LANG', 'en')[0:2]
+trials = [
+    os.path.join(wiki_path, page + code + ".html")
+    for code in ['.' + lang_code, '.en', '']
+]
+try:
+    uri = 'file://' + next(trial for trial in trials if os.path.isfile(trial))
+except StopIteration:
+    sys.exit('error: could not find the requested documentation page')
+if '..' in uri.split(os.sep):
+    sys.exit('error: cannot escape from {}'.format(wiki_path))
+
+helpwindow = DocumentationWindow(uri)
+helpwindow.connect("delete-event", Gtk.main_quit)
+helpwindow.window.set_title(gettext.gettext('Tails documentation'))
+helpwindow.show()
+Gtk.main()

features/documentation.feature

 @product @doc
 Feature: Tails documentation
 
+  Scenario: The Tails documentation launcher on the desktop works
+    Given I have started Tails from DVD without network and logged in
+    When I double-click on the Tails documentation launcher on the desktop
+    Then the documentation viewer opens the "Getting started" page
+
   Scenario: The Report an Error launcher will open the support documentation
     Given I have started Tails from DVD without network and logged in
     When I double-click on the Report an Error launcher on the desktop
-    Then the support documentation page opens in Tor Browser
+    Then the documentation viewer opens the "Support" page

features/localization.feature

@@ -9,7 +9,7 @@ Feature: Localization
     Given I have started Tails from DVD without network and stopped at Tails Greeter's login screen
     And I log in to a new session in German
     When I double-click on the Report an Error launcher on the desktop
-    Then the support documentation page opens in Tor Browser
+    Then the documentation viewer opens the "Support" page
 
   #11711
   @fragile

features/step_definitions/checks.rb

@@ -94,21 +94,25 @@ Then /^the VirtualBox guest modules are available$/ do
          "The vboxguest module is not available.")
 end
 
-Then /^the support documentation page opens in Tor Browser$/ do
+Then /^the documentation viewer opens the "(Support|Getting started)" page$/ do |page|
   if @language == 'German'
-    expected_title = 'Tails - Hilfe & Support'
-    expected_heading = 'Die Dokumentation durchsuchen'
+    expected_title = 'Tails-Dokumentation'
+    if page == 'Support'
+      expected_heading = 'Die Dokumentation durchsuchen'
+    else
+      page = 'Einen Fehler gefunden?'
+    end
   else
-    expected_title = 'Tails - Support'
-    expected_heading = 'Search the documentation'
+    expected_title = 'Tails documentation'
+    if page == 'Support'
+      expected_heading = 'Search the documentation'
+    else
+      expected_heading = 'Found a bug?'
+    end
   end
-  step "\"#{expected_title}\" has loaded in the Tor Browser"
-  headings = @torbrowser
-             .child(expected_title, roleName: 'document frame')
-             .children(roleName: 'heading')
-  assert(
-    headings.any? { |heading| heading.text == expected_heading }
-  )
+  app = Dogtail::Application.new('tails-documentation')
+  app.child(expected_title, roleName: 'frame', recursive: false)
+  app.child(expected_heading, roleName: 'heading')
 end
 
 Given /^I plug and mount a USB drive containing a sample PNG$/ do

features/step_definitions/common_steps.rb

@@ -727,11 +727,9 @@ end
 
 When /^I double-click on the (Tails documentation|Report an Error) launcher on the desktop$/ do |launcher|
   image = 'Desktop' + launcher.split.map { |s| s.capitalize } .join + '.png'
-  info = xul_application_info('Tor Browser')
   # Sometimes the double-click is lost (#12131).
   retry_action(10) do
-    @screen.wait_and_double_click(image, 10) if $vm.execute("pgrep --uid #{info[:user]} --full --exact '#{info[:cmd_regex]}'").failure?
-    step 'the Tor Browser has started'
+    @screen.wait_and_double_click(image, 10) if $vm.execute("pgrep --uid #{LIVE_USER} --full --full tails-documentation").failure?
   end
 end
 

features/torified_browsing.feature

@@ -99,13 +99,6 @@ Feature: Browsing the web using the Tor Browser
     When I open the address "file:///tmp/synaptic.html" in the Tor Browser
     Then I do not see "TorBrowserSynapticManual.png" after at most 5 seconds
 
-  @doc
-  Scenario: The Tails documentation launcher on the desktop works
-    Given I have started Tails from DVD and logged in and the network is connected
-    When I double-click on the Tails documentation launcher on the desktop
-    Then the Tor Browser has started
-    And "Tails - Getting started..." has loaded in the Tor Browser
-
   Scenario: The Tor Browser uses TBB's shared libraries
     Given I have started Tails from DVD and logged in and the network is connected
     When I start the Tor Browser