Mark diff colors safe and escape raw diff input

For HTML escaping of the diff view we have to consider two things.

1. Diff input comes from two git checkouts of the project at specific
   revisions. The revisions sdocs are considered untrusted user input,
   could contain special characters and must be escaped.
2. After analyzing with difflib we add a bit HTML to colorize the
   output. This specific HTML fragments are trusted and safe.

Relates to #1920.

strictdoc/export/html/generators/view_objects/diff_screen_results_view_object.py

@@ -3,6 +3,8 @@
 from datetime import datetime
 from typing import Optional
 
+from markupsafe import Markup
+
 from strictdoc import __version__
 from strictdoc.core.project_config import ProjectConfig
 from strictdoc.export.html.html_templates import JinjaEnvironment
@@ -58,31 +60,31 @@ def __init__(
         self.strictdoc_version = __version__
         self.error_message: Optional[str] = None
 
-    def render_screen(self, jinja_environment: JinjaEnvironment):
+    def render_screen(self, jinja_environment: JinjaEnvironment) -> Markup:
         template = jinja_environment.environment.overlay(
             autoescape=False
         ).get_template("screens/git/index.jinja")
-        return template.render(view_object=self)
+        return Markup(template.render(view_object=self))
 
-    def render_url(self, url: str):
-        return self.link_renderer.render_url(url)
+    def render_url(self, url: str) -> Markup:
+        return Markup(self.link_renderer.render_url(url))
 
-    def render_node_link(self, incoming_link, document, document_type):
+    def render_node_link(self, incoming_link, document, document_type) -> str:
         return self.link_renderer.render_node_link(
             incoming_link, document, document_type
         )
 
-    def render_static_url(self, url: str):
-        return self.link_renderer.render_static_url(url)
+    def render_static_url(self, url: str) -> Markup:
+        return Markup(self.link_renderer.render_static_url(url))
 
     def render_static_url_with_prefix(self, url: str) -> str:
         return self.link_renderer.render_static_url_with_prefix(url)
 
-    def render_local_anchor(self, node):
+    def render_local_anchor(self, node) -> str:
         return self.link_renderer.render_local_anchor(node)
 
     def is_empty_tree(self) -> bool:
         return self.document_tree_iterator.is_empty_tree()
 
-    def date_today(self):
+    def date_today(self) -> str:
         return datetime.today().strftime("%Y-%m-%d")

strictdoc/export/html/generators/view_objects/diff_screen_view_object.py

@@ -2,6 +2,8 @@
 from dataclasses import dataclass
 from datetime import datetime
 
+from markupsafe import Markup
+
 from strictdoc import __version__
 from strictdoc.core.project_config import ProjectConfig
 from strictdoc.export.html.html_templates import JinjaEnvironment
@@ -39,27 +41,27 @@ def __init__(
         self.is_running_on_server: bool = project_config.is_running_on_server
         self.strictdoc_version = __version__
 
-    def render_screen(self, jinja_environment: JinjaEnvironment):
+    def render_screen(self, jinja_environment: JinjaEnvironment) -> Markup:
         return jinja_environment.render_template_as_markup(
             "screens/git/index.jinja", view_object=self
         )
 
-    def render_url(self, url: str):
-        return self.link_renderer.render_url(url)
+    def render_url(self, url: str) -> Markup:
+        return Markup(self.link_renderer.render_url(url))
 
-    def render_node_link(self, incoming_link, document, document_type):
+    def render_node_link(self, incoming_link, document, document_type) -> str:
         return self.link_renderer.render_node_link(
             incoming_link, document, document_type
         )
 
-    def render_static_url(self, url: str):
-        return self.link_renderer.render_static_url(url)
+    def render_static_url(self, url: str) -> Markup:
+        return Markup(self.link_renderer.render_static_url(url))
 
     def render_static_url_with_prefix(self, url: str) -> str:
         return self.link_renderer.render_static_url_with_prefix(url)
 
-    def render_local_anchor(self, node):
+    def render_local_anchor(self, node) -> str:
         return self.link_renderer.render_local_anchor(node)
 
-    def date_today(self):
+    def date_today(self) -> str:
         return datetime.today().strftime("%Y-%m-%d")

strictdoc/git/project_diff_analyzer.py

@@ -24,7 +24,7 @@
     SectionChange,
 )
 from strictdoc.helpers.cast import assert_cast, assert_optional_cast
-from strictdoc.helpers.diff import get_colored_diff_string, similar
+from strictdoc.helpers.diff import get_colored_html_diff_string, similar
 from strictdoc.helpers.mid import MID
 
 
@@ -366,12 +366,12 @@ def _iterate_one_index(
                 if other_document_or_none is not None:
                     if document.title != other_document_or_none.title:
                         title_modified = True
-                        lhs_colored_title_diff = get_colored_diff_string(
+                        lhs_colored_title_diff = get_colored_html_diff_string(
                             document.title,
                             other_document_or_none.title,
                             "left",
                         )
-                        rhs_colored_title_diff = get_colored_diff_string(
+                        rhs_colored_title_diff = get_colored_html_diff_string(
                             document.title,
                             other_document_or_none.title,
                             "right",
@@ -481,14 +481,14 @@ def _iterate_one_index(
                             if node.title != other_section_or_none.title:
                                 title_modified = True
                                 lhs_colored_title_diff = (
-                                    get_colored_diff_string(
+                                    get_colored_html_diff_string(
                                         node.title,
                                         other_section_or_none.title,
                                         "left",
                                     )
                                 )
                                 rhs_colored_title_diff = (
-                                    get_colored_diff_string(
+                                    get_colored_html_diff_string(
                                         node.title,
                                         other_section_or_none.title,
                                         "right",
@@ -769,10 +769,10 @@ def create_field_change(
             other_requirement_field_value = (
                 other_requirement_field.get_text_value()
             )
-            left_diff = get_colored_diff_string(
+            left_diff = get_colored_html_diff_string(
                 requirement_field_value, other_requirement_field_value, "left"
             )
-            right_diff = get_colored_diff_string(
+            right_diff = get_colored_html_diff_string(
                 requirement_field_value, other_requirement_field_value, "right"
             )
 
@@ -857,12 +857,12 @@ def create_comment_field_changes(
             comment_other_value = changed_other_field_.get_text_value()
             assert comment_other_value is not None
 
-            left_diff = get_colored_diff_string(
+            left_diff = get_colored_html_diff_string(
                 comment_value,
                 comment_other_value,
                 "left",
             )
-            right_diff = get_colored_diff_string(
+            right_diff = get_colored_html_diff_string(
                 comment_value,
                 comment_other_value,
                 "right",

strictdoc/helpers/diff.py

@@ -2,17 +2,19 @@
 import difflib
 from difflib import SequenceMatcher
 
+from markupsafe import Markup, escape
+
 
 def similar(a, b):
     return SequenceMatcher(None, a, b).ratio()
 
 
-red = lambda text: f'<span class="lambda_red">{text}</span>'
-green = lambda text: f'<span class="lambda_green">{text}</span>'
-white = lambda text: f"<span>{text}</span>"
+red = lambda text: f'<span class="lambda_red">{escape(text)}</span>'
+green = lambda text: f'<span class="lambda_green">{escape(text)}</span>'
+white = lambda text: f"<span>{escape(text)}</span>"
 
 
-def get_colored_diff_string(old: str, new: str, flag: str):
+def get_colored_html_diff_string(old: str, new: str, flag: str) -> Markup:
     assert old is not None
     assert new is not None
     assert flag in ("left", "right")
@@ -33,4 +35,4 @@ def get_colored_diff_string(old: str, new: str, flag: str):
                 result += red(old[code[1] : code[2]])
             else:
                 result += green(new[code[3] : code[4]])
-    return result
+    return Markup(result)