Swift: Update the qhelp and example.

Author: geoffw0

swift/ql/src/queries/Security/CWE-116/BadTagFilter.qhelp

@@ -5,13 +5,13 @@
 
 <overview>
 <p>
-It is possible to match some single HTML tags using regular expressions (parsing general HTML using 
-regular expressions is impossible). However, if the regular expression is not written well it might 
+It is possible to match some single HTML tags using regular expressions (parsing general HTML using
+regular expressions is impossible). However, if the regular expression is not written well it might
 be possible to circumvent it, which can lead to cross-site scripting or other security issues.
 </p>
 <p>
 Some of these mistakes are caused by browsers having very forgiving HTML parsers, and
-will often render invalid HTML containing syntax errors. 
+will often render invalid HTML containing syntax errors.
 Regular expressions that attempt to match HTML should also recognize tags containing such syntax errors.
 </p>
 </overview>
@@ -28,17 +28,17 @@ likely to handle corner cases correctly than a custom implementation.
 The following example attempts to filters out all <code>&lt;script&gt;</code> tags.
 </p>
 
-<sample src="examples/BadTagFilter.rb" />
+<sample src="examples/BadTagFilterBad.swift" />
 
 <p>
-The above sanitizer does not filter out all <code>&lt;script&gt;</code> tags. 
+The above sanitizer does not filter out all <code>&lt;script&gt;</code> tags.
 Browsers will not only accept <code>&lt;/script&gt;</code> as script end tags, but also tags such as <code>&lt;/script foo="bar"&gt;</code> even though it is a parser error.
-This means that an attack string such as <code>&lt;script&gt;alert(1)&lt;/script foo="bar"&gt;</code> will not be filtered by 
+This means that an attack string such as <code>&lt;script&gt;alert(1)&lt;/script foo="bar"&gt;</code> will not be filtered by
 the function, and <code>alert(1)</code> will be executed by a browser if the string is rendered as HTML.
 </p>
 
 <p>
-Other corner cases include that HTML comments can end with <code>--!&gt;</code>, 
+Other corner cases include that HTML comments can end with <code>--!&gt;</code>,
 and that HTML tag names can contain upper case characters.
 </p>
 </example>
@@ -50,5 +50,3 @@ and that HTML tag names can contain upper case characters.
 <li>stackoverflow.com: <a href="https://stackoverflow.com/questions/25559999/why-arent-browsers-strict-about-html">Why aren't browsers strict about HTML?</a>.</li>
 </references>
 </qhelp>
-
-

swift/ql/src/queries/Security/CWE-116/BadTagFilter.swift

@@ -0,0 +1,9 @@
+let script_tag_regex = /<script[^>]*>.*<\/script>/
+
+var old_html = ""
+while (html != old_html) {
+  old_html = html
+  html.replace(script_tag_regex, with: "")
+}
+
+...