1 files changed, 135 insertions, 3 deletions

diff --git a/src/xml.rs b/src/xml.rs
index d3b088e..9ca5b0c 100644
--- a/src/xml.rs
+++ b/src/xml.rs
@@ -3,6 +3,59 @@ use std::{
   fmt::{Display, Write},
 };
 
+fn escape_xml_text(value: &str) -> String { escape_xml_value(value, false) }
+
+fn escape_xml_attribute(value: &str) -> String { escape_xml_value(value, true) }
+
+const fn is_valid_xml_char(character: char) -> bool {
+  matches!(
+    character as u32,
+    0x09
+      | 0x0A
+      | 0x0D
+      | 0x20..=0xD7FF
+      | 0xE000..=0xFFFD
+      | 0x10000..=0x0010_FFFF
+  )
+}
+
+fn sanitize_xml_chars(value: &str) -> String {
+  value.chars().filter(|character| is_valid_xml_char(*character)).collect()
+}
+
+fn escape_xml_value(value: &str, escape_attribute_whitespace: bool) -> String {
+  let sanitized = sanitize_xml_chars(value);
+  let mut escaped = String::with_capacity(sanitized.len());
+
+  for character in sanitized.chars() {
+    match character {
+      '&' => escaped.push_str("&"),
+      '<' => escaped.push_str("&lt;"),
+      '>' => escaped.push_str("&gt;"),
+      '"' => escaped.push_str("&quot;"),
+      '\'' => escaped.push_str("&apos;"),
+      '\n' if escape_attribute_whitespace => escaped.push_str("&#xA;"),
+      '\r' if escape_attribute_whitespace => escaped.push_str("&#xD;"),
+      '\t' if escape_attribute_whitespace => escaped.push_str("&#x9;"),
+      _ => escaped.push(character),
+    }
+  }
+
+  escaped
+}
+
+fn escape_cdata_text(value: &str) -> String {
+  sanitize_xml_chars(value).replace("]]>", "]]]]><![CDATA[>")
+}
+
+fn render_field(key: &str, value: &str) -> String {
+  if key == "description" {
+    format!("<{key}><![CDATA[{}]]></{key}>", escape_cdata_text(value))
+  } else {
+    format!("<{key}>{}</{key}>", escape_xml_text(value))
+  }
+}
+
 pub struct Item {
   fields: HashMap<String, String>,
 }
@@ -21,7 +74,7 @@ impl Display for Item {
       f,
       "<item>{}</item>",
       self.fields.iter().fold(String::new(), |mut acc, (k, v)| {
-        let _ = write!(acc, "<{k}>{v}</{k}>");
+        let _ = write!(acc, "{}", render_field(k, v));
 
         acc
       })
@@ -70,12 +123,91 @@ impl Display for Writer {
        version=\"2.0\"><channel>{}<atom:link href=\"{}\" rel=\"self\" \
        type=\"application/rss+xml\" />{}</channel></rss>",
       self.fields.iter().fold(String::new(), |mut acc, (k, v)| {
-        let _ = write!(acc, "<{k}>{v}</{k}>");
+        let _ = write!(acc, "{}", render_field(k, v));
 
         acc
       }),
-      self.link,
+      escape_xml_attribute(&self.link),
       self.content
     )
   }
 }
+
+#[cfg(test)]
+mod tests {
+  use super::{Item, Writer};
+
+  #[test]
+  fn multiline_description_is_wrapped_in_cdata() {
+    let mut item = Item::builder();
+
+    item.add_field("description", "first line\nsecond line");
+
+    let xml = item.to_string();
+
+    assert!(xml.contains(
+      "<description><![CDATA[first line\nsecond line]]></description>"
+    ));
+  }
+
+  #[test]
+  fn cdata_end_marker_is_escaped_safely() {
+    let mut item = Item::builder();
+
+    item.add_field("description", "before ]]> after");
+
+    let xml = item.to_string();
+
+    assert!(xml.contains(
+      "<description><![CDATA[before ]]]]><![CDATA[> after]]></description>"
+    ));
+  }
+
+  #[test]
+  fn non_description_fields_are_xml_escaped() {
+    let mut writer = Writer::builder();
+
+    writer.add_field("title", "Fish & Chips <3");
+
+    let xml = writer.to_string();
+
+    assert!(xml.contains("<title>Fish &amp; Chips &lt;3</title>"));
+  }
+
+  #[test]
+  fn text_fields_escape_quotes_and_apostrophes() {
+    let mut writer = Writer::builder();
+
+    writer.add_field("title", "\"quoted\" and 'single'");
+
+    let xml = writer.to_string();
+
+    assert!(
+      xml.contains("<title>&quot;quoted&quot; and &apos;single&apos;</title>")
+    );
+  }
+
+  #[test]
+  fn link_attribute_is_xml_escaped() {
+    let mut writer = Writer::builder();
+
+    writer.add_link("https://example.com/?a=1&b=\"two\"'three'<four>");
+
+    let xml = writer.to_string();
+
+    assert!(xml.contains(
+      "<atom:link href=\"https://example.com/?a=1&amp;b=&quot;two&quot;&apos;three&apos;&lt;four&gt;\" rel=\"self\" type=\"application/rss+xml\" />"
+    ));
+  }
+
+  #[test]
+  fn invalid_xml_chars_are_filtered() {
+    let mut writer = Writer::builder();
+
+    writer.add_field("title", "ok\u{0001}\u{0002}\u{0000}text");
+
+    let xml = writer.to_string();
+
+    assert!(xml.contains("<title>oktext</title>"));
+  }
+}