1 files changed, 50 insertions, 0 deletions
diff --git a/askama_shared/src/escaping.rs b/askama_shared/src/escaping.rs
new file mode 100644
index 0000000..54f58e4
--- /dev/null
+++ b/askama_shared/src/escaping.rs
@@ -0,0 +1,50 @@
+fn escapable(b: &u8) -> bool {
+    *b == b'<' || *b == b'>' || *b == b'&'
+}
+
+pub fn escape(s: String) -> String {
+    let mut found = Vec::new();
+    for (i, b) in s.as_bytes().iter().enumerate() {
+        if escapable(b) {
+            found.push(i);
+        }
+    }
+    if found.is_empty() {
+        return s;
+    }
+
+    let bytes = s.as_bytes();
+    let max_len = bytes.len() + found.len() * 3;
+    let mut res = Vec::<u8>::with_capacity(max_len);
+    let mut start = 0;
+    for idx in &found {
+        if start < *idx {
+            res.extend(&bytes[start..*idx]);
+        }
+        start = *idx + 1;
+        match bytes[*idx] {
+            b'<' => { res.extend(b"&lt;"); },
+            b'>' => { res.extend(b"&gt;"); },
+            b'&' => { res.extend(b"&amp;"); },
+            _ => panic!("incorrect indexing"),
+        }
+    }
+    if start < bytes.len() - 1 {
+        res.extend(&bytes[start..]);
+    }
+
+    String::from_utf8(res).unwrap()
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_escape() {
+        assert_eq!(escape("".to_string()), "");
+        assert_eq!(escape("<&>".to_string()), "&lt;&amp;&gt;");
+        assert_eq!(escape("bla&".to_string()), "bla&amp;");
+        assert_eq!(escape("<foo".to_string()), "&lt;foo");
+    }
+}