1 files changed, 36 insertions, 0 deletions
diff --git a/myst_parser/mdit_to_docutils/utils.py b/myst_parser/mdit_to_docutils/utils.py
new file mode 100644
index 0000000..b31d8c7
--- /dev/null
+++ b/myst_parser/mdit_to_docutils/utils.py
@@ -0,0 +1,36 @@
+import html
+from typing import Iterable, Optional
+from urllib.parse import quote, urlparse
+
+
+def escape_url(raw: str) -> str:
+    """
+    Escape urls to prevent code injection craziness. (Hopefully.)
+    """
+    return html.escape(quote(html.unescape(raw), safe="/#:()*?=%@+,&"))
+
+
+def is_external_url(
+    reference: str,
+    known_url_schemes: Optional[Iterable[str]],
+    match_fragment: bool = False,
+) -> bool:
+    """Return if a reference should be recognised as an external URL.
+
+    URLs are of the format: scheme://netloc/path;parameters?query#fragment
+
+    This checks if there is a url scheme (e.g. 'https') and, if so,
+    if the scheme is is the list of known_url_schemes (if supplied).
+
+    :param known_url_schemes: e.g. ["http", "https", "mailto"]
+        If None, match all schemes
+    :param match_fragment: If True and a fragment found, then True will be returned,
+        irrespective of a scheme match
+
+    """
+    url_check = urlparse(reference)
+    if known_url_schemes is not None:
+        scheme_known = url_check.scheme in known_url_schemes
+    else:
+        scheme_known = bool(url_check.scheme)
+    return scheme_known or (match_fragment and url_check.fragment != "")