Parse input of search filters to prevent errors based on invalid regex, fixes #113

Signed-off-by: Yohann D'ANELLO <ynerant@crans.org>

apps/api/filters.py

@@ -0,0 +1,42 @@
+import re
+from functools import lru_cache
+
+from rest_framework.filters import SearchFilter
+
+
+class RegexSafeSearchFilter(SearchFilter):
+    @lru_cache
+    def validate_regex(self, search_term) -> bool:
+        try:
+            re.compile(search_term)
+            return True
+        except re.error:
+            return False
+
+    def get_search_fields(self, view, request):
+        """
+        Ensure that given regex are valid.
+        If not, we consider that the user is trying to search by substring.
+        """
+        search_fields = super().get_search_fields(view, request)
+        search_terms = self.get_search_terms(request)
+
+        for search_term in search_terms:
+            if not self.validate_regex(search_term):
+                # Invalid regex. We assume we don't query by regex but by substring.
+                search_fields = [f.replace('$', '') for f in search_fields]
+                break
+
+        return search_fields
+
+    def get_search_terms(self, request):
+        """
+        Ensure that search field is a valid regex query. If not, we remove extra characters.
+        """
+        terms = super().get_search_terms(request)
+        if not all(self.validate_regex(term) for term in terms):
+            # Invalid regex. If a ^ is prefixed to the search term, we remove it.
+            terms = [term[1:] if term[0] == '^' else term for term in terms]
+            # Same for dollars.
+            terms = [term[:-1] if term[-1] == '$' else term for term in terms]
+        return terms