[MongoDB] Escape special characters in keys (#2212)

Essentially resolves #2038, although this is escaping and not rejecting keys as that issue implies.

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

redbot/core/drivers/red_mongo.py

@@ -1,7 +1,12 @@
-import motor.motor_asyncio
-from .red_base import BaseDriver
+import re
+from typing import Match, Pattern
 from urllib.parse import quote_plus
 
+import motor.core
+import motor.motor_asyncio
+
+from .red_base import BaseDriver
+
 __all__ = ["Mongo"]
 
 
@@ -80,6 +85,7 @@ class Mongo(BaseDriver):
     async def get(self, *identifiers: str):
         mongo_collection = self.get_collection()
 
+        identifiers = (*map(self._escape_key, identifiers),)
         dot_identifiers = ".".join(identifiers)
 
         partial = await mongo_collection.find_one(
@@ -91,10 +97,14 @@ class Mongo(BaseDriver):
 
         for i in identifiers:
             partial = partial[i]
+        if isinstance(partial, dict):
+            return self._unescape_dict_keys(partial)
         return partial
 
     async def set(self, *identifiers: str, value=None):
-        dot_identifiers = ".".join(identifiers)
+        dot_identifiers = ".".join(map(self._escape_key, identifiers))
+        if isinstance(value, dict):
+            value = self._escape_dict_keys(value)
 
         mongo_collection = self.get_collection()
 
@@ -105,7 +115,7 @@ class Mongo(BaseDriver):
         )
 
     async def clear(self, *identifiers: str):
-        dot_identifiers = ".".join(identifiers)
+        dot_identifiers = ".".join(map(self._escape_key, identifiers))
         mongo_collection = self.get_collection()
 
         if len(identifiers) > 0:
@@ -115,6 +125,62 @@ class Mongo(BaseDriver):
         else:
             await mongo_collection.delete_one({"_id": self.unique_cog_identifier})
 
+    @staticmethod
+    def _escape_key(key: str) -> str:
+        return _SPECIAL_CHAR_PATTERN.sub(_replace_with_escaped, key)
+
+    @staticmethod
+    def _unescape_key(key: str) -> str:
+        return _CHAR_ESCAPE_PATTERN.sub(_replace_with_unescaped, key)
+
+    @classmethod
+    def _escape_dict_keys(cls, data: dict) -> dict:
+        """Recursively escape all keys in a dict."""
+        ret = {}
+        for key, value in data.items():
+            key = cls._escape_key(key)
+            if isinstance(value, dict):
+                value = cls._escape_dict_keys(value)
+            ret[key] = value
+        return ret
+
+    @classmethod
+    def _unescape_dict_keys(cls, data: dict) -> dict:
+        """Recursively unescape all keys in a dict."""
+        ret = {}
+        for key, value in data.items():
+            key = cls._unescape_key(key)
+            if isinstance(value, dict):
+                value = cls._unescape_dict_keys(value)
+            ret[key] = value
+        return ret
+
+
+_SPECIAL_CHAR_PATTERN: Pattern[str] = re.compile(r"([.$]|\\U0000002E|\\U00000024)")
+_SPECIAL_CHARS = {
+    ".": "\\U0000002E",
+    "$": "\\U00000024",
+    "\\U0000002E": "\\U&0000002E",
+    "\\U00000024": "\\U&00000024",
+}
+
+
+def _replace_with_escaped(match: Match[str]) -> str:
+    return _SPECIAL_CHARS[match[0]]
+
+
+_CHAR_ESCAPE_PATTERN: Pattern[str] = re.compile(r"(\\U0000002E|\\U00000024)")
+_CHAR_ESCAPES = {
+    "\\U0000002E": ".",
+    "\\U00000024": "$",
+    "\\U&0000002E": "\\U0000002E",
+    "\\U&00000024": "\\U00000024",
+}
+
+
+def _replace_with_unescaped(match: Match[str]) -> str:
+    return _CHAR_ESCAPES[match[0]]
+
 
 def get_config_details():
     uri = None