diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index f157132210..95f23e27b6 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -14,8 +14,9 @@
import json
import logging
+import re
import typing
-from typing import Any, Callable, Dict, Generator, Optional
+from typing import Any, Callable, Dict, Generator, Optional, Pattern
import attr
from frozendict import frozendict
@@ -34,6 +35,9 @@ if typing.TYPE_CHECKING:
logger = logging.getLogger(__name__)
+_WILDCARD_RUN = re.compile(r"([\?\*]+)")
+
+
def _reject_invalid_json(val: Any) -> None:
"""Do not allow Infinity, -Infinity, or NaN values in JSON."""
raise ValueError("Invalid JSON value: '%s'" % val)
@@ -181,3 +185,56 @@ def log_failure(
if not consumeErrors:
return failure
return None
+
+
+def glob_to_regex(glob: str, word_boundary: bool = False) -> Pattern:
+ """Converts a glob to a compiled regex object.
+
+ Args:
+ glob: pattern to match
+ word_boundary: If True, the pattern will be allowed to match at word boundaries
+ anywhere in the string. Otherwise, the pattern is anchored at the start and
+ end of the string.
+
+ Returns:
+ compiled regex pattern
+ """
+
+ # Patterns with wildcards must be simplified to avoid performance cliffs
+ # - The glob `?**?**?` is equivalent to the glob `???*`
+ # - The glob `???*` is equivalent to the regex `.{3,}`
+ chunks = []
+ for chunk in _WILDCARD_RUN.split(glob):
+ # No wildcards? re.escape()
+ if not _WILDCARD_RUN.match(chunk):
+ chunks.append(re.escape(chunk))
+ continue
+
+ # Wildcards? Simplify.
+ qmarks = chunk.count("?")
+ if "*" in chunk:
+ chunks.append(".{%d,}" % qmarks)
+ else:
+ chunks.append(".{%d}" % qmarks)
+
+ res = "".join(chunks)
+
+ if word_boundary:
+ res = re_word_boundary(res)
+ else:
+ # \A anchors at start of string, \Z at end of string
+ res = r"\A" + res + r"\Z"
+
+ return re.compile(res, re.IGNORECASE)
+
+
+def re_word_boundary(r: str) -> str:
+ """
+ Adds word boundary characters to the start and end of an
+ expression to require that the match occur as a whole word,
+ but do so respecting the fact that strings starting or ending
+ with non-word characters will change word boundaries.
+ """
+ # we can't use \b as it chokes on unicode. however \W seems to be okay
+ # as shorthand for [^0-9A-Za-z_].
+ return r"(^|\W)%s(\W|$)" % (r,)
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