Update implementation of MSC4306: Thread Subscriptions to include automatic subscription conflict prevention as introduced in later drafts.

synapse/util/pydantic_models.py

@@ -13,7 +13,11 @@
 #
 #
 
-from synapse._pydantic_compat import BaseModel, Extra
+import re
+from typing import Any, Callable, Generator
+
+from synapse._pydantic_compat import BaseModel, Extra, StrictStr
+from synapse.types import EventID
 
 
 class ParseModel(BaseModel):
@@ -37,3 +41,43 @@ class Config:
         extra = Extra.ignore
         # By default, don't allow fields to be reassigned after parsing.
         allow_mutation = False
+
+
+class AnyEventId(StrictStr):
+    """
+    A validator for strings that need to be an Event ID.
+
+    Accepts any valid grammar of Event ID from any room version.
+    """
+
+    EVENT_ID_HASH_ROOM_VERSION_3_PLUS = re.compile(
+        r"^([a-zA-Z0-9-_]{43}|[a-zA-Z0-9+/]{43})$"
+    )
+
+    @classmethod
+    def __get_validators__(cls) -> Generator[Callable[..., Any], Any, Any]:
+        yield from super().__get_validators__()  # type: ignore
+        yield cls.validate_event_id
+
+    @classmethod
+    def validate_event_id(cls, value: str) -> str:
+        if not value.startswith("$"):
+            raise ValueError("Event ID must start with `$`")
+
+        if ":" in value:
+            # Room versions 1 and 2
+            EventID.from_string(value)  # throws on fail
+        else:
+            # Room versions 3+: event ID is $ + a base64 sha256 hash
+            # Room version 3 is base64, 4+ are base64Url
+            # In both cases, the base64 is unpadded.
+            # refs:
+            # - https://spec.matrix.org/v1.15/rooms/v3/
+            # - https://spec.matrix.org/v1.15/rooms/v4/
+            b64_hash = value[1:]
+            if cls.EVENT_ID_HASH_ROOM_VERSION_3_PLUS.fullmatch(b64_hash) is None:
+                raise ValueError(
+                    "Event ID must either have a domain part or be a valid hash"
+                )
+
+        return value