Add generic file attachments to chat messages

Messages can now carry an arbitrary file (MessageFile), parallel to the
existing MessageImage feature rather than a refactor of it. Files serve
with Content-Disposition: attachment to force a download and prevent an
uploaded HTML/SVG from executing same-origin. No content-type allowlist,
same 8MB cap as images for now (a separate size-limit redesign is tracked
as its own issue).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -5,6 +5,7 @@ from app.models.event_subscription import EventSubscription
 from app.models.invite import InviteStatus
 from app.models.membership import RoomMembership, RoomRole
 from app.models.message import Message
+from app.models.message_file import MessageFile
 from app.models.message_image import MessageImage
 from app.models.message_reaction import MessageReaction
 from app.models.password_reset import PasswordReset
@@ -22,6 +23,7 @@ __all__ = [
     "RoomMembership",
     "RoomRole",
     "Message",
+    "MessageFile",
     "MessageImage",
     "MessageReaction",
     "InviteStatus",

backend/app/models/message.py

@@ -11,8 +11,8 @@ class Message(Base):
     __tablename__ = "messages"
     __table_args__ = (
         CheckConstraint(
-            "content IS NOT NULL OR image_id IS NOT NULL",
-            name="messages_content_or_image_required",
+            "content IS NOT NULL OR image_id IS NOT NULL OR file_id IS NOT NULL",
+            name="messages_content_or_attachment_required",
         ),
     )
 
@@ -21,9 +21,10 @@ class Message(Base):
     user_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), nullable=False)
     # Nullable since Phase "image uploads": a message can be an image with
     # no caption. The CheckConstraint above still requires at least one of
-    # content/image_id.
+    # content/image_id/file_id.
     content: Mapped[str | None] = mapped_column(Text)
     image_id: Mapped[uuid.UUID | None] = mapped_column(ForeignKey("message_images.id"))
+    file_id: Mapped[uuid.UUID | None] = mapped_column(ForeignKey("message_files.id"))
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now(), index=True, nullable=False
     )
@@ -32,3 +33,4 @@ class Message(Base):
 
     user = relationship("User")
     image = relationship("MessageImage")
+    file = relationship("MessageFile")

backend/app/models/message_file.py

@@ -0,0 +1,28 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import BigInteger, DateTime, ForeignKey, String, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class MessageFile(Base):
+    __tablename__ = "message_files"
+
+    id: Mapped[uuid.UUID] = mapped_column(primary_key=True, default=uuid.uuid4)
+    room_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("rooms.id"), index=True, nullable=False)
+    uploaded_by: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), nullable=False)
+    storage_filename: Mapped[str] = mapped_column(String(64), nullable=False)
+    original_filename: Mapped[str] = mapped_column(String(255), nullable=False)
+    # Wider than MessageImage's content_type column -- generic MIME strings
+    # (e.g. the Office Open XML types) run 60-80 chars, unlike images'
+    # four known short values.
+    content_type: Mapped[str] = mapped_column(String(150), nullable=False)
+    size_bytes: Mapped[int] = mapped_column(BigInteger, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), nullable=False
+    )
+
+    room = relationship("Room")
+    uploader = relationship("User")