From f323faaf92bd24576c0f0521c64149842d79a9e8 Mon Sep 17 00:00:00 2001
From: avdb13 <avdb@keemail.me>
Date: Tue, 28 Jan 2025 23:00:08 +0000
Subject: [PATCH] fix: prevent stripping the room's invite state

---
 book/changelog.md                           |  2 ++
 src/database/key_value/rooms/state_cache.rs | 37 +++++++++++++++++----
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/book/changelog.md b/book/changelog.md
index 7ed662b9..c1342a6b 100644
--- a/book/changelog.md
+++ b/book/changelog.md
@@ -239,6 +239,8 @@ This will be the first release of Grapevine since it was forked from Conduit
     ([!158](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/158))
 28. Fix read receipts not being sent over federation (or only arbitrarily late)
     ([!162](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/162))
+29. Prevent stripping the room's invite state.
+    ([!159](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/159))
 
 ### Added
 
diff --git a/src/database/key_value/rooms/state_cache.rs b/src/database/key_value/rooms/state_cache.rs
index c90a18b1..74f2530a 100644
--- a/src/database/key_value/rooms/state_cache.rs
+++ b/src/database/key_value/rooms/state_cache.rs
@@ -1,7 +1,7 @@
 use std::collections::HashSet;
 
 use ruma::{
-    events::{AnyStrippedStateEvent, AnySyncStateEvent},
+    events::{AnyStateEvent, AnyStrippedStateEvent, AnySyncStateEvent},
     serde::Raw,
     OwnedRoomId, OwnedServerName, OwnedUserId, RoomId, ServerName, UserId,
 };
@@ -466,11 +466,36 @@ impl service::rooms::state_cache::Data for KeyValueDatabase {
                     )
                 })?;
 
-                let state = serde_json::from_slice(&state).map_err(|_| {
-                    Error::bad_database(
-                        "Invalid state in userroomid_invitestate.",
-                    )
-                })?;
+                let state: Vec<Raw<AnyStateEvent>> =
+                    serde_json::from_slice(&state).map_err(|_| {
+                        Error::bad_database(
+                            "Invalid state in userroomid_invitestate.",
+                        )
+                    })?;
+
+                // The semantics here are omitted by the spec, as the example
+                // does not strip the membership event: we cast the
+                // "m.room.member" event to avoid stripping it.
+                // See: https://spec.matrix.org/latest/server-server-api/#put_matrixfederationv2inviteroomideventid
+                let state: Vec<_> = state
+                    .into_iter()
+                    .map(|raw| {
+                        match raw.deserialize().map_err(|_| {
+                            Error::bad_database(
+                                "Invalid state in userroomid_invitestate.",
+                            )
+                        })? {
+                            AnyStateEvent::RoomMember(_) => Ok(raw.cast()),
+                            _ => serde_json::from_str(raw.json().get())
+                                .map_err(|_| {
+                                    Error::bad_database(
+                                        "Invalid state in \
+                                         userroomid_invitestate.",
+                                    )
+                                }),
+                        }
+                    })
+                    .collect::<Result<_>>()?;
 
                 Ok((room_id, state))
             },