From 36e32f14e6b9337da265a6a1c8453a016b091e7e Mon Sep 17 00:00:00 2001
From: Matthew Hodgson <matthew@matrix.org>
Date: Sat, 12 Sep 2020 23:01:43 +0100
Subject: [PATCH] add perform_handle_remote_peek.go

---
 .../perform/perform_handle_remote_peek.go     | 118 ++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 roomserver/internal/perform/perform_handle_remote_peek.go

diff --git a/roomserver/internal/perform/perform_handle_remote_peek.go b/roomserver/internal/perform/perform_handle_remote_peek.go
new file mode 100644
index 000000000..bcacdc726
--- /dev/null
+++ b/roomserver/internal/perform/perform_handle_remote_peek.go
@@ -0,0 +1,118 @@
+// Copyright 2020 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package perform
+
+import (
+	"context"
+
+	"github.com/matrix-org/dendrite/roomserver/api"
+    "github.com/matrix-org/dendrite/roomserver/internal/helpers"
+    "github.com/matrix-org/dendrite/roomserver/internal/query"
+	"github.com/matrix-org/dendrite/roomserver/internal/input"
+    "github.com/matrix-org/dendrite/roomserver/state"
+    "github.com/matrix-org/dendrite/roomserver/storage"
+    "github.com/matrix-org/dendrite/roomserver/types"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+)
+
+type HandleRemotePeeker struct {
+	DB         storage.Database
+	Inputer *input.Inputer
+}
+
+// PerformHandleRemotePeek handles peeking into matrix rooms, including over
+// federation by talking to the federationsender. called when a remote server
+// initiates a /peek over federation.
+//
+// It should atomically figure out the current state of the room (for the
+// response to /peek) while adding the remotepeek to the kafka stream so the
+// fed sender can start sending peeked events without a race between the state
+// snapshot and the stream of peeked events.
+func (r *HandleRemotePeeker) PerformHandleRemotePeek(
+    ctx context.Context,
+    request *api.PerformHandleRemotePeekRequest,
+    response *api.PerformHandleRemotePeekResponse,
+) error {
+    info, err := r.DB.RoomInfo(ctx, request.RoomID)
+    if err != nil {
+        return err
+    }
+    if info == nil || info.IsStub {
+        return nil
+    }
+    response.RoomExists = true
+    response.RoomVersion = info.RoomVersion
+
+    var stateEvents []gomatrixserverlib.Event
+
+    // XXX: is this right?
+    roomState := state.NewStateResolution(r.DB, *info)
+
+    var currentStateSnapshotNID types.StateSnapshotNID
+    _, currentStateSnapshotNID, _, err =
+            r.DB.LatestEventIDs(ctx, info.RoomNID)
+    if err != nil {
+            return err
+    }
+    var stateEntries []types.StateEntry
+    stateEntries, err = roomState.LoadStateAtSnapshot(
+            ctx, currentStateSnapshotNID,
+    )
+    if err != nil {
+            return err
+    }
+    stateEvents, err = helpers.LoadStateEvents(ctx, r.DB, stateEntries)
+    if err != nil {
+            return err
+    }
+
+    // get the auth event IDs for the current state events
+    var authEventIDs []string
+    for _, se := range stateEvents {
+        authEventIDs = append(authEventIDs, se.AuthEventIDs()...)
+    }
+    authEventIDs = util.UniqueStrings(authEventIDs) // de-dupe
+
+    authEvents, err := query.GetAuthChain(ctx, r.DB.EventsFromIDs, authEventIDs)
+    if err != nil {
+        return err
+    }
+
+    for _, event := range stateEvents {
+        response.StateEvents = append(response.StateEvents, event.Headered(info.RoomVersion))
+    }
+
+    for _, event := range authEvents {
+        response.AuthChainEvents = append(response.AuthChainEvents, event.Headered(info.RoomVersion))
+    }
+
+    // FIXME: there's a race here - we really should be atomically telling the
+    // federationsender to start sending peek events alongside having captured
+    // the current state, but it's unclear if/how we can do that.
+
+	err = r.Inputer.WriteOutputEvents(request.RoomID, []api.OutputEvent{
+		{
+			Type: api.OutputTypeNewRemotePeek,
+			NewRemotePeek: &api.OutputNewRemotePeek{
+				RoomID:   request.RoomID,
+				PeekID:   request.PeekID,
+				ServerName: request.ServerName,
+			},
+		},
+	})
+    return err
+}
+