Roomserver API changes (#1118)

* s/QueryBackfill/PerformBackfill/g

* OutputEvent now includes AddStateEvents which contain the full event of extra state events

* Only include adds not the current event

* Get adding state right

4 files changed, 59 insertions, 32 deletions

diff --git a/roomserver/api/api.go b/roomserver/api/api.go
index 3a2ad059..967f58ba 100644
--- a/roomserver/api/api.go
+++ b/roomserver/api/api.go
@@ -89,10 +89,10 @@ type RoomserverInternalAPI interface {
 	) error
 
 	// Query a given amount (or less) of events prior to a given set of events.
-	QueryBackfill(
+	PerformBackfill(
 		ctx context.Context,
-		request *QueryBackfillRequest,
-		response *QueryBackfillResponse,
+		request *PerformBackfillRequest,
+		response *PerformBackfillResponse,
 	) error
 
 	// Asks for the default room version as preferred by the server.
diff --git a/roomserver/api/output.go b/roomserver/api/output.go
index 92a468a9..2bbd97af 100644
--- a/roomserver/api/output.go
+++ b/roomserver/api/output.go
@@ -63,6 +63,13 @@ type OutputNewRoomEvent struct {
 	// Together with RemovesStateEventIDs this allows the receiver to keep an up to date
 	// view of the current state of the room.
 	AddsStateEventIDs []string `json:"adds_state_event_ids"`
+	// All extra newly added state events. This is only set if there are *extra* events
+	// other than `Event`. This can happen when forks get merged because state resolution
+	// may decide a bunch of state events on one branch are now valid, so they will be
+	// present in this list. This is useful when trying to maintain the current state of a room
+	// as to do so you need to include both these events and `Event`.
+	AddStateEvents []gomatrixserverlib.HeaderedEvent `json:"adds_state_events"`
+
 	// The state event IDs that were removed from the state of the room by this event.
 	RemovesStateEventIDs []string `json:"removes_state_event_ids"`
 	// The ID of the event that was output before this event.
@@ -112,6 +119,26 @@ type OutputNewRoomEvent struct {
 	TransactionID *TransactionID `json:"transaction_id"`
 }
 
+// AddsState returns all added state events from this event.
+//
+// This function is needed because `AddStateEvents` will not include a copy of
+// the original event to save space, so you cannot use that slice alone.
+// Instead, use this function which will add the original event if it is present
+// in `AddsStateEventIDs`.
+func (ore *OutputNewRoomEvent) AddsState() []gomatrixserverlib.HeaderedEvent {
+	includeOutputEvent := false
+	for _, id := range ore.AddsStateEventIDs {
+		if id == ore.Event.EventID() {
+			includeOutputEvent = true
+			break
+		}
+	}
+	if !includeOutputEvent {
+		return ore.AddStateEvents
+	}
+	return append(ore.AddStateEvents, ore.Event)
+}
+
 // An OutputNewInviteEvent is written whenever an invite becomes active.
 // Invite events can be received outside of an existing room so have to be
 // tracked separately from the room events themselves.
diff --git a/roomserver/api/perform.go b/roomserver/api/perform.go
index 1cf54144..3e5cae1b 100644
--- a/roomserver/api/perform.go
+++ b/roomserver/api/perform.go
@@ -2,6 +2,7 @@ package api
 
 import (
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
 )
 
 type PerformJoinRequest struct {
@@ -22,3 +23,31 @@ type PerformLeaveRequest struct {
 
 type PerformLeaveResponse struct {
 }
+
+// PerformBackfillRequest is a request to PerformBackfill.
+type PerformBackfillRequest struct {
+	// The room to backfill
+	RoomID string `json:"room_id"`
+	// A map of backwards extremity event ID to a list of its prev_event IDs.
+	BackwardsExtremities map[string][]string `json:"backwards_extremities"`
+	// The maximum number of events to retrieve.
+	Limit int `json:"limit"`
+	// The server interested in the events.
+	ServerName gomatrixserverlib.ServerName `json:"server_name"`
+}
+
+// PrevEventIDs returns the prev_event IDs of all backwards extremities, de-duplicated in a lexicographically sorted order.
+func (r *PerformBackfillRequest) PrevEventIDs() []string {
+	var prevEventIDs []string
+	for _, pes := range r.BackwardsExtremities {
+		prevEventIDs = append(prevEventIDs, pes...)
+	}
+	prevEventIDs = util.UniqueStrings(prevEventIDs)
+	return prevEventIDs
+}
+
+// PerformBackfillResponse is a response to PerformBackfill.
+type PerformBackfillResponse struct {
+	// Missing events, arbritrary order.
+	Events []gomatrixserverlib.HeaderedEvent `json:"events"`
+}
diff --git a/roomserver/api/query.go b/roomserver/api/query.go
index c9a46ae9..b1525342 100644
--- a/roomserver/api/query.go
+++ b/roomserver/api/query.go
@@ -18,7 +18,6 @@ package api
 
 import (
 	"github.com/matrix-org/gomatrixserverlib"
-	"github.com/matrix-org/util"
 )
 
 // QueryLatestEventsAndStateRequest is a request to QueryLatestEventsAndState
@@ -204,34 +203,6 @@ type QueryStateAndAuthChainResponse struct {
 	AuthChainEvents []gomatrixserverlib.HeaderedEvent `json:"auth_chain_events"`
 }
 
-// QueryBackfillRequest is a request to QueryBackfill.
-type QueryBackfillRequest struct {
-	// The room to backfill
-	RoomID string `json:"room_id"`
-	// A map of backwards extremity event ID to a list of its prev_event IDs.
-	BackwardsExtremities map[string][]string `json:"backwards_extremities"`
-	// The maximum number of events to retrieve.
-	Limit int `json:"limit"`
-	// The server interested in the events.
-	ServerName gomatrixserverlib.ServerName `json:"server_name"`
-}
-
-// PrevEventIDs returns the prev_event IDs of all backwards extremities, de-duplicated in a lexicographically sorted order.
-func (r *QueryBackfillRequest) PrevEventIDs() []string {
-	var prevEventIDs []string
-	for _, pes := range r.BackwardsExtremities {
-		prevEventIDs = append(prevEventIDs, pes...)
-	}
-	prevEventIDs = util.UniqueStrings(prevEventIDs)
-	return prevEventIDs
-}
-
-// QueryBackfillResponse is a response to QueryBackfill.
-type QueryBackfillResponse struct {
-	// Missing events, arbritrary order.
-	Events []gomatrixserverlib.HeaderedEvent `json:"events"`
-}
-
 // QueryRoomVersionCapabilitiesRequest asks for the default room version
 type QueryRoomVersionCapabilitiesRequest struct{}