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

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"`
+}