Mark device list as stale, if we don't have the requesting device (#2728)

This hopefully makes E2EE chats a little bit more reliable by re-syncing
devices if we don't have the `requesting_device_id` in our database. (As
seen in
[Synapse](c52abc1cfd/synapse/handlers/devicemessage.py (L157-L201)))

keyserver/inthttp/client.go

@@ -37,6 +37,7 @@ const (
 	QueryOneTimeKeysPath              = "/keyserver/queryOneTimeKeys"
 	QueryDeviceMessagesPath           = "/keyserver/queryDeviceMessages"
 	QuerySignaturesPath               = "/keyserver/querySignatures"
+	PerformMarkAsStalePath            = "/keyserver/markAsStale"
 )
 
 // NewKeyServerClient creates a KeyInternalAPI implemented by talking to a HTTP POST API.
@@ -172,3 +173,14 @@ func (h *httpKeyInternalAPI) QuerySignatures(
 		h.httpClient, ctx, request, response,
 	)
 }
+
+func (h *httpKeyInternalAPI) PerformMarkAsStaleIfNeeded(
+	ctx context.Context,
+	request *api.PerformMarkAsStaleRequest,
+	response *struct{},
+) error {
+	return httputil.CallInternalRPCAPI(
+		"MarkAsStale", h.apiURL+PerformMarkAsStalePath,
+		h.httpClient, ctx, request, response,
+	)
+}

keyserver/inthttp/server.go

@@ -16,6 +16,7 @@ package inthttp
 
 import (
 	"github.com/gorilla/mux"
+
 	"github.com/matrix-org/dendrite/internal/httputil"
 	"github.com/matrix-org/dendrite/keyserver/api"
 )
@@ -70,4 +71,9 @@ func AddRoutes(internalAPIMux *mux.Router, s api.KeyInternalAPI) {
 		QuerySignaturesPath,
 		httputil.MakeInternalRPCAPI("KeyserverQuerySignatures", s.QuerySignatures),
 	)
+
+	internalAPIMux.Handle(
+		PerformMarkAsStalePath,
+		httputil.MakeInternalRPCAPI("KeyserverMarkAsStale", s.PerformMarkAsStaleIfNeeded),
+	)
 }