Solve Outbound federation rejects invite response which include invalid

JSON for room version 6

roomserver/api/perform.go

@@ -56,6 +56,11 @@ func (p *PerformError) JSONResponse() util.JSONResponse {
 			// TODO: Should we assert this is in fact JSON? E.g gjson parse?
 			JSON: json.RawMessage(p.Msg),
 		}
+	case PerformErrCanonicalJSON:
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON(p.Msg),
+		}
 	default:
 		return util.ErrorResponse(p)
 	}
@@ -72,6 +77,8 @@ const (
 	PerformErrorNoOperation PerformErrorCode = 4
 	// PerformErrRemote means that the request failed and the PerformError.Msg is the raw remote JSON error response
 	PerformErrRemote PerformErrorCode = 5
+	// PerformErrCanonicalJSON means that the request failed due to invalid json
+	PerformErrCanonicalJSON PerformErrorCode = 6
 )
 
 type PerformJoinRequest struct {

roomserver/internal/perform/perform_invite.go

@@ -17,6 +17,7 @@ package perform
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	federationSenderAPI "github.com/matrix-org/dendrite/federationsender/api"
 	"github.com/matrix-org/dendrite/internal/config"
@@ -158,6 +159,12 @@ func (r *Inviter) PerformInvite(
 					Msg:  err.Error(),
 					Code: api.PerformErrorNotAllowed,
 				}
+
+				if strings.Contains(err.Error(), "value is outside of safe range") {
+					log.Debug("setting error to PerformErrCanonicalJSON")
+					res.Error.Code = api.PerformErrCanonicalJSON
+				}
+
 				log.WithError(err).WithField("event_id", event.EventID()).Error("r.FSAPI.PerformInvite failed")
 				return nil, nil
 			}