Add PerformInvite and refactor how errors get handled (#1158)

* Add PerformInvite and refactor how errors get handled

- Rename `JoinError` to `PerformError`
- Remove `error` from the API function signature entirely. This forces
  errors to be bundled into `PerformError` which makes it easier for callers
  to detect and handle errors. On network errors, HTTP clients will make a
  `PerformError`.

* Unbreak everything; thanks Go!

* Send back JSONResponse according to the PerformError

* Update federation invite code too

roomserver/api/perform.go

@@ -1,19 +1,57 @@
 package api
 
 import (
+	"fmt"
+	"net/http"
+
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 )
 
-type JoinError int
+type PerformErrorCode int
+
+type PerformError struct {
+	Msg  string
+	Code PerformErrorCode
+}
+
+func (p *PerformError) Error() string {
+	return fmt.Sprintf("%d : %s", p.Code, p.Msg)
+}
+
+// JSONResponse maps error codes to suitable HTTP error codes, defaulting to 500.
+func (p *PerformError) JSONResponse() util.JSONResponse {
+	switch p.Code {
+	case PerformErrorBadRequest:
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.Unknown(p.Msg),
+		}
+	case PerformErrorNoRoom:
+		return util.JSONResponse{
+			Code: http.StatusNotFound,
+			JSON: jsonerror.NotFound(p.Msg),
+		}
+	case PerformErrorNotAllowed:
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: jsonerror.Forbidden(p.Msg),
+		}
+	default:
+		return util.ErrorResponse(p)
+	}
+}
 
 const (
-	// JoinErrorNotAllowed means the user is not allowed to join this room (e.g join_rule:invite or banned)
-	JoinErrorNotAllowed JoinError = 1
-	// JoinErrorBadRequest means the request was wrong in some way (invalid user ID, wrong server, etc)
-	JoinErrorBadRequest JoinError = 2
-	// JoinErrorNoRoom means that the room being joined doesn't exist.
-	JoinErrorNoRoom JoinError = 3
+	// PerformErrorNotAllowed means the user is not allowed to invite/join/etc this room (e.g join_rule:invite or banned)
+	PerformErrorNotAllowed PerformErrorCode = 1
+	// PerformErrorBadRequest means the request was wrong in some way (invalid user ID, wrong server, etc)
+	PerformErrorBadRequest PerformErrorCode = 2
+	// PerformErrorNoRoom means that the room being joined doesn't exist.
+	PerformErrorNoRoom PerformErrorCode = 3
+	// PerformErrorNoOperation means that the request resulted in nothing happening e.g invite->invite or leave->leave.
+	PerformErrorNoOperation PerformErrorCode = 4
 )
 
 type PerformJoinRequest struct {
@@ -26,10 +64,8 @@ type PerformJoinRequest struct {
 type PerformJoinResponse struct {
 	// The room ID, populated on success.
 	RoomID string `json:"room_id"`
-	// The reason why the join failed. Can be blank.
-	Error JoinError `json:"error"`
-	// Debugging description of the error. Always present on failure.
-	ErrMsg string `json:"err_msg"`
+	// If non-nil, the join request failed. Contains more information why it failed.
+	Error *PerformError
 }
 
 type PerformLeaveRequest struct {
@@ -40,6 +76,19 @@ type PerformLeaveRequest struct {
 type PerformLeaveResponse struct {
 }
 
+type PerformInviteRequest struct {
+	RoomVersion     gomatrixserverlib.RoomVersion             `json:"room_version"`
+	Event           gomatrixserverlib.HeaderedEvent           `json:"event"`
+	InviteRoomState []gomatrixserverlib.InviteV2StrippedState `json:"invite_room_state"`
+	SendAsServer    string                                    `json:"send_as_server"`
+	TransactionID   *TransactionID                            `json:"transaction_id"`
+}
+
+type PerformInviteResponse struct {
+	// If non-nil, the invite request failed. Contains more information why it failed.
+	Error *PerformError
+}
+
 // PerformBackfillRequest is a request to PerformBackfill.
 type PerformBackfillRequest struct {
 	// The room to backfill