Return remote errors from FS.PerformJoin (#1164)

* Return remote errors from FS.PerformJoin

Follows the same pattern as PerformJoin on roomserver (no error return).

Also return the right format for incompatible room version errors.

Makes a bunch of tests pass!

* Handle network errors better when returning remote HTTP errors

* Linting

* Fix tests

* Update whitelist, pass network errors through in API=1 mode

roomserver/api/perform.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"encoding/json"
 	"fmt"
 	"net/http"
 
@@ -12,8 +13,9 @@ import (
 type PerformErrorCode int
 
 type PerformError struct {
-	Msg  string
-	Code PerformErrorCode
+	Msg        string
+	RemoteCode int // remote HTTP status code, for PerformErrRemote
+	Code       PerformErrorCode
 }
 
 func (p *PerformError) Error() string {
@@ -43,6 +45,17 @@ func (p *PerformError) JSONResponse() util.JSONResponse {
 			Code: http.StatusForbidden,
 			JSON: jsonerror.Forbidden(p.Msg),
 		}
+	case PerformErrRemote:
+		// if the code is 0 then something bad happened and it isn't
+		// a remote HTTP error being encapsulated, e.g network error to remote.
+		if p.RemoteCode == 0 {
+			return util.ErrorResponse(fmt.Errorf("%s", p.Msg))
+		}
+		return util.JSONResponse{
+			Code: p.RemoteCode,
+			// TODO: Should we assert this is in fact JSON? E.g gjson parse?
+			JSON: json.RawMessage(p.Msg),
+		}
 	default:
 		return util.ErrorResponse(p)
 	}
@@ -57,6 +70,8 @@ const (
 	PerformErrorNoRoom PerformErrorCode = 3
 	// PerformErrorNoOperation means that the request resulted in nothing happening e.g invite->invite or leave->leave.
 	PerformErrorNoOperation PerformErrorCode = 4
+	// PerformErrRemote means that the request failed and the PerformError.Msg is the raw remote JSON error response
+	PerformErrRemote PerformErrorCode = 5
 )
 
 type PerformJoinRequest struct {

roomserver/internal/perform_join.go

@@ -270,9 +270,13 @@ func (r *RoomserverInternalAPI) performFederatedJoinRoomByID(
 		Content:     req.Content,       // the membership event content
 	}
 	fedRes := fsAPI.PerformJoinResponse{}
-	if err := r.fsAPI.PerformJoin(ctx, &fedReq, &fedRes); err != nil {
-		return fmt.Errorf("Error joining federated room: %q", err)
+	r.fsAPI.PerformJoin(ctx, &fedReq, &fedRes)
+	if fedRes.LastError != nil {
+		return &api.PerformError{
+			Code:       api.PerformErrRemote,
+			Msg:        fedRes.LastError.Message,
+			RemoteCode: fedRes.LastError.Code,
+		}
 	}
-
 	return nil
 }