Function federatedAuthProvider

federationapi/internal/perform.go:701–760

FederatedAuthProvider is an auth chain provider which fetches events from the server provided

(
	ctx context.Context, federation api.FederationClient,
	keyRing gomatrixserverlib.JSONVerifier, server gomatrixserverlib.ServerName,
)

// FederatedAuthProvider is an auth chain provider which fetches events from the server provided
func federatedAuthProvider(
	ctx context.Context, federation api.FederationClient,
	keyRing gomatrixserverlib.JSONVerifier, server gomatrixserverlib.ServerName,
) gomatrixserverlib.AuthChainProvider {
	// A list of events that we have retried, if they were not included in
	// the auth events supplied in the send_join.
	retries := map[string][]*gomatrixserverlib.Event{}

	// Define a function which we can pass to Check to retrieve missing
	// auth events inline. This greatly increases our chances of not having
	// to repeat the entire set of checks just for a missing event or two.
	return func(roomVersion gomatrixserverlib.RoomVersion, eventIDs []string) ([]*gomatrixserverlib.Event, error) {
		returning := []*gomatrixserverlib.Event{}

		// See if we have retry entries for each of the supplied event IDs.
		for _, eventID := range eventIDs {
			// If we've already satisfied a request for this event ID before then
			// just append the results. We won't retry the request.
			if retry, ok := retries[eventID]; ok {
				if retry == nil {
					return nil, fmt.Errorf("missingAuth: not retrying failed event ID %q", eventID)
				}
				returning = append(returning, retry...)
				continue
			}

			// Make a note of the fact that we tried to do something with this
			// event ID, even if we don't succeed.
			retries[eventID] = nil

			// Try to retrieve the event from the server that sent us the send
			// join response.
			tx, txerr := federation.GetEvent(ctx, server, eventID)
			if txerr != nil {
				return nil, fmt.Errorf("missingAuth r.federation.GetEvent: %w", txerr)
			}

			// For each event returned, add it to the set of return events. We
			// also will populate the retries, in case someone asks for this
			// event ID again.
			for _, pdu := range tx.PDUs {
				// Try to parse the event.
				ev, everr := gomatrixserverlib.NewEventFromUntrustedJSON(pdu, roomVersion)
				if everr != nil {
					return nil, fmt.Errorf("missingAuth gomatrixserverlib.NewEventFromUntrustedJSON: %w", everr)
				}

				// Check the signatures of the event.
				if err := ev.VerifyEventSignatures(ctx, keyRing); err != nil {
					return nil, fmt.Errorf("missingAuth VerifyEventSignatures: %w", err)
				}

				// If the event is OK then add it to the results and the retry map.
				returning = append(returning, ev)
				retries[ev.EventID()] = append(retries[ev.EventID()], ev)
			}
		}
		return returning, nil