Function readPreferenceServerSelector

src/sdam/server_selection.ts:383–415

(readPreference: ReadPreference)

 * @param readPreference - The read preference to select with
 */
export function readPreferenceServerSelector(readPreference: ReadPreference): ServerSelector {
  if (!readPreference.isValid()) {
    throw new MongoInvalidArgumentError('Invalid read preference specified');
  }

  return function readPreferenceServers(
    topologyDescription: TopologyDescription,
    servers: ServerDescription[],
    deprioritized: DeprioritizedServers
  ): ServerDescription[] {
    switch (topologyDescription.type) {
      case 'Single':
        return latencyWindowReducer(topologyDescription, servers.filter(knownFilter));
      case 'ReplicaSetNoPrimary':
      case 'ReplicaSetWithPrimary':
        return secondarySelector(readPreference, topologyDescription, servers, deprioritized);
      case 'Sharded': {
        const selectable = filterDeprioritized(servers, deprioritized);
        return latencyWindowReducer(topologyDescription, selectable.filter(knownFilter));
      }
      case 'Unknown':
        return [];
      case 'LoadBalanced':
        return servers.filter(loadBalancerFilter);
      default: {
        const _exhaustiveCheck: never = topologyDescription.type;
        throw new MongoRuntimeError(
          `unexpected topology type: ${topologyDescription.type} (this should never happen).  Please file a bug in the Node driver Jira project.`
        );
      }
    }
  };
}