Function latencyWindowReducer

src/sdam/server_selection.ts:243–254

* Reduces a list of servers to ensure they fall within an acceptable latency window. This is * further specified in the "Server Selection" specification, found here: * * @see https://github.com/mongodb/specifications/blob/master/source/server-selection/server-selection.md * * @param topologyDes

(
  topologyDescription: TopologyDescription,
  servers: ServerDescription[]
)

 * @returns The servers which fall within an acceptable latency window
 */
function latencyWindowReducer(
  topologyDescription: TopologyDescription,
  servers: ServerDescription[]
): ServerDescription[] {
  const low = servers.reduce(
    (min: number, server: ServerDescription) => Math.min(server.roundTripTime, min),
    Infinity
  );

  const high = low + topologyDescription.localThresholdMS;
  return servers.filter(server => server.roundTripTime <= high && server.roundTripTime >= low);
}

// filters
function primaryFilter(server: ServerDescription): boolean {