public static InternalDistributedMember readEssentialData(DataInput in)
      throws IOException, ClassNotFoundException {
    final InternalDistributedMember mbr = new InternalDistributedMember();
    mbr._readEssentialData(in, InternalDistributedMember::getHostName);
    return mbr;
  }
this reads an ID written with writeEssentialData
geode-core/src/main/java/org/apache/geode/distributed/internal/membership/InternalDistributedMember.java