Function trust_dns_proto::op::update_message::compare_and_swap

pub fn compare_and_swap(
    current: RecordSet,
    new: RecordSet,
    zone_origin: Name,
    use_edns: bool
) -> Message

Compares and if it matches, swaps it for the new value (atomicity depends on the server)

 2.4.2 - RRset Exists (Value Dependent)

  A set of RRs with a specified NAME and TYPE exists and has the same
  members with the same RDATAs as the RRset specified here in this
  section.  While RRset ordering is undefined and therefore not
  significant to this comparison, the sets be identical in their
  extent.

  For this prerequisite, a requestor adds to the section an entire
  RRset whose preexistence is required.  NAME and TYPE are that of the
  RRset being denoted.  CLASS is that of the zone.  TTL must be
  specified as zero (0) and is ignored when comparing RRsets for
  identity.

 2.5.4 - Delete An RR From An RRset

  RRs to be deleted are added to the Update Section.  The NAME, TYPE,
  RDLENGTH and RDATA must match the RR being deleted.  TTL must be
  specified as zero (0) and will otherwise be ignored by the Primary
  Zone Server.  CLASS must be specified as NONE to distinguish this from an
  RR addition.  If no such RRs exist, then this Update RR will be
  silently ignored by the Primary Zone Server.

 2.5.1 - Add To An RRset

  RRs are added to the Update Section whose NAME, TYPE, TTL, RDLENGTH
  and RDATA are those being added, and CLASS is the same as the zone
  class.  Any duplicate RRs will be silently ignored by the Primary
  Zone Server.

Arguments

• current - the current rrset which must exist for the swap to complete
• new - the new rrset with which to replace the current rrset
• zone_origin - the zone name to update, i.e. SOA name

The update must go to a zone authority (i.e. the server used in the ClientConnection).