Function append

pub fn append(
    rrset: RecordSet,
    zone_origin: Name,
    must_exist: bool,
    use_edns: bool,
) -> Message

Appends a record to an existing rrset, optionally require the rrset to exist (atomicity depends on the server)

RFC 2136, DNS Update, April 1997

2.4.1 - RRset Exists (Value Independent)

  At least one RR with a specified NAME and TYPE (in the zone and class
  specified in the Zone Section) must exist.

  For this prerequisite, a requestor adds to the section a single RR
  whose NAME and TYPE are equal to that of the zone RRset whose
  existence is required.  RDLENGTH is zero and RDATA is therefore
  empty.  CLASS must be specified as ANY to differentiate this
  condition from that of an actual RR whose RDLENGTH is naturally zero
  (0) (e.g., NULL).  TTL is specified as zero (0).

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

• rrset - the record(s) to append to an RRSet
• zone_origin - the zone name to update, i.e. SOA name
• must_exist - if true, the request will fail if the record does not exist

The update must go to a zone authority (i.e. the server used in the ClientConnection). If the rrset does not exist and must_exist is false, then the RRSet will be created.