buildCidExtension

fnubyte[] buildCidExtension(DtlsConnectionId cid, ubyte localCidLength = 0)

Builds the connection_id extension body for ClientHello/ServerHello.

Wire format (RFC 9147 §5.6): 

uint8 cid_length;
  opaque cid<0..255>;

The client sends the desired local CID length. The server responds with the actual CID it wants the client to use (the server's local CID).

Parameters

cidThe Connection ID to include, or DtlsConnectionId.none() to signal support without a specific CID.
localCidLengthFor ClientHello: the desired local CID length. For ServerHello: ignored (cid.bytes used directly).

Returns

The extension body bytes ready to be wrapped with extension header.