Function parse_entry 

fn parse_entry<I: Iterator<Item = char>>(
    origin: Option<&DomainName>,
    previous_domain: Option<&MaybeWildcard>,
    previous_ttl: Option<u32>,
    stream: &mut Peekable<I>,
) -> Result<Option<Entry>, Error>

Parse a single entry, skipping comments and whitespace. Entries are of the form:

$ORIGIN <domain-name>
$INCLUDE <file-name> [<domain-name>]
<rr>

Where <rr> is one of these forms:

<domain-name> <ttl>   <class> <type> <rdata>
<domain-name> <class> <ttl>   <type> <rdata>
<domain-name> <ttl>           <type> <rdata>
<domain-name>         <class> <type> <rdata>
<domain-name>                 <type> <rdata>
              <ttl>   <class> <type> <rdata>
              <class> <ttl>   <type> <rdata>
              <ttl>           <type> <rdata>
                      <class> <type> <rdata>
                              <type> <rdata>

This is annoyingly flexible:

• If the <domain-name>, <ttl>, or <class> are missing, the previous is used (so it is an error to omit it in the first RR).

• But since this implementation only supports IN-class records, if the class is missing in the first RR, IN is used.

• The <domain-name> can be an absolute domain, given as a dotted string ending in a .; or a relative domain, given as a dotted string not ending in a ., in which case the origin is prepended; or @, in which case it is the origin.

The <rdata> format depends on the record type.

Some special characters are:

• @ - the current origin
• ; - the rest of the line is a comment
• " ... " - a string (used for rdata)
• ( ... ) - a group of data which crosses a newline
• \X - quotes a character, where X is a non-digit
• \DDD - an octet, given as a decimal number

Returns None if the stream is empty.

Errors

If the string cannot be parsed.