DNS server support

Support for writing DNS servers, and various API changes to accomplish that, specifically:

 - `DnsType` -> `DnsType<RecordType>` where RecordType is a subclass of `DnsEntry`, and has payload decoders for specific types
 - Introduced record-specific subclasses of `DnsEntry` for common types, with fallback to the ByteBuf-based `DnsResource`
 - `DnsEntry` gains public `writeTo()` and `writePayload()` to write itself correctly into a ByteBuf
 - Added `DnsQueryDecoder` and `DnsResponseEncoder`
 - Introduced `NameWriter` for writing names, so that it's possible to implement a stateful `NameWriter` to do DNS name compression
 - `DnsMessage` is threadsafe (needed for proxy DNS servers where multiple calls to remote DNS servers may contribute partial responses)
    - If someone really feels strongly that creating the `List` instances it uses internally should be lazy, that could be done, but it would be good to have some evidence that really accomplishes something - feels like premature optimization
 - `DnsQuestion` is no longer a subclass of `DnsEntry` (which now has a time-to-live, since that is common to all other record types).
 - Added the package io.netty.handler.codec.dns.server with `DnsServerHandler`, a `SimpleChannelInboundHandler<DatagramPacket>` that handles the common plumbing of writing a DNS server that is unlikely to differ between implementations
 - Corrected error codes in `DnsResponseCode` to match https://tools.ietf.org/html/rfc2929 (they were sequential, but in fact 11-15 are unused and numbering restarts at 16)
 - Added error codes that exist but were not included in `DnsResponseCode` but are part of the spec
 - Added `DnsDecoderException` which can specify a `DnsResponseCode`
 - `DnsQuery` implements `Iterable<DnsQuestion>`, simply because it's intuitive
 - Reasonable `toString()` implementations on entity classes for logging purposes
 - Added to netty-examples:  DNS server, DNS client, proxy DNS server

These objects are mainly used in lists, not sets, so I don't expect
`hashCode()` will be frequently called on them, if at all.  And we're not
talking about expensive computations for any of these - mostly numbers and
a few strings.  So, I will if you insist, but it doesn't seem worth it.

On Mon, Nov 17, 2014 at 4:59 AM, Norman Maurer <notifications@github.com>
wrote:

> In codec-dns/src/main/java/io/netty/handler/codec/dns/CNameDnsRecord.java:
>
> > +        this.cname = cname;
> > +    }
> > +
> > +    public String cname() {
> > +        return cname;
> > +    }
> > +
> > +    @Override
> > +    protected void writePayload(NameWriter nameWriter, ByteBuf into, Charset charset) {
> > +        nameWriter.writeName(cname, into, charset);
> > +    }
> > +
> > +    @Override
> > +    public int hashCode() {
> > +        int hash = super.hashCode();
> > +        hash = 83 * hash + (this.cname != null ? this.cname.hashCode() : 0);
>
> How about cache this ?
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/netty/netty/pull/3146/files#r20425396>.
>



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