standard compliant errors on EDNS0

[miekg]

Support NSID (middleware thingy?)

And correctly return an EDNS0 error when we don't understand the OPT RR. Google for some ravings of marka on this subject.

[miekg]

See https://ednscomp.isc.org/compliance/summary.html

[miekg]

First test:

% dig +norec +edns=0 soa miek.nl @linode.atoom.net                            ~
;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 59413
;; Flags: qr aa ra; QUERY: 1; ANSWER: 1; AUTHORITY: 0; ADDITIONAL: 0

;; QUESTION SECTION:
;; miek.nl.                 IN  SOA

;; ANSWER SECTION:
miek.nl.                1800    IN  SOA linode.atoom.net. miek.miek.nl. 1460088781 14400 3600 604800 14400

;; Received 82 B
;; Time 2016-04-08 07:40:23 BST
;; From 2a01:7e00::f03c:91ff:feae:e74c@53(UDP) in 9.7 ms

Missing

;; EDNS PSEUDOSECTION:
;; Version: 0; flags: ; UDP size: 4096 B; ext-rcode: Unused

For instance...

Should just put the above page in an edns0_test.go file, load a fake zone. Also take care that that "dropped" zone (i.e. did not enter the middleware) takes care of this. Also check the etcd middleware, prolly need a function in the middleware directory that does most of this, or on state and cache a few bits...

[miekg]

I could add a middleware to add or fixes the EDNS0 in the packet, this would work similar to the rewrite middleware, but is on by default. The only downside is TSIG signed packets - also [IA]XFR... might just go ahead and fix this for the file middleware, see what can be applied to etcd middleware, abstract that and put in the middleware directory.

[miekg]

Fixed in all middleware, respond correctly to EDNS0 options in the middleware.