* core: replace GetMiddleware

See the discussion in #881. GetMiddleware would add a `nil` middleware
to the callstack thereby breaking functionality.

This PR drops it in favor of RegisterHandler which is a completely
standalone registry for middleware that want to let it self know to
other middleware.

Currenly *autopath* uses this to call *kubernetes*'s AutoPath method
for dynamic autopathing.

* Drop GetMiddleware

* Register metrics

* drop the panic

Only use was in k8s middleware; no tests other than subzone_test.go
existed; not exercised: remove.

* middleware/autopath: some fixes

This fix a small issue in autopath, but unearthed a bigger one.
See #881.

* Fix test

* middleware/authpath: Fix return from k8s mw

Return the correct search path from the kubernetes' AutoPath function.
Based on preliminary discussion in #870

* PodWithIP can be private

Fix and add docs to functions.

* CR: remove the error from AutoPathFunc

Add some docs about normalize.Host and normalize.Name. They are used
correctly in the middleware even though they are somewhat confusing,
esp when you copy from ServerBlockKeys in your middleware.

* mw/kubernetes: fix parseTests

Make parse tests table driven to remove a duplicate code, i.e. most
of the contents of parse_test.go can be removed as well as the
expectString helper function.

* cleanup parse tests

* middleware/kubernetes: pull TXT out of parseRequest

Put the TXT handling one layer higher and remove it from parseRequest.
Also rename the podsvc field in there to podOrSvc. Now that it isn't
used anymore for TXT record (dns-version) that was put in there. We can
make this a boolean (in a future PR).

Make parseRequest get an optional Zone that is from state.Zone and use
that instead of its own code. Removed some tests and other smaller
cleanups.

Fixes #836

* add this reverse

* another check

* readd

* Rename to kPod and kService for some clarity

Some `go vet` cleanup
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

The current badge styles have 4 flat and 1 regular, which were
rather inconsistent. This fix changes to one style and matches
with Caddy.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Move healthcheck out
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Move healthcheck to middleware/pkg/healthcheck
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

So that pull request build failure does not impact project status.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Move reverse function and (some) test code to reverse*.go

Pull in the contents of routeRequest as it is only called once.

Call out to kubernetes to get the search path - this still needs
to return something sensible, but all infrastructure has landed
to make it work.

autopath as middleware

Add log statement pointing to replacement.
remove cidr from README and use replacement syntax.

Fixes #851

*ugh*: forgot to add these files. This add the dnsutil.TrimZone
function.

Add a Zone field in request.Request and a dnsutil.Trimzone help
function.

Factor out as much of autopath into a subpackage as possible right now.
apw.Sent is not needed, we should see this from the rcode returned by
the middleware. See #852 on why this was needed.

Disable the tests for now as to not break the main build.

* Core: convert IP addresses to reverse zone

If we see IP/mask syntax and the mask mod 8 == 0 we assume a reverse
zone and convert to in-addr or .arpa.

* typos

* integration test

* Addr is not used

* core: clean up normalize

Create a SplitHostPort function that can be used both from normalize.go
and address.go. This removes some (not all!) duplication between the
both and makes it work with reverse address notations.

* More tests

Make ClientWrite available for middleware to use.

Put the autopath stuff in a separate sub package. Tests are still
included in the main kubernetes directory.

Next steps (after this is merged), is pulling the autopath handling
into the subpackage and fixing the tests.

Add the DNS message response flags as {rflags} to the default logging
Also complete the replacer testing that is was commented out.
And (unrelated) Switch erratic and whoami to ease testing.

Note: {flags} could and should be added as well - but we can leave that
as a beginners bug.

* kubernetes/reverse: remove deadcode
* deadcode in errors and kubernetes removed
* unnecessary conversion
* constants
* proxy: time.Since()
* simplications
* static check
* Disable test/external_test

randomize the times when doing transfers and checks.

Fixes #840

dedent code, use shorter names.
use strings.EqualFold instead ToLower to avoid create garbage.

Use the same OnStartup setup as in the file middleware. We need to copy
the variable from range, otherwise it gets overwriten in the next loop
because of the async goroutine call.

Hard to test, we have secondary_test.go which we could extend with
multiple zones for instance. For now this fix does not have an test case
with it...

Do a go generate to generate all middleware we want/need before
releasing a new CoreDNS version.

Clean up some golint related issues.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Did a `misspell . | grep -v ^vendor` and fixed
several typos.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Define two consts Pod and Svc, makes it stand out a little more
when used in switches in case.

We have opted for a new type, but then you need to convert them
all the time with string(Foo).

* Treat absence of port/service in SRV as wildcard

Normally, a SRV-request should have the form
_<service>._<port>.<name>.<zone>. The k8s peer-finder which is used for
bootstrapping by some applications will however query for SRV at
<name>.<zone>.

To compensate for this behaviour, treat the absence of _<service> and
_<port> as wildcards.

* Modified tests with new SRV behaviour

Added a testcase for a SRV request without port & service
Removed now valid query from invalidSRVQueries

* Forgot to run gofmt on test/kubernetes_test.go

Drop the interfaceAddr interfaces and just use a function. Cleanup
all fallout from that. Remove the use of global variables and cleanup
the tests a bit.

* Added Pod testing

* Cleanup

* fixed formatting

* mw/kubernete: small cleanup

Small cleanup, avoid pointer to []msg.Services and just returns the
msg.Service.

* Actually compile

* testss

SOA would blindly add "." + zone, which when using the root
zone would create a unparseable packet with "name.."