Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

1 files changed, 0 insertions, 148 deletions

diff --git a/middleware.md b/middleware.md
deleted file mode 100644
index f946e63e5..000000000
--- a/middleware.md
+++ /dev/null
@@ -1,148 +0,0 @@
-# Middleware
-
-## Writing Middleware
-
-From the Caddy docs:
-
-> Oh yes, those pesky return values on ServeHTTP(). You read the documentation so you already know
-> what they mean. But what does that imply for the behavior of your middleware?
->
-> Basically, return a status code only if you did NOT write to the response body. If you DO write to
-> the response body, return a status code of 0. Return an error value if your middleware encountered
-> an error that you want logged. It is common to return an error status and an error value together,
-> so that the error handler up the chain can write the correct error page.
->
-> The returned status code is not logged directly; rather, it tells middleware higher up the chain
-> what status code to use if/when the response body is written. Again, return a 0 status if you've
-> already written a body!
-
-In the DNS status codes are called rcodes and it's slightly harder to return the correct
-answer in case of failure.
-
-So CoreDNS treats:
-
-* SERVFAIL (dns.RcodeServerFailure)
-* REFUSED (dns.RcodeRefused)
-* FORMERR (dns.RcodeFormatError)
-* NOTIMP (dns.RcodeNotImplemented)
-
-as special and will then assume nothing has written to the client. In all other cases it is assumes
-something has been written to the client (by the middleware).
-
-## Hooking It Up
-
-See a couple of blog posts on how to write and add middleware to CoreDNS:
-
-* <https://blog.coredns.io/2017/03/01/how-to-add-middleware-to-coredns/>
-* <https://blog.coredns.io/2016/12/19/writing-middleware-for-coredns/>, slightly older, but useful.
-
-## Metrics
-
-When exporting metrics the *Namespace* should be `middleware.Namespace` (="coredns"), and the
-*Subsystem* should be the name of the middleware. The README.md for the middleware should then
-also contain a *Metrics* section detailing the metrics. If the middleware supports dynamic health
-reporting it should also have *Health* section detailing on its inner workings.
-
-## Documentation
-
-Each middleware should have a README.md explaining what the middleware does and how it is
-configured. The file should have the following layout:
-
-* Title: use the middleware's name
-* Subsection titled: "Syntax"
-* Subsection titled: "Examples"
-
-More sections are of course possible.
-
-### Style
-
-We use the Unix manual page style:
-
-* The name of middleware in the running text should be italic: *middleware*.
-* all CAPITAL: user supplied argument, in the running text references this use strong text: `**`:
-  **EXAMPLE**.
-* Optional text: in block quotes: `[optional]`.
-* Use three dots to indicate multiple options are allowed: `arg...`.
-* Item used literal: `literal`.
-
-### Example Domain Names
-
-Please be sure to use `example.org` or `example.net` in any examples you provide. These are the
-standard domain names created for this purpose.
-
-## Fallthrough
-
-In a perfect world the following would be true for middleware: "Either you are responsible for
-a zone or not". If the answer is "not", the middleware should call the next middleware in the chain.
-If "yes" it should handle *all* names that fall in this zone and the names below - i.e. it should
-handle the entire domain.
-
-~~~ txt
-. {
-    file example.org db.example
-}
-~~~
-In this example the *file* middleware is handling all names below (and including) `example.org`. If
-a query comes in that is not a subdomain (or equal to) `example.org` the next middleware is called.
-
-Now, the world isn't perfect, and there are good reasons to "fallthrough" to the next middlware,
-meaning a middleware is only responsible for a subset of names within the zone. The first of these
-to appear was the *reverse* middleware that synthesis PTR and A/AAAA responses (useful with IPv6).
-
-The nature of the *reverse* middleware is such that it only deals with A,AAAA and PTR and then only
-for a subset of the names. Ideally you would want to layer *reverse* **in front off** another
-middleware such as *file* or *auto* (or even *proxy*). This means *reverse* handles some special
-reverse cases and **all other** request are handled by the backing middleware. This is exactly what
-"fallthrough" does. To keep things explicit we've opted that middlewares implement such behavior
-should implement a `fallthrough` keyword.
-
-### Example Fallthrough Usage
-
-The following Corefile example, sets up the *reverse* middleware, but disables fallthrough. It
-also defines a zonefile for use with the *file* middleware for other names in the `compute.internal`.
-
-~~~ txt
-arpa compute.internal {
-    reverse 10.32.0.0/16 {
-        hostname ip-{ip}.{zone[2]}
-        #fallthrough
-    }
-    file db.compute.internal compute.internal
-}
-~~~
-
-This works for returning a response to a PTR request:
-
-~~~ sh
-% dig +nocmd @localhost +noall +ans -x 10.32.0.1
-1.0.32.10.in-addr.arpa.	3600	IN	PTR	ip-10-32-0-1.compute.internal.
-~~~
-
-And for the forward:
-
-~~~ sh
-% dig +nocmd @localhost +noall +ans A ip-10-32-0-1.compute.internal
-ip-10-32-0-1.compute.internal. 3600 IN	A	10.32.0.1
-~~~
-
-But a query for `mx compute.internal` will return SERVFAIL. Now when we remove the '#' from
-fallthrough and reload (on Unix: `kill -SIGUSR1 $(pidof coredns)`) CoreDNS, we *should* get an
-answer for the MX query:
-
-~~~ sh
-% dig +nocmd @localhost +noall +ans MX compute.internal
-compute.internal.	3600	IN	MX	10 mx.compute.internal.
-~~~
-
-## Qualifying for main repo
-
-Middleware for CoreDNS can live out-of-tree, `middleware.cfg` defaults to CoreDNS' repo but other
-repos work just as well. So when do we consider the inclusion of a new middleware in the main repo?
-
-* First, the middleware should be useful for other people. "Useful" is a subjective term. We will
-  probably need to further refine this.
-* It should be sufficiently different from other middleware to warrant inclusion.
-* Current internet standards need be supported: IPv4 and IPv6, so A and AAAA records should be
-  handled (if your middleware is in the business of dealing with address records that is).
-* It must have tests.
-* It must have a README.md for documentation.