Move alias middleware to it's own repo

README.md

@@ -1,2 +1,45 @@
-# alias
-Middleware for replacing CNAME records on zone apex. 
+
+# Alias middleware
+
+This middleware eliminates CNAME records from zone apex by making the subsequent resolved records look like they belong to the zone apex. This behaves similarily to [CloudFlare's Zone Flattening](https://support.cloudflare.com/hc/en-us/articles/200169056-CNAME-Flattening-RFC-compliant-support-for-CNAME-at-the-root).
+
+Preferrably, this should not be used in favour of the RFC drafts for the new [ANAME](https://tools.ietf.org/html/draft-ietf-dnsop-aname-00) records, but the DNS library used by CoreDNS does not support ANAME records yet. 
+
+# Usage
+
+```
+$ go get https://github.com/coredns/coredns
+$ go get https://github.com/serverwentdown/alias
+$ cd $GOPATH/src/github.com/coredns/coredns
+$ vim middleware.cfg
+# Add the line 145:alias:github.com/serverwentdown/alias
+$ go generate
+$ go build
+$ ./coredns -plugins | grep alias
+```
+
+This middleware only works with the `file` middleware with `upstream` set, or when A or AAAA records exist alongside the CNAME record.
+
+```
+example.com {
+  file example.com.db {
+    upstream 8.8.8.8
+  }
+  alias
+}
+```
+
+All it does is transform records like this:
+
+```
+;; ANSWER SECTION:
+example.com.	300	IN	CNAME	some.magic.example.org.
+some.magic.example.org. 299 IN A	123.123.45.67
+```
+
+into
+
+```
+;; ANSWER SECTION:
+example.com.	299	IN	A	123.123.45.67
+```

alias.go

@@ -0,0 +1,82 @@
+package alias
+
+import (
+	"github.com/coredns/coredns/middleware"
+
+	"github.com/miekg/dns"
+
+	"golang.org/x/net/context"
+)
+
+// Rewrite is middleware to rewrite requests internally before being handled.
+type Alias struct {
+	Next middleware.Handler
+}
+
+// ServeDNS implements the middleware.Handler interface.
+func (al Alias) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	mw := NewResponseModifier(w)
+	return middleware.NextOrFailure(al.Name(), al.Next, ctx, mw, r)
+}
+
+// Name implements the Handler interface.
+func (al Alias) Name() string { return "alias" }
+
+type ResponseModifier struct {
+	dns.ResponseWriter
+}
+
+// Returns a dns.Msg modifier that replaces CNAME on root zones with other records.
+func NewResponseModifier(w dns.ResponseWriter) *ResponseModifier {
+	return &ResponseModifier{
+		ResponseWriter: w,
+	}
+}
+
+// WriteMsg records the status code and calls the
+// underlying ResponseWriter's WriteMsg method.
+func (r *ResponseModifier) WriteMsg(res *dns.Msg) error {
+	// Guess zone based on authority section.
+	var zone string
+	for i := 0; i < len(res.Ns); i++ {
+		rr := res.Ns[i]
+		if rr.Header().Rrtype == dns.TypeNS {
+			zone = rr.Header().Name
+		}
+	}
+
+	// Find and delete CNAME record on that zone, storing the canonical name.
+	var cname string
+	for i := 0; i < len(res.Answer); i++ {
+		rr := res.Answer[i]
+		if rr.Header().Rrtype == dns.TypeCNAME && rr.Header().Name == zone {
+			cname = rr.(*dns.CNAME).Target
+			// Remove the CNAME record
+			res.Answer = append(res.Answer[:i], res.Answer[i+1:]...)
+			break
+		}
+	}
+
+	// Rename all the records with the above canonical name to the zone name
+	for i := 0; i < len(res.Answer); i++ {
+		rr := res.Answer[i]
+		if rr.Header().Name == cname {
+			rr.Header().Name = zone
+		}
+	}
+
+	return r.ResponseWriter.WriteMsg(res)
+}
+
+// Write is a wrapper that records the size of the message that gets written.
+func (r *ResponseModifier) Write(buf []byte) (int, error) {
+	n, err := r.ResponseWriter.Write(buf)
+	return n, err
+}
+
+// Hijack implements dns.Hijacker. It simply wraps the underlying
+// ResponseWriter's Hijack method if there is one, or returns an error.
+func (r *ResponseModifier) Hijack() {
+	r.ResponseWriter.Hijack()
+	return
+}

setup.go

@@ -0,0 +1,28 @@
+package alias
+
+import (
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/middleware"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("alias", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	c.Next()
+	if c.NextArg() {
+		return middleware.Error("alias", c.ArgErr())
+	}
+
+	dnsserver.GetConfig(c).AddMiddleware(func(next middleware.Handler) middleware.Handler {
+		return Alias{Next: next}
+	})
+
+	return nil
+}