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

plugin/auto/zone.go

@@ -0,0 +1,76 @@
+// Package auto implements a on-the-fly loading file backend.
+package auto
+
+import (
+	"sync"
+
+	"github.com/coredns/coredns/plugin/file"
+)
+
+// Zones maps zone names to a *Zone. This keep track of what we zones we have loaded at
+// any one time.
+type Zones struct {
+	Z     map[string]*file.Zone // A map mapping zone (origin) to the Zone's data.
+	names []string              // All the keys from the map Z as a string slice.
+
+	origins []string // Any origins from the server block.
+
+	sync.RWMutex
+}
+
+// Names returns the names from z.
+func (z *Zones) Names() []string {
+	z.RLock()
+	n := z.names
+	z.RUnlock()
+	return n
+}
+
+// Origins returns the origins from z.
+func (z *Zones) Origins() []string {
+	// doesn't need locking, because there aren't multiple Go routines accessing it.
+	return z.origins
+}
+
+// Zones returns a zone with origin name from z, nil when not found.
+func (z *Zones) Zones(name string) *file.Zone {
+	z.RLock()
+	zo := z.Z[name]
+	z.RUnlock()
+	return zo
+}
+
+// Add adds a new zone into z. If zo.NoReload is false, the
+// reload goroutine is started.
+func (z *Zones) Add(zo *file.Zone, name string) {
+	z.Lock()
+
+	if z.Z == nil {
+		z.Z = make(map[string]*file.Zone)
+	}
+
+	z.Z[name] = zo
+	z.names = append(z.names, name)
+	zo.Reload()
+
+	z.Unlock()
+}
+
+// Remove removes the zone named name from z. It also stop the the zone's reload goroutine.
+func (z *Zones) Remove(name string) {
+	z.Lock()
+
+	if zo, ok := z.Z[name]; ok && !zo.NoReload {
+		zo.ReloadShutdown <- true
+	}
+
+	delete(z.Z, name)
+
+	// TODO(miek): just regenerate Names (might be bad if you have a lot of zones...)
+	z.names = []string{}
+	for n := range z.Z {
+		z.names = append(z.names, n)
+	}
+
+	z.Unlock()
+}