Revert "Implement notifies for transfer plugin (#3972)" (#3995)

This reverts commit 68f1dd5ddf.

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

plugin/file/zone.go

@@ -2,6 +2,7 @@ package file
 
 import (
 	"fmt"
+	"net"
 	"path/filepath"
 	"strings"
 	"sync"
@@ -9,6 +10,7 @@ import (
 
 	"github.com/coredns/coredns/plugin/file/tree"
 	"github.com/coredns/coredns/plugin/pkg/upstream"
+	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
 )
@@ -24,6 +26,7 @@ type Zone struct {
 
 	sync.RWMutex
 
+	TransferTo   []string
 	StartupOnce  sync.Once
 	TransferFrom []string
 
@@ -55,6 +58,7 @@ func NewZone(name, file string) *Zone {
 // Copy copies a zone.
 func (z *Zone) Copy() *Zone {
 	z1 := NewZone(z.origin, z.file)
+	z1.TransferTo = z.TransferTo
 	z1.TransferFrom = z.TransferFrom
 	z1.Expired = z.Expired
 
@@ -65,6 +69,7 @@ func (z *Zone) Copy() *Zone {
 // CopyWithoutApex copies zone z without the Apex records.
 func (z *Zone) CopyWithoutApex() *Zone {
 	z1 := NewZone(z.origin, z.file)
+	z1.TransferTo = z.TransferTo
 	z1.TransferFrom = z.TransferFrom
 	z1.Expired = z.Expired
 
@@ -129,6 +134,26 @@ func (z *Zone) SetFile(path string) {
 	z.Unlock()
 }
 
+// TransferAllowed checks if incoming request for transferring the zone is allowed according to the ACLs.
+func (z *Zone) TransferAllowed(state request.Request) bool {
+	for _, t := range z.TransferTo {
+		if t == "*" {
+			return true
+		}
+		// If remote IP matches we accept.
+		remote := state.IP()
+		to, _, err := net.SplitHostPort(t)
+		if err != nil {
+			continue
+		}
+		if to == remote {
+			return true
+		}
+	}
+	// TODO(miek): future matching against IP/CIDR notations
+	return false
+}
+
 // ApexIfDefined returns the apex nodes from z. The SOA record is the first record, if it does not exist, an error is returned.
 func (z *Zone) ApexIfDefined() ([]dns.RR, error) {
 	z.RLock()