plugin/file: trigger reload of zones based on mtime (#8085)

* Added fs.FileInfo.ModTime() based reload feature

Signed-off-by: Endre Szabo <git@end.re>

* Updated the plugin documentation.

Signed-off-by: Endre Szabo <git@end.re>

---------

Signed-off-by: Endre Szabo <git@end.re>

plugin/file/README.md

@@ -27,6 +27,7 @@ If you want to round-robin A and AAAA responses look at the *loadbalance* plugin
 ~~~
 file DBFILE [ZONES... ] {
     reload DURATION
+    reload_by_mtime
     fallthrough [ZONES...]
 }
 ~~~
@@ -34,6 +35,8 @@ file DBFILE [ZONES... ] {
 * `reload` interval to perform a reload of the zone if the SOA version changes. Default is one minute.
   Value of `0` means to not scan for changes and reload. For example, `30s` checks the zonefile every 30 seconds
   and reloads the zone when serial changes.
+* `reload_by_mtime` if set, decision to reload the zone will be based on the zone file modification time,
+  instead of change in the SOA serial.
 * `fallthrough` If zone matches and no record can be generated, pass request to the next plugin.
   If **[ZONES...]** is omitted, then fallthrough happens for all zones for which the plugin
   is authoritative. If specific zones are listed (for example `in-addr.arpa` and `ip6.arpa`), then only

plugin/file/file.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/pkg/fall"
@@ -148,6 +149,15 @@ func Parse(f io.Reader, origin, fileName string, serial int64) (*Zone, error) {
 	zp := dns.NewZoneParser(f, dns.Fqdn(origin), fileName)
 	zp.SetIncludeAllowed(true)
 	z := NewZone(origin, fileName)
+
+	if z.ReloadByMtime {
+		fi, err := os.Stat(fileName)
+		if err != nil {
+			return nil, fmt.Errorf("failed to stat file %q with error %v", fileName, err)
+		}
+		z.file_mtime = fi.ModTime()
+	}
+
 	seenSOA := false
 	for rr, ok := zp.Next(); ok; rr, ok = zp.Next() {
 		if !seenSOA {

plugin/file/reload.go

@@ -20,13 +20,26 @@ func (z *Zone) Reload(t *transfer.Transfer) error {
 			select {
 			case <-tick.C:
 				zFile := z.File()
+				serial := z.SOASerialIfDefined()
+
+				if z.ReloadByMtime {
+					fi, err := os.Stat(zFile)
+					if err != nil {
+						log.Errorf("Failed to stat zone %q in %q: %v", z.origin, zFile, err)
+						continue
+					}
+					if !fi.ModTime().After(z.file_mtime) {
+						continue
+					}
+					serial = 0 // force reload of the zone
+				}
+
 				reader, err := os.Open(filepath.Clean(zFile))
 				if err != nil {
 					log.Errorf("Failed to open zone %q in %q: %v", z.origin, zFile, err)
 					continue
 				}
 
-				serial := z.SOASerialIfDefined()
 				zone, err := Parse(reader, z.origin, zFile, serial)
 				reader.Close()
 				if err != nil {

plugin/file/reload_test.go

@@ -77,6 +77,253 @@ func TestZoneReloadSOAChange(t *testing.T) {
 	}
 }
 
+func TestZoneReloadByMtime(t *testing.T) {
+	// Test 1: Basic mtime trigger - file modification should trigger reload
+	t.Run("BasicMtimeTrigger", func(t *testing.T) {
+		fileName, rm, err := test.TempFile(".", reloadZoneTest)
+		if err != nil {
+			t.Fatalf("Failed to create zone: %s", err)
+		}
+		defer rm()
+
+		reader, err := os.Open(fileName)
+		if err != nil {
+			t.Fatalf("Failed to open zone: %s", err)
+		}
+		z, err := Parse(reader, "miek.nl", fileName, 0)
+		if err != nil {
+			t.Fatalf("Failed to parse zone: %s", err)
+		}
+		reader.Close()
+
+		// Enable mtime-based reload
+		z.ReloadInterval = 10 * time.Millisecond
+		z.ReloadByMtime = true
+		z.Reload(&transfer.Transfer{})
+
+		// Wait for initial load to complete
+		time.Sleep(20 * time.Millisecond)
+
+		// Verify initial content (5 records)
+		rrs, err := z.ApexIfDefined()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(rrs) != 5 {
+			t.Fatalf("Expected 5 initial RRs, got %d", len(rrs))
+		}
+
+		// Modify the zone file (this changes mtime)
+		if err := os.WriteFile(fileName, []byte(reloadZone2Test), 0644); err != nil {
+			t.Fatalf("Failed to write new zone data: %s", err)
+		}
+
+		// Wait for reload to trigger
+		time.Sleep(30 * time.Millisecond)
+
+		// Verify reload occurred (3 records now)
+		rrs, err = z.ApexIfDefined()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(rrs) != 3 {
+			t.Fatalf("Expected 3 RRs after reload, got %d", len(rrs))
+		}
+	})
+
+	// Test 2: No reload when mtime unchanged
+	t.Run("NoReloadWhenMtimeUnchanged", func(t *testing.T) {
+		fileName, rm, err := test.TempFile(".", reloadZoneTest)
+		if err != nil {
+			t.Fatalf("Failed to create zone: %s", err)
+		}
+		defer rm()
+
+		reader, err := os.Open(fileName)
+		if err != nil {
+			t.Fatalf("Failed to open zone: %s", err)
+		}
+		z, err := Parse(reader, "miek.nl", fileName, 0)
+		if err != nil {
+			t.Fatalf("Failed to parse zone: %s", err)
+		}
+		reader.Close()
+
+		// Enable mtime-based reload
+		z.ReloadInterval = 10 * time.Millisecond
+		z.ReloadByMtime = true
+		z.Reload(&transfer.Transfer{})
+
+		// Wait for initial load
+		time.Sleep(20 * time.Millisecond)
+
+		// Record initial SOA serial
+		initialSerial := z.SOASerialIfDefined()
+		if initialSerial == -1 {
+			t.Fatal("Failed to get initial SOA serial")
+		}
+
+		// Record initial record count
+		rrs, err := z.ApexIfDefined()
+		if err != nil {
+			t.Fatal(err)
+		}
+		initialCount := len(rrs)
+
+		// Wait for multiple reload intervals WITHOUT modifying the file
+		time.Sleep(50 * time.Millisecond)
+
+		// Verify no reload occurred
+		currentSerial := z.SOASerialIfDefined()
+		if currentSerial != initialSerial {
+			t.Fatalf("SOA serial changed unexpectedly: %d -> %d", initialSerial, currentSerial)
+		}
+
+		rrs, err = z.ApexIfDefined()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(rrs) != initialCount {
+			t.Fatalf("Record count changed unexpectedly: %d -> %d", initialCount, len(rrs))
+		}
+	})
+
+	// Test 3: Content verification after reload
+	t.Run("ContentVerificationAfterReload", func(t *testing.T) {
+		fileName, rm, err := test.TempFile(".", reloadZoneTest)
+		if err != nil {
+			t.Fatalf("Failed to create zone: %s", err)
+		}
+		defer rm()
+
+		reader, err := os.Open(fileName)
+		if err != nil {
+			t.Fatalf("Failed to open zone: %s", err)
+		}
+		z, err := Parse(reader, "miek.nl", fileName, 0)
+		if err != nil {
+			t.Fatalf("Failed to parse zone: %s", err)
+		}
+		reader.Close()
+
+		// Enable mtime-based reload
+		z.ReloadInterval = 10 * time.Millisecond
+		z.ReloadByMtime = true
+		z.Reload(&transfer.Transfer{})
+
+		ctx := context.TODO()
+
+		// Query initial content
+		r := new(dns.Msg)
+		r.SetQuestion("miek.nl", dns.TypeNS)
+		state := request.Request{W: &test.ResponseWriter{}, Req: r}
+
+		records, _, _, res := z.Lookup(ctx, state, "miek.nl.")
+		if res != Success {
+			t.Fatalf("Failed to lookup initial NS records, got %d", res)
+		}
+
+		// Initial zone has 4 NS records
+		if len(records) != 4 {
+			t.Fatalf("Expected 4 initial NS records, got %d", len(records))
+		}
+
+		// Modify to new zone content (only 2 NS records)
+		if err := os.WriteFile(fileName, []byte(reloadZone2Test), 0644); err != nil {
+			t.Fatalf("Failed to write new zone data: %s", err)
+		}
+
+		// Wait for reload
+		time.Sleep(30 * time.Millisecond)
+
+		// Query new content
+		records, _, _, res = z.Lookup(ctx, state, "miek.nl.")
+		if res != Success {
+			t.Fatalf("Failed to lookup reloaded NS records, got %d", res)
+		}
+
+		// Reloaded zone has 2 NS records
+		if len(records) != 2 {
+			t.Fatalf("Expected 2 reloaded NS records, got %d", len(records))
+		}
+
+		// Verify the actual NS record names match the new zone
+		nsNames := make([]string, len(records))
+		for i, rr := range records {
+			nsNames[i] = rr.(*dns.NS).Ns
+		}
+
+		expectedNS := []string{"ext.ns.whyscream.net.", "omval.tednet.nl."}
+		for i, expected := range expectedNS {
+			if nsNames[i] != expected {
+				t.Errorf("Expected NS record %d to be %s, got %s", i, expected, nsNames[i])
+			}
+		}
+	})
+
+	// Test 4: File deleted/missing during reload
+	t.Run("FileMissingDuringReload", func(t *testing.T) {
+		fileName, rm, err := test.TempFile(".", reloadZoneTest)
+		if err != nil {
+			t.Fatalf("Failed to create zone: %s", err)
+		}
+		defer rm()
+
+		reader, err := os.Open(fileName)
+		if err != nil {
+			t.Fatalf("Failed to open zone: %s", err)
+		}
+		z, err := Parse(reader, "miek.nl", fileName, 0)
+		if err != nil {
+			t.Fatalf("Failed to parse zone: %s", err)
+		}
+		reader.Close()
+
+		// Enable mtime-based reload
+		z.ReloadInterval = 10 * time.Millisecond
+		z.ReloadByMtime = true
+		z.Reload(&transfer.Transfer{})
+
+		// Wait for initial load
+		time.Sleep(20 * time.Millisecond)
+
+		// Verify initial content is loaded
+		rrs, err := z.ApexIfDefined()
+		if err != nil {
+			t.Fatal(err)
+		}
+		initialCount := len(rrs)
+
+		// Delete the zone file
+		if err := os.Remove(fileName); err != nil {
+			t.Fatalf("Failed to remove zone file: %s", err)
+		}
+
+		// Wait for reload interval (reload should fail gracefully)
+		time.Sleep(30 * time.Millisecond)
+
+		// Verify zone still serves old content (didn't crash)
+		rrs, err = z.ApexIfDefined()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(rrs) != initialCount {
+			t.Fatalf("Zone content changed unexpectedly after file deletion: %d -> %d", initialCount, len(rrs))
+		}
+
+		// Verify DNS queries still work
+		ctx := context.TODO()
+		r := new(dns.Msg)
+		r.SetQuestion("miek.nl", dns.TypeSOA)
+		state := request.Request{W: &test.ResponseWriter{}, Req: r}
+
+		_, _, _, res := z.Lookup(ctx, state, "miek.nl.")
+		if res != Success {
+			t.Fatalf("Zone should still serve queries after file deletion, got result %d", res)
+		}
+	})
+}
+
 const reloadZoneTest = `miek.nl.		1627	IN	SOA	linode.atoom.net. miek.miek.nl. 1460175181 14400 3600 604800 14400
 miek.nl.		1627	IN	NS	ext.ns.whyscream.net.
 miek.nl.		1627	IN	NS	omval.tednet.nl.

plugin/file/setup.go

@@ -77,6 +77,7 @@ func fileParse(c *caddy.Controller) (Zones, fall.F, error) {
 
 	var openErr error
 	reload := 1 * time.Minute
+	reload_by_mtime := false
 
 	for c.Next() {
 		// file db.file [zones...]
@@ -131,6 +132,8 @@ func fileParse(c *caddy.Controller) (Zones, fall.F, error) {
 					return Zones{}, fall, plugin.Error("file", err)
 				}
 				reload = d
+			case "reload_by_mtime":
+				reload_by_mtime = true
 			case "upstream":
 				// remove soon
 				c.RemainingArgs()
@@ -143,6 +146,7 @@ func fileParse(c *caddy.Controller) (Zones, fall.F, error) {
 		for i := range origins {
 			z[origins[i]].ReloadInterval = reload
 			z[origins[i]].Upstream = upstream.New()
+			z[origins[i]].ReloadByMtime = reload_by_mtime
 		}
 	}
 

plugin/file/zone.go

@@ -15,9 +15,10 @@ import (
 
 // Zone is a structure that contains all data related to a DNS zone.
 type Zone struct {
-	origin  string
+	origin     string
-	origLen int
+	origLen    int
-	file    string
+	file       string
+	file_mtime time.Time
 	*tree.Tree
 	Apex
 	Expired bool
@@ -28,6 +29,7 @@ type Zone struct {
 	TransferFrom []string
 
 	ReloadInterval time.Duration
+	ReloadByMtime  bool
 	reloadShutdown chan bool
 
 	Upstream *upstream.Upstream // Upstream for looking up external names during the resolution process.