plugin/auto: Fix panic caused by config invalid reload value (#4986)

Automatically submitted.

plugin/auto/setup.go

 package auto
 
 import (
+	"errors"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -44,7 +45,9 @@ func setup(c *caddy.Controller) error {
 		if err != nil {
 			return err
 		}
-
+		if a.loader.ReloadInterval == 0 {
+			return nil
+		}
 		go func() {
 			ticker := time.NewTicker(a.loader.ReloadInterval)
 			for {
@@ -131,7 +134,14 @@ func autoParse(c *caddy.Controller) (Auto, error) {
 				}
 
 			case "reload":
-				d, err := time.ParseDuration(c.RemainingArgs()[0])
+				t := c.RemainingArgs()
+				if len(t) < 1 {
+					return a, errors.New("reload duration value is expected")
+				}
+				d, err := time.ParseDuration(t[0])
+				if d < 0 {
+					err = errors.New("invalid duration")
+				}
 				if err != nil {
 					return a, plugin.Error("file", err)
 				}

plugin/auto/setup_test.go

@@ -126,3 +126,52 @@ func TestAutoParse(t *testing.T) {
 		}
 	}
 }
+
+func TestSetupReload(t *testing.T) {
+	tests := []struct {
+		name    string
+		config  string
+		wantErr bool
+	}{
+		{
+			name: "reload valid",
+			config: `auto {
+				directory .
+				reload 5s
+			}`,
+			wantErr: false,
+		},
+		{
+			name: "reload disable",
+			config: `auto {
+				directory .
+				reload 0
+			}`,
+			wantErr: false,
+		},
+		{
+			name: "reload invalid",
+			config: `auto {
+				directory .
+				reload -1s
+			}`,
+			wantErr: true,
+		},
+		{
+			name: "reload invalid",
+			config: `auto {
+				directory .
+				reload
+			}`,
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctr := caddy.NewTestController("dns", tt.config)
+			if err := setup(ctr); (err != nil) != tt.wantErr {
+				t.Errorf("Error: setup() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}

plugin/file/setup.go

 package file
 
 import (
+	"errors"
 	"os"
 	"path/filepath"
 	"time"
@@ -108,7 +109,11 @@ func fileParse(c *caddy.Controller) (Zones, error) {
 		for c.NextBlock() {
 			switch c.Val() {
 			case "reload":
-				d, err := time.ParseDuration(c.RemainingArgs()[0])
+				t := c.RemainingArgs()
+				if len(t) < 1 {
+					return Zones{}, errors.New("reload duration value is expected")
+				}
+				d, err := time.ParseDuration(t[0])
 				if err != nil {
 					return Zones{}, plugin.Error("file", err)
 				}