cleanup deprecated package io/ioutil (#4920)

Signed-off-by: zounengren <zouyee1989@gmail.com>

plugin/pkg/doh/doh.go

@@ -5,7 +5,6 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 
 	"github.com/miekg/dns"
@@ -93,7 +92,7 @@ func requestToMsgGet(req *http.Request) (*dns.Msg, error) {
 }
 
 func toMsg(r io.ReadCloser) (*dns.Msg, error) {
-	buf, err := ioutil.ReadAll(r)
+	buf, err := io.ReadAll(r)
 	if err != nil {
 		return nil, err
 	}

plugin/pkg/log/log.go

@@ -10,7 +10,7 @@ package log
 
 import (
 	"fmt"
-	"io/ioutil"
+	"io"
 	golog "log"
 	"os"
 	"sync"
@@ -102,7 +102,7 @@ func Fatal(v ...interface{}) { log(fatal, v...); os.Exit(1) }
 func Fatalf(format string, v ...interface{}) { logf(fatal, format, v...); os.Exit(1) }
 
 // Discard sets the log output to /dev/null.
-func Discard() { golog.SetOutput(ioutil.Discard) }
+func Discard() { golog.SetOutput(io.Discard) }
 
 const (
 	debug   = "[DEBUG] "

plugin/pkg/parse/host_test.go

@@ -1,7 +1,6 @@
 package parse
 
 import (
-	"io/ioutil"
 	"os"
 	"testing"
 
@@ -61,7 +60,7 @@ func TestHostPortOrFile(t *testing.T) {
 		},
 	}
 
-	err := ioutil.WriteFile("resolv.conf", []byte("nameserver 127.0.0.1\n"), 0600)
+	err := os.WriteFile("resolv.conf", []byte("nameserver 127.0.0.1\n"), 0600)
 	if err != nil {
 		t.Fatalf("Failed to write test resolv.conf")
 	}

plugin/pkg/tls/tls.go

@@ -4,9 +4,9 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"fmt"
-	"io/ioutil"
 	"net"
 	"net/http"
+	"os"
 	"time"
 )
 
@@ -95,7 +95,7 @@ func loadRoots(caPath string) (*x509.CertPool, error) {
 	}
 
 	roots := x509.NewCertPool()
-	pem, err := ioutil.ReadFile(caPath)
+	pem, err := os.ReadFile(caPath)
 	if err != nil {
 		return nil, fmt.Errorf("error reading %s: %s", caPath, err)
 	}