fix: io and os instead of deprecated ioutil

Deprecated: As of Go 1.16, the same functionality is now provided by package io or package os, and those implementations should be preferred in new code. See the specific function documentation for details.
https://pkg.go.dev/io/ioutil

doh-client/google.go

@@ -27,7 +27,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"net/url"
@@ -140,7 +140,7 @@ func (c *Client) parseResponseGoogle(ctx context.Context, w dns.ResponseWriter,
 		}
 	}
 
-	body, err := ioutil.ReadAll(req.response.Body)
+	body, err := io.ReadAll(req.response.Body)
 	if err != nil {
 		log.Println(err)
 		req.reply.Rcode = dns.RcodeServerFailure

doh-client/ietf.go

@@ -28,7 +28,7 @@ import (
 	"context"
 	"encoding/base64"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net"
 	"net/http"
@@ -178,7 +178,7 @@ func (c *Client) parseResponseIETF(ctx context.Context, w dns.ResponseWriter, r
 		}
 	}
 
-	body, err := ioutil.ReadAll(req.response.Body)
+	body, err := io.ReadAll(req.response.Body)
 	if err != nil {
 		log.Printf("read error from upstream %s: %v\n", req.currentUpstream, err)
 		req.reply.Rcode = dns.RcodeServerFailure

doh-client/main.go

@@ -27,7 +27,6 @@ import (
 	"flag"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"os"
 	"runtime"
@@ -40,7 +39,7 @@ func checkPIDFile(pidFile string) (bool, error) {
 retry:
 	f, err := os.OpenFile(pidFile, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0666)
 	if os.IsExist(err) {
-		pidStr, err := ioutil.ReadFile(pidFile)
+		pidStr, err := os.ReadFile(pidFile)
 		if err != nil {
 			return false, err
 		}