refactor: move from io/ioutil to io and os packages

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

Reference: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

logtail/example/logadopt/logadopt.go

@@ -6,7 +6,7 @@ package main
 
 import (
 	"flag"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"net/url"
@@ -39,7 +39,7 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-	b, err := ioutil.ReadAll(resp.Body)
+	b, err := io.ReadAll(resp.Body)
 	resp.Body.Close()
 	if err != nil {
 		log.Fatalf("logadopt: response read failed %d: %v", resp.StatusCode, err)

logtail/example/logreprocess/logreprocess.go

@@ -9,7 +9,7 @@ import (
 	"bufio"
 	"encoding/json"
 	"flag"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"os"
@@ -50,7 +50,7 @@ func main() {
 	defer resp.Body.Close()
 
 	if resp.StatusCode != 200 {
-		b, err := ioutil.ReadAll(resp.Body)
+		b, err := io.ReadAll(resp.Body)
 		if err != nil {
 			log.Fatalf("logreprocess: read error %d: %v", resp.StatusCode, err)
 		}

logtail/filch/filch_test.go

@@ -6,7 +6,7 @@ package filch
 
 import (
 	"fmt"
-	"io/ioutil"
+	"io"
 	"os"
 	"runtime"
 	"strings"
@@ -195,7 +195,7 @@ func TestFilchStderr(t *testing.T) {
 	f.close(t)
 
 	pipeW.Close()
-	b, err := ioutil.ReadAll(pipeR)
+	b, err := io.ReadAll(pipeR)
 	if err != nil {
 		t.Fatal(err)
 	}

logtail/logtail.go

@@ -13,7 +13,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"strconv"
@@ -430,7 +429,7 @@ func (l *Logger) upload(ctx context.Context, body []byte, origlen int) (uploaded
 
 	if resp.StatusCode != 200 {
 		uploaded = resp.StatusCode == 400 // the server saved the logs anyway
-		b, _ := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
+		b, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
 		return uploaded, fmt.Errorf("log upload of %d bytes %s failed %d: %q", len(body), compressedNote, resp.StatusCode, b)
 	}
 
@@ -654,7 +653,7 @@ func (l *Logger) Write(buf []byte) (int, error) {
 		return 0, nil
 	}
 	level, buf := parseAndRemoveLogLevel(buf)
-	if l.stderr != nil && l.stderr != ioutil.Discard && int64(level) <= atomic.LoadInt64(&l.stderrLevel) {
+	if l.stderr != nil && l.stderr != io.Discard && int64(level) <= atomic.LoadInt64(&l.stderrLevel) {
 		if buf[len(buf)-1] == '\n' {
 			l.stderr.Write(buf)
 		} else {

logtail/logtail_test.go

@@ -9,7 +9,6 @@ import (
 	"context"
 	"encoding/json"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -52,7 +51,7 @@ func NewLogtailTestHarness(t *testing.T) (*LogtailTestServer, *Logger) {
 
 	ts.srv = httptest.NewServer(http.HandlerFunc(
 		func(w http.ResponseWriter, r *http.Request) {
-			body, err := ioutil.ReadAll(r.Body)
+			body, err := io.ReadAll(r.Body)
 			if err != nil {
 				t.Error("failed to read HTTP request")
 			}