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

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

cmd/ctr/app/main.go

@@ -18,7 +18,7 @@ package app
 
 import (
 	"fmt"
-	"io/ioutil"
+	"io"
 
 	"github.com/containerd/containerd/cmd/ctr/commands/containers"
 	"github.com/containerd/containerd/cmd/ctr/commands/content"
@@ -46,7 +46,7 @@ var extraCmds = []cli.Command{}
 
 func init() {
 	// Discard grpc logs so that they don't mess with our stdio
-	grpclog.SetLoggerV2(grpclog.NewLoggerV2(ioutil.Discard, ioutil.Discard, ioutil.Discard))
+	grpclog.SetLoggerV2(grpclog.NewLoggerV2(io.Discard, io.Discard, io.Discard))
 
 	cli.VersionPrinter = func(c *cli.Context) {
 		fmt.Println(c.App.Name, version.Package, c.App.Version)

cmd/ctr/commands/content/content.go

@@ -19,7 +19,6 @@ package content
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"strings"
 	"text/tabwriter"
@@ -519,7 +518,7 @@ func edit(context *cli.Context, rd io.Reader) (io.ReadCloser, error) {
 		return nil, fmt.Errorf("editor is required")
 	}
 
-	tmp, err := ioutil.TempFile(os.Getenv("XDG_RUNTIME_DIR"), "edit-")
+	tmp, err := os.CreateTemp(os.Getenv("XDG_RUNTIME_DIR"), "edit-")
 	if err != nil {
 		return nil, err
 	}

cmd/ctr/commands/resolver.go

@@ -23,10 +23,10 @@ import (
 	"crypto/x509"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/http/httptrace"
 	"net/http/httputil"
+	"os"
 	"strings"
 
 	"github.com/containerd/console"
@@ -124,7 +124,7 @@ func resolverDefaultTLS(clicontext *cli.Context) (*tls.Config, error) {
 	}
 
 	if tlsRootPath := clicontext.String("tlscacert"); tlsRootPath != "" {
-		tlsRootData, err := ioutil.ReadFile(tlsRootPath)
+		tlsRootData, err := os.ReadFile(tlsRootPath)
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed to read %q", tlsRootPath)
 		}

cmd/ctr/commands/shim/shim.go

@@ -22,8 +22,8 @@ package shim
 import (
 	gocontext "context"
 	"fmt"
-	"io/ioutil"
 	"net"
+	"os"
 	"path/filepath"
 	"strings"
 
@@ -174,7 +174,7 @@ var execCommand = cli.Command{
 		}
 
 		// read spec file and extract Any object
-		spec, err := ioutil.ReadFile(context.String("spec"))
+		spec, err := os.ReadFile(context.String("spec"))
 		if err != nil {
 			return err
 		}