Replace usage of io/ioutil package (#9613)

`io/ioutil` has been deprecated since go 1.16 and the linter started to
complain about it.

cli/cmd/check_test.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"testing"
 
 	"github.com/linkerd/linkerd2/pkg/healthcheck"
@@ -33,7 +33,7 @@ func TestCheckStatus(t *testing.T) {
 		output := bytes.NewBufferString("")
 		healthcheck.RunChecks(output, stderr, hc, tableOutput)
 
-		goldenFileBytes, err := ioutil.ReadFile("testdata/check_output.golden")
+		goldenFileBytes, err := os.ReadFile("testdata/check_output.golden")
 		if err != nil {
 			t.Fatalf("Unexpected error: %v", err)
 		}
@@ -67,7 +67,7 @@ func TestCheckStatus(t *testing.T) {
 		output := bytes.NewBufferString("")
 		healthcheck.RunChecks(output, stderr, hc, jsonOutput)
 
-		goldenFileBytes, err := ioutil.ReadFile("testdata/check_output_json.golden")
+		goldenFileBytes, err := os.ReadFile("testdata/check_output_json.golden")
 		if err != nil {
 			t.Fatalf("Unexpected error: %v", err)
 		}

cli/cmd/inject_test.go

@@ -5,7 +5,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
@@ -630,10 +629,10 @@ func TestWalk(t *testing.T) {
 		file1 = filepath.Join(tmpFolderRoot, "root.txt")
 		file2 = filepath.Join(tmpFolderData, "data.txt")
 	)
-	if err := ioutil.WriteFile(file1, data, 0600); err != nil {
+	if err := os.WriteFile(file1, data, 0600); err != nil {
 		t.Fatal("Unexpected error: ", err)
 	}
-	if err := ioutil.WriteFile(file2, data, 0600); err != nil {
+	if err := os.WriteFile(file2, data, 0600); err != nil {
 		t.Fatal("Unexpected error: ", err)
 	}
 

cli/cmd/install_test.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -319,7 +319,7 @@ func testInstallOptionsHA(ha bool) (*charts.Values, error) {
 		return nil, err
 	}
 
-	data, err := ioutil.ReadFile(filepath.Join("testdata", "valid-crt.pem"))
+	data, err := os.ReadFile(filepath.Join("testdata", "valid-crt.pem"))
 	if err != nil {
 		return nil, err
 	}
@@ -336,7 +336,7 @@ func testInstallOptionsHA(ha bool) (*charts.Values, error) {
 	}
 	values.Identity.Issuer.TLS.KeyPEM = key
 
-	data, err = ioutil.ReadFile(filepath.Join("testdata", "valid-trust-anchors.pem"))
+	data, err = os.ReadFile(filepath.Join("testdata", "valid-trust-anchors.pem"))
 	if err != nil {
 		return nil, err
 	}
@@ -376,15 +376,15 @@ func testInstallValues() (*charts.Values, error) {
 	values.PolicyController.Image.Version = installControlPlaneVersion
 	values.HeartbeatSchedule = fakeHeartbeatSchedule()
 
-	identityCert, err := ioutil.ReadFile(filepath.Join("testdata", "valid-crt.pem"))
+	identityCert, err := os.ReadFile(filepath.Join("testdata", "valid-crt.pem"))
 	if err != nil {
 		return nil, err
 	}
-	identityKey, err := ioutil.ReadFile(filepath.Join("testdata", "valid-key.pem"))
+	identityKey, err := os.ReadFile(filepath.Join("testdata", "valid-key.pem"))
 	if err != nil {
 		return nil, err
 	}
-	trustAnchorsPEM, err := ioutil.ReadFile(filepath.Join("testdata", "valid-trust-anchors.pem"))
+	trustAnchorsPEM, err := os.ReadFile(filepath.Join("testdata", "valid-trust-anchors.pem"))
 	if err != nil {
 		return nil, err
 	}
@@ -516,7 +516,7 @@ func TestValidate(t *testing.T) {
 			}
 			values.Identity.Issuer.TLS.KeyPEM = key
 
-			ca, err := ioutil.ReadFile(filepath.Join("testdata", tc.crtFilePrefix+"-trust-anchors.pem"))
+			ca, err := os.ReadFile(filepath.Join("testdata", tc.crtFilePrefix+"-trust-anchors.pem"))
 			if err != nil {
 				t.Fatal(err)
 			}

cli/cmd/metrics_diagnostics_util_test.go

@@ -4,7 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"os"
 	"testing"
 
@@ -84,7 +84,7 @@ func Test_obfuscateMetrics(t *testing.T) {
 				t.Errorf("error opening test input file: %v\n", err)
 			}
 
-			fileBytes, err := ioutil.ReadAll(file)
+			fileBytes, err := io.ReadAll(file)
 			if err != nil {
 				t.Errorf("error reading test input file: %v\n", err)
 			}

cli/cmd/options.go

@@ -7,7 +7,6 @@ import (
 	"path/filepath"
 
 	"fmt"
-	"io/ioutil"
 	"net"
 	"strings"
 	"time"
@@ -152,7 +151,7 @@ func makeInstallUpgradeFlags(defaults *l5dcharts.Values) ([]flag.Flag, *pflag.Fl
 			"A path to a PEM-encoded file containing Linkerd Identity trust anchors (generated by default)",
 			func(values *l5dcharts.Values, value string) error {
 				if value != "" {
-					data, err := ioutil.ReadFile(filepath.Clean(value))
+					data, err := os.ReadFile(filepath.Clean(value))
 					if err != nil {
 						return err
 					}
@@ -184,7 +183,7 @@ func makeInstallUpgradeFlags(defaults *l5dcharts.Values) ([]flag.Flag, *pflag.Fl
 }
 
 func loadCrtPEM(path string) (string, error) {
-	data, err := ioutil.ReadFile(filepath.Clean(path))
+	data, err := os.ReadFile(filepath.Clean(path))
 	if err != nil {
 		return "", err
 	}
@@ -197,7 +196,7 @@ func loadCrtPEM(path string) (string, error) {
 }
 
 func loadKeyPEM(path string) (string, error) {
-	data, err := ioutil.ReadFile(filepath.Clean(path))
+	data, err := os.ReadFile(filepath.Clean(path))
 	if err != nil {
 		return "", err
 	}

cli/cmd/upgrade_test.go

@@ -6,7 +6,6 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"strings"
 	"testing"
@@ -462,15 +461,15 @@ func generateCerts(t *testing.T, name string, b64encode bool) issuerCerts {
 	keyPem := strings.TrimSpace(issuer.Cred.EncodePrivateKeyPEM())
 	crtPem := strings.TrimSpace(issuer.Cred.EncodeCertificatePEM())
 
-	caFile, err := ioutil.TempFile("", "ca.*.pem")
+	caFile, err := os.CreateTemp("", "ca.*.pem")
 	if err != nil {
 		t.Fatal(err)
 	}
-	crtFile, err := ioutil.TempFile("", "crt.*.pem")
+	crtFile, err := os.CreateTemp("", "crt.*.pem")
 	if err != nil {
 		t.Fatal(err)
 	}
-	keyFile, err := ioutil.TempFile("", "key.*.pem")
+	keyFile, err := os.CreateTemp("", "key.*.pem")
 	if err != nil {
 		t.Fatal(err)
 	}

cni-plugin/test/install-cni_test.go

@@ -19,7 +19,6 @@ import (
 	"bytes"
 	"flag"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"os/user"
@@ -58,7 +57,7 @@ func setEnv(key, value string, t *testing.T) {
 }
 
 func mktemp(dir, prefix string, t *testing.T) string {
-	tempDir, err := ioutil.TempDir(dir, prefix)
+	tempDir, err := os.MkdirTemp(dir, prefix)
 	if err != nil {
 		testutil.AnnotatedFatalf(t, "couldn't get current working directory",
 			"couldn't get current working directory: %v", err)
@@ -77,7 +76,7 @@ func pwd(t *testing.T) string {
 }
 
 func ls(dir string, t *testing.T) []string {
-	files, err := ioutil.ReadDir(dir)
+	files, err := os.ReadDir(dir)
 	if err != nil {
 		testutil.AnnotatedFatalf(t, "failed to list files",
 			"failed to list files: %v", err)
@@ -90,12 +89,12 @@ func ls(dir string, t *testing.T) []string {
 }
 
 func cp(src, dest string, t *testing.T) {
-	data, err := ioutil.ReadFile(src)
+	data, err := os.ReadFile(src)
 	if err != nil {
 		testutil.AnnotatedFatalf(t, fmt.Sprintf("failed to read file %v", src),
 			"failed to read file %v: %v", src, err)
 	}
-	if err = ioutil.WriteFile(dest, data, 0600); err != nil {
+	if err = os.WriteFile(dest, data, 0600); err != nil {
 		testutil.AnnotatedFatalf(t, fmt.Sprintf("failed to write file %v", dest),
 			"failed to write file %v: %v", dest, err)
 	}
@@ -192,7 +191,7 @@ func startDocker(testNum int, wd string, testWorkRootDir string, tempCNINetDir s
 
 	containerID, err := cmd.Output()
 	if err != nil {
-		errFileContents, _ := ioutil.ReadFile(errFileName)
+		errFileContents, _ := os.ReadFile(errFileName)
 		t.Logf("%v contents:\n\n%v\n\n", errFileName, string(errFileContents))
 		testutil.Fatalf(t,
 			"test %v ERROR: failed to start docker container '%v', see %v", testNum, dockerImage, errFileName)
@@ -214,13 +213,13 @@ func docker(cmd, containerID string, t *testing.T) {
 // compareConfResult does a string compare of 2 test files.
 func compareConfResult(testWorkRootDir string, tempCNINetDir string, result string, expected string, t *testing.T) {
 	tempResult := tempCNINetDir + "/" + result
-	resultFile, err := ioutil.ReadFile(tempResult)
+	resultFile, err := os.ReadFile(tempResult)
 	if err != nil {
 		testutil.AnnotatedFatalf(t, "failed to read file",
 			"failed to read file %v: %v", tempResult, err)
 	}
 
-	expectedFile, err := ioutil.ReadFile(expected)
+	expectedFile, err := os.ReadFile(expected)
 	if err != nil {
 		testutil.AnnotatedFatalf(t, fmt.Sprintf("failed to read file %v", expected),
 			"failed to read file %v, err: %v", expected, err)
@@ -265,7 +264,7 @@ func doTest(testNum int, wd string, initialNetConfFile string, finalNetConfFile
 	if initialNetConfFile != "NONE" {
 		setEnv(cniConfName, initialNetConfFile, t)
 	}
-	defaultData, err := ioutil.ReadFile(wd + "../deployment/linkerd-cni.conf.default")
+	defaultData, err := os.ReadFile(wd + "../deployment/linkerd-cni.conf.default")
 	if err != nil {
 		testutil.AnnotatedFatalf(t, "failed to read file linkerd-cni.conf.default",
 			"failed to read file %v, err: %v", wd+"../deployment/linkerd-cni.conf.default", err)

controller/cmd/identity/main.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	"io/ioutil"
 	"net"
 	"os"
 	"os/signal"
@@ -53,7 +52,7 @@ func Main(args []string) {
 
 	flags.ConfigureAndParse(cmd, args)
 
-	identityTrustAnchorPEM, err := ioutil.ReadFile(k8s.MountPathTrustRootsPEM)
+	identityTrustAnchorPEM, err := os.ReadFile(k8s.MountPathTrustRootsPEM)
 	if err != nil {
 		log.Fatalf("could not read identity trust anchors PEM: %s", err.Error())
 	}

controller/proxy-injector/fake/factory.go

@@ -1,7 +1,7 @@
 package fake
 
 import (
-	"io/ioutil"
+	"os"
 	"path/filepath"
 
 	admissionv1beta1 "k8s.io/api/admission/v1beta1"
@@ -31,7 +31,7 @@ func NewFactory(rootDir string) *Factory {
 // bytes. If the file doesn't exist in the 'fake/data' folder, an error will be
 // returned.
 func (f *Factory) FileContents(filename string) ([]byte, error) {
-	return ioutil.ReadFile(filepath.Join(f.rootDir, filename))
+	return os.ReadFile(filepath.Join(f.rootDir, filename))
 }
 
 // AdmissionReview returns the content of the specified file as an
@@ -40,7 +40,7 @@ func (f *Factory) FileContents(filename string) ([]byte, error) {
 // ii. the file content isn't a valid YAML structure that can be unmarshalled
 // into AdmissionReview type
 func (f *Factory) AdmissionReview(filename string) (*admissionv1beta1.AdmissionReview, error) {
-	b, err := ioutil.ReadFile(filepath.Join(f.rootDir, filename))
+	b, err := os.ReadFile(filepath.Join(f.rootDir, filename))
 	if err != nil {
 		return nil, err
 	}
@@ -58,7 +58,7 @@ func (f *Factory) AdmissionReview(filename string) (*admissionv1beta1.AdmissionR
 // ii. the file content isn't a valid YAML structure that can be unmarshalled
 // into Deployment type
 func (f *Factory) Deployment(filename string) (*appsv1.Deployment, error) {
-	b, err := ioutil.ReadFile(filepath.Join(f.rootDir, filename))
+	b, err := os.ReadFile(filepath.Join(f.rootDir, filename))
 	if err != nil {
 		return nil, err
 	}
@@ -77,7 +77,7 @@ func (f *Factory) Deployment(filename string) (*appsv1.Deployment, error) {
 // ii. the file content isn't a valid YAML structure that can be unmarshalled
 // into Container type
 func (f *Factory) Container(filename string) (*corev1.Container, error) {
-	b, err := ioutil.ReadFile(filepath.Join(f.rootDir, filename))
+	b, err := os.ReadFile(filepath.Join(f.rootDir, filename))
 	if err != nil {
 		return nil, err
 	}
@@ -96,7 +96,7 @@ func (f *Factory) Container(filename string) (*corev1.Container, error) {
 // ii. the file content isn't a valid YAML structure that can be unmarshalled
 // into ConfigMap type
 func (f *Factory) ConfigMap(filename string) (*corev1.ConfigMap, error) {
-	b, err := ioutil.ReadFile(filepath.Join(f.rootDir, filename))
+	b, err := os.ReadFile(filepath.Join(f.rootDir, filename))
 	if err != nil {
 		return nil, err
 	}
@@ -115,7 +115,7 @@ func (f *Factory) ConfigMap(filename string) (*corev1.ConfigMap, error) {
 // ii. the file content isn't a valid YAML structure that can be unmarshalled
 // into Namespace type
 func (f *Factory) Namespace(filename string) (*corev1.Namespace, error) {
-	b, err := ioutil.ReadFile(filepath.Join(f.rootDir, filename))
+	b, err := os.ReadFile(filepath.Join(f.rootDir, filename))
 	if err != nil {
 		return nil, err
 	}
@@ -134,7 +134,7 @@ func (f *Factory) Namespace(filename string) (*corev1.Namespace, error) {
 // ii. the file content isn't a valid YAML structure that can be unmarshalled
 // into Volume type
 func (f *Factory) Volume(filename string) (*corev1.Volume, error) {
-	b, err := ioutil.ReadFile(filepath.Join(f.rootDir, filename))
+	b, err := os.ReadFile(filepath.Join(f.rootDir, filename))
 	if err != nil {
 		return nil, err
 	}

controller/proxy-injector/webhook.go

@@ -3,7 +3,7 @@ package injector
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"strings"
 
 	"github.com/linkerd/linkerd2/controller/k8s"
@@ -45,7 +45,7 @@ func Inject(linkerdNamespace string) webhook.Handler {
 			return nil, err
 		}
 
-		caPEM, err := ioutil.ReadFile(pkgK8s.MountPathTrustRootsPEM)
+		caPEM, err := os.ReadFile(pkgK8s.MountPathTrustRootsPEM)
 		if err != nil {
 			return nil, err
 		}

pkg/config/config.go

@@ -3,7 +3,7 @@ package config
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 
 	"github.com/linkerd/linkerd2/pkg/k8s"
@@ -19,7 +19,7 @@ import (
 // Values returns the Value struct from the linkerd-config ConfigMap
 func Values(path string) (*l5dcharts.Values, error) {
 	p := filepath.Clean(path)
-	configYaml, err := ioutil.ReadFile(p)
+	configYaml, err := os.ReadFile(p)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read config file: %w", err)
 	}

pkg/issuercerts/issuercerts.go

@@ -6,7 +6,7 @@ import (
 	"crypto/rsa"
 	"crypto/x509"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"time"
 
@@ -86,12 +86,12 @@ func FetchExternalIssuerData(ctx context.Context, api kubernetes.Interface, cont
 
 // LoadIssuerCrtAndKeyFromFiles loads the issuer certificate and key from files
 func LoadIssuerCrtAndKeyFromFiles(keyPEMFile, crtPEMFile string) (string, string, error) {
-	key, err := ioutil.ReadFile(filepath.Clean(keyPEMFile))
+	key, err := os.ReadFile(filepath.Clean(keyPEMFile))
 	if err != nil {
 		return "", "", err
 	}
 
-	crt, err := ioutil.ReadFile(filepath.Clean(crtPEMFile))
+	crt, err := os.ReadFile(filepath.Clean(crtPEMFile))
 	if err != nil {
 		return "", "", err
 	}
@@ -106,7 +106,7 @@ func LoadIssuerDataFromFiles(keyPEMFile, crtPEMFile, trustPEMFile string) (*Issu
 		return nil, err
 	}
 
-	anchors, err := ioutil.ReadFile(filepath.Clean(trustPEMFile))
+	anchors, err := os.ReadFile(filepath.Clean(trustPEMFile))
 	if err != nil {
 		return nil, err
 	}

pkg/k8s/metrics.go

@@ -2,7 +2,7 @@ package k8s
 
 import (
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"os"
 
@@ -45,5 +45,5 @@ func getResponse(url string) ([]byte, error) {
 		return nil, err
 	}
 	defer resp.Body.Close()
-	return ioutil.ReadAll(resp.Body)
+	return io.ReadAll(resp.Body)
 }

pkg/k8s/portforward.go

@@ -3,7 +3,7 @@ package k8s
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net"
 	"net/http"
 	"net/url"
@@ -178,8 +178,8 @@ func (pf *PortForward) run() error {
 		return err
 	}
 
-	out := ioutil.Discard
+	out := io.Discard
-	errOut := ioutil.Discard
+	errOut := io.Discard
 	if pf.emitLogs {
 		out = os.Stdout
 		errOut = os.Stderr

pkg/profiles/openapi.go

@@ -3,7 +3,6 @@ package profiles
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"path"
 	"sort"
@@ -29,7 +28,7 @@ func RenderOpenAPI(fileName, namespace, name, clusterDomain string, w io.Writer)
 		return err
 	}
 
-	bytes, err := ioutil.ReadAll(input)
+	bytes, err := io.ReadAll(input)
 	if err != nil {
 		return fmt.Errorf("Error reading file: %w", err)
 	}

pkg/protohttp/protohttp_test.go

@@ -6,7 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"strings"
@@ -363,7 +363,7 @@ func TestCheckIfResponseHasError(t *testing.T) {
 		message := SerializeAsPayload(protoInBytes)
 		response := &http.Response{
 			Header:     make(http.Header),
-			Body:       ioutil.NopCloser(bytes.NewReader(message)),
+			Body:       io.NopCloser(bytes.NewReader(message)),
 			StatusCode: http.StatusInternalServerError,
 		}
 		response.Header.Set(errorHeader, "error")
@@ -394,7 +394,7 @@ func TestCheckIfResponseHasError(t *testing.T) {
 
 		response := &http.Response{
 			Header:     make(http.Header),
-			Body:       ioutil.NopCloser(bytes.NewReader(j)),
+			Body:       io.NopCloser(bytes.NewReader(j)),
 			StatusCode: http.StatusForbidden,
 			Status:     "403 Forbidden",
 		}

pkg/tls/cred.go

@@ -9,7 +9,7 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"time"
 )
@@ -195,12 +195,12 @@ func ValidateAndCreateCreds(crt, key string) (*Cred, error) {
 
 // ReadPEMCreds reads PEM-encoded credentials from the named files.
 func ReadPEMCreds(keyPath, crtPath string) (*Cred, error) {
-	keyb, err := ioutil.ReadFile(filepath.Clean(keyPath))
+	keyb, err := os.ReadFile(filepath.Clean(keyPath))
 	if err != nil {
 		return nil, err
 	}
 
-	crtb, err := ioutil.ReadFile(filepath.Clean(crtPath))
+	crtb, err := os.ReadFile(filepath.Clean(crtPath))
 	if err != nil {
 		return nil, err
 	}

pkg/util/http.go

@@ -3,7 +3,6 @@ package util
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"strings"
 
 	httpPb "github.com/linkerd/linkerd2-proxy-api/go/http_types"
@@ -55,7 +54,7 @@ func ParseMethod(method string) *httpPb.HttpMethod {
 // reached, the full bytes are returned. If the limit is reached, an error is
 // returned.
 func ReadAllLimit(r io.Reader, limit int) ([]byte, error) {
-	bytes, err := ioutil.ReadAll(io.LimitReader(r, int64(limit)))
+	bytes, err := io.ReadAll(io.LimitReader(r, int64(limit)))
 	if err != nil {
 		return nil, err
 	}

proxy-identity/main.go

@@ -7,7 +7,6 @@ import (
 	"crypto/x509/pkix"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"syscall"
@@ -116,7 +115,7 @@ func generateAndStoreKey(p string) (key *ecdsa.PrivateKey, err error) {
 	}
 
 	pemb := tls.EncodePrivateKeyP8(key)
-	err = ioutil.WriteFile(p, pemb, 0600)
+	err = os.WriteFile(p, pemb, 0600)
 	return
 }
 
@@ -138,7 +137,7 @@ func generateAndStoreCSR(p, id string, key *ecdsa.PrivateKey) ([]byte, error) {
 		return nil, fmt.Errorf("failed to create CSR: %w", err)
 	}
 
-	if err = ioutil.WriteFile(p, csrb, 0600); err != nil {
+	if err = os.WriteFile(p, csrb, 0600); err != nil {
 		return nil, fmt.Errorf("failed to write CSR: %w", err)
 	}
 

test/integration/viz/edges/edges_test.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"regexp"
 	"strings"
@@ -108,7 +107,7 @@ func TestDirectEdges(t *testing.T) {
 		}
 		ip = strings.Trim(ip, "\"") // strip quotes
 
-		b, err := ioutil.ReadFile("testdata/slow-cooker.yaml")
+		b, err := os.ReadFile("testdata/slow-cooker.yaml")
 		if err != nil {
 			testutil.AnnotatedError(t, "error reading file slow-cooker.yaml", err)
 		}

testutil/test_data_diff.go

@@ -5,7 +5,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -83,7 +82,7 @@ func ReadTestdata(fileName string) string {
 		panic(fmt.Sprintf("Failed to open expected output file: %v", err))
 	}
 
-	fixture, err := ioutil.ReadAll(file)
+	fixture, err := io.ReadAll(file)
 	if err != nil {
 		panic(fmt.Sprintf("Failed to read expected output file: %v", err))
 	}
@@ -110,14 +109,14 @@ func unmarshalYAML(data []byte) ([]interface{}, error) {
 
 func writeTestdata(fileName string, data []byte) {
 	p := filepath.Join("testdata", fileName)
-	if err := ioutil.WriteFile(p, data, 0600); err != nil {
+	if err := os.WriteFile(p, data, 0600); err != nil {
 		panic(err)
 	}
 }
 
 func writeRejects(origFileName string, data []byte, rejectPath string) {
 	p := filepath.Join(rejectPath, origFileName+".rej")
-	if err := ioutil.WriteFile(p, data, 0600); err != nil {
+	if err := os.WriteFile(p, data, 0600); err != nil {
 		panic(err)
 	}
 }

testutil/test_helper.go

@@ -9,7 +9,6 @@ import (
 	"flag"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"os/exec"
@@ -656,7 +655,7 @@ func (h *TestHelper) HTTPGetURL(url string) (string, error) {
 		}
 
 		defer resp.Body.Close()
-		bytes, err := ioutil.ReadAll(resp.Body)
+		bytes, err := io.ReadAll(resp.Body)
 		if err != nil {
 			return fmt.Errorf("Error reading response body: %w", err)
 		}
@@ -728,7 +727,7 @@ func (h *TestHelper) DownloadCLIBinary(filepath, version string) error {
 
 // ReadFile reads a file from disk and returns the contents as a string.
 func ReadFile(file string) (string, error) {
-	b, err := ioutil.ReadFile(file)
+	b, err := os.ReadFile(file)
 	if err != nil {
 		return "", err
 	}

viz/cmd/tap_test.go

@@ -3,9 +3,9 @@ package cmd
 import (
 	"bytes"
 	"context"
-	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"testing"
 
 	"github.com/golang/protobuf/ptypes/duration"
@@ -149,7 +149,7 @@ func busyTest(t *testing.T, output string) {
 		goldenFilePath = "testdata/tap_busy_output.golden"
 	}
 
-	goldenFileBytes, err := ioutil.ReadFile(goldenFilePath)
+	goldenFileBytes, err := os.ReadFile(goldenFilePath)
 	if err != nil {
 		t.Fatalf("Unexpected error: %v", err)
 	}
@@ -207,7 +207,7 @@ func TestRequestTapByResourceFromAPI(t *testing.T) {
 			t.Fatalf("Unexpected error: %v", err)
 		}
 
-		goldenFileBytes, err := ioutil.ReadFile("testdata/tap_empty_output.golden")
+		goldenFileBytes, err := os.ReadFile("testdata/tap_empty_output.golden")
 		if err != nil {
 			t.Fatalf("Unexpected error: %v", err)
 		}

web/srv/api_handlers_test.go

@@ -4,9 +4,10 @@ import (
 	"bytes"
 	"encoding/json"
 	"errors"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"testing"
 
 	"github.com/go-test/deep"
@@ -71,7 +72,7 @@ func TestHandleApiCheck(t *testing.T) {
 	h.handleAPICheck(w, req, httprouter.Params{})
 	resp := w.Result()
 	defer resp.Body.Close()
-	body, err := ioutil.ReadAll(resp.Body)
+	body, err := io.ReadAll(resp.Body)
 	if err != nil {
 		t.Fatalf("not expecting error reading response body but got: %v", err)
 	}
@@ -83,7 +84,7 @@ func TestHandleApiCheck(t *testing.T) {
 	if diff := deep.Equal(resp.Header, expectedHeaders); diff != nil {
 		t.Errorf("Unexpected header: %v", diff)
 	}
-	apiCheckOutputGolden, err := ioutil.ReadFile("testdata/api_check_output.json")
+	apiCheckOutputGolden, err := os.ReadFile("testdata/api_check_output.json")
 	if err != nil {
 		t.Fatalf("not expecting error reading api check output golden file but got: %v", err)
 	}
@@ -129,7 +130,7 @@ func TestHandleApiGateway(t *testing.T) {
 		handler.handleAPIGateways(recorder, req, httprouter.Params{})
 		resp := recorder.Result()
 		defer resp.Body.Close()
-		body, err := ioutil.ReadAll(resp.Body)
+		body, err := io.ReadAll(resp.Body)
 		if err != nil {
 			t.Fatalf("not expecting error reading response body but got: %v", err)
 		}
@@ -146,7 +147,7 @@ func TestHandleApiGateway(t *testing.T) {
 			t.Errorf("Unexpected header: %v", diff)
 		}
 
-		apiGatewayOutputGolden, err := ioutil.ReadFile("testdata/api_gateway_output.json")
+		apiGatewayOutputGolden, err := os.ReadFile("testdata/api_gateway_output.json")
 		if err != nil {
 			t.Fatalf("not expecting error reading api check output golden file but got: %v", err)
 		}
@@ -171,7 +172,7 @@ func TestHandleApiGateway(t *testing.T) {
 		handler.handleAPIGateways(recorder, req, httprouter.Params{})
 		resp := recorder.Result()
 		defer resp.Body.Close()
-		_, err := ioutil.ReadAll(resp.Body)
+		_, err := io.ReadAll(resp.Body)
 		if err != nil {
 			t.Fatalf("not expecting error reading response body but got: %v", err)
 		}