libct/int: switch from bytes.Buffer to strings.Builder

The latter is simpler and provides just enough functionality to be used
here.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit 9970cbfdb6)
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/integration/bench_test.go

@@ -1,7 +1,6 @@
 package integration
 
 import (
-	"bytes"
 	"math/rand"
 	"os"
 	"strings"
@@ -95,7 +94,7 @@ func BenchmarkExecInBigEnv(b *testing.B) {
 	const numEnv = 5000
 	env := append(standardEnvironment, genBigEnv(numEnv)...)
 	// Construct the expected output.
-	var wantOut bytes.Buffer
+	var wantOut strings.Builder
 	for _, e := range env {
 		wantOut.WriteString(e + "\n")
 	}
@@ -112,7 +111,7 @@ func BenchmarkExecInBigEnv(b *testing.B) {
 		err = container.Run(exec)
 		ok(b, err)
 		waitProcess(exec, b)
-		if !bytes.Equal(buffers.Stdout.Bytes(), wantOut.Bytes()) {
+		if buffers.Stdout.String() != wantOut.String() {
 			b.Fatalf("unexpected output: %s (stderr: %s)", buffers.Stdout, buffers.Stderr)
 		}
 	}

libcontainer/integration/checkpoint_test.go

@@ -1,7 +1,6 @@
 package integration
 
 import (
-	"bytes"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -54,7 +53,7 @@ func testCheckpoint(t *testing.T, userns bool) {
 	stdinR, stdinW, err := os.Pipe()
 	ok(t, err)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 
 	pconfig := libcontainer.Process{
 		Cwd:    "/",
@@ -131,7 +130,7 @@ func testCheckpoint(t *testing.T, userns bool) {
 	restoreStdinR, restoreStdinW, err := os.Pipe()
 	ok(t, err)
 
-	var restoreStdout bytes.Buffer
+	var restoreStdout strings.Builder
 	restoreProcessConfig := &libcontainer.Process{
 		Cwd:    "/",
 		Stdin:  restoreStdinR,

libcontainer/integration/exec_test.go

@@ -1,7 +1,6 @@
 package integration
 
 import (
-	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -163,7 +162,7 @@ func TestEnter(t *testing.T) {
 	stdinR, stdinW, err := os.Pipe()
 	ok(t, err)
 
-	var stdout, stdout2 bytes.Buffer
+	var stdout, stdout2 strings.Builder
 
 	pconfig := libcontainer.Process{
 		Cwd:    "/",
@@ -242,7 +241,7 @@ func TestProcessEnv(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:  "/",
 		Args: []string{"sh", "-c", "env"},
@@ -288,7 +287,7 @@ func TestProcessEmptyCaps(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:    "/",
 		Args:   []string{"sh", "-c", "cat /proc/self/status"},
@@ -332,7 +331,7 @@ func TestProcessCaps(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:          "/",
 		Args:         []string{"sh", "-c", "cat /proc/self/status"},
@@ -393,7 +392,7 @@ func TestAdditionalGroups(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:              "/",
 		Args:             []string{"sh", "-c", "id", "-Gn"},
@@ -772,7 +771,7 @@ func TestPassExtraFiles(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pipeout1, pipein1, err := os.Pipe()
 	ok(t, err)
 	pipeout2, pipein2, err := os.Pipe()
@@ -831,7 +830,7 @@ func TestSysctl(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:    "/proc/sys/kernel",
 		Args:   []string{"sh", "-c", cmd},
@@ -941,7 +940,7 @@ func TestOomScoreAdj(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:    "/",
 		Args:   []string{"sh", "-c", "cat /proc/self/oom_score_adj"},
@@ -1081,7 +1080,7 @@ func TestHook(t *testing.T) {
 		cmd.WriteString("/" + hook + " ")
 	}
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:    "/",
 		Args:   []string{"sh", "-c", cmd.String()},
@@ -1193,7 +1192,7 @@ func TestRootfsPropagationSlaveMount(t *testing.T) {
 	ok(t, err)
 
 	// Run "cat /proc/self/mountinfo" in container and look at mount points.
-	var stdout2 bytes.Buffer
+	var stdout2 strings.Builder
 
 	stdinR2, stdinW2, err := os.Pipe()
 	ok(t, err)
@@ -1305,7 +1304,7 @@ func TestRootfsPropagationSharedMount(t *testing.T) {
 	dir2cont = filepath.Join(dir1cont, filepath.Base(dir2host))
 
 	// Mount something in container and see if it is visible on host.
-	var stdout2 bytes.Buffer
+	var stdout2 strings.Builder
 
 	stdinR2, stdinW2, err := os.Pipe()
 	ok(t, err)
@@ -1340,7 +1339,7 @@ func TestRootfsPropagationSharedMount(t *testing.T) {
 
 	// Check if mount is visible on host or not.
 	out, err := exec.Command("findmnt", "-n", "-f", "-oTARGET", dir2host).CombinedOutput()
-	outtrim := string(bytes.TrimSpace(out))
+	outtrim := strings.TrimSpace(string(out))
 	if err != nil {
 		t.Logf("findmnt error %q: %q", err, outtrim)
 	}
@@ -1627,7 +1626,7 @@ func TestTmpfsCopyUp(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Args:   []string{"ls", "/etc/passwd"},
 		Env:    standardEnvironment,
@@ -1818,7 +1817,7 @@ func TestBindMountAndUser(t *testing.T) {
 	ok(t, err)
 	defer destroyContainer(container)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 
 	pconfig := libcontainer.Process{
 		Cwd:    "/",

libcontainer/integration/execin_test.go

@@ -1,7 +1,6 @@
 package integration
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 	"os"
@@ -151,7 +150,7 @@ func TestExecInAdditionalGroups(t *testing.T) {
 	defer stdinW.Close()
 	ok(t, err)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pconfig := libcontainer.Process{
 		Cwd:              "/",
 		Args:             []string{"sh", "-c", "id", "-Gn"},
@@ -264,7 +263,7 @@ func TestExecInTTY(t *testing.T) {
 	// Repeat to increase chances to catch a race; see
 	// https://github.com/opencontainers/runc/issues/2425.
 	for range 300 {
-		var stdout bytes.Buffer
+		var stdout strings.Builder
 
 		parent, child, err := utils.NewSockPair("console")
 		ok(t, err)
@@ -410,7 +409,7 @@ func TestExecinPassExtraFiles(t *testing.T) {
 	defer stdinW.Close()
 	ok(t, err)
 
-	var stdout bytes.Buffer
+	var stdout strings.Builder
 	pipeout1, pipein1, err := os.Pipe()
 	ok(t, err)
 	pipeout2, pipein2, err := os.Pipe()

libcontainer/integration/update_test.go

@@ -1,7 +1,6 @@
 package integration
 
 import (
-	"bytes"
 	"os"
 	"strings"
 	"testing"
@@ -40,7 +39,7 @@ func testUpdateDevices(t *testing.T, systemd bool) {
 	}()
 	ok(t, err)
 
-	var buf bytes.Buffer
+	var buf strings.Builder
 	devCheck := &libcontainer.Process{
 		Cwd:    "/",
 		Args:   []string{"/bin/sh", "-c", "echo > /dev/full; cat /dev/null; true"},

libcontainer/integration/utils_test.go

@@ -1,7 +1,6 @@
 package integration
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"os"
@@ -55,14 +54,14 @@ func ptrInt(v int) *int {
 
 func newStdBuffers() *stdBuffers {
 	return &stdBuffers{
-		Stdout: bytes.NewBuffer(nil),
-		Stderr: bytes.NewBuffer(nil),
+		Stdout: new(strings.Builder),
+		Stderr: new(strings.Builder),
 	}
 }
 
 type stdBuffers struct {
-	Stdout *bytes.Buffer
-	Stderr *bytes.Buffer
+	Stdout *strings.Builder
+	Stderr *strings.Builder
 }
 
 func (b *stdBuffers) String() string {