Add a log-file-max-size flag to fix large logfile (>1.8GB) truncation.

klog.go

@@ -78,6 +78,7 @@ import (
 	"fmt"
 	"io"
 	stdLog "log"
+	"math"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -410,6 +411,9 @@ func InitFlags(flagset *flag.FlagSet) {
 	}
 	flagset.StringVar(&logging.logDir, "log_dir", "", "If non-empty, write log files in this directory")
 	flagset.StringVar(&logging.logFile, "log_file", "", "If non-empty, use this log file")
+	flagset.Uint64Var(&logging.logFileMaxSizeMB, "log_file_max_size", 1800,
+		"Defines the maximum size a log file can grow to. Unit is megabytes. "+
+			"If the value is 0, the maximum file size is unlimited.")
 	flagset.BoolVar(&logging.toStderr, "logtostderr", true, "log to standard error instead of files")
 	flagset.BoolVar(&logging.alsoToStderr, "alsologtostderr", false, "log to standard error as well as files")
 	flagset.Var(&logging.verbosity, "v", "number for the log level verbosity")
@@ -472,6 +476,10 @@ type loggingT struct {
 	// with the log-dir option.
 	logFile string
 
+	// When logFile is specified, this limiter makes sure the logFile won't exceeds a certain size. When exceeds, the
+	// logFile will be cleaned up. If this value is 0, no size limitation will be applied to logFile.
+	logFileMaxSizeMB uint64
+
 	// If true, do not add the prefix headers, useful when used with SetOutput
 	skipHeaders bool
 
@@ -865,17 +873,32 @@ func (l *loggingT) exit(err error) {
 type syncBuffer struct {
 	logger *loggingT
 	*bufio.Writer
-	file   *os.File
-	sev    severity
-	nbytes uint64 // The number of bytes written to this file
+	file     *os.File
+	sev      severity
+	nbytes   uint64 // The number of bytes written to this file
+	maxbytes uint64 // The max number of bytes this syncBuffer.file can hold before cleaning up.
 }
 
 func (sb *syncBuffer) Sync() error {
 	return sb.file.Sync()
 }
 
+// CalculateMaxSize returns the real max size in bytes after considering the default max size and the flag options.
+func CalculateMaxSize() uint64 {
+	if logging.logFile != "" {
+		if logging.logFileMaxSizeMB == 0 {
+			// If logFileMaxSizeMB is zero, we don't have limitations on the log size.
+			return math.MaxUint64
+		}
+		// Flag logFileMaxSizeMB is in MB for user convenience.
+		return logging.logFileMaxSizeMB * 1024 * 1024
+	}
+	// If "log_file" flag is not specified, the target file (sb.file) will be cleaned up when reaches a fixed size.
+	return MaxSize
+}
+
 func (sb *syncBuffer) Write(p []byte) (n int, err error) {
-	if sb.nbytes+uint64(len(p)) >= MaxSize {
+	if sb.nbytes+uint64(len(p)) >= sb.maxbytes {
 		if err := sb.rotateFile(time.Now(), false); err != nil {
 			sb.logger.exit(err)
 		}
@@ -890,7 +913,7 @@ func (sb *syncBuffer) Write(p []byte) (n int, err error) {
 
 // rotateFile closes the syncBuffer's file and starts a new one.
 // The startup argument indicates whether this is the initial startup of klog.
-// If startup is true, existing files are opened for apending instead of truncated.
+// If startup is true, existing files are opened for appending instead of truncated.
 func (sb *syncBuffer) rotateFile(now time.Time, startup bool) error {
 	if sb.file != nil {
 		sb.Flush()
@@ -933,8 +956,9 @@ func (l *loggingT) createFiles(sev severity) error {
 	// has already been created, we can stop.
 	for s := sev; s >= infoLog && l.file[s] == nil; s-- {
 		sb := &syncBuffer{
-			logger: l,
-			sev:    s,
+			logger:   l,
+			sev:      s,
+			maxbytes: CalculateMaxSize(),
 		}
 		if err := sb.rotateFile(now, true); err != nil {
 			return err

klog_file.go

@@ -98,7 +98,7 @@ var onceLogDirs sync.Once
 // successfully, create also attempts to update the symlink for that tag, ignoring
 // errors.
 // The startup argument indicates whether this is the initial startup of klog.
-// If startup is true, existing files are opened for apending instead of truncated.
+// If startup is true, existing files are opened for appending instead of truncated.
 func create(tag string, t time.Time, startup bool) (f *os.File, filename string, err error) {
 	if logging.logFile != "" {
 		f, err := openOrCreate(logging.logFile, startup)

klog_test.go

@@ -339,7 +339,6 @@ func TestRollover(t *testing.T) {
 	}
 	defer func(previous uint64) { MaxSize = previous }(MaxSize)
 	MaxSize = 512
-
 	Info("x") // Be sure we have a file.
 	info, ok := logging.file[infoLog].(*syncBuffer)
 	if !ok {
@@ -370,7 +369,7 @@ func TestRollover(t *testing.T) {
 	if fname0 == fname1 {
 		t.Errorf("info.f.Name did not change: %v", fname0)
 	}
-	if info.nbytes >= MaxSize {
+	if info.nbytes >= info.maxbytes {
 		t.Errorf("file size was not reset: %d", info.nbytes)
 	}
 }
@@ -487,3 +486,50 @@ func BenchmarkHeader(b *testing.B) {
 		logging.putBuffer(buf)
 	}
 }
+
+// Test the logic on checking log size limitation.
+func TestFileSizeCheck(t *testing.T) {
+	setFlags()
+	testData := map[string]struct {
+		testLogFile          string
+		testLogFileMaxSizeMB uint64
+		testCurrentSize      uint64
+		expectedResult       bool
+	}{
+		"logFile not specified, exceeds max size": {
+			testLogFile:          "",
+			testLogFileMaxSizeMB: 1,
+			testCurrentSize:      1024 * 1024 * 2000, //exceeds the maxSize
+			expectedResult:       true,
+		},
+
+		"logFile not specified, not exceeds max size": {
+			testLogFile:          "",
+			testLogFileMaxSizeMB: 1,
+			testCurrentSize:      1024 * 1024 * 1000, //smaller than the maxSize
+			expectedResult:       false,
+		},
+		"logFile specified, exceeds max size": {
+			testLogFile:          "/tmp/test.log",
+			testLogFileMaxSizeMB: 500,                // 500MB
+			testCurrentSize:      1024 * 1024 * 1000, //exceeds the logFileMaxSizeMB
+			expectedResult:       true,
+		},
+		"logFile specified, not exceeds max size": {
+			testLogFile:          "/tmp/test.log",
+			testLogFileMaxSizeMB: 500,               // 500MB
+			testCurrentSize:      1024 * 1024 * 300, //smaller than the logFileMaxSizeMB
+			expectedResult:       false,
+		},
+	}
+
+	for name, test := range testData {
+		logging.logFile = test.testLogFile
+		logging.logFileMaxSizeMB = test.testLogFileMaxSizeMB
+		actualResult := test.testCurrentSize >= CalculateMaxSize()
+		if test.expectedResult != actualResult {
+			t.Fatalf("Error on test case '%v': Was expecting result equals %v, got %v",
+				name, test.expectedResult, actualResult)
+		}
+	}
+}