Use lumberjack library to rotate logs and add config that enables it (#1399)

Gopkg.lock

@@ -1013,6 +1013,14 @@
   revision = "48a433ba4bcadc5be9aa16d4bdcb383d3f57a741"
   version = "v9.9.3"
 
+[[projects]]
+  digest = "1:80c34337e8a734e190f2d1b716cae774cca74db98315166f92074434e9af0227"
+  name = "gopkg.in/natefinch/lumberjack.v2"
+  packages = ["."]
+  pruneopts = "NUT"
+  revision = "a96e63847dc3c67d17befa69c303767e2f84e54f"
+  version = "v2.1"
+
 [[projects]]
   digest = "1:85815bf6f46dc1855ae4e236b496bfa463f04fce83f700d74357ef220476abb7"
   name = "gopkg.in/natefinch/npipe.v2"
@@ -1106,6 +1114,7 @@
     "golang.org/x/crypto/ssh/terminal",
     "golang.org/x/text/unicode/norm",
     "gopkg.in/go-playground/validator.v9",
+    "gopkg.in/natefinch/lumberjack.v2",
   ]
   solver-name = "gps-cdcl"
   solver-version = 1

Gopkg.toml

@@ -298,3 +298,7 @@
 [[constraint]]
   name = "github.com/status-im/migrate"
   version = "=v3.5.1-status"
+
+[[constraint]]
+  name = "gopkg.in/natefinch/lumberjack.v2"
+  version = "2.1.0"

cmd/node-canary/main.go

@@ -91,7 +91,7 @@ func init() {
 		colors = terminal.IsTerminal(int(os.Stdin.Fd()))
 	}
 
-	if err := logutils.OverrideRootLog(*logLevel != "", *logLevel, *logFile, colors); err != nil {
+	if err := logutils.OverrideRootLog(*logLevel != "", *logLevel, logutils.FileOptions{Filename: *logFile}, colors); err != nil {
 		stdlog.Fatalf("Error initializing logger: %s", err)
 	}
 }

cmd/statusd/main.go

@@ -67,7 +67,7 @@ func init() {
 	flag.Var(&configFiles, "c", "JSON configuration file(s). Multiple configuration files can be specified, and will be merged in occurrence order")
 
 	colors := terminal.IsTerminal(int(os.Stdin.Fd()))
-	if err := logutils.OverrideRootLog(true, "ERROR", "", colors); err != nil {
+	if err := logutils.OverrideRootLog(true, "ERROR", logutils.FileOptions{}, colors); err != nil {
 		stdlog.Fatalf("Error initializing logger: %v", err)
 	}
 
@@ -181,12 +181,7 @@ func setupLogging(config *params.NodeConfig) {
 	}
 
 	colors := !(*logWithoutColors) && terminal.IsTerminal(int(os.Stdin.Fd()))
-	if err := logutils.OverrideRootLog(
+	if err := logutils.OverrideRootLogWithConfig(config, colors); err != nil {
-		logEnabled(config),
-		config.LogLevel,
-		config.LogFile,
-		colors,
-	); err != nil {
 		stdlog.Fatalf("Error initializing logger: %v", err)
 	}
 }
@@ -220,10 +215,6 @@ func startCollectingNodeMetrics(interruptCh <-chan struct{}, statusNode *node.St
 	<-interruptCh
 }
 
-func logEnabled(config *params.NodeConfig) bool {
-	return config.LogLevel != "" || config.LogFile != ""
-}
-
 var (
 	errStatusServiceRequiresIPC  = errors.New("to enable the StatusService on IPC, -ipc flag must be set")
 	errStatusServiceRequiresHTTP = errors.New("to enable the StatusService on HTTP, -http flag must be set")

lib/library.go

@@ -33,7 +33,7 @@ func StartNode(configJSON *C.char) *C.char {
 		return makeJSONResponse(err)
 	}
 
-	if err := logutils.OverrideRootLog(config.LogEnabled, config.LogLevel, config.LogFile, false); err != nil {
+	if err := logutils.OverrideRootLogWithConfig(config, false); err != nil {
 		return makeJSONResponse(err)
 	}
 
@@ -507,13 +507,13 @@ func makeJSONResponse(err error) *C.char {
 // SendDataNotification sends push notifications by given tokens.
 // dataPayloadJSON is a JSON string that looks like this:
 // {
-// 	"data": {
+//	"data": {
-// 		"msg-v2": {
+//		"msg-v2": {
-// 			"from": "0x2cea3bd5", // hash of sender (first 10 characters/4 bytes of sha3 hash)
+//			"from": "0x2cea3bd5", // hash of sender (first 10 characters/4 bytes of sha3 hash)
-// 			"to": "0xb1f89744", // hash of recipient (first 10 characters/4 bytes of sha3 hash)
+//			"to": "0xb1f89744", // hash of recipient (first 10 characters/4 bytes of sha3 hash)
-// 			"id": "0x872653ad", // message ID hash (first 10 characters/4 bytes of sha3 hash)
+//			"id": "0x872653ad", // message ID hash (first 10 characters/4 bytes of sha3 hash)
-// 		}
+//		}
-// 	}
+//	}
 // }
 //export SendDataNotification
 func SendDataNotification(dataPayloadJSON, tokensArray *C.char) (outCBytes *C.char) {

logutils/logrotation.go

@@ -0,0 +1,29 @@
+package logutils
+
+import (
+	"github.com/ethereum/go-ethereum/log"
+	lumberjack "gopkg.in/natefinch/lumberjack.v2"
+)
+
+// FileOptions are all options supported by internal rotation module.
+type FileOptions struct {
+	// Base name for log file.
+	Filename string
+	// Size in megabytes.
+	MaxSize int
+	// Number of rotated log files.
+	MaxBackups int
+	// If true rotated log files will be gzipped.
+	Compress bool
+}
+
+// FileHandlerWithRotation instantiates log.Handler with a configured rotation
+func FileHandlerWithRotation(opts FileOptions, format log.Format) log.Handler {
+	logger := &lumberjack.Logger{
+		Filename:   opts.Filename,
+		MaxSize:    opts.MaxSize,
+		MaxBackups: opts.MaxBackups,
+		Compress:   opts.Compress,
+	}
+	return log.StreamHandler(logger, format)
+}

logutils/override.go

@@ -5,34 +5,42 @@ import (
 	"strings"
 
 	"github.com/ethereum/go-ethereum/log"
+	"github.com/status-im/status-go/params"
 )
 
+// OverrideRootLogWithConfig derives all configuration from params.NodeConfig and configures logger using it.
+func OverrideRootLogWithConfig(config *params.NodeConfig, colors bool) error {
+	return OverrideRootLog(config.LogEnabled, config.LogLevel, FileOptions{
+		Filename:   config.LogFile,
+		MaxSize:    config.LogMaxSize,
+		MaxBackups: config.LogMaxBackups,
+		Compress:   config.LogCompressRotated,
+	}, colors)
+
+}
+
 // OverrideRootLog overrides root logger with file handler, if defined,
 // and log level (defaults to INFO).
-func OverrideRootLog(enabled bool, levelStr string, logFile string, terminal bool) error {
+func OverrideRootLog(enabled bool, levelStr string, fileOpts FileOptions, terminal bool) error {
 	if !enabled {
 		disableRootLog()
 		return nil
 	}
 
-	return enableRootLog(levelStr, logFile, terminal)
+	return enableRootLog(levelStr, fileOpts, terminal)
 }
 
 func disableRootLog() {
 	log.Root().SetHandler(log.DiscardHandler())
 }
 
-func enableRootLog(levelStr string, logFile string, terminal bool) error {
+func enableRootLog(levelStr string, fileOpts FileOptions, terminal bool) error {
 	var (
 		handler log.Handler
 		err     error
 	)
-
+	if fileOpts.Filename != "" {
-	if logFile != "" {
+		handler = FileHandlerWithRotation(fileOpts, log.LogfmtFormat())
-		handler, err = log.FileHandler(logFile, log.LogfmtFormat())
-		if err != nil {
-			return err
-		}
 	} else {
 		handler = log.StreamHandler(os.Stderr, log.TerminalFormat(terminal))
 	}

mobile/status.go

@@ -46,7 +46,7 @@ func StartNode(configJSON string) string {
 		return makeJSONResponse(err)
 	}
 
-	if err := logutils.OverrideRootLog(true, config.LogLevel, config.LogFile, true); err != nil {
+	if err := logutils.OverrideRootLogWithConfig(config, false); err != nil {
 		return makeJSONResponse(err)
 	}
 
@@ -459,13 +459,13 @@ func makeJSONResponse(err error) string {
 // SendDataNotification sends push notifications by given tokens.
 // dataPayloadJSON is a JSON string that looks like this:
 // {
-// 	"data": {
+//	"data": {
-// 		"msg-v2": {
+//		"msg-v2": {
-// 			"from": "0x2cea3bd5", // hash of sender (first 10 characters/4 bytes of sha3 hash)
+//			"from": "0x2cea3bd5", // hash of sender (first 10 characters/4 bytes of sha3 hash)
-// 			"to": "0xb1f89744", // hash of recipient (first 10 characters/4 bytes of sha3 hash)
+//			"to": "0xb1f89744", // hash of recipient (first 10 characters/4 bytes of sha3 hash)
-// 			"id": "0x872653ad", // message ID hash (first 10 characters/4 bytes of sha3 hash)
+//			"id": "0x872653ad", // message ID hash (first 10 characters/4 bytes of sha3 hash)
-// 		}
+//		}
-// 	}
+//	}
 // }
 func SendDataNotification(dataPayloadJSON, tokensArray string) (result string) {
 	var (

params/config.go

@@ -265,6 +265,15 @@ type NodeConfig struct {
 	// LogLevel defines minimum log level. Valid names are "ERROR", "WARN", "INFO", "DEBUG", and "TRACE".
 	LogLevel string `validate:"eq=ERROR|eq=WARN|eq=INFO|eq=DEBUG|eq=TRACE"`
 
+	// LogMaxBackups defines number of rotated log files that will be stored.
+	LogMaxBackups int
+
+	// LogMaxSize after current size is reached log file will be rotated
+	LogMaxSize int
+
+	// LogCompressRotated if true all rotated files will be gzipped.
+	LogCompressRotated bool
+
 	// LogToStderr defines whether logged info should also be output to os.Stderr
 	LogToStderr bool
 
@@ -380,6 +389,9 @@ func NewNodeConfigWithDefaults(dataDir string, networkID uint64, opts ...Option)
 	c.ListenAddr = ":30303"
 	c.LogEnabled = true
 	c.LogLevel = "INFO"
+	c.LogMaxSize = 100
+	c.LogCompressRotated = true
+	c.LogMaxBackups = 3
 	c.LogToStderr = true
 	c.WhisperConfig.Enabled = true
 	c.WhisperConfig.EnableNTPSync = true

t/utils/utils.go

@@ -70,7 +70,7 @@ func init() {
 
 	// set up logger
 	loggerEnabled := *logLevel != ""
-	if err := logutils.OverrideRootLog(loggerEnabled, *logLevel, "", true); err != nil {
+	if err := logutils.OverrideRootLog(loggerEnabled, *logLevel, logutils.FileOptions{}, true); err != nil {
 		panic(err)
 	}
 

vendor/gopkg.in/natefinch/lumberjack.v2/LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2014 Nate Finch 
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vendor/gopkg.in/natefinch/lumberjack.v2/chown.go

@@ -0,0 +1,11 @@
+// +build !linux
+
+package lumberjack
+
+import (
+	"os"
+)
+
+func chown(_ string, _ os.FileInfo) error {
+	return nil
+}

vendor/gopkg.in/natefinch/lumberjack.v2/chown_linux.go

@@ -0,0 +1,19 @@
+package lumberjack
+
+import (
+	"os"
+	"syscall"
+)
+
+// os_Chown is a var so we can mock it out during tests.
+var os_Chown = os.Chown
+
+func chown(name string, info os.FileInfo) error {
+	f, err := os.OpenFile(name, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, info.Mode())
+	if err != nil {
+		return err
+	}
+	f.Close()
+	stat := info.Sys().(*syscall.Stat_t)
+	return os_Chown(name, int(stat.Uid), int(stat.Gid))
+}

vendor/gopkg.in/natefinch/lumberjack.v2/lumberjack.go

@@ -0,0 +1,541 @@
+// Package lumberjack provides a rolling logger.
+//
+// Note that this is v2.0 of lumberjack, and should be imported using gopkg.in
+// thusly:
+//
+//   import "gopkg.in/natefinch/lumberjack.v2"
+//
+// The package name remains simply lumberjack, and the code resides at
+// https://github.com/natefinch/lumberjack under the v2.0 branch.
+//
+// Lumberjack is intended to be one part of a logging infrastructure.
+// It is not an all-in-one solution, but instead is a pluggable
+// component at the bottom of the logging stack that simply controls the files
+// to which logs are written.
+//
+// Lumberjack plays well with any logging package that can write to an
+// io.Writer, including the standard library's log package.
+//
+// Lumberjack assumes that only one process is writing to the output files.
+// Using the same lumberjack configuration from multiple processes on the same
+// machine will result in improper behavior.
+package lumberjack
+
+import (
+	"compress/gzip"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	backupTimeFormat = "2006-01-02T15-04-05.000"
+	compressSuffix   = ".gz"
+	defaultMaxSize   = 100
+)
+
+// ensure we always implement io.WriteCloser
+var _ io.WriteCloser = (*Logger)(nil)
+
+// Logger is an io.WriteCloser that writes to the specified filename.
+//
+// Logger opens or creates the logfile on first Write.  If the file exists and
+// is less than MaxSize megabytes, lumberjack will open and append to that file.
+// If the file exists and its size is >= MaxSize megabytes, the file is renamed
+// by putting the current time in a timestamp in the name immediately before the
+// file's extension (or the end of the filename if there's no extension). A new
+// log file is then created using original filename.
+//
+// Whenever a write would cause the current log file exceed MaxSize megabytes,
+// the current file is closed, renamed, and a new log file created with the
+// original name. Thus, the filename you give Logger is always the "current" log
+// file.
+//
+// Backups use the log file name given to Logger, in the form
+// `name-timestamp.ext` where name is the filename without the extension,
+// timestamp is the time at which the log was rotated formatted with the
+// time.Time format of `2006-01-02T15-04-05.000` and the extension is the
+// original extension.  For example, if your Logger.Filename is
+// `/var/log/foo/server.log`, a backup created at 6:30pm on Nov 11 2016 would
+// use the filename `/var/log/foo/server-2016-11-04T18-30-00.000.log`
+//
+// Cleaning Up Old Log Files
+//
+// Whenever a new logfile gets created, old log files may be deleted.  The most
+// recent files according to the encoded timestamp will be retained, up to a
+// number equal to MaxBackups (or all of them if MaxBackups is 0).  Any files
+// with an encoded timestamp older than MaxAge days are deleted, regardless of
+// MaxBackups.  Note that the time encoded in the timestamp is the rotation
+// time, which may differ from the last time that file was written to.
+//
+// If MaxBackups and MaxAge are both 0, no old log files will be deleted.
+type Logger struct {
+	// Filename is the file to write logs to.  Backup log files will be retained
+	// in the same directory.  It uses <processname>-lumberjack.log in
+	// os.TempDir() if empty.
+	Filename string `json:"filename" yaml:"filename"`
+
+	// MaxSize is the maximum size in megabytes of the log file before it gets
+	// rotated. It defaults to 100 megabytes.
+	MaxSize int `json:"maxsize" yaml:"maxsize"`
+
+	// MaxAge is the maximum number of days to retain old log files based on the
+	// timestamp encoded in their filename.  Note that a day is defined as 24
+	// hours and may not exactly correspond to calendar days due to daylight
+	// savings, leap seconds, etc. The default is not to remove old log files
+	// based on age.
+	MaxAge int `json:"maxage" yaml:"maxage"`
+
+	// MaxBackups is the maximum number of old log files to retain.  The default
+	// is to retain all old log files (though MaxAge may still cause them to get
+	// deleted.)
+	MaxBackups int `json:"maxbackups" yaml:"maxbackups"`
+
+	// LocalTime determines if the time used for formatting the timestamps in
+	// backup files is the computer's local time.  The default is to use UTC
+	// time.
+	LocalTime bool `json:"localtime" yaml:"localtime"`
+
+	// Compress determines if the rotated log files should be compressed
+	// using gzip.
+	Compress bool `json:"compress" yaml:"compress"`
+
+	size int64
+	file *os.File
+	mu   sync.Mutex
+
+	millCh    chan bool
+	startMill sync.Once
+}
+
+var (
+	// currentTime exists so it can be mocked out by tests.
+	currentTime = time.Now
+
+	// os_Stat exists so it can be mocked out by tests.
+	os_Stat = os.Stat
+
+	// megabyte is the conversion factor between MaxSize and bytes.  It is a
+	// variable so tests can mock it out and not need to write megabytes of data
+	// to disk.
+	megabyte = 1024 * 1024
+)
+
+// Write implements io.Writer.  If a write would cause the log file to be larger
+// than MaxSize, the file is closed, renamed to include a timestamp of the
+// current time, and a new log file is created using the original log file name.
+// If the length of the write is greater than MaxSize, an error is returned.
+func (l *Logger) Write(p []byte) (n int, err error) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	writeLen := int64(len(p))
+	if writeLen > l.max() {
+		return 0, fmt.Errorf(
+			"write length %d exceeds maximum file size %d", writeLen, l.max(),
+		)
+	}
+
+	if l.file == nil {
+		if err = l.openExistingOrNew(len(p)); err != nil {
+			return 0, err
+		}
+	}
+
+	if l.size+writeLen > l.max() {
+		if err := l.rotate(); err != nil {
+			return 0, err
+		}
+	}
+
+	n, err = l.file.Write(p)
+	l.size += int64(n)
+
+	return n, err
+}
+
+// Close implements io.Closer, and closes the current logfile.
+func (l *Logger) Close() error {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	return l.close()
+}
+
+// close closes the file if it is open.
+func (l *Logger) close() error {
+	if l.file == nil {
+		return nil
+	}
+	err := l.file.Close()
+	l.file = nil
+	return err
+}
+
+// Rotate causes Logger to close the existing log file and immediately create a
+// new one.  This is a helper function for applications that want to initiate
+// rotations outside of the normal rotation rules, such as in response to
+// SIGHUP.  After rotating, this initiates compression and removal of old log
+// files according to the configuration.
+func (l *Logger) Rotate() error {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	return l.rotate()
+}
+
+// rotate closes the current file, moves it aside with a timestamp in the name,
+// (if it exists), opens a new file with the original filename, and then runs
+// post-rotation processing and removal.
+func (l *Logger) rotate() error {
+	if err := l.close(); err != nil {
+		return err
+	}
+	if err := l.openNew(); err != nil {
+		return err
+	}
+	l.mill()
+	return nil
+}
+
+// openNew opens a new log file for writing, moving any old log file out of the
+// way.  This methods assumes the file has already been closed.
+func (l *Logger) openNew() error {
+	err := os.MkdirAll(l.dir(), 0744)
+	if err != nil {
+		return fmt.Errorf("can't make directories for new logfile: %s", err)
+	}
+
+	name := l.filename()
+	mode := os.FileMode(0644)
+	info, err := os_Stat(name)
+	if err == nil {
+		// Copy the mode off the old logfile.
+		mode = info.Mode()
+		// move the existing file
+		newname := backupName(name, l.LocalTime)
+		if err := os.Rename(name, newname); err != nil {
+			return fmt.Errorf("can't rename log file: %s", err)
+		}
+
+		// this is a no-op anywhere but linux
+		if err := chown(name, info); err != nil {
+			return err
+		}
+	}
+
+	// we use truncate here because this should only get called when we've moved
+	// the file ourselves. if someone else creates the file in the meantime,
+	// just wipe out the contents.
+	f, err := os.OpenFile(name, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
+	if err != nil {
+		return fmt.Errorf("can't open new logfile: %s", err)
+	}
+	l.file = f
+	l.size = 0
+	return nil
+}
+
+// backupName creates a new filename from the given name, inserting a timestamp
+// between the filename and the extension, using the local time if requested
+// (otherwise UTC).
+func backupName(name string, local bool) string {
+	dir := filepath.Dir(name)
+	filename := filepath.Base(name)
+	ext := filepath.Ext(filename)
+	prefix := filename[:len(filename)-len(ext)]
+	t := currentTime()
+	if !local {
+		t = t.UTC()
+	}
+
+	timestamp := t.Format(backupTimeFormat)
+	return filepath.Join(dir, fmt.Sprintf("%s-%s%s", prefix, timestamp, ext))
+}
+
+// openExistingOrNew opens the logfile if it exists and if the current write
+// would not put it over MaxSize.  If there is no such file or the write would
+// put it over the MaxSize, a new file is created.
+func (l *Logger) openExistingOrNew(writeLen int) error {
+	l.mill()
+
+	filename := l.filename()
+	info, err := os_Stat(filename)
+	if os.IsNotExist(err) {
+		return l.openNew()
+	}
+	if err != nil {
+		return fmt.Errorf("error getting log file info: %s", err)
+	}
+
+	if info.Size()+int64(writeLen) >= l.max() {
+		return l.rotate()
+	}
+
+	file, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, 0644)
+	if err != nil {
+		// if we fail to open the old log file for some reason, just ignore
+		// it and open a new log file.
+		return l.openNew()
+	}
+	l.file = file
+	l.size = info.Size()
+	return nil
+}
+
+// genFilename generates the name of the logfile from the current time.
+func (l *Logger) filename() string {
+	if l.Filename != "" {
+		return l.Filename
+	}
+	name := filepath.Base(os.Args[0]) + "-lumberjack.log"
+	return filepath.Join(os.TempDir(), name)
+}
+
+// millRunOnce performs compression and removal of stale log files.
+// Log files are compressed if enabled via configuration and old log
+// files are removed, keeping at most l.MaxBackups files, as long as
+// none of them are older than MaxAge.
+func (l *Logger) millRunOnce() error {
+	if l.MaxBackups == 0 && l.MaxAge == 0 && !l.Compress {
+		return nil
+	}
+
+	files, err := l.oldLogFiles()
+	if err != nil {
+		return err
+	}
+
+	var compress, remove []logInfo
+
+	if l.MaxBackups > 0 && l.MaxBackups < len(files) {
+		preserved := make(map[string]bool)
+		var remaining []logInfo
+		for _, f := range files {
+			// Only count the uncompressed log file or the
+			// compressed log file, not both.
+			fn := f.Name()
+			if strings.HasSuffix(fn, compressSuffix) {
+				fn = fn[:len(fn)-len(compressSuffix)]
+			}
+			preserved[fn] = true
+
+			if len(preserved) > l.MaxBackups {
+				remove = append(remove, f)
+			} else {
+				remaining = append(remaining, f)
+			}
+		}
+		files = remaining
+	}
+	if l.MaxAge > 0 {
+		diff := time.Duration(int64(24*time.Hour) * int64(l.MaxAge))
+		cutoff := currentTime().Add(-1 * diff)
+
+		var remaining []logInfo
+		for _, f := range files {
+			if f.timestamp.Before(cutoff) {
+				remove = append(remove, f)
+			} else {
+				remaining = append(remaining, f)
+			}
+		}
+		files = remaining
+	}
+
+	if l.Compress {
+		for _, f := range files {
+			if !strings.HasSuffix(f.Name(), compressSuffix) {
+				compress = append(compress, f)
+			}
+		}
+	}
+
+	for _, f := range remove {
+		errRemove := os.Remove(filepath.Join(l.dir(), f.Name()))
+		if err == nil && errRemove != nil {
+			err = errRemove
+		}
+	}
+	for _, f := range compress {
+		fn := filepath.Join(l.dir(), f.Name())
+		errCompress := compressLogFile(fn, fn+compressSuffix)
+		if err == nil && errCompress != nil {
+			err = errCompress
+		}
+	}
+
+	return err
+}
+
+// millRun runs in a goroutine to manage post-rotation compression and removal
+// of old log files.
+func (l *Logger) millRun() {
+	for _ = range l.millCh {
+		// what am I going to do, log this?
+		_ = l.millRunOnce()
+	}
+}
+
+// mill performs post-rotation compression and removal of stale log files,
+// starting the mill goroutine if necessary.
+func (l *Logger) mill() {
+	l.startMill.Do(func() {
+		l.millCh = make(chan bool, 1)
+		go l.millRun()
+	})
+	select {
+	case l.millCh <- true:
+	default:
+	}
+}
+
+// oldLogFiles returns the list of backup log files stored in the same
+// directory as the current log file, sorted by ModTime
+func (l *Logger) oldLogFiles() ([]logInfo, error) {
+	files, err := ioutil.ReadDir(l.dir())
+	if err != nil {
+		return nil, fmt.Errorf("can't read log file directory: %s", err)
+	}
+	logFiles := []logInfo{}
+
+	prefix, ext := l.prefixAndExt()
+
+	for _, f := range files {
+		if f.IsDir() {
+			continue
+		}
+		if t, err := l.timeFromName(f.Name(), prefix, ext); err == nil {
+			logFiles = append(logFiles, logInfo{t, f})
+			continue
+		}
+		if t, err := l.timeFromName(f.Name(), prefix, ext+compressSuffix); err == nil {
+			logFiles = append(logFiles, logInfo{t, f})
+			continue
+		}
+		// error parsing means that the suffix at the end was not generated
+		// by lumberjack, and therefore it's not a backup file.
+	}
+
+	sort.Sort(byFormatTime(logFiles))
+
+	return logFiles, nil
+}
+
+// timeFromName extracts the formatted time from the filename by stripping off
+// the filename's prefix and extension. This prevents someone's filename from
+// confusing time.parse.
+func (l *Logger) timeFromName(filename, prefix, ext string) (time.Time, error) {
+	if !strings.HasPrefix(filename, prefix) {
+		return time.Time{}, errors.New("mismatched prefix")
+	}
+	if !strings.HasSuffix(filename, ext) {
+		return time.Time{}, errors.New("mismatched extension")
+	}
+	ts := filename[len(prefix) : len(filename)-len(ext)]
+	return time.Parse(backupTimeFormat, ts)
+}
+
+// max returns the maximum size in bytes of log files before rolling.
+func (l *Logger) max() int64 {
+	if l.MaxSize == 0 {
+		return int64(defaultMaxSize * megabyte)
+	}
+	return int64(l.MaxSize) * int64(megabyte)
+}
+
+// dir returns the directory for the current filename.
+func (l *Logger) dir() string {
+	return filepath.Dir(l.filename())
+}
+
+// prefixAndExt returns the filename part and extension part from the Logger's
+// filename.
+func (l *Logger) prefixAndExt() (prefix, ext string) {
+	filename := filepath.Base(l.filename())
+	ext = filepath.Ext(filename)
+	prefix = filename[:len(filename)-len(ext)] + "-"
+	return prefix, ext
+}
+
+// compressLogFile compresses the given log file, removing the
+// uncompressed log file if successful.
+func compressLogFile(src, dst string) (err error) {
+	f, err := os.Open(src)
+	if err != nil {
+		return fmt.Errorf("failed to open log file: %v", err)
+	}
+	defer f.Close()
+
+	fi, err := os_Stat(src)
+	if err != nil {
+		return fmt.Errorf("failed to stat log file: %v", err)
+	}
+
+	if err := chown(dst, fi); err != nil {
+		return fmt.Errorf("failed to chown compressed log file: %v", err)
+	}
+
+	// If this file already exists, we presume it was created by
+	// a previous attempt to compress the log file.
+	gzf, err := os.OpenFile(dst, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, fi.Mode())
+	if err != nil {
+		return fmt.Errorf("failed to open compressed log file: %v", err)
+	}
+	defer gzf.Close()
+
+	gz := gzip.NewWriter(gzf)
+
+	defer func() {
+		if err != nil {
+			os.Remove(dst)
+			err = fmt.Errorf("failed to compress log file: %v", err)
+		}
+	}()
+
+	if _, err := io.Copy(gz, f); err != nil {
+		return err
+	}
+	if err := gz.Close(); err != nil {
+		return err
+	}
+	if err := gzf.Close(); err != nil {
+		return err
+	}
+
+	if err := f.Close(); err != nil {
+		return err
+	}
+	if err := os.Remove(src); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// logInfo is a convenience struct to return the filename and its embedded
+// timestamp.
+type logInfo struct {
+	timestamp time.Time
+	os.FileInfo
+}
+
+// byFormatTime sorts by newest time formatted in the name.
+type byFormatTime []logInfo
+
+func (b byFormatTime) Less(i, j int) bool {
+	return b[i].timestamp.After(b[j].timestamp)
+}
+
+func (b byFormatTime) Swap(i, j int) {
+	b[i], b[j] = b[j], b[i]
+}
+
+func (b byFormatTime) Len() int {
+	return len(b)
+}