lnd: remove seelog logger

The btclog package has been changed to defining its own logging
interface (rather than seelog's) and provides a default implementation
for callers to use.

There are two primary advantages to the new logger implementation.

First, all log messages are created before the call returns.  Compared
to seelog, this prevents data races when mutable variables are logged.

Second, the new logger does not implement any kind of artifical rate
limiting (what seelog refers to as "adaptive logging").  Log messages
are outputted as soon as possible and the application will appear to
perform much better when watching standard output.

Because log rotation is not a feature of the btclog logging
implementation, it is handled by the main package by importing a file
rotation package that provides an io.Reader interface for creating
output to a rotating file output.  The rotator has been configured
with the same defaults that btcd previously used in the seelog config
(10MB file limits with maximum of 3 rolls) but now compresses newly
created roll files.  Due to the high compressibility of log text, the
compressed files typically reduce to around 15-30% of the original
10MB file.

log.go

@@ -1,11 +1,15 @@
 package main
 
 import (
-	"fmt"
 	"os"
 
+	"io"
+
+	"fmt"
+	"path/filepath"
+
 	"github.com/btcsuite/btclog"
-	"github.com/btcsuite/seelog"
+	"github.com/jrick/logrotate/rotator"
 	"github.com/lightninglabs/neutrino"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
@@ -16,29 +20,67 @@ import (
 	"github.com/roasbeef/btcd/connmgr"
 )
 
-// Loggers per subsystem.  Note that backendLog is a seelog logger that all of
-// the subsystem loggers route their messages to.  When adding new subsystems,
-// add a reference here, to the subsystemLoggers map, and the useLogger
-// function.
+// logWriter implements an io.Writer that outputs to both standard output and
+// the write-end pipe of an initialized log rotator.
+type logWriter struct{}
+
+func (logWriter) Write(p []byte) (n int, err error) {
+	os.Stdout.Write(p)
+	logRotatorPipe.Write(p)
+	return len(p), nil
+}
+
+// Loggers per subsystem.  A single backend logger is created and all subsytem
+// loggers created from it will write to the backend.  When adding new
+// subsystems, add the subsystem logger variable here and to the
+// subsystemLoggers map.
+//
+// Loggers can not be used before the log rotator has been initialized with a
+// log file.  This must be performed early during application startup by calling
+// initLogRotator.
 var (
-	backendLog = seelog.Disabled
-	ltndLog    = btclog.Disabled
-	lnwlLog    = btclog.Disabled
-	peerLog    = btclog.Disabled
-	discLog    = btclog.Disabled
-	fndgLog    = btclog.Disabled
-	rpcsLog    = btclog.Disabled
-	srvrLog    = btclog.Disabled
-	ntfnLog    = btclog.Disabled
-	chdbLog    = btclog.Disabled
-	hswcLog    = btclog.Disabled
-	utxnLog    = btclog.Disabled
-	brarLog    = btclog.Disabled
-	cmgrLog    = btclog.Disabled
-	crtrLog    = btclog.Disabled
-	btcnLog    = btclog.Disabled
+	// backendLog is the logging backend used to create all subsystem loggers.
+	// The backend must not be used before the log rotator has been initialized,
+	// or data races and/or nil pointer dereferences will occur.
+	backendLog = btclog.NewBackend(logWriter{})
+
+	// logRotator is one of the logging outputs.  It should be closed on
+	// application shutdown.
+	logRotator *rotator.Rotator
+
+	// logRotatorPipe is the write-end pipe for writing to the log rotator.  It
+	// is written to by the Write method of the logWriter type.
+	logRotatorPipe *io.PipeWriter
+
+	ltndLog = backendLog.Logger("LTND")
+	lnwlLog = backendLog.Logger("LNWL")
+	peerLog = backendLog.Logger("PEER")
+	discLog = backendLog.Logger("DISC")
+	rpcsLog = backendLog.Logger("RPCS")
+	srvrLog = backendLog.Logger("SRVR")
+	ntfnLog = backendLog.Logger("NTFN")
+	chdbLog = backendLog.Logger("CHDB")
+	fndgLog = backendLog.Logger("FNDG")
+	hswcLog = backendLog.Logger("HSWC")
+	utxnLog = backendLog.Logger("UTXN")
+	brarLog = backendLog.Logger("BRAR")
+	cmgrLog = backendLog.Logger("CMGR")
+	crtrLog = backendLog.Logger("CRTR")
+	btcnLog = backendLog.Logger("BTCN")
 )
 
+// Initialize package-global logger variables.
+func init() {
+	lnwallet.UseLogger(lnwlLog)
+	discovery.UseLogger(discLog)
+	chainntnfs.UseLogger(ntfnLog)
+	channeldb.UseLogger(chdbLog)
+	htlcswitch.UseLogger(hswcLog)
+	connmgr.UseLogger(cmgrLog)
+	routing.UseLogger(crtrLog)
+	neutrino.UseLogger(btcnLog)
+}
+
 // subsystemLoggers maps each subsystem identifier to its associated logger.
 var subsystemLoggers = map[string]btclog.Logger{
 	"LTND": ltndLog,
@@ -58,93 +100,27 @@ var subsystemLoggers = map[string]btclog.Logger{
 	"BTCN": btcnLog,
 }
 
-// useLogger updates the logger references for subsystemID to logger.  Invalid
-// subsystems are ignored.
-func useLogger(subsystemID string, logger btclog.Logger) {
-	if _, ok := subsystemLoggers[subsystemID]; !ok {
-		return
-	}
-	subsystemLoggers[subsystemID] = logger
-
-	switch subsystemID {
-	case "LTND":
-		ltndLog = logger
-
-	case "LNWL":
-		lnwlLog = logger
-		lnwallet.UseLogger(logger)
-
-	case "PEER":
-		peerLog = logger
-
-	case "DISC":
-		discLog = logger
-		discovery.UseLogger(logger)
-
-	case "RPCS":
-		rpcsLog = logger
-
-	case "SRVR":
-		srvrLog = logger
-
-	case "NTFN":
-		ntfnLog = logger
-		chainntnfs.UseLogger(logger)
-
-	case "CHDB":
-		chdbLog = logger
-		channeldb.UseLogger(logger)
-
-	case "FNDG":
-		fndgLog = logger
-
-	case "HSWC":
-		hswcLog = logger
-		htlcswitch.UseLogger(logger)
-
-	case "UTXN":
-		utxnLog = logger
-
-	case "BRAR":
-		brarLog = logger
-
-	case "CMGR":
-		cmgrLog = logger
-		connmgr.UseLogger(logger)
-
-	case "CRTR":
-		crtrLog = logger
-		routing.UseLogger(crtrLog)
-
-	case "BTCN":
-		btcnLog = logger
-		neutrino.UseLogger(logger)
-	}
-}
-
-// initSeelogLogger initializes a new seelog logger that is used as the backend
-// for all logging subsystems.
-func initSeelogLogger(logFile string) {
-	config := `
-	<seelog type="adaptive" mininterval="2000000" maxinterval="100000000"
-		critmsgcount="500" minlevel="trace">
-		<outputs formatid="all">
-			<console />
-			<rollingfile type="size" filename="%s" maxsize="10485760" maxrolls="3" />
-		</outputs>
-		<formats>
-			<format id="all" format="%%Time %%Date [%%LEV] %%Msg%%n" />
-		</formats>
-	</seelog>`
-	config = fmt.Sprintf(config, logFile)
-
-	logger, err := seelog.LoggerFromConfigAsString(config)
+// initLogRotator initializes the logging rotater to write logs to logFile and
+// create roll files in the same directory.  It must be called before the
+// package-global log rotater variables are used.
+func initLogRotator(logFile string) {
+	logDir, _ := filepath.Split(logFile)
+	err := os.MkdirAll(logDir, 0700)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "failed to create logger: %v", err)
+		fmt.Fprintf(os.Stderr, "failed to create log directory: %v\n", err)
+		os.Exit(1)
+	}
+	pr, pw := io.Pipe()
+	r, err := rotator.New(pr, logFile, 10*1024, false, 3)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "failed to create file rotator: %v\n", err)
 		os.Exit(1)
 	}
 
-	backendLog = logger
+	go r.Run()
+
+	logRotator = r
+	logRotatorPipe = pw
 }
 
 // setLogLevel sets the logging level for provided subsystem.  Invalid
@@ -157,17 +133,8 @@ func setLogLevel(subsystemID string, logLevel string) {
 		return
 	}
 
-	// Default to info if the log level is invalid.
-	level, ok := btclog.LogLevelFromString(logLevel)
-	if !ok {
-		level = btclog.InfoLvl
-	}
-
-	// Create new logger for the subsystem if needed.
-	if logger == btclog.Disabled {
-		logger = btclog.NewSubsystemLogger(backendLog, subsystemID+": ")
-		useLogger(subsystemID, logger)
-	}
+	// Defaults to info if the log level is invalid.
+	level, _ := btclog.LevelFromString(logLevel)
 	logger.SetLevel(level)
 }
 
@@ -175,7 +142,7 @@ func setLogLevel(subsystemID string, logLevel string) {
 // level. It also dynamically creates the subsystem loggers as needed, so it
 // can be used to initialize the logging system.
 func setLogLevels(logLevel string) {
-	// Configure all subsystems with the new logging level. Dynamically
+	// Configure all sub-systems with the new logging level.  Dynamically
 	// create loggers as needed.
 	for subsystemID := range subsystemLoggers {
 		setLogLevel(subsystemID, logLevel)