device: change logging interface to use functions

This commit overhauls wireguard-go's logging.

The primary, motivating change is to use a function instead
of a *log.Logger as the basic unit of logging.
Using functions provides a lot more flexibility for
people to bring their own logging system.

It also introduces logging helper methods on Device.
These reduce line noise at the call site.
They also allow for log functions to be nil;
when nil, instead of generating a log line and throwing it away,
we don't bother generating it at all.
This spares allocation and pointless work.

This is a breaking change, although the fix required
of clients is fairly straightforward.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

11 files changed, 147 insertions, 182 deletions

diff --git a/device/device.go b/device/device.go
index 5d11766..27c42f2 100644
--- a/device/device.go
+++ b/device/device.go
@@ -177,7 +177,7 @@ func deviceUpdateState(device *Device) {
 	switch newIsUp {
 	case true:
 		if err := device.BindUpdate(); err != nil {
-			device.log.Error.Println("Unable to update bind:", err)
+			device.errorf("Unable to update bind: %v", err)
 			device.isUp.Set(false)
 			break
 		}
@@ -303,7 +303,7 @@ func NewDevice(tunDevice tun.Device, logger *Logger) *Device {
 	device.tun.device = tunDevice
 	mtu, err := device.tun.device.MTU()
 	if err != nil {
-		logger.Error.Println("Trouble determining MTU, assuming default:", err)
+		device.errorf("Trouble determining MTU, assuming default: %v", err)
 		mtu = DefaultMTU
 	}
 	device.tun.mtu = int32(mtu)
@@ -397,7 +397,7 @@ func (device *Device) Close() {
 		return
 	}
 
-	device.log.Info.Println("Device closing")
+	device.infof("Device closing")
 	device.state.changing.Set(true)
 	device.state.Lock()
 	defer device.state.Unlock()
@@ -422,7 +422,7 @@ func (device *Device) Close() {
 	device.rate.limiter.Close()
 
 	device.state.changing.Set(false)
-	device.log.Info.Println("Interface closed")
+	device.infof("Interface closed")
 }
 
 func (device *Device) Wait() chan struct{} {
@@ -562,7 +562,7 @@ func (device *Device) BindUpdate() error {
 		go device.RoutineReceiveIncoming(ipv4.Version, netc.bind)
 		go device.RoutineReceiveIncoming(ipv6.Version, netc.bind)
 
-		device.log.Debug.Println("UDP bind has been updated")
+		device.debugf("UDP bind has been updated")
 	}
 
 	return nil
diff --git a/device/logger.go b/device/logger.go
index 3c4d744..6869a24 100644
--- a/device/logger.go
+++ b/device/logger.go
@@ -6,12 +6,22 @@
 package device
 
 import (
-	"io"
-	"io/ioutil"
 	"log"
 	"os"
 )
 
+// A Logger provides logging for a Device.
+// The functions are Printf-style functions.
+// They must be safe for concurrent use.
+// They do not require a trailing newline in the format.
+// If nil, that level of logging will be silent.
+type Logger struct {
+	Debugf func(format string, args ...interface{})
+	Infof  func(format string, args ...interface{})
+	Errorf func(format string, args ...interface{})
+}
+
+// Log levels for use with NewLogger.
 const (
 	LogLevelSilent = iota
 	LogLevelError
@@ -19,41 +29,40 @@ const (
 	LogLevelDebug
 )
 
-type Logger struct {
-	Debug *log.Logger
-	Info  *log.Logger
-	Error *log.Logger
-}
-
+// NewLogger constructs a Logger that writes to stdout.
+// It logs at the specified log level and above.
+// It decorates log lines with the log level, date, time, and prepend.
 func NewLogger(level int, prepend string) *Logger {
-	output := os.Stdout
 	logger := new(Logger)
-
-	logErr, logInfo, logDebug := func() (io.Writer, io.Writer, io.Writer) {
-		if level >= LogLevelDebug {
-			return output, output, output
-		}
-		if level >= LogLevelInfo {
-			return output, output, ioutil.Discard
-		}
-		if level >= LogLevelError {
-			return output, ioutil.Discard, ioutil.Discard
-		}
-		return ioutil.Discard, ioutil.Discard, ioutil.Discard
-	}()
-
-	logger.Debug = log.New(logDebug,
-		"DEBUG: "+prepend,
-		log.Ldate|log.Ltime,
-	)
-
-	logger.Info = log.New(logInfo,
-		"INFO: "+prepend,
-		log.Ldate|log.Ltime,
-	)
-	logger.Error = log.New(logErr,
-		"ERROR: "+prepend,
-		log.Ldate|log.Ltime,
-	)
+	logf := func(prefix string) func(string, ...interface{}) {
+		return log.New(os.Stdout, prefix+": "+prepend, log.Ldate|log.Ltime).Printf
+	}
+	if level >= LogLevelDebug {
+		logger.Debugf = logf("DEBUG")
+	}
+	if level >= LogLevelInfo {
+		logger.Infof = logf("INFO")
+	}
+	if level >= LogLevelError {
+		logger.Errorf = logf("ERROR")
+	}
 	return logger
 }
+
+func (device *Device) debugf(format string, args ...interface{}) {
+	if device.log.Debugf != nil {
+		device.log.Debugf(format, args...)
+	}
+}
+
+func (device *Device) infof(format string, args ...interface{}) {
+	if device.log.Infof != nil {
+		device.log.Infof(format, args...)
+	}
+}
+
+func (device *Device) errorf(format string, args ...interface{}) {
+	if device.log.Errorf != nil {
+		device.log.Errorf(format, args...)
+	}
+}
diff --git a/device/noise-protocol.go b/device/noise-protocol.go
index e34da83..df520d0 100644
--- a/device/noise-protocol.go
+++ b/device/noise-protocol.go
@@ -319,11 +319,11 @@ func (device *Device) ConsumeMessageInitiation(msg *MessageInitiation) *Peer {
 	flood := time.Since(handshake.lastInitiationConsumption) <= HandshakeInitationRate
 	handshake.mutex.RUnlock()
 	if replay {
-		device.log.Debug.Printf("%v - ConsumeMessageInitiation: handshake replay @ %v\n", peer, timestamp)
+		device.debugf("%v - ConsumeMessageInitiation: handshake replay @ %v", peer, timestamp)
 		return nil
 	}
 	if flood {
-		device.log.Debug.Printf("%v - ConsumeMessageInitiation: handshake flood\n", peer)
+		device.debugf("%v - ConsumeMessageInitiation: handshake flood", peer)
 		return nil
 	}
 
diff --git a/device/peer.go b/device/peer.go
index 96040e6..46edaeb 100644
--- a/device/peer.go
+++ b/device/peer.go
@@ -190,7 +190,7 @@ func (peer *Peer) Start() {
 	}
 
 	device := peer.device
-	device.log.Debug.Println(peer, "- Starting...")
+	device.debugf("%v - Starting...", peer)
 
 	// reset routine state
 
@@ -278,7 +278,7 @@ func (peer *Peer) Stop() {
 	peer.routines.Lock()
 	defer peer.routines.Unlock()
 
-	peer.device.log.Debug.Println(peer, "- Stopping...")
+	peer.device.debugf("%v - Stopping...", peer)
 
 	peer.timersStop()
 
diff --git a/device/receive.go b/device/receive.go
index 605303e..38d018c 100644
--- a/device/receive.go
+++ b/device/receive.go
@@ -10,7 +10,6 @@ import (
 	"encoding/binary"
 	"errors"
 	"net"
-	"strconv"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -79,15 +78,13 @@ func (peer *Peer) keepKeyFreshReceiving() {
  * IPv4 and IPv6 (separately)
  */
 func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
-
-	logDebug := device.log.Debug
 	defer func() {
-		logDebug.Println("Routine: receive incoming IPv" + strconv.Itoa(IP) + " - stopped")
+		device.debugf("Routine: receive incoming IPv%d - stopped", IP)
 		device.queue.decryption.wg.Done()
 		device.net.stopping.Done()
 	}()
 
-	logDebug.Println("Routine: receive incoming IPv" + strconv.Itoa(IP) + " - started")
+	device.debugf("Routine: receive incoming IPv%d - started", IP)
 
 	// receive datagrams until conn is closed
 
@@ -115,7 +112,7 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 			if errors.Is(err, conn.NetErrClosed) {
 				return
 			}
-			device.log.Error.Printf("Failed to receive packet: %v", err)
+			device.errorf("Failed to receive packet: %v", err)
 			if deathSpiral < 10 {
 				deathSpiral++
 				time.Sleep(time.Second / 3)
@@ -202,7 +199,7 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 			okay = len(packet) == MessageCookieReplySize
 
 		default:
-			logDebug.Println("Received message with unknown type")
+			device.debugf("Received message with unknown type")
 		}
 
 		if okay {
@@ -222,15 +219,12 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 }
 
 func (device *Device) RoutineDecryption() {
-
 	var nonce [chacha20poly1305.NonceSize]byte
-
-	logDebug := device.log.Debug
 	defer func() {
-		logDebug.Println("Routine: decryption worker - stopped")
+		device.debugf("Routine: decryption worker - stopped")
 		device.state.stopping.Done()
 	}()
-	logDebug.Println("Routine: decryption worker - started")
+	device.debugf("Routine: decryption worker - started")
 
 	for elem := range device.queue.decryption.c {
 		// split message into fields
@@ -258,23 +252,18 @@ func (device *Device) RoutineDecryption() {
 /* Handles incoming packets related to handshake
  */
 func (device *Device) RoutineHandshake() {
-
-	logInfo := device.log.Info
-	logError := device.log.Error
-	logDebug := device.log.Debug
-
 	var elem QueueHandshakeElement
 	var ok bool
 
 	defer func() {
-		logDebug.Println("Routine: handshake worker - stopped")
+		device.debugf("Routine: handshake worker - stopped")
 		device.state.stopping.Done()
 		if elem.buffer != nil {
 			device.PutMessageBuffer(elem.buffer)
 		}
 	}()
 
-	logDebug.Println("Routine: handshake worker - started")
+	device.debugf("Routine: handshake worker - started")
 
 	for {
 		if elem.buffer != nil {
@@ -304,7 +293,7 @@ func (device *Device) RoutineHandshake() {
 			reader := bytes.NewReader(elem.packet)
 			err := binary.Read(reader, binary.LittleEndian, &reply)
 			if err != nil {
-				logDebug.Println("Failed to decode cookie reply")
+				device.debugf("Failed to decode cookie reply")
 				return
 			}
 
@@ -319,9 +308,9 @@ func (device *Device) RoutineHandshake() {
 			// consume reply
 
 			if peer := entry.peer; peer.isRunning.Get() {
-				logDebug.Println("Receiving cookie response from ", elem.endpoint.DstToString())
+				device.debugf("Receiving cookie response from %s", elem.endpoint.DstToString())
 				if !peer.cookieGenerator.ConsumeReply(&reply) {
-					logDebug.Println("Could not decrypt invalid cookie response")
+					device.debugf("Could not decrypt invalid cookie response")
 				}
 			}
 
@@ -332,7 +321,7 @@ func (device *Device) RoutineHandshake() {
 			// check mac fields and maybe ratelimit
 
 			if !device.cookieChecker.CheckMAC1(elem.packet) {
-				logDebug.Println("Received packet with invalid mac1")
+				device.debugf("Received packet with invalid mac1")
 				continue
 			}
 
@@ -355,7 +344,7 @@ func (device *Device) RoutineHandshake() {
 			}
 
 		default:
-			logError.Println("Invalid packet ended up in the handshake queue")
+			device.errorf("Invalid packet ended up in the handshake queue")
 			continue
 		}
 
@@ -370,7 +359,7 @@ func (device *Device) RoutineHandshake() {
 			reader := bytes.NewReader(elem.packet)
 			err := binary.Read(reader, binary.LittleEndian, &msg)
 			if err != nil {
-				logError.Println("Failed to decode initiation message")
+				device.errorf("Failed to decode initiation message")
 				continue
 			}
 
@@ -378,10 +367,7 @@ func (device *Device) RoutineHandshake() {
 
 			peer := device.ConsumeMessageInitiation(&msg)
 			if peer == nil {
-				logInfo.Println(
-					"Received invalid initiation message from",
-					elem.endpoint.DstToString(),
-				)
+				device.infof("Received invalid initiation message from %s", elem.endpoint.DstToString())
 				continue
 			}
 
@@ -393,7 +379,7 @@ func (device *Device) RoutineHandshake() {
 			// update endpoint
 			peer.SetEndpointFromPacket(elem.endpoint)
 
-			logDebug.Println(peer, "- Received handshake initiation")
+			device.debugf("%v - Received handshake initiation", peer)
 			atomic.AddUint64(&peer.stats.rxBytes, uint64(len(elem.packet)))
 
 			peer.SendHandshakeResponse()
@@ -406,7 +392,7 @@ func (device *Device) RoutineHandshake() {
 			reader := bytes.NewReader(elem.packet)
 			err := binary.Read(reader, binary.LittleEndian, &msg)
 			if err != nil {
-				logError.Println("Failed to decode response message")
+				device.errorf("Failed to decode response message")
 				continue
 			}
 
@@ -414,17 +400,14 @@ func (device *Device) RoutineHandshake() {
 
 			peer := device.ConsumeMessageResponse(&msg)
 			if peer == nil {
-				logInfo.Println(
-					"Received invalid response message from",
-					elem.endpoint.DstToString(),
-				)
+				device.infof("Received invalid response message from %s", elem.endpoint.DstToString())
 				continue
 			}
 
 			// update endpoint
 			peer.SetEndpointFromPacket(elem.endpoint)
 
-			logDebug.Println(peer, "- Received handshake response")
+			device.debugf("%v - Received handshake response", peer)
 			atomic.AddUint64(&peer.stats.rxBytes, uint64(len(elem.packet)))
 
 			// update timers
@@ -437,7 +420,7 @@ func (device *Device) RoutineHandshake() {
 			err = peer.BeginSymmetricSession()
 
 			if err != nil {
-				logError.Println(peer, "- Failed to derive keypair:", err)
+				device.errorf("%v - Failed to derive keypair: %v", peer, err)
 				continue
 			}
 
@@ -453,16 +436,11 @@ func (device *Device) RoutineHandshake() {
 }
 
 func (peer *Peer) RoutineSequentialReceiver() {
-
 	device := peer.device
-	logInfo := device.log.Info
-	logError := device.log.Error
-	logDebug := device.log.Debug
-
 	var elem *QueueInboundElement
 
 	defer func() {
-		logDebug.Println(peer, "- Routine: sequential receiver - stopped")
+		device.debugf("%v - Routine: sequential receiver - stopped", peer)
 		peer.routines.stopping.Done()
 		if elem != nil {
 			device.PutMessageBuffer(elem.buffer)
@@ -470,7 +448,7 @@ func (peer *Peer) RoutineSequentialReceiver() {
 		}
 	}()
 
-	logDebug.Println(peer, "- Routine: sequential receiver - started")
+	device.debugf("%v - Routine: sequential receiver - started", peer)
 
 	for {
 		if elem != nil {
@@ -521,7 +499,7 @@ func (peer *Peer) RoutineSequentialReceiver() {
 		// check for keepalive
 
 		if len(elem.packet) == 0 {
-			logDebug.Println(peer, "- Receiving keepalive packet")
+			device.debugf("%v - Receiving keepalive packet", peer)
 			continue
 		}
 		peer.timersDataReceived()
@@ -549,10 +527,7 @@ func (peer *Peer) RoutineSequentialReceiver() {
 
 			src := elem.packet[IPv4offsetSrc : IPv4offsetSrc+net.IPv4len]
 			if device.allowedips.LookupIPv4(src) != peer {
-				logInfo.Println(
-					"IPv4 packet with disallowed source address from",
-					peer,
-				)
+				device.infof("IPv4 packet with disallowed source address from %v", peer)
 				continue
 			}
 
@@ -577,15 +552,12 @@ func (peer *Peer) RoutineSequentialReceiver() {
 
 			src := elem.packet[IPv6offsetSrc : IPv6offsetSrc+net.IPv6len]
 			if device.allowedips.LookupIPv6(src) != peer {
-				logInfo.Println(
-					"IPv6 packet with disallowed source address from",
-					peer,
-				)
+				device.infof("IPv6 packet with disallowed source address from %v", peer)
 				continue
 			}
 
 		default:
-			logInfo.Println("Packet with invalid IP version from", peer)
+			device.infof("Packet with invalid IP version from %v", peer)
 			continue
 		}
 
@@ -594,12 +566,12 @@ func (peer *Peer) RoutineSequentialReceiver() {
 		offset := MessageTransportOffsetContent
 		_, err := device.tun.device.Write(elem.buffer[:offset+len(elem.packet)], offset)
 		if err != nil && !device.isClosed.Get() {
-			logError.Println("Failed to write packet to TUN device:", err)
+			device.errorf("Failed to write packet to TUN device: %v", err)
 		}
 		if len(peer.queue.inbound) == 0 {
 			err := device.tun.device.Flush()
 			if err != nil {
-				peer.device.log.Error.Printf("Unable to flush packets: %v", err)
+				peer.device.errorf("Unable to flush packets: %v", err)
 			}
 		}
 	}
diff --git a/device/send.go b/device/send.go
index 1d27799..8cf985d 100644
--- a/device/send.go
+++ b/device/send.go
@@ -99,7 +99,7 @@ func (peer *Peer) SendKeepalive() bool {
 	elem.packet = nil
 	select {
 	case peer.queue.nonce <- elem:
-		peer.device.log.Debug.Println(peer, "- Sending keepalive packet")
+		peer.device.debugf("%v - Sending keepalive packet", peer)
 		return true
 	default:
 		peer.device.PutMessageBuffer(elem.buffer)
@@ -128,11 +128,11 @@ func (peer *Peer) SendHandshakeInitiation(isRetry bool) error {
 	peer.handshake.lastSentHandshake = time.Now()
 	peer.handshake.mutex.Unlock()
 
-	peer.device.log.Debug.Println(peer, "- Sending handshake initiation")
+	peer.device.debugf("%v - Sending handshake initiation", peer)
 
 	msg, err := peer.device.CreateMessageInitiation(peer)
 	if err != nil {
-		peer.device.log.Error.Println(peer, "- Failed to create initiation message:", err)
+		peer.device.errorf("%v - Failed to create initiation message: %v", peer, err)
 		return err
 	}
 
@@ -147,7 +147,7 @@ func (peer *Peer) SendHandshakeInitiation(isRetry bool) error {
 
 	err = peer.SendBuffer(packet)
 	if err != nil {
-		peer.device.log.Error.Println(peer, "- Failed to send handshake initiation:", err)
+		peer.device.errorf("%v - Failed to send handshake initiation: %v", peer, err)
 	}
 	peer.timersHandshakeInitiated()
 
@@ -159,11 +159,11 @@ func (peer *Peer) SendHandshakeResponse() error {
 	peer.handshake.lastSentHandshake = time.Now()
 	peer.handshake.mutex.Unlock()
 
-	peer.device.log.Debug.Println(peer, "- Sending handshake response")
+	peer.device.debugf("%v - Sending handshake response", peer)
 
 	response, err := peer.device.CreateMessageResponse(peer)
 	if err != nil {
-		peer.device.log.Error.Println(peer, "- Failed to create response message:", err)
+		peer.device.errorf("%v - Failed to create response message: %v", peer, err)
 		return err
 	}
 
@@ -175,7 +175,7 @@ func (peer *Peer) SendHandshakeResponse() error {
 
 	err = peer.BeginSymmetricSession()
 	if err != nil {
-		peer.device.log.Error.Println(peer, "- Failed to derive keypair:", err)
+		peer.device.errorf("%v - Failed to derive keypair: %v", peer, err)
 		return err
 	}
 
@@ -185,19 +185,19 @@ func (peer *Peer) SendHandshakeResponse() error {
 
 	err = peer.SendBuffer(packet)
 	if err != nil {
-		peer.device.log.Error.Println(peer, "- Failed to send handshake response:", err)
+		peer.device.errorf("%v - Failed to send handshake response: %v", peer, err)
 	}
 	return err
 }
 
 func (device *Device) SendHandshakeCookie(initiatingElem *QueueHandshakeElement) error {
 
-	device.log.Debug.Println("Sending cookie response for denied handshake message for", initiatingElem.endpoint.DstToString())
+	device.debugf("Sending cookie response for denied handshake message for %v", initiatingElem.endpoint.DstToString())
 
 	sender := binary.LittleEndian.Uint32(initiatingElem.packet[4:8])
 	reply, err := device.cookieChecker.CreateReply(initiatingElem.packet, sender, initiatingElem.endpoint.DstToBytes())
 	if err != nil {
-		device.log.Error.Println("Failed to create cookie reply:", err)
+		device.errorf("Failed to create cookie reply: %v", err)
 		return err
 	}
 
@@ -225,16 +225,12 @@ func (peer *Peer) keepKeyFreshSending() {
  * Obs. Single instance per TUN device
  */
 func (device *Device) RoutineReadFromTUN() {
-
-	logDebug := device.log.Debug
-	logError := device.log.Error
-
 	defer func() {
-		logDebug.Println("Routine: TUN reader - stopped")
+		device.debugf("Routine: TUN reader - stopped")
 		device.state.stopping.Done()
 	}()
 
-	logDebug.Println("Routine: TUN reader - started")
+	device.debugf("Routine: TUN reader - started")
 
 	var elem *QueueOutboundElement
 
@@ -252,7 +248,7 @@ func (device *Device) RoutineReadFromTUN() {
 
 		if err != nil {
 			if !device.isClosed.Get() {
-				logError.Println("Failed to read packet from TUN device:", err)
+				device.errorf("Failed to read packet from TUN device: %v", err)
 				device.Close()
 			}
 			device.PutMessageBuffer(elem.buffer)
@@ -285,7 +281,7 @@ func (device *Device) RoutineReadFromTUN() {
 			peer = device.allowedips.LookupIPv6(dst)
 
 		default:
-			logDebug.Println("Received packet with unknown IP version")
+			device.debugf("Received packet with unknown IP version")
 		}
 
 		if peer == nil {
@@ -321,9 +317,7 @@ func (peer *Peer) FlushNonceQueue() {
  */
 func (peer *Peer) RoutineNonce() {
 	var keypair *Keypair
-
 	device := peer.device
-	logDebug := device.log.Debug
 
 	flush := func() {
 		for {
@@ -339,14 +333,14 @@ func (peer *Peer) RoutineNonce() {
 
 	defer func() {
 		flush()
-		logDebug.Println(peer, "- Routine: nonce worker - stopped")
+		device.debugf("%v - Routine: nonce worker - stopped", peer)
 		peer.queue.packetInNonceQueueIsAwaitingKey.Set(false)
 		device.queue.encryption.wg.Done() // no more writes from us
 		close(peer.queue.outbound)        // no more writes to this channel
 		peer.routines.stopping.Done()
 	}()
 
-	logDebug.Println(peer, "- Routine: nonce worker - started")
+	device.debugf("%v - Routine: nonce worker - started", peer)
 
 NextPacket:
 	for {
@@ -391,11 +385,11 @@ NextPacket:
 
 				// wait for key to be established
 
-				logDebug.Println(peer, "- Awaiting keypair")
+				device.debugf("%v - Awaiting keypair", peer)
 
 				select {
 				case <-peer.signals.newKeypairArrived:
-					logDebug.Println(peer, "- Obtained awaited keypair")
+					device.debugf("%v - Obtained awaited keypair", peer)
 
 				case <-peer.signals.flushNonceQueue:
 					device.PutMessageBuffer(elem.buffer)
@@ -459,10 +453,8 @@ func (device *Device) RoutineEncryption() {
 
 	var nonce [chacha20poly1305.NonceSize]byte
 
-	logDebug := device.log.Debug
-
-	defer logDebug.Println("Routine: encryption worker - stopped")
-	logDebug.Println("Routine: encryption worker - started")
+	defer device.debugf("Routine: encryption worker - stopped")
+	device.debugf("Routine: encryption worker - started")
 
 	for elem := range device.queue.encryption.c {
 		// populate header fields
@@ -505,11 +497,8 @@ func (peer *Peer) RoutineSequentialSender() {
 
 	device := peer.device
 
-	logDebug := device.log.Debug
-	logError := device.log.Error
-
-	defer logDebug.Println(peer, "- Routine: sequential sender - stopped")
-	logDebug.Println(peer, "- Routine: sequential sender - started")
+	defer device.debugf("%v - Routine: sequential sender - stopped", peer)
+	device.debugf("%v - Routine: sequential sender - started", peer)
 
 	for elem := range peer.queue.outbound {
 		elem.Lock()
@@ -537,7 +526,7 @@ func (peer *Peer) RoutineSequentialSender() {
 		device.PutMessageBuffer(elem.buffer)
 		device.PutOutboundElement(elem)
 		if err != nil {
-			logError.Println(peer, "- Failed to send data packet", err)
+			device.errorf("%v - Failed to send data packet: %v", peer, err)
 			continue
 		}
 
diff --git a/device/timers.go b/device/timers.go
index dbd4c66..ddc47ad 100644
--- a/device/timers.go
+++ b/device/timers.go
@@ -78,7 +78,7 @@ func (peer *Peer) timersActive() bool {
 
 func expiredRetransmitHandshake(peer *Peer) {
 	if atomic.LoadUint32(&peer.timers.handshakeAttempts) > MaxTimerHandshakes {
-		peer.device.log.Debug.Printf("%s - Handshake did not complete after %d attempts, giving up\n", peer, MaxTimerHandshakes+2)
+		peer.device.debugf("%s - Handshake did not complete after %d attempts, giving up", peer, MaxTimerHandshakes+2)
 
 		if peer.timersActive() {
 			peer.timers.sendKeepalive.Del()
@@ -97,7 +97,7 @@ func expiredRetransmitHandshake(peer *Peer) {
 		}
 	} else {
 		atomic.AddUint32(&peer.timers.handshakeAttempts, 1)
-		peer.device.log.Debug.Printf("%s - Handshake did not complete after %d seconds, retrying (try %d)\n", peer, int(RekeyTimeout.Seconds()), atomic.LoadUint32(&peer.timers.handshakeAttempts)+1)
+		peer.device.debugf("%s - Handshake did not complete after %d seconds, retrying (try %d)", peer, int(RekeyTimeout.Seconds()), atomic.LoadUint32(&peer.timers.handshakeAttempts)+1)
 
 		/* We clear the endpoint address src address, in case this is the cause of trouble. */
 		peer.Lock()
@@ -121,7 +121,7 @@ func expiredSendKeepalive(peer *Peer) {
 }
 
 func expiredNewHandshake(peer *Peer) {
-	peer.device.log.Debug.Printf("%s - Retrying handshake because we stopped hearing back after %d seconds\n", peer, int((KeepaliveTimeout + RekeyTimeout).Seconds()))
+	peer.device.debugf("%s - Retrying handshake because we stopped hearing back after %d seconds", peer, int((KeepaliveTimeout + RekeyTimeout).Seconds()))
 	/* We clear the endpoint address src address, in case this is the cause of trouble. */
 	peer.Lock()
 	if peer.endpoint != nil {
@@ -133,7 +133,7 @@ func expiredNewHandshake(peer *Peer) {
 }
 
 func expiredZeroKeyMaterial(peer *Peer) {
-	peer.device.log.Debug.Printf("%s - Removing all keys, since we haven't received a new one in %d seconds\n", peer, int((RejectAfterTime * 3).Seconds()))
+	peer.device.debugf("%s - Removing all keys, since we haven't received a new one in %d seconds", peer, int((RejectAfterTime * 3).Seconds()))
 	peer.ZeroAndFlushAll()
 }
 
diff --git a/device/tun.go b/device/tun.go
index 3816f9b..97f1276 100644
--- a/device/tun.go
+++ b/device/tun.go
@@ -15,41 +15,37 @@ const DefaultMTU = 1420
 
 func (device *Device) RoutineTUNEventReader() {
 	setUp := false
-	logDebug := device.log.Debug
-	logInfo := device.log.Info
-	logError := device.log.Error
-
-	logDebug.Println("Routine: event worker - started")
+	device.debugf("Routine: event worker - started")
 
 	for event := range device.tun.device.Events() {
 		if event&tun.EventMTUUpdate != 0 {
 			mtu, err := device.tun.device.MTU()
 			old := atomic.LoadInt32(&device.tun.mtu)
 			if err != nil {
-				logError.Println("Failed to load updated MTU of device:", err)
+				device.errorf("Failed to load updated MTU of device: %v", err)
 			} else if int(old) != mtu {
 				if mtu+MessageTransportSize > MaxMessageSize {
-					logInfo.Println("MTU updated:", mtu, "(too large)")
+					device.infof("MTU updated: %v (too large)", mtu)
 				} else {
-					logInfo.Println("MTU updated:", mtu)
+					device.infof("MTU updated: %v", mtu)
 				}
 				atomic.StoreInt32(&device.tun.mtu, int32(mtu))
 			}
 		}
 
 		if event&tun.EventUp != 0 && !setUp {
-			logInfo.Println("Interface set up")
+			device.infof("Interface set up")
 			setUp = true
 			device.Up()
 		}
 
 		if event&tun.EventDown != 0 && setUp {
-			logInfo.Println("Interface set down")
+			device.infof("Interface set down")
 			setUp = false
 			device.Down()
 		}
 	}
 
-	logDebug.Println("Routine: event worker - stopped")
+	device.debugf("Routine: event worker - stopped")
 	device.state.stopping.Done()
 }
diff --git a/device/uapi.go b/device/uapi.go
index 277c02f..76b6fb8 100644
--- a/device/uapi.go
+++ b/device/uapi.go
@@ -130,7 +130,7 @@ func (device *Device) IpcSetOperation(r io.Reader) (err error) {
 
 	defer func() {
 		if err != nil {
-			device.log.Error.Println(err)
+			device.errorf("%v", err)
 		}
 	}()
 
@@ -188,7 +188,7 @@ func (device *Device) handleDeviceLine(key, value string) error {
 		if err != nil {
 			return ipcErrorf(ipc.IpcErrorInvalid, "failed to set private_key: %w", err)
 		}
-		device.log.Debug.Println("UAPI: Updating private key")
+		device.debugf("UAPI: Updating private key")
 		device.SetPrivateKey(sk)
 
 	case "listen_port":
@@ -198,7 +198,7 @@ func (device *Device) handleDeviceLine(key, value string) error {
 		}
 
 		// update port and rebind
-		device.log.Debug.Println("UAPI: Updating listen port")
+		device.debugf("UAPI: Updating listen port")
 
 		device.net.Lock()
 		device.net.port = uint16(port)
@@ -214,7 +214,7 @@ func (device *Device) handleDeviceLine(key, value string) error {
 			return ipcErrorf(ipc.IpcErrorInvalid, "invalid fwmark: %w", err)
 		}
 
-		device.log.Debug.Println("UAPI: Updating fwmark")
+		device.debugf("UAPI: Updating fwmark")
 		if err := device.BindSetMark(uint32(mark)); err != nil {
 			return ipcErrorf(ipc.IpcErrorPortInUse, "failed to update fwmark: %w", err)
 		}
@@ -223,7 +223,7 @@ func (device *Device) handleDeviceLine(key, value string) error {
 		if value != "true" {
 			return ipcErrorf(ipc.IpcErrorInvalid, "failed to set replace_peers, invalid value: %v", value)
 		}
-		device.log.Debug.Println("UAPI: Removing all peers")
+		device.debugf("UAPI: Removing all peers")
 		device.RemoveAllPeers()
 
 	default:
@@ -265,7 +265,7 @@ func (device *Device) handlePublicKeyLine(peer *ipcSetPeer, value string) error
 		if err != nil {
 			return ipcErrorf(ipc.IpcErrorInvalid, "failed to create new peer: %w", err)
 		}
-		device.log.Debug.Println(peer, "- UAPI: Created")
+		device.debugf("%v - UAPI: Created", peer.Peer)
 	}
 	return nil
 }
@@ -289,14 +289,14 @@ func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error
 			return ipcErrorf(ipc.IpcErrorInvalid, "failed to set remove, invalid value: %v", value)
 		}
 		if !peer.dummy {
-			device.log.Debug.Println(peer, "- UAPI: Removing")
+			device.debugf("%v - UAPI: Removing", peer.Peer)
 			device.RemovePeer(peer.handshake.remoteStatic)
 		}
 		peer.Peer = &Peer{}
 		peer.dummy = true
 
 	case "preshared_key":
-		device.log.Debug.Println(peer, "- UAPI: Updating preshared key")
+		device.debugf("%v - UAPI: Updating preshared key", peer.Peer)
 
 		peer.handshake.mutex.Lock()
 		err := peer.handshake.presharedKey.FromHex(value)
@@ -307,7 +307,7 @@ func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error
 		}
 
 	case "endpoint":
-		device.log.Debug.Println(peer, "- UAPI: Updating endpoint")
+		device.debugf("%v - UAPI: Updating endpoint", peer.Peer)
 		endpoint, err := conn.CreateEndpoint(value)
 		if err != nil {
 			return ipcErrorf(ipc.IpcErrorInvalid, "failed to set endpoint %v: %w", value, err)
@@ -317,7 +317,7 @@ func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error
 		peer.endpoint = endpoint
 
 	case "persistent_keepalive_interval":
-		device.log.Debug.Println(peer, "- UAPI: Updating persistent keepalive interval")
+		device.debugf("%v - UAPI: Updating persistent keepalive interval", peer.Peer)
 
 		secs, err := strconv.ParseUint(value, 10, 16)
 		if err != nil {
@@ -337,7 +337,7 @@ func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error
 		}
 
 	case "replace_allowed_ips":
-		device.log.Debug.Println(peer, "- UAPI: Removing all allowedips")
+		device.debugf("%v - UAPI: Removing all allowedips", peer.Peer)
 		if value != "true" {
 			return ipcErrorf(ipc.IpcErrorInvalid, "failed to replace allowedips, invalid value: %v", value)
 		}
@@ -347,7 +347,7 @@ func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error
 		device.allowedips.RemoveByPeer(peer.Peer)
 
 	case "allowed_ip":
-		device.log.Debug.Println(peer, "- UAPI: Adding allowedip")
+		device.debugf("%v - UAPI: Adding allowedip", peer.Peer)
 
 		_, network, err := net.ParseCIDR(value)
 		if err != nil {
@@ -414,7 +414,7 @@ func (device *Device) IpcHandle(socket net.Conn) {
 			}
 			err = device.IpcGetOperation(buffered.Writer)
 		default:
-			device.log.Error.Println("invalid UAPI operation:", op)
+			device.errorf("invalid UAPI operation: %v", op)
 			return
 		}
 
@@ -425,7 +425,7 @@ func (device *Device) IpcHandle(socket net.Conn) {
 			status = ipcErrorf(ipc.IpcErrorUnknown, "other UAPI error: %w", err)
 		}
 		if status != nil {
-			device.log.Error.Println(status)
+			device.errorf("%v", status)
 			fmt.Fprintf(buffered, "errno=%d\n\n", status.ErrorCode())
 		} else {
 			fmt.Fprintf(buffered, "errno=0\n\n")
diff --git a/main.go b/main.go
index 75c922d..3d7f23f 100644
--- a/main.go
+++ b/main.go
@@ -143,12 +143,11 @@ func main() {
 		fmt.Sprintf("(%s) ", interfaceName),
 	)
 
-	logger.Info.Println("Starting wireguard-go version", device.WireGuardGoVersion)
-
-	logger.Debug.Println("Debug log enabled")
+	logger.Infof("Starting wireguard-go version %v", device.WireGuardGoVersion)
+	logger.Debugf("Debug log enabled")
 
 	if err != nil {
-		logger.Error.Println("Failed to create TUN device:", err)
+		logger.Errorf("Failed to create TUN device: %v", err)
 		os.Exit(ExitSetupFailed)
 	}
 
@@ -171,7 +170,7 @@ func main() {
 	}()
 
 	if err != nil {
-		logger.Error.Println("UAPI listen error:", err)
+		logger.Errorf("UAPI listen error: %v", err)
 		os.Exit(ExitSetupFailed)
 		return
 	}
@@ -206,7 +205,7 @@ func main() {
 
 		path, err := os.Executable()
 		if err != nil {
-			logger.Error.Println("Failed to determine executable:", err)
+			logger.Errorf("Failed to determine executable: %v", err)
 			os.Exit(ExitSetupFailed)
 		}
 
@@ -216,7 +215,7 @@ func main() {
 			attr,
 		)
 		if err != nil {
-			logger.Error.Println("Failed to daemonize:", err)
+			logger.Errorf("Failed to daemonize: %v", err)
 			os.Exit(ExitSetupFailed)
 		}
 		process.Release()
@@ -225,14 +224,14 @@ func main() {
 
 	device := device.NewDevice(tun, logger)
 
-	logger.Info.Println("Device started")
+	logger.Infof("Device started")
 
 	errs := make(chan error)
 	term := make(chan os.Signal, 1)
 
 	uapi, err := ipc.UAPIListen(interfaceName, fileUAPI)
 	if err != nil {
-		logger.Error.Println("Failed to listen on uapi socket:", err)
+		logger.Errorf("Failed to listen on uapi socket: %v", err)
 		os.Exit(ExitSetupFailed)
 	}
 
@@ -247,7 +246,7 @@ func main() {
 		}
 	}()
 
-	logger.Info.Println("UAPI listener started")
+	logger.Infof("UAPI listener started")
 
 	// wait for program to terminate
 
@@ -265,5 +264,5 @@ func main() {
 	uapi.Close()
 	device.Close()
 
-	logger.Info.Println("Shutting down")
+	logger.Infof("Shutting down")
 }
diff --git a/main_windows.go b/main_windows.go
index 291b00d..fea1b16 100644
--- a/main_windows.go
+++ b/main_windows.go
@@ -34,8 +34,8 @@ func main() {
 		device.LogLevelDebug,
 		fmt.Sprintf("(%s) ", interfaceName),
 	)
-	logger.Info.Println("Starting wireguard-go version", device.WireGuardGoVersion)
-	logger.Debug.Println("Debug log enabled")
+	logger.Infof("Starting wireguard-go version %v", device.WireGuardGoVersion)
+	logger.Debugf("Debug log enabled")
 
 	tun, err := tun.CreateTUN(interfaceName, 0)
 	if err == nil {
@@ -44,17 +44,17 @@ func main() {
 			interfaceName = realInterfaceName
 		}
 	} else {
-		logger.Error.Println("Failed to create TUN device:", err)
+		logger.Errorf("Failed to create TUN device: %v", err)
 		os.Exit(ExitSetupFailed)
 	}
 
 	device := device.NewDevice(tun, logger)
 	device.Up()
-	logger.Info.Println("Device started")
+	logger.Infof("Device started")
 
 	uapi, err := ipc.UAPIListen(interfaceName)
 	if err != nil {
-		logger.Error.Println("Failed to listen on uapi socket:", err)
+		logger.Errorf("Failed to listen on uapi socket: %v", err)
 		os.Exit(ExitSetupFailed)
 	}
 
@@ -71,7 +71,7 @@ func main() {
 			go device.IpcHandle(conn)
 		}
 	}()
-	logger.Info.Println("UAPI listener started")
+	logger.Infof("UAPI listener started")
 
 	// wait for program to terminate
 
@@ -90,5 +90,5 @@ func main() {
 	uapi.Close()
 	device.Close()
 
-	logger.Info.Println("Shutting down")
+	logger.Infof("Shutting down")
 }