1 files changed, 45 insertions, 36 deletions
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...)
+	}
+}