docs: add documentation for godoc

formatter.go

@@ -1,5 +1,15 @@
 package logrus
 
+// The Formatter interface is used to implement a custom Formatter. It takes an
+// `Entry`. It exposes all the fields, including the default ones:
+//
+// * `entry.Data["msg"]`. The message passed from Info, Warn, Error ..
+// * `entry.Data["time"]`. The timestamp.
+// * `entry.Data["level"]. The level the entry was logged at.
+//
+// Any additional fields added with `WithField` or `WithFields` are also in
+// `entry.Data`. Format is expected to return an array of bytes which are then
+// logged to `logger.Out`.
 type Formatter interface {
 	Format(*Entry) ([]byte, error)
 }

hooks.go

@@ -1,18 +1,28 @@
 package logrus
 
+// A hook to be fired when logging on the logging levels returned from
+// `Levels()` on your implementation of the interface. Note that this is not
+// fired in a goroutine or a channel with workers, you should handle such
+// functionality yourself if your call is non-blocking and you don't wish for
+// the logging calls for levels returned from `Levels()` to block.
 type Hook interface {
 	Levels() []Level
 	Fire(*Entry) error
 }
 
+// Internal type for storing the hooks on a logger instance.
 type levelHooks map[Level][]Hook
 
+// Add a hook to an instance of logger. This is called with
+// `log.Hooks.Add(new(MyHook))` where `MyHook` implements the `Hook` interface.
 func (hooks levelHooks) Add(hook Hook) {
 	for _, level := range hook.Levels() {
 		hooks[level] = append(hooks[level], hook)
 	}
 }
 
+// Fire all the hooks for the passed level. Used by `entry.log` to fire
+// appropriate hooks for a log entry.
 func (hooks levelHooks) Fire(level Level, entry *Entry) error {
 	for _, hook := range hooks[level] {
 		if err := hook.Fire(entry); err != nil {

logger.go

@@ -7,32 +7,63 @@ import (
 )
 
 type Logger struct {
-	Out       io.Writer
-	Hooks     levelHooks
+	// The logs are `io.Copy`'d to this in a mutex. It's common to set this to a
+	// file, or leave it default which is `os.Stdout`. You can also set this to
+	// something more adventorous, such as logging to Kafka.
+	Out io.Writer
+	// Hooks for the logger instance. These allow firing events based on logging
+	// levels and log entries. For example, to send errors to an error tracking
+	// service, log to StatsD or dump the core on fatal errors.
+	Hooks levelHooks
+	// All log entries pass through the formatter before logged to Out. The
+	// included formatters are `TextFormatter` and `JSONFormatter` for which
+	// TextFormatter is the default. In development (when a TTY is attached) it
+	// logs with colors, but to a file it wouldn't. You can easily implement your
+	// own that implements the `Formatter` interface, see the `README` or included
+	// formatters for examples.
 	Formatter Formatter
-	Level     Level
-	mu        sync.Mutex
+	// The logging level the logger should log at. This is typically (and defaults
+	// to) `logrus.Info`, which allows Info(), Warn(), Error() and Fatal() to be
+	// logged. `logrus.Debug` is useful in
+	Level Level
+	// Used to sync writing to the log.
+	mu sync.Mutex
 }
 
+// Creates a new logger. Configuration should be set by changing `Formatter`,
+// `Out` and `Hooks` directly on the default logger instance. You can also just
+// instantiate your own:
+//
+//    var log = &Logger{
+//      Out: os.Stderr,
+//      Formatter: new(JSONFormatter),
+//      Hooks: make(levelHooks),
+//      Level: logrus.Debug,
+//    }
+//
+// It's recommended to make this a global instance called `log`.
 func New() *Logger {
 	return &Logger{
-		Out:       os.Stdout, // Default to stdout, change it if you want.
+		Out:       os.Stdout,
 		Formatter: new(TextFormatter),
 		Hooks:     make(levelHooks),
 		Level:     Info,
 	}
 }
 
+// Adds a field to the log entry, note that you it doesn't log until you call
+// Debug, Print, Info, Warn, Fatal or Panic. It only creates a log entry.
+// Ff you want multiple fields, use `WithFields`.
 func (logger *Logger) WithField(key string, value interface{}) *Entry {
 	return NewEntry(logger).WithField(key, value)
 }
 
+// Adds a struct of fields to the log entry. All it does is call `WithField` for
+// each `Field`.
 func (logger *Logger) WithFields(fields Fields) *Entry {
 	return NewEntry(logger).WithFields(fields)
 }
 
-// Logger Printf family functions
-
 func (logger *Logger) Debugf(format string, args ...interface{}) {
 	NewEntry(logger).Debugf(format, args...)
 }
@@ -65,8 +96,6 @@ func (logger *Logger) Panicf(format string, args ...interface{}) {
 	NewEntry(logger).Panicf(format, args...)
 }
 
-// Logger Print family functions
-
 func (logger *Logger) Debug(args ...interface{}) {
 	NewEntry(logger).Debug(args...)
 }
@@ -99,8 +128,6 @@ func (logger *Logger) Panic(args ...interface{}) {
 	NewEntry(logger).Panic(args...)
 }
 
-// Logger Println family functions
-
 func (logger *Logger) Debugln(args ...interface{}) {
 	NewEntry(logger).Debugln(args...)
 }

logrus.go

@@ -1,15 +1,29 @@
 package logrus
 
+// Fields type, used to pass to `WithFields`.
 type Fields map[string]interface{}
 
+// Level type
 type Level uint8
 
+// These are the different logging levels. You can set the logging level to log
+// on your instance of logger, obtained with `logrus.New()`.
 const (
+	// Panic level, highest level of severity. Logs and then calls panic with the
+	// message passed to Debug, Info, ...
 	Panic Level = iota
+	// Fatal level. Logs and then calls `os.Exit(1)`. It will exit even if the
+	// logging level is set to Panic.
 	Fatal
+	// Error level. Logs. Used for errors that should definitely be noted.
+	// Commonly used for hooks to send errors to an error tracking service.
 	Error
+	// Warn level. Non-critical entries that deserve eyes.
 	Warn
+	// Info level. General operational entries about what's going on inside the
+	// application.
 	Info
+	// Debug level. Usually only enabled when debugging. Very verbose logging.
 	Debug
 )