Split reader interface from logger interface

Implement new reader interface on jsonfile.
Moves jsonlog decoding from daemon to jsonfile logger.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

daemon/logger/logger.go

@@ -2,11 +2,19 @@ package logger
 
 import (
 	"errors"
-	"io"
 	"time"
+
+	"github.com/docker/docker/pkg/timeutils"
 )
 
-var ReadLogsNotSupported = errors.New("configured logging reader does not support reading")
+// ErrReadLogsNotSupported is returned when the logger does not support reading logs
+var ErrReadLogsNotSupported = errors.New("configured logging reader does not support reading")
+
+const (
+	// TimeFormat is the time format used for timestamps sent to log readers
+	TimeFormat           = timeutils.RFC3339NanoFixed
+	logWatcherBufferSize = 4096
+)
 
 // Message is datastructure that represents record from some container
 type Message struct {
@@ -16,14 +24,51 @@ type Message struct {
 	Timestamp   time.Time
 }
 
-// Logger is interface for docker logging drivers
+// Logger is the interface for docker logging drivers
 type Logger interface {
 	Log(*Message) error
 	Name() string
 	Close() error
 }
 
-//Reader is an interface for docker logging drivers that support reading
-type Reader interface {
-	ReadLog(args ...string) (io.Reader, error)
+// ReadConfig is the configuration passed into ReadLogs
+type ReadConfig struct {
+	Since  time.Time
+	Tail   int
+	Follow bool
+}
+
+// LogReader is the interface for reading log messages for loggers that support reading
+type LogReader interface {
+	// Read logs from underlying logging backend
+	ReadLogs(ReadConfig) *LogWatcher
+}
+
+// LogWatcher is used when consuming logs read from the LogReader interface
+type LogWatcher struct {
+	// For sending log messages to a reader
+	Msg chan *Message
+	// For sending error messages that occur while while reading logs
+	Err           chan error
+	closeNotifier chan struct{}
+}
+
+// NewLogWatcher returns a new LogWatcher.
+func NewLogWatcher() *LogWatcher {
+	return &LogWatcher{
+		Msg:           make(chan *Message, logWatcherBufferSize),
+		Err:           make(chan error, 1),
+		closeNotifier: make(chan struct{}),
+	}
+}
+
+// Close notifies the underlying log reader to stop
+func (w *LogWatcher) Close() {
+	close(w.closeNotifier)
+}
+
+// WatchClose returns a channel receiver that receives notification when the watcher has been closed
+// This should only be called from one goroutine
+func (w *LogWatcher) WatchClose() <-chan struct{} {
+	return w.closeNotifier
 }