Move json log reading into log file object

This allows much of the read logic to be shared for other things,
especially for the new log driver proposed in
moby#33475

The only logic for reads in the json logger is around decoding log
messages, which gets passed into the log file object.

This also helps with implementing compression as it allows us to
simplify locking strategies.

Signed-off-by: Brian Goff <[email protected]>

daemon/logger/jsonfilelog/jsonfilelog.go

@@ -23,9 +23,9 @@ const Name = "json-file"
 
 // JSONFileLogger is Logger implementation for default Docker logging.
 type JSONFileLogger struct {
-	mu      sync.RWMutex
+	mu      sync.Mutex
 	closed  bool
-	writer  *loggerutils.RotateFileWriter
+	writer  *loggerutils.LogFile
 	readers map[*logger.LogWatcher]struct{} // stores the active log followers
 }
 
@@ -83,7 +83,8 @@ func New(info logger.Info) (logger.Logger, error) {
 		buf.Reset()
 		return b, nil
 	}
-	writer, err := loggerutils.NewRotateFileWriter(info.LogPath, capval, maxFiles, marshalFunc)
+
+	writer, err := loggerutils.NewLogFile(info.LogPath, capval, maxFiles, marshalFunc, decodeFunc)
 	if err != nil {
 		return nil, err
 	}

daemon/logger/jsonfilelog/jsonfilelog_test.go

@@ -82,7 +82,7 @@ func BenchmarkJSONFileLoggerLog(b *testing.B) {
 	}
 
 	buf := bytes.NewBuffer(nil)
-	require.NoError(b, marshalMessage(msg, jsonlogger.(*JSONFileLogger).extra, buf))
+	require.NoError(b, marshalMessage(msg, nil, buf))
 	b.SetBytes(int64(buf.Len()))
 
 	b.ResetTimer()