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moby--moby/daemon/logger/jsonfilelog/read.go
Daniel Nephin 4f0d95fa6e Add canonical import comment
Signed-off-by: Daniel Nephin <dnephin@docker.com>
2018-02-05 16:51:57 -05:00

89 lines
2.3 KiB
Go

package jsonfilelog // import "github.com/docker/docker/daemon/logger/jsonfilelog"
import (
"encoding/json"
"io"
"github.com/docker/docker/api/types/backend"
"github.com/docker/docker/daemon/logger"
"github.com/docker/docker/daemon/logger/jsonfilelog/jsonlog"
)
const maxJSONDecodeRetry = 20000
// ReadLogs implements the logger's LogReader interface for the logs
// created by this driver.
func (l *JSONFileLogger) ReadLogs(config logger.ReadConfig) *logger.LogWatcher {
logWatcher := logger.NewLogWatcher()
go l.readLogs(logWatcher, config)
return logWatcher
}
func (l *JSONFileLogger) readLogs(watcher *logger.LogWatcher, config logger.ReadConfig) {
defer close(watcher.Msg)
l.mu.Lock()
l.readers[watcher] = struct{}{}
l.mu.Unlock()
l.writer.ReadLogs(config, watcher)
l.mu.Lock()
delete(l.readers, watcher)
l.mu.Unlock()
}
func decodeLogLine(dec *json.Decoder, l *jsonlog.JSONLog) (*logger.Message, error) {
l.Reset()
if err := dec.Decode(l); err != nil {
return nil, err
}
var attrs []backend.LogAttr
if len(l.Attrs) != 0 {
attrs = make([]backend.LogAttr, 0, len(l.Attrs))
for k, v := range l.Attrs {
attrs = append(attrs, backend.LogAttr{Key: k, Value: v})
}
}
msg := &logger.Message{
Source: l.Stream,
Timestamp: l.Created,
Line: []byte(l.Log),
Attrs: attrs,
}
return msg, nil
}
// decodeFunc is used to create a decoder for the log file reader
func decodeFunc(rdr io.Reader) func() (*logger.Message, error) {
l := &jsonlog.JSONLog{}
dec := json.NewDecoder(rdr)
return func() (msg *logger.Message, err error) {
for retries := 0; retries < maxJSONDecodeRetry; retries++ {
msg, err = decodeLogLine(dec, l)
if err == nil {
break
}
// try again, could be due to a an incomplete json object as we read
if _, ok := err.(*json.SyntaxError); ok {
dec = json.NewDecoder(rdr)
retries++
continue
}
// io.ErrUnexpectedEOF is returned from json.Decoder when there is
// remaining data in the parser's buffer while an io.EOF occurs.
// If the json logger writes a partial json log entry to the disk
// while at the same time the decoder tries to decode it, the race condition happens.
if err == io.ErrUnexpectedEOF {
reader := io.MultiReader(dec.Buffered(), rdr)
dec = json.NewDecoder(reader)
retries++
}
}
return msg, err
}
}