Decouple logfile from tailfile.

This makes it so consumers of `LogFile` should pass in how to get an
io.Reader to the requested number of lines to tail.

This is also much more efficient when tailing a large number of lines.

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

daemon/logger/jsonfilelog/jsonfilelog.go

@@ -110,7 +110,7 @@ func New(info logger.Info) (logger.Logger, error) {
 		return b, nil
 	}
 
-	writer, err := loggerutils.NewLogFile(info.LogPath, capval, maxFiles, compress, marshalFunc, decodeFunc, 0640)
+	writer, err := loggerutils.NewLogFile(info.LogPath, capval, maxFiles, compress, marshalFunc, decodeFunc, 0640, getTailReader)
 	if err != nil {
 		return nil, err
 	}

daemon/logger/jsonfilelog/jsonfilelog_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"compress/gzip"
 	"encoding/json"
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -107,7 +108,10 @@ func BenchmarkJSONFileLoggerLog(b *testing.B) {
 		ContainerID: "a7317399f3f857173c6179d44823594f8294678dea9999662e5c625b5a1c7657",
 		LogPath:     tmp.Join("container.log"),
 		Config: map[string]string{
-			"labels": "first,second",
+			"labels":   "first,second",
+			"max-file": "10",
+			"compress": "true",
+			"max-size": "20m",
 		},
 		ContainerLabels: map[string]string{
 			"first":  "label_value",
@@ -117,21 +121,34 @@ func BenchmarkJSONFileLoggerLog(b *testing.B) {
 	assert.NilError(b, err)
 	defer jsonlogger.Close()
 
-	msg := &logger.Message{
-		Line:      []byte("Line that thinks that it is log line from docker\n"),
-		Source:    "stderr",
-		Timestamp: time.Now().UTC(),
-	}
-
-	buf := bytes.NewBuffer(nil)
-	assert.NilError(b, marshalMessage(msg, nil, buf))
-	b.SetBytes(int64(buf.Len()))
+	t := time.Now().UTC()
+	for _, data := range [][]byte{
+		[]byte(""),
+		[]byte("a short string"),
+		bytes.Repeat([]byte("a long string"), 100),
+		bytes.Repeat([]byte("a really long string"), 10000),
+	} {
+		b.Run(fmt.Sprintf("%d", len(data)), func(b *testing.B) {
+			testMsg := &logger.Message{
+				Line:      data,
+				Source:    "stderr",
+				Timestamp: t,
+			}
 
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		if err := jsonlogger.Log(msg); err != nil {
-			b.Fatal(err)
-		}
+			buf := bytes.NewBuffer(nil)
+			assert.NilError(b, marshalMessage(testMsg, nil, buf))
+			b.SetBytes(int64(buf.Len()))
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				msg := logger.NewMessage()
+				msg.Line = testMsg.Line
+				msg.Timestamp = testMsg.Timestamp
+				msg.Source = testMsg.Source
+				if err := jsonlogger.Log(msg); err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
 	}
 }
 

daemon/logger/jsonfilelog/read.go

@@ -1,12 +1,16 @@
 package jsonfilelog // import "github.com/docker/docker/daemon/logger/jsonfilelog"
 
 import (
+	"context"
 	"encoding/json"
 	"io"
 
 	"github.com/docker/docker/api/types/backend"
 	"github.com/docker/docker/daemon/logger"
 	"github.com/docker/docker/daemon/logger/jsonfilelog/jsonlog"
+	"github.com/docker/docker/daemon/logger/loggerutils"
+	"github.com/docker/docker/pkg/tailfile"
+	"github.com/sirupsen/logrus"
 )
 
 const maxJSONDecodeRetry = 20000
@@ -63,14 +67,14 @@ func decodeFunc(rdr io.Reader) func() (*logger.Message, error) {
 	return func() (msg *logger.Message, err error) {
 		for retries := 0; retries < maxJSONDecodeRetry; retries++ {
 			msg, err = decodeLogLine(dec, l)
-			if err == nil {
+			if err == nil || err == io.EOF {
 				break
 			}
 
+			logrus.WithError(err).WithField("retries", retries).Warn("got error while decoding json")
 			// 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
 			}
 
@@ -81,9 +85,13 @@ func decodeFunc(rdr io.Reader) func() (*logger.Message, error) {
 			if err == io.ErrUnexpectedEOF {
 				reader := io.MultiReader(dec.Buffered(), rdr)
 				dec = json.NewDecoder(reader)
-				retries++
+				continue
 			}
 		}
 		return msg, err
 	}
 }
+
+func getTailReader(ctx context.Context, r loggerutils.SizeReaderAt, req int) (io.Reader, int, error) {
+	return tailfile.NewTailReader(ctx, r, req)
+}

daemon/logger/jsonfilelog/read_test.go

@@ -2,6 +2,7 @@ package jsonfilelog // import "github.com/docker/docker/daemon/logger/jsonfilelo
 
 import (
 	"bytes"
+	"io"
 	"testing"
 	"time"
 
@@ -62,3 +63,32 @@ func BenchmarkJSONFileLoggerReadLogs(b *testing.B) {
 		}
 	}
 }
+
+func TestEncodeDecode(t *testing.T) {
+	t.Parallel()
+
+	m1 := &logger.Message{Line: []byte("hello 1"), Timestamp: time.Now(), Source: "stdout"}
+	m2 := &logger.Message{Line: []byte("hello 2"), Timestamp: time.Now(), Source: "stdout"}
+	m3 := &logger.Message{Line: []byte("hello 3"), Timestamp: time.Now(), Source: "stdout"}
+
+	buf := bytes.NewBuffer(nil)
+	assert.Assert(t, marshalMessage(m1, nil, buf))
+	assert.Assert(t, marshalMessage(m2, nil, buf))
+	assert.Assert(t, marshalMessage(m3, nil, buf))
+
+	decode := decodeFunc(buf)
+	msg, err := decode()
+	assert.Assert(t, err)
+	assert.Assert(t, string(msg.Line) == "hello 1\n", string(msg.Line))
+
+	msg, err = decode()
+	assert.Assert(t, err)
+	assert.Assert(t, string(msg.Line) == "hello 2\n")
+
+	msg, err = decode()
+	assert.Assert(t, err)
+	assert.Assert(t, string(msg.Line) == "hello 3\n")
+
+	_, err = decode()
+	assert.Assert(t, err == io.EOF)
+}

daemon/logger/loggerutils/logfile.go

@@ -1,7 +1,6 @@
 package loggerutils // import "github.com/docker/docker/daemon/logger/loggerutils"
 
 import (
-	"bytes"
 	"compress/gzip"
 	"context"
 	"encoding/json"
@@ -14,11 +13,9 @@ import (
 	"time"
 
 	"github.com/docker/docker/daemon/logger"
-	"github.com/docker/docker/daemon/logger/loggerutils/multireader"
 	"github.com/docker/docker/pkg/filenotify"
 	"github.com/docker/docker/pkg/pools"
 	"github.com/docker/docker/pkg/pubsub"
-	"github.com/docker/docker/pkg/tailfile"
 	"github.com/fsnotify/fsnotify"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
@@ -92,13 +89,27 @@ type LogFile struct {
 	notifyRotate    *pubsub.Publisher
 	marshal         logger.MarshalFunc
 	createDecoder   makeDecoderFunc
+	getTailReader   GetTailReaderFunc
 	perms           os.FileMode
 }
 
 type makeDecoderFunc func(rdr io.Reader) func() (*logger.Message, error)
 
+// SizeReaderAt defines a ReaderAt that also reports its size.
+// This is used for tailing log files.
+type SizeReaderAt interface {
+	io.ReaderAt
+	Size() int64
+}
+
+// GetTailReaderFunc is used to truncate a reader to only read as much as is required
+// in order to get the passed in number of log lines.
+// It returns the sectioned reader, the number of lines that the section reader
+// contains, and any error that occurs.
+type GetTailReaderFunc func(ctx context.Context, f SizeReaderAt, nLogLines int) (rdr io.Reader, nLines int, err error)
+
 // NewLogFile creates new LogFile
-func NewLogFile(logPath string, capacity int64, maxFiles int, compress bool, marshaller logger.MarshalFunc, decodeFunc makeDecoderFunc, perms os.FileMode) (*LogFile, error) {
+func NewLogFile(logPath string, capacity int64, maxFiles int, compress bool, marshaller logger.MarshalFunc, decodeFunc makeDecoderFunc, perms os.FileMode, getTailReader GetTailReaderFunc) (*LogFile, error) {
 	log, err := os.OpenFile(logPath, os.O_WRONLY|os.O_APPEND|os.O_CREATE, perms)
 	if err != nil {
 		return nil, err
@@ -120,6 +131,7 @@ func NewLogFile(logPath string, capacity int64, maxFiles int, compress bool, mar
 		marshal:         marshaller,
 		createDecoder:   decodeFunc,
 		perms:           perms,
+		getTailReader:   getTailReader,
 	}, nil
 }
 
@@ -309,33 +321,45 @@ func (w *LogFile) ReadLogs(config logger.ReadConfig, watcher *logger.LogWatcher)
 	}
 
 	if config.Tail != 0 {
+		// TODO(@cpuguy83): Instead of opening every file, only get the files which
+		// are needed to tail.
+		// This is especially costly when compression is enabled.
 		files, err := w.openRotatedFiles(config)
+		w.mu.RUnlock()
 		if err != nil {
-			w.mu.RUnlock()
 			watcher.Err <- err
 			return
 		}
-		w.mu.RUnlock()
-		seekers := make([]io.ReadSeeker, 0, len(files)+1)
-		for _, f := range files {
-			seekers = append(seekers, f)
-		}
-		if currentChunk.Size() > 0 {
-			seekers = append(seekers, currentChunk)
-		}
-		if len(seekers) > 0 {
-			tailFile(multireader.MultiReadSeeker(seekers...), watcher, w.createDecoder, config)
+
+		closeFiles := func() {
+			for _, f := range files {
+				f.Close()
+				fileName := f.Name()
+				if strings.HasSuffix(fileName, tmpLogfileSuffix) {
+					err := w.filesRefCounter.Dereference(fileName)
+					if err != nil {
+						logrus.Errorf("Failed to dereference the log file %q: %v", fileName, err)
+					}
+				}
+			}
 		}
+
+		readers := make([]SizeReaderAt, 0, len(files)+1)
 		for _, f := range files {
-			f.Close()
-			fileName := f.Name()
-			if strings.HasSuffix(fileName, tmpLogfileSuffix) {
-				err := w.filesRefCounter.Dereference(fileName)
-				if err != nil {
-					logrus.Errorf("Failed to dereference log file %q: %v", fileName, err)
-				}
+			stat, err := f.Stat()
+			if err != nil {
+				watcher.Err <- errors.Wrap(err, "error reading size of rotated file")
+				closeFiles()
+				return
 			}
+			readers = append(readers, io.NewSectionReader(f, 0, stat.Size()))
 		}
+		if currentChunk.Size() > 0 {
+			readers = append(readers, currentChunk)
+		}
+
+		tailFiles(readers, watcher, w.createDecoder, w.getTailReader, config)
+		closeFiles()
 
 		w.mu.RLock()
 	}
@@ -454,19 +478,39 @@ func newSectionReader(f *os.File) (*io.SectionReader, error) {
 	return io.NewSectionReader(f, 0, size), nil
 }
 
-type decodeFunc func() (*logger.Message, error)
+func tailFiles(files []SizeReaderAt, watcher *logger.LogWatcher, createDecoder makeDecoderFunc, getTailReader GetTailReaderFunc, config logger.ReadConfig) {
+	nLines := config.Tail
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	// TODO(@cpuguy83): we should plumb a context through instead of dealing with `WatchClose()` here.
+	go func() {
+		select {
+		case <-ctx.Done():
+		case <-watcher.WatchClose():
+			cancel()
+		}
+	}()
+
+	readers := make([]io.Reader, 0, len(files))
 
-func tailFile(f io.ReadSeeker, watcher *logger.LogWatcher, createDecoder makeDecoderFunc, config logger.ReadConfig) {
-	var rdr io.Reader = f
 	if config.Tail > 0 {
-		ls, err := tailfile.TailFile(f, config.Tail)
-		if err != nil {
-			watcher.Err <- err
-			return
+		for i := len(files) - 1; i >= 0 && nLines > 0; i-- {
+			tail, n, err := getTailReader(ctx, files[i], nLines)
+			if err != nil {
+				watcher.Err <- errors.Wrap(err, "error finding file position to start log tailing")
+				return
+			}
+			nLines -= n
+			readers = append([]io.Reader{tail}, readers...)
+		}
+	} else {
+		for _, r := range files {
+			readers = append(readers, &wrappedReaderAt{ReaderAt: r})
 		}
-		rdr = bytes.NewBuffer(bytes.Join(ls, []byte("\n")))
 	}
 
+	rdr := io.MultiReader(readers...)
 	decodeLogLine := createDecoder(rdr)
 	for {
 		msg, err := decodeLogLine()
@@ -483,7 +527,7 @@ func tailFile(f io.ReadSeeker, watcher *logger.LogWatcher, createDecoder makeDec
 			return
 		}
 		select {
-		case <-watcher.WatchClose():
+		case <-ctx.Done():
 			return
 		case watcher.Msg <- msg:
 		}
@@ -664,3 +708,14 @@ func watchFile(name string) (filenotify.FileWatcher, error) {
 	}
 	return fileWatcher, nil
 }
+
+type wrappedReaderAt struct {
+	io.ReaderAt
+	pos int64
+}
+
+func (r *wrappedReaderAt) Read(p []byte) (int, error) {
+	n, err := r.ReaderAt.ReadAt(p, r.pos)
+	r.pos += int64(n)
+	return n, err
+}

daemon/logger/loggerutils/logfile_test.go

@@ -0,0 +1,76 @@
+package loggerutils
+
+import (
+	"bufio"
+	"context"
+	"io"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/docker/docker/daemon/logger"
+	"github.com/docker/docker/pkg/tailfile"
+	"gotest.tools/assert"
+)
+
+func TestTailFiles(t *testing.T) {
+	s1 := strings.NewReader("Hello.\nMy name is Inigo Montoya.\n")
+	s2 := strings.NewReader("I'm serious.\nDon't call me Shirley!\n")
+	s3 := strings.NewReader("Roads?\nWhere we're going we don't need roads.\n")
+
+	files := []SizeReaderAt{s1, s2, s3}
+	watcher := logger.NewLogWatcher()
+	createDecoder := func(r io.Reader) func() (*logger.Message, error) {
+		scanner := bufio.NewScanner(r)
+		return func() (*logger.Message, error) {
+			if !scanner.Scan() {
+				return nil, scanner.Err()
+			}
+			// some comment
+			return &logger.Message{Line: scanner.Bytes(), Timestamp: time.Now()}, nil
+		}
+	}
+
+	tailReader := func(ctx context.Context, r SizeReaderAt, lines int) (io.Reader, int, error) {
+		return tailfile.NewTailReader(ctx, r, lines)
+	}
+
+	for desc, config := range map[string]logger.ReadConfig{} {
+		t.Run(desc, func(t *testing.T) {
+			started := make(chan struct{})
+			go func() {
+				close(started)
+				tailFiles(files, watcher, createDecoder, tailReader, config)
+			}()
+			<-started
+		})
+	}
+
+	config := logger.ReadConfig{Tail: 2}
+	started := make(chan struct{})
+	go func() {
+		close(started)
+		tailFiles(files, watcher, createDecoder, tailReader, config)
+	}()
+	<-started
+
+	select {
+	case <-time.After(60 * time.Second):
+		t.Fatal("timeout waiting for tail line")
+	case err := <-watcher.Err:
+		assert.Assert(t, err)
+	case msg := <-watcher.Msg:
+		assert.Assert(t, msg != nil)
+		assert.Assert(t, string(msg.Line) == "Roads?", string(msg.Line))
+	}
+
+	select {
+	case <-time.After(60 * time.Second):
+		t.Fatal("timeout waiting for tail line")
+	case err := <-watcher.Err:
+		assert.Assert(t, err)
+	case msg := <-watcher.Msg:
+		assert.Assert(t, msg != nil)
+		assert.Assert(t, string(msg.Line) == "Where we're going we don't need roads.", string(msg.Line))
+	}
+}