AUTH-1943: Adds session logging

sshlog/logger.go

@@ -0,0 +1,156 @@
+package sshlog
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+
+	"github.com/sirupsen/logrus"
+)
+
+const (
+	logTimeFormat = "2006-01-02T15-04-05.000"
+	megabyte      = 1024 * 1024
+)
+
+// Logger will buffer and write events to disk
+type Logger struct {
+	sync.Mutex
+	filename    string
+	file        *os.File
+	writeBuffer *bufio.Writer
+	logger      *logrus.Logger
+	done        chan struct{}
+	once        sync.Once
+}
+
+// NewLogger creates a Logger instance. A buffer is created that needs to be
+// drained and closed when the caller is finished, so instances should call
+// Close when finished with this Logger instance. Writes will be flushed to disk
+// every second (fsync). filename is the name of the logfile to be created. The
+// logger variable is a logrus that will log all i/o, filesystem error etc, that
+// that shouldn't end execution of the logger, but are useful to report to the
+// caller.
+func NewLogger(filename string, logger *logrus.Logger) (*Logger, error) {
+	f, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.FileMode(0600))
+	if err != nil {
+		return nil, err
+	}
+	l := &Logger{filename: filename,
+		file:        f,
+		writeBuffer: bufio.NewWriter(f),
+		logger:      logger,
+		done:        make(chan struct{})}
+	go l.writer()
+	return l, nil
+}
+
+// Writes to a log buffer. Implements the io.Writer interface.
+func (l *Logger) Write(p []byte) (n int, err error) {
+	l.Lock()
+	defer l.Unlock()
+	return l.writeBuffer.Write(p)
+}
+
+// Close drains anything left in the buffer and cleans up any resources still
+// in use.
+func (l *Logger) Close() error {
+	l.once.Do(func() {
+		close(l.done)
+	})
+	if err := l.write(); err != nil {
+		return err
+	}
+	return l.file.Close()
+}
+
+// writer is the run loop that handles draining the write buffer and syncing
+// data to disk.
+func (l *Logger) writer() {
+	ticker := time.NewTicker(time.Second)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ticker.C:
+			if err := l.write(); err != nil {
+				l.logger.Errorln(err)
+			}
+		case <-l.done:
+			return
+		}
+	}
+}
+
+// write does the actual system write calls to disk and does a rotation if the
+// file size limit has been reached. Since the rotation happens at the end,
+// the rotation is a soft limit (aka the file can be bigger than the max limit
+// because of the final buffer flush)
+func (l *Logger) write() error {
+	l.Lock()
+	defer l.Unlock()
+
+	if l.writeBuffer.Buffered() <= 0 {
+		return nil
+	}
+
+	if err := l.writeBuffer.Flush(); err != nil {
+		return err
+	}
+
+	if err := l.file.Sync(); err != nil {
+		return err
+	}
+
+	if l.shouldRotate() {
+		return l.rotate()
+	}
+	return nil
+}
+
+// shouldRotate checks to see if the current file should be rotated to a new
+// logfile.
+func (l *Logger) shouldRotate() bool {
+	info, err := l.file.Stat()
+	if err != nil {
+		return false
+	}
+
+	return info.Size() >= 100*megabyte
+}
+
+// rotate creates a new logfile with the existing filename and renames the
+// existing file with a current timestamp.
+func (l *Logger) rotate() error {
+	if err := l.file.Close(); err != nil {
+		return err
+	}
+
+	// move the existing file
+	newname := rotationName(l.filename)
+	if err := os.Rename(l.filename, newname); err != nil {
+		return fmt.Errorf("can't rename log file: %s", err)
+	}
+
+	f, err := os.OpenFile(l.filename, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.FileMode(0600))
+	if err != nil {
+		return fmt.Errorf("failed to open new logfile %s", err)
+	}
+	l.file = f
+	l.writeBuffer = bufio.NewWriter(f)
+	return nil
+}
+
+// rotationName creates a new filename from the given name, inserting a timestamp
+// between the filename and the extension.
+func rotationName(name string) string {
+	dir := filepath.Dir(name)
+	filename := filepath.Base(name)
+	ext := filepath.Ext(filename)
+	prefix := filename[:len(filename)-len(ext)]
+	t := time.Now()
+	timestamp := t.Format(logTimeFormat)
+	return filepath.Join(dir, fmt.Sprintf("%s-%s%s", prefix, timestamp, ext))
+}