json tracer

trace.go

@@ -1,6 +1,10 @@
 package pubsub
 
 import (
+	"encoding/json"
+	"io"
+	"os"
+	"sync"
 	"time"
 
 	"github.com/libp2p/go-libp2p-core/peer"
@@ -14,6 +18,75 @@ type EventTracer interface {
 	Trace(evt interface{})
 }
 
+// JSONTracer is a tracer that writes events to a file, encoded in json.
+type JSONTracer struct {
+	w   io.WriteCloser
+	ch  chan struct{}
+	mx  sync.Mutex
+	buf []interface{}
+}
+
+// NewJsonTracer creates a new JSON tracer writing to file.
+func NewJSONTracer(file string) (*JSONTracer, error) {
+	return OpenJSONTracer(file, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+}
+
+// OpenJsonTracer creates a new JSON tracer, with explicit control of OpenFile flags and permissions.
+func OpenJSONTracer(file string, flags int, perm os.FileMode) (*JSONTracer, error) {
+	f, err := os.OpenFile(file, flags, perm)
+	if err != nil {
+		return nil, err
+	}
+
+	tr := &JSONTracer{w: f, ch: make(chan struct{}, 1)}
+	go tr.doWrite()
+
+	return tr, nil
+}
+
+func (t *JSONTracer) Trace(evt interface{}) {
+	t.mx.Lock()
+	t.buf = append(t.buf, evt)
+	t.mx.Unlock()
+
+	select {
+	case t.ch <- struct{}{}:
+	default:
+	}
+}
+
+func (t *JSONTracer) Close() {
+	close(t.ch)
+}
+
+func (t *JSONTracer) doWrite() {
+	var buf []interface{}
+	enc := json.NewEncoder(t.w)
+	for {
+		_, ok := <-t.ch
+
+		t.mx.Lock()
+		tmp := t.buf
+		t.buf = buf[:0]
+		buf = tmp
+		t.mx.Unlock()
+
+		for i, evt := range buf {
+			err := enc.Encode(evt)
+			if err != nil {
+				log.Errorf("error writing event trace: %s", err.Error())
+			}
+			buf[i] = nil
+		}
+
+		if !ok {
+			t.w.Close()
+			return
+		}
+	}
+}
+
+// pubsub tracer details
 type pubsubTracer struct {
 	tracer EventTracer
 	pid    peer.ID