don't create a trace file here, write trace to io.Writer

Arguably, it's not a library's responsibility to create a trace file,
and to decide on the compression algorithm. The design is cleaner if we
just dump the trace to an io.WriteCloser, and let the application decide
how to handle the concrete implementation.

trace.go

@@ -1,11 +1,9 @@
 package rcmgr
 
 import (
-	"compress/gzip"
 	"context"
 	"encoding/json"
 	"io"
-	"os"
 	"sync"
 	"time"
 
@@ -13,7 +11,7 @@ import (
 )
 
 type trace struct {
-	path string
+	out io.WriteCloser
 
 	ctx    context.Context
 	cancel func()
@@ -24,9 +22,9 @@ type trace struct {
 	pend []interface{}
 }
 
-func WithTrace(path string) Option {
+func WithTrace(out io.WriteCloser) Option {
 	return func(r *resourceManager) error {
-		r.trace = &trace{path: path}
+		r.trace = &trace{out: out}
 		return nil
 	}
 }
@@ -83,14 +81,11 @@ func (t *trace) push(evt TraceEvt) {
 	t.pend = append(t.pend, evt)
 }
 
-func (t *trace) background(out io.WriteCloser) {
+func (t *trace) background() {
 	defer close(t.closed)
-	defer out.Close()
+	defer t.out.Close()
 
-	gzOut := gzip.NewWriter(out)
-	defer gzOut.Close()
-
-	jsonOut := json.NewEncoder(gzOut)
+	jsonOut := json.NewEncoder(t.out)
 
 	ticker := time.NewTicker(time.Second)
 	defer ticker.Stop()
@@ -121,15 +116,6 @@ func (t *trace) background(out io.WriteCloser) {
 				t.mx.Unlock()
 				return
 			}
-
-			if err := gzOut.Flush(); err != nil {
-				log.Warnf("error flushing rcmgr trace: %s", err)
-				t.mx.Lock()
-				t.done = true
-				t.mx.Unlock()
-				return
-			}
-
 		case <-t.ctx.Done():
 			getEvents()
 
@@ -141,11 +127,6 @@ func (t *trace) background(out io.WriteCloser) {
 				log.Warnf("error writing rcmgr trace: %s", err)
 				return
 			}
-
-			if err := gzOut.Flush(); err != nil {
-				log.Warnf("error flushing rcmgr trace: %s", err)
-			}
-
 			return
 		}
 	}
@@ -169,12 +150,7 @@ func (t *trace) Start(limits Limiter) error {
 	t.ctx, t.cancel = context.WithCancel(context.Background())
 	t.closed = make(chan struct{})
 
-	out, err := os.OpenFile(t.path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
-	if err != nil {
-		return nil
-	}
-
-	go t.background(out)
+	go t.background()
 
 	t.push(TraceEvt{
 		Type:  traceStartEvt,