Replace polling of buffer with channel to fix detected race

internal/tool/srv/srv.go

@@ -17,16 +17,23 @@ func Serve(args []string, _ io.Reader) error {
 		dir = args[1]
 	}
 
-	return serve(dir, os.Stderr)
+	ch := make(chan net.Addr)
+
+	go func() {
+		addr := <-ch
+		fmt.Fprintf(os.Stderr, "Serving %s on %s\n", dir, addr)
+	}()
+
+	return serve(dir, ch)
 }
 
-func serve(dir string, log io.Writer) error {
+func serve(dir string, log chan net.Addr) error {
 	listener, err := net.Listen("tcp", ":0")
 	if err != nil {
 		return errors.Wrap(err, "net.Listen")
 	}
 
-	fmt.Fprintf(log, "Serving %s on %s\n", dir, listener.Addr())
+	log <- listener.Addr()
 
 	return http.Serve(listener, http.FileServer(http.Dir(dir)))
 }

internal/tool/srv/srv_test.go

@@ -1,42 +1,31 @@
 package srv
 
 import (
-	"bytes"
 	"io/ioutil"
-	"math/rand"
+	"net"
 	"net/http"
 	"os"
-	"regexp"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 )
 
 func TestServe(t *testing.T) {
-	buf := &bytes.Buffer{}
-	go serve(".", buf)
-
-	sock := regexp.MustCompile("^Serving . on (.+)\n")
-
-	var resp *http.Response
-	var err error
-	for i := 1; i < 11; i++ {
-		m := sock.FindStringSubmatch(buf.String())
-		if len(m) == 0 {
-			time.Sleep(time.Millisecond * time.Duration(rand.Intn(i)))
-			continue
-		}
-
-		resp, err = http.Get("http://" + m[1] + "/srv.go")
-		if err != nil {
-			t.Fatalf("Couldn't fetch srv.go: %s", err)
-		}
-		break
-	}
+	ch := make(chan net.Addr)
+	go serve(".", ch)
 
-	if resp == nil {
+	var addr net.Addr
+	timer := time.NewTimer(time.Second)
+	select {
+	case <-timer.C:
 		t.Fatalf("couldn't get response from server within timeout")
+	case addr = <-ch:
+	}
+
+	resp, err := http.Get("http://" + string(addr.String()) + "/srv.go")
+	if err != nil {
+		t.Fatalf("Couldn't fetch srv.go: %s", err)
 	}
 
 	f, err := os.Open("./srv.go")