prevent a data race caused by unprotected access to testing.*.Log

The following commit

golang/go@5c83e65

which was released in go 1.7, fixes a possible data race that can happen
during testing.

The fix is in common.flushToParent which is now used to protect read
access to `output`.

client_test.go

@@ -33,8 +33,8 @@ func newSession(t *testing.T) (io.ReadWriteCloser, *server) {
 	rs, wc := io.Pipe()
 	rc, ws := io.Pipe()
 
-	rws := &logIO{t, "server", &pipe{r: rs, w: ws}}
-	rwc := &logIO{t, "client", &pipe{r: rc, w: wc}}
+	rws := &logIO{t: t, prefix: "server", proxy: &pipe{r: rs, w: ws}}
+	rwc := &logIO{t: t, prefix: "client", proxy: &pipe{r: rc, w: wc}}
 
 	server := server{
 		T: t,

integration_test.go

@@ -1708,7 +1708,7 @@ func integrationURLFromEnv() string {
 
 func loggedConnection(t *testing.T, conn *Connection, name string) *Connection {
 	if name != "" {
-		conn.conn = &logIO{t, name, conn.conn}
+		conn.conn = &logIO{t: t, prefix: name, proxy: conn.conn}
 	}
 	return conn
 }

shared_test.go

@@ -48,10 +48,14 @@ func (p *pipe) Close() error {
 type logIO struct {
 	t      *testing.T
 	prefix string
-	proxy  io.ReadWriteCloser
+
+	m     sync.Mutex
+	proxy io.ReadWriteCloser
 }
 
 func (me *logIO) Read(p []byte) (n int, err error) {
+	me.m.Lock()
+	defer me.m.Unlock()
 	me.t.Logf("%s reading %d\n", me.prefix, len(p))
 	n, err = me.proxy.Read(p)
 	if err != nil {
@@ -64,6 +68,8 @@ func (me *logIO) Read(p []byte) (n int, err error) {
 }
 
 func (me *logIO) Write(p []byte) (n int, err error) {
+	me.m.Lock()
+	defer me.m.Unlock()
 	me.t.Logf("%s writing %d\n", me.prefix, len(p))
 	n, err = me.proxy.Write(p)
 	if err != nil {
@@ -76,6 +82,8 @@ func (me *logIO) Write(p []byte) (n int, err error) {
 }
 
 func (me *logIO) Close() (err error) {
+	me.m.Lock()
+	defer me.m.Unlock()
 	err = me.proxy.Close()
 	if err != nil {
 		me.t.Logf("%s close : %v\n", me.prefix, err)