Wait for stdout pipe to close before calling runner.Wait() (#299)

If the two goroutines are left to race each other, when runner.Wait() wins it will close the file and cause the stdout scanner to log a spurious os.ErrClosed error instead of returning nil after encountering an io.EOF error.

client.go

@@ -104,9 +104,9 @@ type Client struct {
 	// goroutines.
 	clientWaitGroup sync.WaitGroup
 
-	// stderrWaitGroup is used to prevent the command's Wait() function from
-	// being called before we've finished reading from the stderr pipe.
-	stderrWaitGroup sync.WaitGroup
+	// pipesWaitGroup is used to prevent the command's Wait() function from
+	// being called before we've finished reading from the stdout and stderr pipe.
+	pipesWaitGroup sync.WaitGroup
 
 	// processKilled is used for testing only, to flag when the process was
 	// forcefully killed.
@@ -756,8 +756,8 @@ func (c *Client) Start() (addr net.Addr, err error) {
 
 	// Start goroutine that logs the stderr
 	c.clientWaitGroup.Add(1)
-	c.stderrWaitGroup.Add(1)
-	// logStderr calls Done()
+	c.pipesWaitGroup.Add(1)
+	// logStderr calls c.pipesWaitGroup.Done()
 	go c.logStderr(runner.Name(), runner.Stderr())
 
 	c.clientWaitGroup.Add(1)
@@ -767,9 +767,9 @@ func (c *Client) Start() (addr net.Addr, err error) {
 
 		defer c.clientWaitGroup.Done()
 
-		// wait to finish reading from stderr since the stderr pipe reader
+		// wait to finish reading from stdout/stderr since the stdout/stderr pipe readers
 		// will be closed by the subsequent call to cmd.Wait().
-		c.stderrWaitGroup.Wait()
+		c.pipesWaitGroup.Wait()
 
 		// Wait for the command to end.
 		err := runner.Wait(context.Background())
@@ -792,8 +792,10 @@ func (c *Client) Start() (addr net.Addr, err error) {
 	// out of stdout
 	linesCh := make(chan string)
 	c.clientWaitGroup.Add(1)
+	c.pipesWaitGroup.Add(1)
 	go func() {
 		defer c.clientWaitGroup.Done()
+		defer c.pipesWaitGroup.Done()
 		defer close(linesCh)
 
 		scanner := bufio.NewScanner(runner.Stdout())
@@ -1159,7 +1161,7 @@ func (c *Client) getGRPCMuxer(addr net.Addr) (*grpcmux.GRPCClientMuxer, error) {
 
 func (c *Client) logStderr(name string, r io.Reader) {
 	defer c.clientWaitGroup.Done()
-	defer c.stderrWaitGroup.Done()
+	defer c.pipesWaitGroup.Done()
 	l := c.logger.Named(filepath.Base(name))
 
 	reader := bufio.NewReaderSize(r, c.config.PluginLogBufferSize)

client_test.go

@@ -1503,7 +1503,7 @@ this line is short
 
 	reader := strings.NewReader(msg)
 
-	c.stderrWaitGroup.Add(1)
+	c.pipesWaitGroup.Add(1)
 	c.logStderr(c.config.Cmd.Path, reader)
 	read := stderr.String()
 
@@ -1531,7 +1531,7 @@ func TestClient_logStderrParseJSON(t *testing.T) {
 {"@message": "this is a large message that is more than 64 bytes long", "@level": "info"}`
 	reader := strings.NewReader(msg)
 
-	c.stderrWaitGroup.Add(1)
+	c.pipesWaitGroup.Add(1)
 	c.logStderr(c.config.Cmd.Path, reader)
 	logs := strings.Split(strings.TrimSpace(logBuf.String()), "\n")