ensure we finish reading stderr pipe before calling cmd.Wait()

client.go

@@ -87,6 +87,10 @@ 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
+
 	// processKilled is used for testing only, to flag when the process was
 	// forcefully killed.
 	processKilled bool
@@ -590,6 +594,12 @@ func (c *Client) Start() (addr net.Addr, err error) {
 	// Create a context for when we kill
 	c.doneCtx, c.ctxCancel = context.WithCancel(context.Background())
 
+	// Start goroutine that logs the stderr
+	c.clientWaitGroup.Add(1)
+	c.stderrWaitGroup.Add(1)
+	// logStderr calls Done()
+	go c.logStderr(cmdStderr)
+
 	c.clientWaitGroup.Add(1)
 	go func() {
 		// ensure the context is cancelled when we're done
@@ -602,6 +612,10 @@ func (c *Client) Start() (addr net.Addr, err error) {
 		pid := c.process.Pid
 		path := cmd.Path
 
+		// wait to finish reading from stderr since the stderr pipe reader
+		// will be closed by the subsequent call to cmd.Wait().
+		c.stderrWaitGroup.Wait()
+
 		// Wait for the command to end.
 		err := cmd.Wait()
 
@@ -624,11 +638,6 @@ func (c *Client) Start() (addr net.Addr, err error) {
 		c.exited = true
 	}()
 
-	// Start goroutine that logs the stderr
-	c.clientWaitGroup.Add(1)
-	// logStderr calls Done()
-	go c.logStderr(cmdStderr)
-
 	// Start a goroutine that is going to be reading the lines
 	// out of stdout
 	linesCh := make(chan string)
@@ -936,6 +945,7 @@ var stdErrBufferSize = 64 * 1024
 
 func (c *Client) logStderr(r io.Reader) {
 	defer c.clientWaitGroup.Done()
+	defer c.stderrWaitGroup.Done()
 	l := c.logger.Named(filepath.Base(c.config.Cmd.Path))
 
 	reader := bufio.NewReaderSize(r, stdErrBufferSize)