From f078f75bf25353720f28f9f1ea180374fe205302 Mon Sep 17 00:00:00 2001
From: Brian Goff <cpuguy83@gmail.com>
Date: Mon, 10 Aug 2015 09:48:39 -0400
Subject: [PATCH] Return better errors from exec

Also cleans up some of the API side of exec.
Was writing the header twice (two different headers).

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
---
 api/server/exec.go | 26 +++++++++-----------------
 daemon/exec.go     | 13 +++++++++----
 2 files changed, 18 insertions(+), 21 deletions(-)

diff --git a/api/server/exec.go b/api/server/exec.go
index ed586569d5..70dcfacc00 100644
--- a/api/server/exec.go
+++ b/api/server/exec.go
@@ -64,10 +64,9 @@ func (s *Server) postContainerExecStart(version version.Version, w http.Response
 		return err
 	}
 	var (
-		execName = vars["name"]
-		stdin    io.ReadCloser
-		stdout   io.Writer
-		stderr   io.Writer
+		execName                  = vars["name"]
+		stdin, inStream           io.ReadCloser
+		stdout, stderr, outStream io.Writer
 	)
 
 	execStartCheck := &types.ExecStartCheck{}
@@ -76,15 +75,14 @@ func (s *Server) postContainerExecStart(version version.Version, w http.Response
 	}
 
 	if !execStartCheck.Detach {
+		var err error
 		// Setting up the streaming http interface.
-		inStream, outStream, err := hijackServer(w)
+		inStream, outStream, err = hijackServer(w)
 		if err != nil {
 			return err
 		}
 		defer closeStreams(inStream, outStream)
 
-		var errStream io.Writer
-
 		if _, ok := r.Header["Upgrade"]; ok {
 			fmt.Fprintf(outStream, "HTTP/1.1 101 UPGRADED\r\nContent-Type: application/vnd.docker.raw-stream\r\nConnection: Upgrade\r\nUpgrade: tcp\r\n\r\n")
 		} else {
@@ -92,22 +90,16 @@ func (s *Server) postContainerExecStart(version version.Version, w http.Response
 		}
 
 		if !execStartCheck.Tty {
-			errStream = stdcopy.NewStdWriter(outStream, stdcopy.Stderr)
-			outStream = stdcopy.NewStdWriter(outStream, stdcopy.Stdout)
+			stderr = stdcopy.NewStdWriter(outStream, stdcopy.Stderr)
+			stdout = stdcopy.NewStdWriter(outStream, stdcopy.Stdout)
 		}
-
 		stdin = inStream
-		stdout = outStream
-		stderr = errStream
 	}
+
 	// Now run the user process in container.
-
 	if err := s.daemon.ContainerExecStart(execName, stdin, stdout, stderr); err != nil {
-		logrus.Errorf("Error starting exec command in container %s: %s", execName, err)
-		return err
+		fmt.Fprintf(outStream, "Error running exec in container: %v\n", err)
 	}
-	w.WriteHeader(http.StatusNoContent)
-
 	return nil
 }
 
diff --git a/daemon/exec.go b/daemon/exec.go
index 8b163aec49..73f0f5640f 100644
--- a/daemon/exec.go
+++ b/daemon/exec.go
@@ -175,7 +175,6 @@ func (d *Daemon) ContainerExecCreate(config *runconfig.ExecConfig) (string, erro
 }
 
 func (d *Daemon) ContainerExecStart(execName string, stdin io.ReadCloser, stdout io.Writer, stderr io.Writer) error {
-
 	var (
 		cStdin           io.ReadCloser
 		cStdout, cStderr io.Writer
@@ -246,12 +245,18 @@ func (d *Daemon) ContainerExecStart(execName string, stdin io.ReadCloser, stdout
 		if err != nil {
 			return fmt.Errorf("attach failed with error: %s", err)
 		}
-		break
+		return nil
 	case err := <-execErr:
+		if err == nil {
+			return nil
+		}
+
+		// Maybe the container stopped while we were trying to exec
+		if !container.IsRunning() {
+			return fmt.Errorf("container stopped while running exec")
+		}
 		return err
 	}
-
-	return nil
 }
 
 func (d *Daemon) Exec(c *Container, execConfig *execConfig, pipes *execdriver.Pipes, startCallback execdriver.StartCallback) (int, error) {