exec: always return at least an empty ExecResponse

exec/exec.go

@@ -196,7 +196,12 @@ func (r *RunParams) Wait() (*ExecResponse, error) {
 		}
 		logger.Infof("run result: %v", ee)
 	}
-	return result, err
+
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
+
+	return result, nil
 }
 
 // ErrCancelled is returned by WaitWithCancel in case it successfully manages to kill
@@ -232,7 +237,10 @@ func (r *RunParams) WaitWithCancel(cancel <-chan struct{}) (*ExecResponse, error
 
 	select {
 	case resWithError := <-done:
-		return resWithError.execResult, errors.Trace(resWithError.err)
+		if resWithError.err != nil {
+			return nil, errors.Trace(resWithError.err)
+		}
+		return resWithError.execResult, nil
 	case <-cancel:
 		logger.Debugf("attempting to kill process")
 		err := r.KillProcess(r.ps.Process)
@@ -243,8 +251,8 @@ func (r *RunParams) WaitWithCancel(cancel <-chan struct{}) (*ExecResponse, error
 		// After we issue a kill we expect the wait above to return within timeWaitForKill.
 		// In case it doesn't we just go on and assume the process is stuck, but we don't block
 		select {
-		case resWithError := <-done:
-			return resWithError.execResult, ErrCancelled
+		case <-done:
+			return nil, ErrCancelled
 		case <-_clock.After(timeWaitForKill):
 			return nil, errors.Errorf("tried to kill process %v, but timed out", r.ps.Process.Pid)
 		}

exec/exec_linux_test.go

@@ -10,10 +10,6 @@ import (
 	"github.com/juju/utils/exec"
 )
 
-// 0 is thrown by linux because RunParams.Wait
-// only sets the code if the process exits cleanly
-const cancelErrCode = 0
-
 func (*execSuite) TestRunCommands(c *gc.C) {
 	newDir := c.MkDir()
 

exec/exec_test.go

@@ -38,9 +38,7 @@ func (*execSuite) TestWaitWithCancel(c *gc.C) {
 	cancelChan <- struct{}{}
 	result, err := params.WaitWithCancel(cancelChan)
 	c.Assert(err, gc.Equals, exec.ErrCancelled)
-	c.Assert(string(result.Stdout), gc.Equals, "")
-	c.Assert(string(result.Stderr), gc.Equals, "")
-	c.Assert(result.Code, gc.Equals, cancelErrCode)
+	c.Assert(result, gc.IsNil)
 }
 
 func (s *execSuite) TestKillAbortedIfUnsuccessfull(c *gc.C) {

exec/exec_windows_test.go

@@ -14,9 +14,6 @@ import (
 	"github.com/juju/utils/exec"
 )
 
-// 1 is thrown by powershell after the a command is cancelled
-const cancelErrCode = 1
-
 // longPath is copied over from the symlink package. This should be removed
 // if we add it to gc or in some other convenience package
 func longPath(path string) ([]uint16, error) {