Return 404 on exec-inspect when container is dead but exec is still around

When a container is removed but it had an exec, that still hasn't been
GC'd per PR #14476, and someone tries to inspect the exec we should
return a 404, not a 500+container not running.  Returning "..not running" is
not only misleading because it could lead people to think the container is
actually still around, but after 5 minutes the error will change to a 404
after the GC. This means that we're externalizing our internall soft-deletion/GC
logic which shouldn't be any of the end user's concern. They should get the
same results immediate or after 5 minutes.

Signed-off-by: Doug Davis <dug@us.ibm.com>

daemon/exec.go

@@ -81,7 +81,16 @@ func (d *Daemon) registerExecCommand(execConfig *execConfig) {
 }
 
 func (d *Daemon) getExecConfig(name string) (*execConfig, error) {
-	if execConfig := d.execCommands.Get(name); execConfig != nil {
+	execConfig := d.execCommands.Get(name)
+
+	// If the exec is found but its container is not in the daemon's list of
+	// containers then it must have been delete, in which case instead of
+	// saying the container isn't running, we should return a 404 so that
+	// the user sees the same error now that they will after the
+	// 5 minute clean-up loop is run which erases old/dead execs.
+
+	if execConfig != nil && d.containers.Get(execConfig.Container.ID) != nil {
+
 		if !execConfig.Container.IsRunning() {
 			return nil, fmt.Errorf("Container %s is not running", execConfig.Container.ID)
 		}

integration-cli/docker_cli_exec_test.go

@@ -481,6 +481,17 @@ func (s *DockerSuite) TestInspectExecID(c *check.C) {
 	if sc != http.StatusOK {
 		c.Fatalf("received status != 200 OK: %s\n%s", sc, body)
 	}
+
+	// Now delete the container and then an 'inspect' on the exec should
+	// result in a 404 (not 'container not running')
+	out, ec := dockerCmd(c, "rm", "-f", id)
+	if ec != 0 {
+		c.Fatalf("error removing container: %s", out)
+	}
+	sc, body, err = sockRequest("GET", "/exec/"+execID+"/json", nil)
+	if sc != http.StatusNotFound {
+		c.Fatalf("received status != 404: %s\n%s", sc, body)
+	}
 }
 
 func (s *DockerSuite) TestLinksPingLinkedContainersOnRename(c *check.C) {