docker: add comment about "connection reset by peer" error

agent/checks/docker.go

@@ -162,6 +162,12 @@ func (c *DockerClient) StartExec(containerID, execID string) (*circbuf.Buffer, e
 	uri := fmt.Sprintf("/exec/%s/start", execID)
 	b, code, err := c.call("POST", uri, data)
 	switch {
+	// todo(fs): https://github.com/hashicorp/consul/pull/3621
+	// todo(fs): for some reason the docker agent closes the connection during the
+	// todo(fs): io.Copy call in c.call which causes a "connection reset by peer" error
+	// todo(fs): even though both body and status code have been received. My current is
+	// todo(fs): that the docker agent closes this prematurely but I don't understand why.
+	// todo(fs): the code below ignores this error.
 	case err != nil && !strings.Contains(err.Error(), "connection reset by peer"):
 		return nil, fmt.Errorf("start exec failed for container %s: %s", containerID, err)
 	case code == 200: