fix: allow resource.Exec to correctly wait for process completion (#383)

This bug was due to a bug in the vendored client library where
StartExec would return early even if opts.Detatch was true, if stderr
and stdout were not provided. This fix always attaches them and falls
back to io.Discard if the user does not provide their own readers.

See: fsouza/go-dockerclient#838
Fixes #372

dockertest.go

@@ -117,15 +117,25 @@ func (r *Resource) Exec(cmd []string, opts ExecOptions) (exitCode int, err error
 		Container:    r.Container.ID,
 		Cmd:          cmd,
 		Env:          opts.Env,
-		AttachStderr: opts.StdErr != nil,
-		AttachStdout: opts.StdOut != nil,
+		AttachStderr: true,
+		AttachStdout: true,
 		AttachStdin:  opts.StdIn != nil,
 		Tty:          opts.TTY,
 	})
 	if err != nil {
 		return -1, errors.Wrap(err, "Create exec failed")
 	}
 
+	// Always attach stderr/stdout, even if not specified, to ensure that exec
+	// waits with opts.Detach as false (default)
+	// ref: https://github.com/fsouza/go-dockerclient/issues/838
+	if opts.StdErr == nil {
+		opts.StdErr = io.Discard
+	}
+	if opts.StdOut == nil {
+		opts.StdOut = io.Discard
+	}
+
 	err = r.pool.Client.StartExec(exec.ID, dc.StartExecOptions{
 		InputStream:  opts.StdIn,
 		OutputStream: opts.StdOut,

dockertest_test.go

@@ -20,8 +20,10 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-var docker = os.Getenv("DOCKER_URL")
-var pool *Pool
+var (
+	docker = os.Getenv("DOCKER_URL")
+	pool   *Pool
+)
 
 func TestMain(m *testing.M) {
 	var err error
@@ -65,7 +67,6 @@ func TestMongo(t *testing.T) {
 
 	err = pool.Retry(func() error {
 		response, err := http.Get(fmt.Sprintf("http://127.0.0.1:%s", port))
-
 		if err != nil {
 			return err
 		}
@@ -197,7 +198,7 @@ func TestBuildImage(t *testing.T) {
 	dockerfilePath := dir + "/Dockerfile"
 	ioutil.WriteFile(dockerfilePath,
 		[]byte("FROM postgres:9.5"),
-		0644,
+		0o644,
 	)
 
 	resource, err := pool.BuildAndRun("postgres-test", dockerfilePath, nil)
@@ -219,7 +220,7 @@ ARG foo
 RUN echo -n $foo > /build-time-value
 CMD sleep 10
 `)),
-		0644,
+		0o644,
 	)
 
 	resource, err := pool.BuildAndRunWithBuildOptions(
@@ -467,3 +468,19 @@ func TestClientRaceCondition(t *testing.T) {
 		})
 	}
 }
+
+func TestExecStatus(t *testing.T) {
+	resource, err := pool.RunWithOptions(&RunOptions{
+		Repository: "alpine",
+		Tag:        "3.16",
+		Cmd:        []string{"tail", "-f", "/dev/null"},
+	})
+	defer resource.Close()
+	require.Nil(t, err)
+	exitCode, err := resource.Exec([]string{"/bin/false"}, ExecOptions{})
+	require.Nil(t, err)
+	require.Equal(t, 1, exitCode)
+	exitCode, err = resource.Exec([]string{"/bin/sh", "-c", "/bin/sleep 2 && exit 42"}, ExecOptions{})
+	require.Nil(t, err)
+	require.Equal(t, 42, exitCode)
+}