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// Copyright 2015 Google Inc. All Rights Reserved.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package samples
import (
var fToolPath = flag.String(
"Path to the mount_sample tool. If unset, we will compile it.")
var fDebug = flag.Bool("debug", false, "If true, print fuse debug info.")
// A struct that implements common behavior needed by tests in the samples/
// directory where the file system is mounted by a subprocess. Use it as an
// embedded field in your test fixture, calling its SetUp method from your
// SetUp method after setting the MountType and MountFlags fields.
type SubprocessTest struct {
// The type of the file system to mount. Must be recognized by mount_sample.
MountType string
// Additional flags to be passed to the mount_sample tool.
MountFlags []string
// A list of files to pass to mount_sample. The given string flag will be
// used to pass the file descriptor number.
MountFiles map[string]*os.File
// A context object that can be used for long-running operations.
Ctx context.Context
// The directory at which the file system is mounted.
Dir string
// Anothing non-nil in this slice will be closed by TearDown. The test will
// fail if closing fails.
ToClose []io.Closer
mountSampleErr <-chan error
// Mount the file system and initialize the other exported fields of the
// struct. Panics on error.
func (t *SubprocessTest) SetUp(ti *ogletest.TestInfo) {
err := t.initialize(ti.Ctx)
if err != nil {
// Private state for getToolPath.
var getToolContents_Contents []byte
var getToolContents_Err error
var getToolContents_Once sync.Once
// Implementation detail of getToolPath.
func getToolContentsImpl() ([]byte, error) {
// Fast path: has the user set the flag?
if *fToolPath != "" {
contents, err := ioutil.ReadFile(*fToolPath)
if err != nil {
return nil, fmt.Errorf("Reading mount_sample contents: %v", err)
return contents, err
// Create a temporary directory into which we will compile the tool.
tempDir, err := ioutil.TempDir("", "sample_test")
if err != nil {
return nil, fmt.Errorf("TempDir: %v", err)
toolPath := path.Join(tempDir, "mount_sample")
// Ensure that we kill the temporary directory when we're finished here.
defer os.RemoveAll(tempDir)
// Run "go build".
cmd := exec.Command(
output, err := cmd.CombinedOutput()
if err != nil {
return nil, fmt.Errorf(
"mount_sample exited with %v, output:\n%s",
// Slurp the tool contents.
contents, err := ioutil.ReadFile(toolPath)
if err != nil {
return nil, fmt.Errorf("ReadFile: %v", err)
return contents, nil
// Build the mount_sample tool if it has not yet been built for this process.
// Return its contents.
func getToolContents() ([]byte, error) {
// Get hold of the binary contents, if we haven't yet.
getToolContents_Once.Do(func() {
getToolContents_Contents, getToolContents_Err = getToolContentsImpl()
return getToolContents_Contents, getToolContents_Err
func waitForMountSample(
cmd *exec.Cmd,
errChan chan<- error,
stderr *bytes.Buffer) {
// However we exit, write the error to the channel.
var err error
defer func() {
errChan <- err
// Wait for the command.
err = cmd.Wait()
if err == nil {
// Make exit errors nicer.
if exitErr, ok := err.(*exec.ExitError); ok {
err = fmt.Errorf(
"mount_sample exited with %v. Stderr:\n%s",
err = fmt.Errorf("Waiting for mount_sample: %v", err)
func waitForReady(readyReader *os.File, c chan<- struct{}) {
_, err := readyReader.Read(make([]byte, 1))
if err != nil {
log.Printf("Readying from ready pipe: %v", err)
c <- struct{}{}
// Like SetUp, but doens't panic.
func (t *SubprocessTest) initialize(ctx context.Context) error {
// Initialize the context.
t.Ctx = ctx
// Set up a temporary directory.
var err error
t.Dir, err = ioutil.TempDir("", "sample_test")
if err != nil {
return fmt.Errorf("TempDir: %v", err)
// Build/read the mount_sample tool.
toolContents, err := getToolContents()
if err != nil {
return fmt.Errorf("getTooltoolContents: %v", err)
// Create a temporary file to hold the contents of the tool.
toolFile, err := ioutil.TempFile("", "sample_test")
if err != nil {
return fmt.Errorf("TempFile: %v", err)
defer toolFile.Close()
// Ensure that it is deleted when we leave.
toolPath := toolFile.Name()
defer os.Remove(toolPath)
// Write out the tool contents and make them executable.
if _, err = toolFile.Write(toolContents); err != nil {
return fmt.Errorf("toolFile.Write: %v", err)
if err = toolFile.Chmod(0500); err != nil {
return fmt.Errorf("toolFile.Chmod: %v", err)
// Close the tool file to prevent "text file busy" errors below.
err = toolFile.Close()
toolFile = nil
if err != nil {
return fmt.Errorf("toolFile.Close: %v", err)
// Set up basic args for the subprocess.
args := []string{
args = append(args, t.MountFlags...)
// Set up a pipe for the "ready" status.
readyReader, readyWriter, err := os.Pipe()
if err != nil {
return fmt.Errorf("Pipe: %v", err)
defer readyReader.Close()
defer readyWriter.Close()
t.MountFiles["ready_file"] = readyWriter
// Set up inherited files and appropriate flags.
var extraFiles []*os.File
for flag, file := range t.MountFiles {
// Cf. os/exec.Cmd.ExtraFiles
fd := 3 + len(extraFiles)
extraFiles = append(extraFiles, file)
args = append(args, "--"+flag)
args = append(args, fmt.Sprintf("%d", fd))
// Set up a command.
var stderr bytes.Buffer
mountCmd := exec.Command(toolPath, args...)
mountCmd.Stderr = &stderr
mountCmd.ExtraFiles = extraFiles
// Handle debug mode.
if *fDebug {
mountCmd.Stderr = os.Stderr
mountCmd.Args = append(mountCmd.Args, "--debug")
// Start the command.
if err := mountCmd.Start(); err != nil {
return fmt.Errorf("mountCmd.Start: %v", err)
// Launch a goroutine that waits for it and returns its status.
mountSampleErr := make(chan error, 1)
go waitForMountSample(mountCmd, mountSampleErr, &stderr)
// Wait for the tool to say the file system is ready. In parallel, watch for
// the tool to fail.
readyChan := make(chan struct{}, 1)
go waitForReady(readyReader, readyChan)
select {
case <-readyChan:
case err := <-mountSampleErr:
return err
// TearDown is no responsible for joining.
t.mountSampleErr = mountSampleErr
return nil
// Unmount the file system and clean up. Panics on error.
func (t *SubprocessTest) TearDown() {
err := t.destroy()
if err != nil {
// Like TearDown, but doesn't panic.
func (t *SubprocessTest) destroy() (err error) {
// Make sure we clean up after ourselves after everything else below.
// Close what is necessary.
for _, c := range t.ToClose {
if c == nil {
ogletest.ExpectEq(nil, c.Close())
// If we didn't try to mount the file system, there's nothing further to do.
if t.mountSampleErr == nil {
return nil
// In the background, initiate an unmount.
unmountErrChan := make(chan error)
go func() {
unmountErrChan <- unmount(t.Dir)
// Make sure we wait for the unmount, even if we've already returned early in
// error. Return its error if we haven't seen any other error.
defer func() {
// Wait.
unmountErr := <-unmountErrChan
if unmountErr != nil {
if err != nil {
log.Println("unmount:", unmountErr)
err = fmt.Errorf("unmount: %v", unmountErr)
// Clean up.
ogletest.ExpectEq(nil, os.Remove(t.Dir))
// Wait for the subprocess.
if err := <-t.mountSampleErr; err != nil {
return err
return nil