Test for runTerraformCmd leaked go-routine (hashicorp#299)

* Update TestContext_sleepTimeoutExpired to check for canceling within timeframe

Add a timeout to the test to ensure that the terraform apply cancels within
a reasonable time of the 5s timeout.

Currently, this test is not canceling the terraform apply as expected. In the
logs you can see that the test takes 1 min rather than ~5s:
```
    --- PASS: TestContext_sleepTimeoutExpired/sleep-0.12.31 (62.13s)
```

```
=== RUN   TestContext_sleepTimeoutExpired/sleep-0.12.31
    util_test.go:113: [INFO] running Terraform command: /var/folders/6y/gy9gggt14379c_k39vwb50lc0000gn/T/terraform_1378921380/terraform apply -no-color -auto-approve -input=false -lock=true -parallelism=10 -refresh=true
    util_test.go:103: CLI Output:
	    // truncated ...
        time_sleep.sleep: Creating...
        time_sleep.sleep: Still creating... [10s elapsed]
        time_sleep.sleep: Still creating... [20s elapsed]
        time_sleep.sleep: Still creating... [30s elapsed]
        time_sleep.sleep: Still creating... [41s elapsed]
        time_sleep.sleep: Still creating... [51s elapsed]
        time_sleep.sleep: Creation complete after 1m0s [id=2022-05-06T17:40:20Z]

        Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
```

* Remove runTerraformCmd check for cmd.ProcessState

Processes were not being killed because cmd.ProcessState was nil. With this
change, processes will be able to make the request to Kill().

Added a temporary log to printout cmd.ProcessState to demonstrate. Will be
removed in next commit.

Note: this will cause hanging `TestContext_sleepTimeoutExpired` due to a known
Golang issue with killing a command when Stdout or Stderr are set to anything
besides `nil` or `*os.File`. This is because the Kill does not notify the
stdout/stderr subprocesses to stop. `cmd.Wait` (called by `cmd.Run`) waits
indefinitely for those subprocesses to stop.

* Read logs from Stderr/out Pipe to avoid hanging

`TestContext_sleepTimeoutExpired` can occasionally hang when killing a command
that has Stdout or Stderr set to anything besides `nil` or `*os.File`.
golang/go#23019

Use workaround to read from StdoutPipe and StderrPipe rather than setting
Stdout / Stderr

* Test for runTerraformCmd leaked go-routine

Currently, when runTerraformCmd is called, it starts a go-routine to kill the
Terraform CLI on context.Done(). However, when the Terraform CLI completes and
runTerraformCmd() finishes, the go-routine continues running unnecessarily.

If the caller cancels the context down the line, this will stop the go-routine
and it will log the error: "error from kill: os: process already finished" because
the Terraform CLI has already finished.

Added a test for this in cmd_default.go and cmd_linux.go. Have not tried it in
linux yet though.

When running with the race detector:
```
==================
WARNING: DATA RACE
Read at 0x00c0002516c8 by goroutine 7:
  bytes.(*Buffer).String()
      /usr/local/go/src/bytes/buffer.go:65 +0x36a
  github.com/hashicorp/terraform-exec/tfexec.Test_runTerraformCmd_default()
      /Users/lornasong/go/src/github.com/hashicorp/terraform-exec/tfexec/cmd_default_test.go:35 +0x360
  testing.tRunner()
  // truncated ...

Previous write at 0x00c0002516c8 by goroutine 8:
  bytes.(*Buffer).grow()
      /usr/local/go/src/bytes/buffer.go:147 +0x3b1
  bytes.(*Buffer).Write()
      /usr/local/go/src/bytes/buffer.go:172 +0xcd
  log.(*Logger).Output()
      /usr/local/go/src/log/log.go:184 +0x466
  log.(*Logger).Printf()
      /usr/local/go/src/log/log.go:191 +0x6e
  github.com/hashicorp/terraform-exec/tfexec.(*Terraform).runTerraformCmd.func1()
      /Users/lornasong/go/src/github.com/hashicorp/terraform-exec/tfexec/cmd_default.go:24 +0x2a5
  // truncated ...
==================

* Use CommandContext to kill instead of manually doing it

* Fix EOF error check to use error.Is()

This also fixes a race condition caused by using the pointer to the io.EOF

* Update tests to use separate string.Builder-s for stdout and stderr

string.Builder is a non-comparable type which is not safe for concurrent use
when shared by Cmd.Stdout and Cmd.Stderr. Causes a race condition when accessing
the the builder when Cmd is running.

* Fixes to runTerraformCmd for race conditions

 - Use waitgroups for more readability
 - Improve handling errors from writeOutput
 - Finish reading from pipes before calling cmd.Wait - fixes a race condition
 that leads to an error :`read |0: file already closed`
 - Because now waiting for pipes to finish reading, need to update waitGroup to
 close buf.Read on context cancel. Otherwise buf.Read blocks until next line
 before stopping. Causes TestContext_sleepTimeoutExpired takes a little too long
 to cancel (~20s)

Co-authored-by: Kyle Carberry <kyle@carberry.com>

tfexec/cmd.go

@@ -1,9 +1,11 @@
 package tfexec
 
 import (
+	"bufio"
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -170,7 +172,7 @@ func (tf *Terraform) buildEnv(mergeEnv map[string]string) []string {
 }
 
 func (tf *Terraform) buildTerraformCmd(ctx context.Context, mergeEnv map[string]string, args ...string) *exec.Cmd {
-	cmd := exec.Command(tf.execPath, args...)
+	cmd := exec.CommandContext(ctx, tf.execPath, args...)
 
 	cmd.Env = tf.buildEnv(mergeEnv)
 	cmd.Dir = tf.workingDir
@@ -229,3 +231,36 @@ func mergeWriters(writers ...io.Writer) io.Writer {
 	}
 	return io.MultiWriter(compact...)
 }
+
+func writeOutput(ctx context.Context, r io.ReadCloser, w io.Writer) error {
+	// ReadBytes will block until bytes are read, which can cause a delay in
+	// returning even if the command's context has been canceled. Use a separate
+	// goroutine to prompt ReadBytes to return on cancel
+	closeCtx, closeCancel := context.WithCancel(ctx)
+	defer closeCancel()
+	go func() {
+		select {
+		case <-ctx.Done():
+			r.Close()
+		case <-closeCtx.Done():
+			return
+		}
+	}()
+
+	buf := bufio.NewReader(r)
+	for {
+		line, err := buf.ReadBytes('\n')
+		if len(line) > 0 {
+			if _, err := w.Write(line); err != nil {
+				return err
+			}
+		}
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				return nil
+			}
+
+			return err
+		}
+	}
+}

tfexec/cmd_default.go

@@ -7,40 +7,79 @@ import (
 	"context"
 	"os/exec"
 	"strings"
+	"sync"
 )
 
 func (tf *Terraform) runTerraformCmd(ctx context.Context, cmd *exec.Cmd) error {
 	var errBuf strings.Builder
 
-	cmd.Stdout = mergeWriters(cmd.Stdout, tf.stdout)
-	cmd.Stderr = mergeWriters(cmd.Stderr, tf.stderr, &errBuf)
-
-	go func() {
-		<-ctx.Done()
-		if ctx.Err() == context.DeadlineExceeded || ctx.Err() == context.Canceled {
-			if cmd != nil && cmd.Process != nil && cmd.ProcessState != nil {
-				err := cmd.Process.Kill()
-				if err != nil {
-					tf.logger.Printf("error from kill: %s", err)
-				}
-			}
-		}
-	}()
-
 	// check for early cancellation
 	select {
 	case <-ctx.Done():
 		return ctx.Err()
 	default:
 	}
 
-	err := cmd.Run()
+	// Read stdout / stderr logs from pipe instead of setting cmd.Stdout and
+	// cmd.Stderr because it can cause hanging when killing the command
+	// https://github.com/golang/go/issues/23019
+	stdoutWriter := mergeWriters(cmd.Stdout, tf.stdout)
+	stderrWriter := mergeWriters(tf.stderr, &errBuf)
+
+	cmd.Stderr = nil
+	cmd.Stdout = nil
+
+	stdoutPipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+
+	stderrPipe, err := cmd.StderrPipe()
+	if err != nil {
+		return err
+	}
+
+	err = cmd.Start()
+	if err == nil && ctx.Err() != nil {
+		err = ctx.Err()
+	}
+	if err != nil {
+		return tf.wrapExitError(ctx, err, "")
+	}
+
+	var errStdout, errStderr error
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		errStdout = writeOutput(ctx, stdoutPipe, stdoutWriter)
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		errStderr = writeOutput(ctx, stderrPipe, stderrWriter)
+	}()
+
+	// Reads from pipes must be completed before calling cmd.Wait(). Otherwise
+	// can cause a race condition
+	wg.Wait()
+
+	err = cmd.Wait()
 	if err == nil && ctx.Err() != nil {
 		err = ctx.Err()
 	}
 	if err != nil {
 		return tf.wrapExitError(ctx, err, errBuf.String())
 	}
 
+	// Return error if there was an issue reading the std out/err
+	if errStdout != nil && ctx.Err() != nil {
+		return tf.wrapExitError(ctx, errStdout, errBuf.String())
+	}
+	if errStderr != nil && ctx.Err() != nil {
+		return tf.wrapExitError(ctx, errStderr, errBuf.String())
+	}
+
 	return nil
 }

tfexec/cmd_default_test.go

@@ -0,0 +1,39 @@
+//go:build !linux
+// +build !linux
+
+package tfexec
+
+import (
+	"bytes"
+	"context"
+	"log"
+	"strings"
+	"testing"
+	"time"
+)
+
+func Test_runTerraformCmd_default(t *testing.T) {
+	// Checks runTerraformCmd for race condition when using
+	// go test -race -run Test_runTerraformCmd_default ./tfexec
+	var buf bytes.Buffer
+
+	tf := &Terraform{
+		logger:   log.New(&buf, "", 0),
+		execPath: "echo",
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	cmd := tf.buildTerraformCmd(ctx, nil, "hello tf-exec!")
+	err := tf.runTerraformCmd(ctx, cmd)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Cancel stops the leaked go routine which logs an error
+	cancel()
+	time.Sleep(time.Second)
+	if strings.Contains(buf.String(), "error from kill") {
+		t.Fatal("canceling context should not lead to logging an error")
+	}
+}

tfexec/cmd_linux.go

@@ -4,51 +4,87 @@ import (
 	"context"
 	"os/exec"
 	"strings"
+	"sync"
 	"syscall"
 )
 
 func (tf *Terraform) runTerraformCmd(ctx context.Context, cmd *exec.Cmd) error {
 	var errBuf strings.Builder
 
-	cmd.Stdout = mergeWriters(cmd.Stdout, tf.stdout)
-	cmd.Stderr = mergeWriters(cmd.Stderr, tf.stderr, &errBuf)
-
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		// kill children if parent is dead
 		Pdeathsig: syscall.SIGKILL,
 		// set process group ID
 		Setpgid: true,
 	}
 
-	go func() {
-		<-ctx.Done()
-		if ctx.Err() == context.DeadlineExceeded || ctx.Err() == context.Canceled {
-			if cmd != nil && cmd.Process != nil && cmd.ProcessState != nil {
-				// send SIGINT to process group
-				err := syscall.Kill(-cmd.Process.Pid, syscall.SIGINT)
-				if err != nil {
-					tf.logger.Printf("error from SIGINT: %s", err)
-				}
-			}
-
-			// TODO: send a kill if it doesn't respond for a bit?
-		}
-	}()
-
 	// check for early cancellation
 	select {
 	case <-ctx.Done():
 		return ctx.Err()
 	default:
 	}
 
-	err := cmd.Run()
+	// Read stdout / stderr logs from pipe instead of setting cmd.Stdout and
+	// cmd.Stderr because it can cause hanging when killing the command
+	// https://github.com/golang/go/issues/23019
+	stdoutWriter := mergeWriters(cmd.Stdout, tf.stdout)
+	stderrWriter := mergeWriters(tf.stderr, &errBuf)
+
+	cmd.Stderr = nil
+	cmd.Stdout = nil
+
+	stdoutPipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+
+	stderrPipe, err := cmd.StderrPipe()
+	if err != nil {
+		return err
+	}
+
+	err = cmd.Start()
+	if err == nil && ctx.Err() != nil {
+		err = ctx.Err()
+	}
+	if err != nil {
+		return tf.wrapExitError(ctx, err, "")
+	}
+
+	var errStdout, errStderr error
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		errStdout = writeOutput(ctx, stdoutPipe, stdoutWriter)
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		errStderr = writeOutput(ctx, stderrPipe, stderrWriter)
+	}()
+
+	// Reads from pipes must be completed before calling cmd.Wait(). Otherwise
+	// can cause a race condition
+	wg.Wait()
+
+	err = cmd.Wait()
 	if err == nil && ctx.Err() != nil {
 		err = ctx.Err()
 	}
 	if err != nil {
 		return tf.wrapExitError(ctx, err, errBuf.String())
 	}
 
+	// Return error if there was an issue reading the std out/err
+	if errStdout != nil && ctx.Err() != nil {
+		return tf.wrapExitError(ctx, errStdout, errBuf.String())
+	}
+	if errStderr != nil && ctx.Err() != nil {
+		return tf.wrapExitError(ctx, errStderr, errBuf.String())
+	}
+
 	return nil
 }

tfexec/cmd_linux_test.go

@@ -0,0 +1,36 @@
+package tfexec
+
+import (
+	"bytes"
+	"context"
+	"log"
+	"strings"
+	"testing"
+	"time"
+)
+
+func Test_runTerraformCmd_linux(t *testing.T) {
+	// Checks runTerraformCmd for race condition when using
+	// go test -race -run Test_runTerraformCmd_linux ./tfexec -tags=linux
+	var buf bytes.Buffer
+
+	tf := &Terraform{
+		logger:   log.New(&buf, "", 0),
+		execPath: "echo",
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	cmd := tf.buildTerraformCmd(ctx, nil, "hello tf-exec!")
+	err := tf.runTerraformCmd(ctx, cmd)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Cancel stops the leaked go routine which logs an error
+	cancel()
+	time.Sleep(time.Second)
+	if strings.Contains(buf.String(), "error from kill") {
+		t.Fatal("canceling context should not lead to logging an error")
+	}
+}

tfexec/internal/e2etest/errors_test.go

@@ -205,13 +205,21 @@ func TestContext_sleepTimeoutExpired(t *testing.T) {
 		ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
 		defer cancel()
 
-		err = tf.Apply(ctx)
-		if err == nil {
-			t.Fatal("expected error, but didn't find one")
-		}
-
-		if !errors.Is(err, context.DeadlineExceeded) {
-			t.Fatalf("expected context.DeadlineExceeded, got %T %s", err, err)
+		errCh := make(chan error)
+		go func() {
+			err = tf.Apply(ctx)
+			if err != nil {
+				errCh <- err
+			}
+		}()
+
+		select {
+		case err := <-errCh:
+			if !errors.Is(err, context.DeadlineExceeded) {
+				t.Fatalf("expected context.DeadlineExceeded, got %T %s", err, err)
+			}
+		case <-time.After(time.Second * 10):
+			t.Fatal("terraform apply should have canceled and returned in ~5s")
 		}
 	})
 }

tfexec/internal/e2etest/util_test.go

@@ -102,16 +102,21 @@ func runTestVersions(t *testing.T, versions []string, fixtureName string, cb fun
 				}
 			}
 
-			var stdouterr strings.Builder
-			tf.SetStdout(&stdouterr)
-			tf.SetStderr(&stdouterr)
+			// Separate strings.Builder because it's not concurrent safe
+			var stdout strings.Builder
+			tf.SetStdout(&stdout)
+			var stderr strings.Builder
+			tf.SetStderr(&stderr)
 
 			tf.SetLogger(&testingPrintfer{t})
 
 			// TODO: capture panics here?
 			cb(t, runningVersion, tf)
 
-			t.Logf("CLI Output:\n%s", stdouterr.String())
+			t.Logf("CLI Output:\n%s", stdout.String())
+			if len(stderr.String()) > 0 {
+				t.Logf("CLI Error:\n%s", stderr.String())
+			}
 		})
 	}
 }