Cancel taskrun using entrypoint binary

The cancellation of taskruns is now done through the entrypoint binary
through a new flag called 'cancel_file'. This removes the need for
deleting the pods to cancel a taskrun, allowing examination of the logs
on the pods from cancelled taskruns. Part of work on issue tektoncd#3238

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

cmd/entrypoint/main.go

@@ -17,6 +17,7 @@ limitations under the License.
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -51,6 +52,7 @@ var (
 	onError             = flag.String("on_error", "", "Set to \"continue\" to ignore an error and continue when a container terminates with a non-zero exit code."+
 		" Set to \"stopAndFail\" to declare a failure with a step error and stop executing the rest of the steps.")
 	stepMetadataDir = flag.String("step_metadata_dir", "", "If specified, create directory to store the step metadata e.g. /tekton/steps/<step-name>/")
+	cancelFile      = flag.String("cancel_file", "", "Path indicating task should be cancelled")
 )
 
 const (
@@ -60,7 +62,7 @@ const (
 
 func checkForBreakpointOnFailure(e entrypoint.Entrypointer, breakpointExitPostFile string) {
 	if e.BreakpointOnFailure {
-		if waitErr := e.Waiter.Wait(breakpointExitPostFile, false, false); waitErr != nil {
+		if waitErr := e.Waiter.Wait(context.Background(), breakpointExitPostFile, false, false); waitErr != nil {
 			log.Println("error occurred while waiting for " + breakpointExitPostFile + " : " + waitErr.Error())
 		}
 		// get exitcode from .breakpointexit
@@ -148,6 +150,7 @@ func main() {
 		BreakpointOnFailure: *breakpointOnFailure,
 		OnError:             *onError,
 		StepMetadataDir:     *stepMetadataDir,
+		CancelFile:          *cancelFile,
 	}
 
 	// Copy any creds injected by the controller into the $HOME directory of the current
@@ -156,7 +159,8 @@ func main() {
 		log.Printf("non-fatal error copying credentials: %q", err)
 	}
 
-	if err := e.Go(); err != nil {
+	ctx := context.Background()
+	if err := e.Go(ctx); err != nil {
 		breakpointExitPostFile := e.PostFile + breakpointExitSuffix
 		switch t := err.(type) {
 		case skipError:

cmd/entrypoint/waiter.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"fmt"
 	"os"
 	"time"
@@ -31,11 +32,17 @@ func (rw *realWaiter) setWaitPollingInterval(pollingInterval time.Duration) *rea
 //
 // If a file of the same name with a ".err" extension exists then this Wait
 // will end with a skipError.
-func (rw *realWaiter) Wait(file string, expectContent bool, breakpointOnFailure bool) error {
+func (rw *realWaiter) Wait(ctx context.Context, file string, expectContent bool, breakpointOnFailure bool) error {
 	if file == "" {
 		return nil
 	}
-	for ; ; time.Sleep(rw.waitPollingInterval) {
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-time.After(rw.waitPollingInterval):
+		}
+
 		if info, err := os.Stat(file); err == nil {
 			if !expectContent || info.Size() > 0 {
 				return nil

cmd/entrypoint/waiter_test.go

@@ -17,14 +17,16 @@ limitations under the License.
 package main
 
 import (
+	"context"
+	"errors"
 	"io/ioutil"
 	"os"
 	"strings"
 	"testing"
 	"time"
 )
 
-const testWaitPollingInterval = 10 * time.Millisecond
+const testWaitPollingInterval = 25 * time.Millisecond
 
 func TestRealWaiterWaitMissingFile(t *testing.T) {
 	// Create a temp file and then immediately delete it to get
@@ -37,8 +39,9 @@ func TestRealWaiterWaitMissingFile(t *testing.T) {
 	os.Remove(tmp.Name())
 	rw := realWaiter{}
 	doneCh := make(chan struct{})
+	ctx := context.Background()
 	go func() {
-		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(tmp.Name(), false, false)
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, tmp.Name(), false, false)
 		if err != nil {
 			t.Errorf("error waiting on tmp file %q", tmp.Name())
 		}
@@ -65,8 +68,9 @@ func TestRealWaiterWaitWithFile(t *testing.T) {
 	defer os.Remove(tmp.Name())
 	rw := realWaiter{}
 	doneCh := make(chan struct{})
+	ctx := context.Background()
 	go func() {
-		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(tmp.Name(), false, false)
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, tmp.Name(), false, false)
 		if err != nil {
 			t.Errorf("error waiting on tmp file %q", tmp.Name())
 		}
@@ -89,8 +93,9 @@ func TestRealWaiterWaitMissingContent(t *testing.T) {
 	defer os.Remove(tmp.Name())
 	rw := realWaiter{}
 	doneCh := make(chan struct{})
+	ctx := context.Background()
 	go func() {
-		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(tmp.Name(), true, false)
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, tmp.Name(), true, false)
 		if err != nil {
 			t.Errorf("error waiting on tmp file %q", tmp.Name())
 		}
@@ -116,8 +121,9 @@ func TestRealWaiterWaitWithContent(t *testing.T) {
 	defer os.Remove(tmp.Name())
 	rw := realWaiter{}
 	doneCh := make(chan struct{})
+	ctx := context.Background()
 	go func() {
-		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(tmp.Name(), true, false)
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, tmp.Name(), true, false)
 		if err != nil {
 			t.Errorf("error waiting on tmp file %q", tmp.Name())
 		}
@@ -144,9 +150,10 @@ func TestRealWaiterWaitWithErrorWaitfile(t *testing.T) {
 	defer os.Remove(tmp.Name())
 	rw := realWaiter{}
 	doneCh := make(chan struct{})
+	ctx := context.Background()
 	go func() {
 		// error of type skipError is returned after encountering a error waitfile
-		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(tmpFileName, false, false)
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, tmpFileName, false, false)
 		if err == nil {
 			t.Errorf("expected skipError upon encounter error waitfile")
 		}
@@ -175,9 +182,10 @@ func TestRealWaiterWaitWithBreakpointOnFailure(t *testing.T) {
 	defer os.Remove(tmp.Name())
 	rw := realWaiter{}
 	doneCh := make(chan struct{})
+	ctx := context.Background()
 	go func() {
 		// When breakpoint on failure is enabled skipError shouldn't be returned for a error waitfile
-		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(tmpFileName, false, true)
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, tmpFileName, false, true)
 		if err != nil {
 			t.Errorf("error waiting on tmp file %q", tmp.Name())
 		}
@@ -191,3 +199,49 @@ func TestRealWaiterWaitWithBreakpointOnFailure(t *testing.T) {
 		t.Errorf("expected Wait() to have detected a non-zero file size by now")
 	}
 }
+
+func TestRealWaiterWaitWithCancel(t *testing.T) {
+	rw := realWaiter{}
+	doneCh := make(chan struct{})
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go func() {
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, "does_not_exist", true, false)
+		if err != nil && !errors.Is(err, context.Canceled) {
+			t.Error("error waiting")
+		}
+		close(doneCh)
+	}()
+	time.Sleep(testWaitPollingInterval)
+	cancel()
+
+	select {
+	case <-doneCh:
+		// Success
+	case <-time.After(2 * testWaitPollingInterval):
+		t.Errorf("expected Wait() to have exited by now")
+	}
+}
+
+func TestRealWaiterWaitWithDeadline(t *testing.T) {
+	rw := realWaiter{}
+	doneCh := make(chan struct{})
+	ctx, cancel := context.WithTimeout(context.Background(), testWaitPollingInterval)
+	defer cancel()
+	go func() {
+		err := rw.setWaitPollingInterval(testWaitPollingInterval).Wait(ctx, "does_not_exist", true, false)
+		if err != nil && !errors.Is(err, context.DeadlineExceeded) {
+			t.Error("error waiting")
+		}
+		close(doneCh)
+	}()
+	time.Sleep(2 * testWaitPollingInterval)
+	cancel()
+
+	select {
+	case <-doneCh:
+		// Success
+	case <-time.After(2 * testWaitPollingInterval):
+		t.Errorf("expected Wait() to have exited by now")
+	}
+}

pkg/entrypoint/entrypointer.go

@@ -80,12 +80,15 @@ type Entrypointer struct {
 	OnError string
 	// StepMetadataDir is the directory for a step where the step related metadata can be stored
 	StepMetadataDir string
+
+	// CancelFile is the file that causes the task to be cancelled.
+	CancelFile string
 }
 
 // Waiter encapsulates waiting for files to exist.
 type Waiter interface {
 	// Wait blocks until the specified file exists.
-	Wait(file string, expectContent bool, breakpointOnFailure bool) error
+	Wait(ctx context.Context, file string, expectContent bool, breakpointOnFailure bool) error
 }
 
 // Runner encapsulates running commands.
@@ -101,7 +104,7 @@ type PostWriter interface {
 
 // Go optionally waits for a file, runs the command, and writes a
 // post file.
-func (e Entrypointer) Go() error {
+func (e Entrypointer) Go(ctx context.Context) error {
 	prod, _ := zap.NewProduction()
 	logger := prod.Sugar()
 
@@ -114,7 +117,7 @@ func (e Entrypointer) Go() error {
 	}()
 
 	for _, f := range e.WaitFiles {
-		if err := e.Waiter.Wait(f, e.WaitFileContent, e.BreakpointOnFailure); err != nil {
+		if err := e.Waiter.Wait(ctx, f, e.WaitFileContent, e.BreakpointOnFailure); err != nil {
 			// An error happened while waiting, so we bail
 			// *but* we write postfile to make next steps bail too.
 			// In case of breakpoint on failure do not write post file.
@@ -142,19 +145,46 @@ func (e Entrypointer) Go() error {
 	}
 
 	if err == nil {
-		ctx := context.Background()
 		var cancel context.CancelFunc
 		if e.Timeout != nil && *e.Timeout != time.Duration(0) {
 			ctx, cancel = context.WithTimeout(ctx, *e.Timeout)
-			defer cancel()
+		} else {
+			ctx, cancel = context.WithCancel(ctx)
+		}
+		defer cancel()
+
+		errChan := make(chan error, 1)
+		go func() {
+			errChan <- e.Runner.Run(ctx, e.Command...)
+			cancel()
+		}()
+
+		var cancelled bool
+		if e.CancelFile != "" {
+			if err := e.Waiter.Wait(ctx, e.CancelFile, true, e.BreakpointOnFailure); err != nil {
+				return err
+			}
+			if ctx.Err() == nil {
+				cancel()
+				cancelled = true
+			}
 		}
-		err = e.Runner.Run(ctx, e.Command...)
+		err = <-errChan
+
 		if err == context.DeadlineExceeded {
 			output = append(output, v1beta1.PipelineResourceResult{
 				Key:        "Reason",
 				Value:      "TimeoutExceeded",
 				ResultType: v1beta1.InternalTektonResultType,
 			})
+		} else if cancelled {
+			// Waiter has found the cancel file: Cancel the run
+			cancel()
+			output = append(output, v1beta1.PipelineResourceResult{
+				Key:        "Reason",
+				Value:      "Cancelled",
+				ResultType: v1beta1.InternalTektonResultType,
+			})
 		}
 	}