pkg/signal: move signal.DumpStacks() to a separate package

It is not directly related to signal-handling, so can well live
in its own package.

Also added a variant that doesn't take a directory to write files
to, for easier consumption / better match to how it's used.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/cluster/cluster.go

@@ -54,7 +54,7 @@ import (
 	"github.com/docker/docker/daemon/cluster/controllers/plugin"
 	executorpkg "github.com/docker/docker/daemon/cluster/executor"
 	lncluster "github.com/docker/docker/libnetwork/cluster"
-	"github.com/docker/docker/pkg/signal"
+	"github.com/docker/docker/pkg/stack"
 	swarmapi "github.com/docker/swarmkit/api"
 	swarmnode "github.com/docker/swarmkit/node"
 	"github.com/pkg/errors"
@@ -393,7 +393,7 @@ func (c *Cluster) Cleanup() {
 
 	if err := node.Stop(); err != nil {
 		logrus.Errorf("failed to shut down cluster node: %v", err)
-		signal.DumpStacks("")
+		stack.Dump()
 	}
 
 	c.mu.Lock()

daemon/cluster/swarm.go

@@ -13,7 +13,7 @@ import (
 	"github.com/docker/docker/daemon/cluster/convert"
 	"github.com/docker/docker/errdefs"
 	"github.com/docker/docker/opts"
-	"github.com/docker/docker/pkg/signal"
+	"github.com/docker/docker/pkg/stack"
 	swarmapi "github.com/docker/swarmkit/api"
 	"github.com/docker/swarmkit/manager/encryption"
 	swarmnode "github.com/docker/swarmkit/node"
@@ -399,7 +399,7 @@ func (c *Cluster) Leave(force bool) error {
 	// release readers in here
 	if err := nr.Stop(); err != nil {
 		logrus.Errorf("failed to shut down cluster node: %v", err)
-		signal.DumpStacks("")
+		stack.Dump()
 		return err
 	}
 

daemon/debugtrap_unix.go

@@ -6,7 +6,7 @@ import (
 	"os"
 	"os/signal"
 
-	stackdump "github.com/docker/docker/pkg/signal"
+	"github.com/docker/docker/pkg/stack"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 )
@@ -16,7 +16,7 @@ func (daemon *Daemon) setupDumpStackTrap(root string) {
 	signal.Notify(c, unix.SIGUSR1)
 	go func() {
 		for range c {
-			path, err := stackdump.DumpStacks(root)
+			path, err := stack.DumpToFile(root)
 			if err != nil {
 				logrus.WithError(err).Error("failed to write goroutines dump")
 			} else {

daemon/debugtrap_windows.go

@@ -5,7 +5,7 @@ import (
 	"os"
 	"unsafe"
 
-	"github.com/docker/docker/pkg/signal"
+	"github.com/docker/docker/pkg/stack"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/windows"
 )
@@ -34,7 +34,7 @@ func (daemon *Daemon) setupDumpStackTrap(root string) {
 		logrus.Debugf("Stackdump - waiting signal at %s", event)
 		for {
 			windows.WaitForSingleObject(h, windows.INFINITE)
-			path, err := signal.DumpStacks(root)
+			path, err := stack.DumpToFile(root)
 			if err != nil {
 				logrus.WithError(err).Error("failed to write goroutines dump")
 			} else {

libnetwork/diagnostic/server.go

@@ -9,7 +9,7 @@ import (
 	"sync/atomic"
 
 	"github.com/docker/docker/libnetwork/internal/caller"
-	stackdump "github.com/docker/docker/pkg/signal"
+	"github.com/docker/docker/pkg/stack"
 	"github.com/sirupsen/logrus"
 )
 
@@ -169,7 +169,7 @@ func stackTrace(ctx interface{}, w http.ResponseWriter, r *http.Request) {
 	log := logrus.WithFields(logrus.Fields{"component": "diagnostic", "remoteIP": r.RemoteAddr, "method": caller.Name(0), "url": r.URL.String()})
 	log.Info("stack trace")
 
-	path, err := stackdump.DumpStacks("/tmp/")
+	path, err := stack.DumpToFile("/tmp/")
 	if err != nil {
 		log.WithError(err).Error("failed to write goroutines dump")
 		HTTPReply(w, FailCommand(err), json) // nolint:errcheck

pkg/signal/signal_deprecated.go

@@ -0,0 +1,8 @@
+package signal
+
+import "github.com/docker/docker/pkg/stack"
+
+// DumpStacks appends the runtime stack into file in dir and returns full path
+// to that file.
+// Deprecated: use github.com/docker/docker/pkg/stack.Dump instead.
+var DumpStacks = stack.DumpToFile

pkg/signal/trap.go

@@ -4,14 +4,10 @@ import (
 	"fmt"
 	"os"
 	gosignal "os/signal"
-	"path/filepath"
-	"runtime"
-	"strings"
 	"sync/atomic"
 	"syscall"
-	"time"
 
-	"github.com/pkg/errors"
+	"github.com/docker/docker/pkg/stack"
 )
 
 // Trap sets up a simplified signal "trap", appropriate for common
@@ -58,7 +54,7 @@ func Trap(cleanup func(), logger interface {
 						logger.Info("Forcing docker daemon shutdown without cleanup; 3 interrupts received")
 					}
 				case syscall.SIGQUIT:
-					DumpStacks("")
+					stack.Dump()
 					logger.Info("Forcing docker daemon shutdown without cleanup on SIGQUIT")
 				}
 				// for the SIGINT/TERM, and SIGQUIT non-clean shutdown case, exit with 128 + signal #
@@ -67,38 +63,3 @@ func Trap(cleanup func(), logger interface {
 		}
 	}()
 }
-
-const stacksLogNameTemplate = "goroutine-stacks-%s.log"
-
-// DumpStacks appends the runtime stack into file in dir and returns full path
-// to that file.
-func DumpStacks(dir string) (string, error) {
-	var (
-		buf       []byte
-		stackSize int
-	)
-	bufferLen := 16384
-	for stackSize == len(buf) {
-		buf = make([]byte, bufferLen)
-		stackSize = runtime.Stack(buf, true)
-		bufferLen *= 2
-	}
-	buf = buf[:stackSize]
-	var f *os.File
-	if dir != "" {
-		path := filepath.Join(dir, fmt.Sprintf(stacksLogNameTemplate, strings.Replace(time.Now().Format(time.RFC3339), ":", "", -1)))
-		var err error
-		f, err = os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0666)
-		if err != nil {
-			return "", errors.Wrap(err, "failed to open file to write the goroutine stacks")
-		}
-		defer f.Close()
-		defer f.Sync()
-	} else {
-		f = os.Stderr
-	}
-	if _, err := f.Write(buf); err != nil {
-		return "", errors.Wrap(err, "failed to write goroutine stacks")
-	}
-	return f.Name(), nil
-}

pkg/signal/trap_linux_test.go

@@ -64,20 +64,3 @@ func TestTrap(t *testing.T) {
 	}
 
 }
-
-func TestDumpStacks(t *testing.T) {
-	directory, err := ioutil.TempDir("", "test-dump-tasks")
-	assert.Check(t, err)
-	defer os.RemoveAll(directory)
-	dumpPath, err := DumpStacks(directory)
-	assert.Check(t, err)
-	readFile, _ := ioutil.ReadFile(dumpPath)
-	fileData := string(readFile)
-	assert.Check(t, is.Contains(fileData, "goroutine"))
-}
-
-func TestDumpStacksWithEmptyInput(t *testing.T) {
-	path, err := DumpStacks("")
-	assert.Check(t, err)
-	assert.Check(t, is.Equal(os.Stderr.Name(), path))
-}

pkg/stack/stackdump.go

@@ -0,0 +1,57 @@
+package stack // import "github.com/docker/docker/pkg/stack"
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+const stacksLogNameTemplate = "goroutine-stacks-%s.log"
+
+// Dump outputs the runtime stack to os.StdErr.
+func Dump() {
+	_ = dump(os.Stderr)
+}
+
+// DumpToFile appends the runtime stack into a file named "goroutine-stacks-<timestamp>.log"
+// in dir and returns the full path to that file. If no directory name is
+// provided, it outputs to os.Stderr.
+func DumpToFile(dir string) (string, error) {
+	var f *os.File
+	if dir != "" {
+		path := filepath.Join(dir, fmt.Sprintf(stacksLogNameTemplate, strings.Replace(time.Now().Format(time.RFC3339), ":", "", -1)))
+		var err error
+		f, err = os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0666)
+		if err != nil {
+			return "", errors.Wrap(err, "failed to open file to write the goroutine stacks")
+		}
+		defer f.Close()
+		defer f.Sync()
+	} else {
+		f = os.Stderr
+	}
+	return f.Name(), dump(f)
+}
+
+func dump(f *os.File) error {
+	var (
+		buf       []byte
+		stackSize int
+	)
+	bufferLen := 16384
+	for stackSize == len(buf) {
+		buf = make([]byte, bufferLen)
+		stackSize = runtime.Stack(buf, true)
+		bufferLen *= 2
+	}
+	buf = buf[:stackSize]
+	if _, err := f.Write(buf); err != nil {
+		return errors.Wrap(err, "failed to write goroutine stacks")
+	}
+	return nil
+}

pkg/stack/stackdump_test.go

@@ -0,0 +1,31 @@
+package stack // import "github.com/docker/docker/pkg/stack"
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"gotest.tools/v3/assert"
+	is "gotest.tools/v3/assert/cmp"
+)
+
+func TestDump(t *testing.T) {
+	Dump()
+}
+
+func TestDumpToFile(t *testing.T) {
+	directory, err := ioutil.TempDir("", "test-dump-tasks")
+	assert.Check(t, err)
+	defer os.RemoveAll(directory)
+	dumpPath, err := DumpToFile(directory)
+	assert.Check(t, err)
+	readFile, _ := ioutil.ReadFile(dumpPath)
+	fileData := string(readFile)
+	assert.Check(t, is.Contains(fileData, "goroutine"))
+}
+
+func TestDumpToFileWithEmptyInput(t *testing.T) {
+	path, err := DumpToFile("")
+	assert.Check(t, err)
+	assert.Check(t, is.Equal(os.Stderr.Name(), path))
+}