Store the runhcs.exe path for faster invocation

pkg/go-runhcs/runhcs.go

@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 	"strings"
 	"sync"
+	"sync/atomic"
 
 	irunhcs "github.com/Microsoft/hcsshim/internal/runhcs"
 	"github.com/containerd/go-runc"
@@ -23,10 +24,35 @@ const (
 	Text Format = "text"
 	// JSON is the JSON formatted log output.
 	JSON Format = "json"
-
-	command = "runhcs"
 )
 
+var runhcsPath atomic.Value
+
+func getCommandPath() string {
+	const command = "runhcs.exe"
+
+	pathi := runhcsPath.Load()
+	if pathi == nil {
+		path, err := exec.LookPath(command)
+		if err != nil {
+			// Failed to look up command just use it directly and let the
+			// Windows loader find it.
+			path = command
+			runhcsPath.Store(path)
+			return path
+		}
+		apath, err := filepath.Abs(path)
+		if err != nil {
+			// We couldnt make `path` an `AbsPath`. Just use `path` directly and
+			// let the Windows loader find it.
+			apath = path
+		}
+		runhcsPath.Store(apath)
+		return apath
+	}
+	return pathi.(string)
+}
+
 var bytesBufferPool = sync.Pool{
 	New: func() interface{} {
 		return bytes.NewBuffer(nil)
@@ -84,7 +110,7 @@ func (r *Runhcs) args() []string {
 }
 
 func (r *Runhcs) command(context context.Context, args ...string) *exec.Cmd {
-	cmd := exec.CommandContext(context, command, append(r.args(), args...)...)
+	cmd := exec.CommandContext(context, getCommandPath(), append(r.args(), args...)...)
 	cmd.Env = os.Environ()
 	return cmd
 }

pkg/go-runhcs/runhcs_integration_test.go

@@ -0,0 +1,7 @@
+// +build runhcs_test
+
+package runhcs
+
+import (
+	_ "github.com/Microsoft/hcsshim/functional/manifest"
+)

pkg/go-runhcs/runhcs_test.go

@@ -1,7 +1,68 @@
-// +build runhcs_test
-
 package runhcs
 
 import (
-	_ "github.com/Microsoft/hcsshim/functional/manifest"
+	"os"
+	"path/filepath"
+	"sync/atomic"
+	"testing"
 )
+
+func resetRunhcsPath() {
+	runhcsPath = atomic.Value{}
+}
+
+func TestGetCommandPath_NoLookPath(t *testing.T) {
+	resetRunhcsPath()
+
+	path := getCommandPath()
+	if path != "runhcs.exe" {
+		t.Fatalf("expected path 'runhcs.exe' got '%s'", path)
+	}
+	pathi := runhcsPath.Load()
+	if pathi == nil {
+		t.Fatal("cache state should be set after first query")
+	}
+	if path != pathi.(string) {
+		t.Fatalf("expected: '%s' in cache got '%s'", path, pathi.(string))
+	}
+}
+
+func TestGetCommandPath_WithLookPath(t *testing.T) {
+	resetRunhcsPath()
+
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("failed to get cwd with err: %v", err)
+	}
+	fakePath := filepath.Join(wd, "runhcs.exe")
+	f, err := os.Create(fakePath)
+	if err != nil {
+		t.Fatalf("failed to create fake runhcs.exe in path with err: %v", err)
+	}
+	f.Close()
+	defer os.Remove(fakePath)
+
+	path := getCommandPath()
+	if path != fakePath {
+		t.Fatalf("expected fake path '%s' got '%s'", fakePath, path)
+	}
+	pathi := runhcsPath.Load()
+	if pathi == nil {
+		t.Fatal("cache state should be set after first query")
+	}
+	if path != pathi.(string) {
+		t.Fatalf("expected: '%s' in cache got '%s'", fakePath, pathi.(string))
+	}
+}
+
+func TestGetCommandPath_WithCache(t *testing.T) {
+	resetRunhcsPath()
+
+	value := "this is a test"
+	runhcsPath.Store(value)
+
+	path := getCommandPath()
+	if path != value {
+		t.Fatalf("expected fake cached path: '%s' got '%s'", value, path)
+	}
+}