add 'surgery clear-page' command

Signed-off-by: Benjamin Wang <wachao@vmware.com>

cmd/bbolt/surgery_commands.go

@@ -45,6 +45,8 @@ func (cmd *surgeryCommand) Run(args ...string) error {
 		return newRevertMetaPageCommand(cmd).Run(args[1:]...)
 	case "copy-page":
 		return newCopyPageCommand(cmd).Run(args[1:]...)
+	case "clear-page":
+		return newClearPageCommand(cmd).Run(args[1:]...)
 	default:
 		return ErrUnknownCommand
 	}
@@ -225,7 +227,7 @@ func (cmd *copyPageCommand) Run(args ...string) error {
 		return fmt.Errorf("copyPageCommand failed: %w", err)
 	}
 
-	fmt.Fprintf(cmd.Stdout, "The page %d was copied to page %d", srcPageId, dstPageId)
+	fmt.Fprintf(cmd.Stdout, "The page %d was copied to page %d\n", srcPageId, dstPageId)
 	return nil
 }
 
@@ -241,3 +243,58 @@ at dstPageId in DST.
 The original database is left untouched.
 `, "\n")
 }
+
+// clearPageCommand represents the "surgery clear-page" command execution.
+type clearPageCommand struct {
+	*surgeryCommand
+}
+
+// newClearPageCommand returns a clearPageCommand.
+func newClearPageCommand(m *surgeryCommand) *clearPageCommand {
+	c := &clearPageCommand{}
+	c.surgeryCommand = m
+	return c
+}
+
+// Run executes the command.
+func (cmd *clearPageCommand) Run(args ...string) error {
+	// Parse flags.
+	fs := flag.NewFlagSet("", flag.ContinueOnError)
+	help := fs.Bool("h", false, "")
+	if err := fs.Parse(args); err != nil {
+		return err
+	} else if *help {
+		fmt.Fprintln(cmd.Stderr, cmd.Usage())
+		return ErrUsage
+	}
+
+	if err := cmd.parsePathsAndCopyFile(fs); err != nil {
+		return fmt.Errorf("clearPageCommand failed to parse paths and copy file: %w", err)
+	}
+
+	// Read page id.
+	pageId, err := strconv.ParseUint(fs.Arg(2), 10, 64)
+	if err != nil {
+		return err
+	}
+
+	if err := surgeon.ClearPage(cmd.dstPath, guts_cli.Pgid(pageId)); err != nil {
+		return fmt.Errorf("clearPageCommand failed: %w", err)
+	}
+
+	fmt.Fprintf(cmd.Stdout, "Page (%d) was cleared\n", pageId)
+	return nil
+}
+
+// Usage returns the help message.
+func (cmd *clearPageCommand) Usage() string {
+	return strings.TrimLeft(`
+usage: bolt surgery clear-page SRC DST pageId
+
+ClearPage copies the database file at SRC to a newly created database
+file at DST. Afterwards, it clears all elements in the page at pageId
+in DST.
+
+The original database is left untouched.
+`, "\n")
+}

cmd/bbolt/surgery_commands_test.go

@@ -70,7 +70,7 @@ func TestSurgery_CopyPage(t *testing.T) {
 
 	defer requireDBNoChange(t, dbData(t, srcPath), srcPath)
 
-	// revert the meta page
+	// copy page 3 to page 2
 	t.Log("copy page 3 to page 2")
 	dstPath := filepath.Join(t.TempDir(), "dstdb")
 	m := NewMain()
@@ -87,6 +87,39 @@ func TestSurgery_CopyPage(t *testing.T) {
 	assert.Equal(t, pageDataWithoutPageId(srcPageId3Data), pageDataWithoutPageId(dstPageId2Data))
 }
 
+// TODO(ahrtr): add test case below for `surgery clear-page` command:
+//  1. The page is a branch page. All its children should become free pages.
+func TestSurgery_ClearPage(t *testing.T) {
+	pageSize := 4096
+	db := btesting.MustCreateDBWithOption(t, &bolt.Options{PageSize: pageSize})
+	srcPath := db.Path()
+
+	// Insert some sample data
+	t.Log("Insert some sample data")
+	err := db.Fill([]byte("data"), 1, 20,
+		func(tx int, k int) []byte { return []byte(fmt.Sprintf("%04d", k)) },
+		func(tx int, k int) []byte { return make([]byte, 10) },
+	)
+	require.NoError(t, err)
+
+	defer requireDBNoChange(t, dbData(t, srcPath), srcPath)
+
+	// clear page 3
+	t.Log("clear page 3")
+	dstPath := filepath.Join(t.TempDir(), "dstdb")
+	m := NewMain()
+	err = m.Run("surgery", "clear-page", srcPath, dstPath, "3")
+	require.NoError(t, err)
+
+	// The page 2 should have exactly the same data as page 3.
+	t.Log("Verify result")
+	dstPageId3Data := readPage(t, dstPath, 3, pageSize)
+
+	p := guts_cli.LoadPage(dstPageId3Data)
+	assert.Equal(t, uint16(0), p.Count())
+	assert.Equal(t, uint32(0), p.Overflow())
+}
+
 func readPage(t *testing.T, path string, pageId int, pageSize int) []byte {
 	dbFile, err := os.Open(path)
 	require.NoError(t, err)

internal/guts_cli/guts_cli.go

@@ -139,6 +139,10 @@ func (p *Page) Overflow() uint32 {
 	return p.overflow
 }
 
+func (p *Page) String() string {
+	return fmt.Sprintf("ID: %d, Type: %s, count: %d, overflow: %d", p.id, p.Type(), p.count, p.overflow)
+}
+
 // DO NOT EDIT. Copied from the "bolt" package.
 
 // TODO(ptabor): Make the page-types an enum.
@@ -178,6 +182,14 @@ func (p *Page) SetId(target Pgid) {
 	p.id = target
 }
 
+func (p *Page) SetCount(target uint16) {
+	p.count = target
+}
+
+func (p *Page) SetOverflow(target uint32) {
+	p.overflow = target
+}
+
 // DO NOT EDIT. Copied from the "bolt" package.
 type BranchPageElement struct {
 	pos   uint32
@@ -276,6 +288,25 @@ func ReadPage(path string, pageID uint64) (*Page, []byte, error) {
 	return p, buf, nil
 }
 
+func WritePage(path string, pageBuf []byte) error {
+	page := LoadPage(pageBuf)
+	pageSize, _, err := ReadPageAndHWMSize(path)
+	if err != nil {
+		return err
+	}
+	expectedLen := pageSize * (uint64(page.Overflow()) + 1)
+	if expectedLen != uint64(len(pageBuf)) {
+		return fmt.Errorf("WritePage: len(buf):%d != pageSize*(overflow+1):%d", len(pageBuf), expectedLen)
+	}
+	f, err := os.OpenFile(path, os.O_WRONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = f.WriteAt(pageBuf, int64(page.Id())*int64(pageSize))
+	return err
+}
+
 // ReadPageAndHWMSize reads Page size and HWM (id of the last+1 Page).
 // This is not transactionally safe.
 func ReadPageAndHWMSize(path string) (uint64, Pgid, error) {

internal/surgeon/surgeon.go

@@ -2,8 +2,6 @@ package surgeon
 
 import (
 	"fmt"
-	"os"
-
 	"go.etcd.io/bbolt/internal/guts_cli"
 )
 
@@ -13,25 +11,24 @@ func CopyPage(path string, srcPage guts_cli.Pgid, target guts_cli.Pgid) error {
 		return err1
 	}
 	p1.SetId(target)
-	return WritePage(path, d1)
+	return guts_cli.WritePage(path, d1)
 }
 
-func WritePage(path string, pageBuf []byte) error {
-	page := guts_cli.LoadPage(pageBuf)
-	pageSize, _, err := guts_cli.ReadPageAndHWMSize(path)
+func ClearPage(path string, pgId guts_cli.Pgid) error {
+	// Read the page
+	p, buf, err := guts_cli.ReadPage(path, uint64(pgId))
 	if err != nil {
-		return err
+		return fmt.Errorf("ReadPage failed: %w", err)
 	}
-	if pageSize != uint64(len(pageBuf)) {
-		return fmt.Errorf("WritePage: len(buf)=%d != pageSize=%d", len(pageBuf), pageSize)
+
+	// Update and rewrite the page
+	p.SetCount(0)
+	p.SetOverflow(0)
+	if err := guts_cli.WritePage(path, buf); err != nil {
+		return fmt.Errorf("WritePage failed: %w", err)
 	}
-	f, err := os.OpenFile(path, os.O_WRONLY, 0)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-	_, err = f.WriteAt(pageBuf, int64(page.Id())*int64(pageSize))
-	return err
+
+	return nil
 }
 
 // RevertMetaPage replaces the newer metadata page with the older.

internal/tests/tx_check_test.go

@@ -69,7 +69,7 @@ func TestTx_RecursivelyCheckPages_CorruptedLeaf(t *testing.T) {
 	require.NoError(t, err)
 	require.Positive(t, p.Count(), "page must be not empty")
 	p.LeafPageElement(p.Count() / 2).Key()[0] = 'z'
-	require.NoError(t, surgeon.WritePage(db.Path(), pbuf))
+	require.NoError(t, guts_cli.WritePage(db.Path(), pbuf))
 
 	db.MustReopen()
 	require.NoError(t, db.Update(func(tx *bolt.Tx) error {