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package guts_cli
// Low level access to pages / data-structures of the bbolt file.
import (
"errors"
"fmt"
"io"
"os"
"go.etcd.io/bbolt/internal/common"
)
var (
// ErrCorrupt is returned when a checking a data file finds errors.
ErrCorrupt = errors.New("invalid value")
)
// ReadPage reads Page info & full Page data from a path.
// This is not transactionally safe.
func ReadPage(path string, pageID uint64) (*common.Page, []byte, error) {
// Find Page size.
pageSize, hwm, err := ReadPageAndHWMSize(path)
if err != nil {
return nil, nil, fmt.Errorf("read Page size: %s", err)
}
// Open database file.
f, err := os.Open(path)
if err != nil {
return nil, nil, err
}
defer f.Close()
// Read one block into buffer.
buf := make([]byte, pageSize)
if n, err := f.ReadAt(buf, int64(pageID*pageSize)); err != nil {
return nil, nil, err
} else if n != len(buf) {
return nil, nil, io.ErrUnexpectedEOF
}
// Determine total number of blocks.
p := common.LoadPage(buf)
if p.Id() != common.Pgid(pageID) {
return nil, nil, fmt.Errorf("error: %w due to unexpected Page id: %d != %d", ErrCorrupt, p.Id(), pageID)
}
overflowN := p.Overflow()
if overflowN >= uint32(hwm)-3 { // we exclude 2 Meta pages and the current Page.
return nil, nil, fmt.Errorf("error: %w, Page claims to have %d overflow pages (>=hwm=%d). Interrupting to avoid risky OOM", ErrCorrupt, overflowN, hwm)
}
if overflowN == 0 {
return p, buf, nil
}
// Re-read entire Page (with overflow) into buffer.
buf = make([]byte, (uint64(overflowN)+1)*pageSize)
if n, err := f.ReadAt(buf, int64(pageID*pageSize)); err != nil {
return nil, nil, err
} else if n != len(buf) {
return nil, nil, io.ErrUnexpectedEOF
}
p = common.LoadPage(buf)
if p.Id() != common.Pgid(pageID) {
return nil, nil, fmt.Errorf("error: %w due to unexpected Page id: %d != %d", ErrCorrupt, p.Id(), pageID)
}
return p, buf, nil
}
func WritePage(path string, pageBuf []byte) error {
page := common.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, common.Pgid, error) {
// Open database file.
f, err := os.Open(path)
if err != nil {
return 0, 0, err
}
defer f.Close()
// Read 4KB chunk.
buf := make([]byte, 4096)
if _, err := io.ReadFull(f, buf); err != nil {
return 0, 0, err
}
// Read Page size from metadata.
m := common.LoadPageMeta(buf)
if m.Magic() != common.Magic {
return 0, 0, fmt.Errorf("the Meta Page has wrong (unexpected) magic")
}
return uint64(m.PageSize()), common.Pgid(m.Pgid()), nil
}
// GetRootPage returns the root-page (according to the most recent transaction).
func GetRootPage(path string) (root common.Pgid, activeMeta common.Pgid, err error) {
m, id, err := GetActiveMetaPage(path)
if err != nil {
return 0, id, err
}
return m.RootBucket().RootPage(), id, nil
}
// GetActiveMetaPage returns the active meta page and its page ID (0 or 1).
func GetActiveMetaPage(path string) (*common.Meta, common.Pgid, error) {
_, buf0, err0 := ReadPage(path, 0)
if err0 != nil {
return nil, 0, err0
}
m0 := common.LoadPageMeta(buf0)
_, buf1, err1 := ReadPage(path, 1)
if err1 != nil {
return nil, 1, err1
}
m1 := common.LoadPageMeta(buf1)
if m0.Txid() < m1.Txid() {
return m1, 1, nil
} else {
return m0, 0, nil
}
}
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