You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: tx.go
    path of file: ./repos/scan4all/vendor/go.etcd.io/bbolt
    
    the code of the file until where you have to start completion: package bbolt

import (
	"fmt"
	"io"
	"os"
	"sort"
	"strings"
	"sync/atomic"
	"time"
	"unsafe"
)

// txid represents the internal transaction identifier.
type txid uint64

// Tx represents a read-only or read/write transaction on the database.
// Read-only transactions can be used for retrieving values for keys and creating cursors.
// Read/write transactions can create and remove buckets and create and remove keys.
//
// IMPORTANT: You must commit or rollback transactions when you are done with
// them. Pages can not be reclaimed by the writer until no more transactions
// are using them. A long running read t
    
func (tx *Tx) WriteTo(w io.Writer) (n int64, err error) {
	// Attempt to open reader with WriteFlag
	f, err := tx.db.openFile(tx.db.path, os.O_RDONLY|tx.WriteFlag, 0)
	if err != nil {
		return 0, err
	}
	defer func() {
		if cerr := f.Close(); err == nil {
			err = cerr
		}
	}()

	// Generate a meta page. We use the same page data for both meta pages.
	buf := make([]byte, tx.db.pageSize)
	page := (*page)(unsafe.Pointer(&buf[0]))
	page.flags = metaPageFlag
	*page.meta() = *tx.meta

	// Write meta 0.
	page.id = 0
	page.meta().checksum = page.meta().sum64()
	nn, err := w.Write(buf)
	n += int64(nn)
	if err != nil {
		return n, fmt.Errorf("meta 0 copy: %s", err)
	}

	// Write meta 1 with a lower transaction id.
	page.id = 1
	page.meta().txid -= 1
	page.meta().checksum = page.meta().sum64()
	nn, err = w.Write(buf)
	n += int64(nn)
	if err != nil {
		return n, fmt.Errorf("meta 1 copy: %s", err)
	}

	// Move past the meta pages in the file.
	if _, err := f.Seek(int64(tx.db.pageSize*2), io.SeekStart); err != nil {
		return n, fmt.Errorf("seek: %s", err)
	}

	// Copy data pages.
	wn, err := io.CopyN(w, f, tx.Size()-int64(tx.db.pageSize*2))
	n += wn
	if err != nil {
		return n, err
	}

	return n, nil
}