minio/docs/bucket/versioning/xl-meta.go

// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package main

import (
	"bytes"
	"encoding/binary"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"

	"github.com/minio/cli"
	"github.com/tinylib/msgp/msgp"
)

func main() {
	app := cli.NewApp()
	app.Copyright = "MinIO, Inc."
	app.Usage = "xl.meta to JSON"
	app.HideVersion = true
	app.CustomAppHelpTemplate = `NAME:
  {{.Name}} - {{.Usage}}

USAGE:
  {{.Name}} {{if .VisibleFlags}}[FLAGS]{{end}} METAFILES...
{{if .VisibleFlags}}
GLOBAL FLAGS:
  {{range .VisibleFlags}}{{.}}
  {{end}}{{end}}
`

	app.HideHelpCommand = true

	app.Flags = []cli.Flag{
		cli.BoolFlag{
			Usage: "Print each file as a separate line without formatting",
			Name:  "ndjson",
		},
		cli.BoolFlag{
			Usage: "Display inline data keys and sizes",
			Name:  "data",
		},
	}

	app.Action = func(c *cli.Context) error {
		files := c.Args()
		if len(files) == 0 {
			// If no args, assume xl.meta
			files = []string{"xl.meta"}
		}
		for _, file := range files {
			var r io.Reader
			switch file {
			case "-":
				r = os.Stdin
			default:
				f, err := os.Open(file)
				if err != nil {
					return err
				}
				defer f.Close()
				r = f
			}

			b, err := ioutil.ReadAll(r)
			if err != nil {
				return err
			}
			b, _, minor, err := checkXL2V1(b)
			if err != nil {
				return err
			}

			buf := bytes.NewBuffer(nil)
			var data xlMetaInlineData
			switch minor {
			case 0:
				_, err = msgp.CopyToJSON(buf, bytes.NewBuffer(b))
				if err != nil {
					return err
				}
			case 1, 2:
				v, b, err := msgp.ReadBytesZC(b)
				if err != nil {
					return err
				}
				if _, nbuf, err := msgp.ReadUint32Bytes(b); err == nil {
					// Read metadata CRC (added in v2, ignore if not found)
					b = nbuf
				}

				_, err = msgp.CopyToJSON(buf, bytes.NewBuffer(v))
				if err != nil {
					return err
				}
				data = b
			default:
				return errors.New("unknown metadata version")
			}

			if c.Bool("data") {
				b, err := data.json()
				if err != nil {
					return err
				}
				buf = bytes.NewBuffer(b)
			}
			if c.Bool("ndjson") {
				fmt.Println(buf.String())
				continue
			}
			var msi map[string]interface{}
			dec := json.NewDecoder(buf)
			// Use number to preserve integers.
			dec.UseNumber()
			err = dec.Decode(&msi)
			if err != nil {
				return err
			}
			b, err = json.MarshalIndent(msi, "", "  ")
			if err != nil {
				return err
			}
			fmt.Println(string(b))
		}
		return nil
	}
	err := app.Run(os.Args)
	if err != nil {
		log.Fatal(err)
	}
}

var (
	// XL header specifies the format
	xlHeader = [4]byte{'X', 'L', '2', ' '}

	// Current version being written.
	xlVersionCurrent [4]byte
)

const (
	// Breaking changes.
	// Newer versions cannot be read by older software.
	// This will prevent downgrades to incompatible versions.
	xlVersionMajor = 1

	// Non breaking changes.
	// Bumping this is informational, but should be done
	// if any change is made to the data stored, bumping this
	// will allow to detect the exact version later.
	xlVersionMinor = 1
)

func init() {
	binary.LittleEndian.PutUint16(xlVersionCurrent[0:2], xlVersionMajor)
	binary.LittleEndian.PutUint16(xlVersionCurrent[2:4], xlVersionMinor)
}

// checkXL2V1 will check if the metadata has correct header and is a known major version.
// The remaining payload and versions are returned.
func checkXL2V1(buf []byte) (payload []byte, major, minor uint16, err error) {
	if len(buf) <= 8 {
		return payload, 0, 0, fmt.Errorf("xlMeta: no data")
	}

	if !bytes.Equal(buf[:4], xlHeader[:]) {
		return payload, 0, 0, fmt.Errorf("xlMeta: unknown XLv2 header, expected %v, got %v", xlHeader[:4], buf[:4])
	}

	if bytes.Equal(buf[4:8], []byte("1   ")) {
		// Set as 1,0.
		major, minor = 1, 0
	} else {
		major, minor = binary.LittleEndian.Uint16(buf[4:6]), binary.LittleEndian.Uint16(buf[6:8])
	}
	if major > xlVersionMajor {
		return buf[8:], major, minor, fmt.Errorf("xlMeta: unknown major version %d found", major)
	}

	return buf[8:], major, minor, nil
}

const xlMetaInlineDataVer = 1

type xlMetaInlineData []byte

// afterVersion returns the payload after the version, if any.
func (x xlMetaInlineData) afterVersion() []byte {
	if len(x) == 0 {
		return x
	}
	return x[1:]
}

// versionOK returns whether the version is ok.
func (x xlMetaInlineData) versionOK() bool {
	if len(x) == 0 {
		return true
	}
	return x[0] > 0 && x[0] <= xlMetaInlineDataVer
}

func (x xlMetaInlineData) json() ([]byte, error) {
	if len(x) == 0 {
		return []byte("{}"), nil
	}
	if !x.versionOK() {
		return nil, errors.New("xlMetaInlineData: unknown version")
	}

	sz, buf, err := msgp.ReadMapHeaderBytes(x.afterVersion())
	if err != nil {
		return nil, err
	}
	res := []byte("{")

	for i := uint32(0); i < sz; i++ {
		var key, val []byte
		key, buf, err = msgp.ReadMapKeyZC(buf)
		if err != nil {
			return nil, err
		}
		if len(key) == 0 {
			return nil, fmt.Errorf("xlMetaInlineData: key %d is length 0", i)
		}
		// Skip data...
		val, buf, err = msgp.ReadBytesZC(buf)
		if err != nil {
			return nil, err
		}
		if i > 0 {
			res = append(res, ',')
		}
		s := fmt.Sprintf(`"%s":%d`, string(key), len(val))
		res = append(res, []byte(s)...)
	}
	res = append(res, '}')
	return res, nil
}