github.com/kubiko/snapd@v0.0.0-20201013125620-d4f3094d9ddf/bootloader/asset.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2020 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package bootloader
    21  
    22  import (
    23  	"bufio"
    24  	"bytes"
    25  	"errors"
    26  	"fmt"
    27  	"io"
    28  	"os"
    29  	"strconv"
    30  	"strings"
    31  
    32  	"github.com/snapcore/snapd/bootloader/assets"
    33  )
    34  
    35  var errNoEdition = errors.New("no edition")
    36  
    37  // editionFromDiskConfigAsset extracts the edition information from a boot
    38  // config asset on disk.
    39  func editionFromDiskConfigAsset(p string) (uint, error) {
    40  	f, err := os.Open(p)
    41  	if err != nil {
    42  		if os.IsNotExist(err) {
    43  			return 0, errNoEdition
    44  		}
    45  		return 0, fmt.Errorf("cannot load existing config asset: %v", err)
    46  	}
    47  	defer f.Close()
    48  	return editionFromConfigAsset(f)
    49  }
    50  
    51  const editionHeader = "# Snapd-Boot-Config-Edition: "
    52  
    53  // editionFromConfigAsset extracts edition information from boot config asset.
    54  func editionFromConfigAsset(asset io.Reader) (uint, error) {
    55  	scanner := bufio.NewScanner(asset)
    56  	if !scanner.Scan() {
    57  		err := fmt.Errorf("cannot read config asset: unexpected EOF")
    58  		if sErr := scanner.Err(); sErr != nil {
    59  			err = fmt.Errorf("cannot read config asset: %v", err)
    60  		}
    61  		return 0, err
    62  	}
    63  
    64  	line := scanner.Text()
    65  	if !strings.HasPrefix(line, editionHeader) {
    66  		return 0, errNoEdition
    67  	}
    68  
    69  	editionStr := line[len(editionHeader):]
    70  	editionStr = strings.TrimSpace(editionStr)
    71  	edition, err := strconv.ParseUint(editionStr, 10, 32)
    72  	if err != nil {
    73  		return 0, fmt.Errorf("cannot parse asset edition: %v", err)
    74  	}
    75  	return uint(edition), nil
    76  }
    77  
    78  // editionFromInternalConfigAsset extracts edition information from a named
    79  // internal boot config asset.
    80  func editionFromInternalConfigAsset(assetName string) (uint, error) {
    81  	data := assets.Internal(assetName)
    82  	if data == nil {
    83  		return 0, fmt.Errorf("internal error: no boot asset for %q", assetName)
    84  	}
    85  	return editionFromConfigAsset(bytes.NewReader(data))
    86  }
    87  
    88  // configAsset is a boot config asset, such as text script, used by grub or
    89  // u-boot.
    90  type configAsset struct {
    91  	body          []byte
    92  	parsedEdition uint
    93  }
    94  
    95  func (g *configAsset) Edition() uint {
    96  	return g.parsedEdition
    97  }
    98  
    99  func (g *configAsset) Raw() []byte {
   100  	return g.body
   101  }
   102  
   103  func configAssetFrom(data []byte) (*configAsset, error) {
   104  	edition, err := editionFromConfigAsset(bytes.NewReader(data))
   105  	if err != nil && err != errNoEdition {
   106  		return nil, err
   107  	}
   108  	gbs := &configAsset{
   109  		body:          data,
   110  		parsedEdition: edition,
   111  	}
   112  	return gbs, nil
   113  }