github.com/apptainer/singularity@v3.1.1+incompatible/pkg/image/reader.go (about)

     1  // Copyright (c) 2019, Sylabs Inc. All rights reserved.
     2  // This software is licensed under a 3-clause BSD license. Please consult the
     3  // LICENSE.md file distributed with the sources of this project regarding your
     4  // rights to use or distribute this software.
     5  
     6  package image
     7  
     8  import (
     9  	"fmt"
    10  	"io"
    11  	"os"
    12  )
    13  
    14  type readerError string
    15  
    16  func (e readerError) Error() string { return string(e) }
    17  
    18  const (
    19  	// ErrNoSection corresponds to an image section not found
    20  	ErrNoSection = readerError("no section found")
    21  	// ErrNoPartition corresponds to an image partition not found
    22  	ErrNoPartition = readerError("no partition found")
    23  )
    24  
    25  func checkImage(image *Image) error {
    26  	if image == nil {
    27  		return fmt.Errorf("image is nil")
    28  	}
    29  	if image.File == nil {
    30  		return fmt.Errorf("image is not open for read")
    31  	}
    32  	return nil
    33  }
    34  
    35  func getSectionReader(file *os.File, section Section) io.Reader {
    36  	return io.NewSectionReader(file, int64(section.Offset), int64(section.Size))
    37  }
    38  
    39  func commonSectionReader(partition bool, image *Image, name string, index int) (io.Reader, error) {
    40  	var err error
    41  
    42  	idx := -1
    43  	if err = checkImage(image); err != nil {
    44  		return nil, err
    45  	}
    46  
    47  	sectionName := "sections"
    48  	sections := image.Sections
    49  	err = ErrNoSection
    50  
    51  	if partition {
    52  		sectionName = "partitions"
    53  		sections = image.Partitions
    54  		err = ErrNoPartition
    55  	}
    56  
    57  	if index >= 0 {
    58  		l := len(sections)
    59  		if index > l-1 {
    60  			return nil, fmt.Errorf("index too large, image contains %d %s", l, sectionName)
    61  		}
    62  		idx = index
    63  	}
    64  	if name == "" && idx < 0 {
    65  		return nil, fmt.Errorf("no name or positive index provided")
    66  	}
    67  	for i, p := range sections {
    68  		if p.Name == name || i == idx {
    69  			return getSectionReader(image.File, p), nil
    70  		}
    71  	}
    72  	return nil, err
    73  }
    74  
    75  // NewPartitionReader searches and returns a reader for an image
    76  // partition identified by name or by index, if index is less than 0
    77  // only partition with provided name will be returned if a matching
    78  // entry is found
    79  func NewPartitionReader(image *Image, name string, index int) (io.Reader, error) {
    80  	return commonSectionReader(true, image, name, index)
    81  }
    82  
    83  // NewSectionReader searches and returns a reader for an image
    84  // section identified by name or by index, if index is less than 0
    85  // only section with provided name will be returned if a matching
    86  // entry is found
    87  func NewSectionReader(image *Image, name string, index int) (io.Reader, error) {
    88  	return commonSectionReader(false, image, name, index)
    89  }