github.com/Schaudge/grailbase@v0.0.0-20240223061707-44c758a471c0/embedbin/footer.go (about)

     1  // Copyright 2019 GRAIL, Inc. All rights reserved.
     2  // Use of this source code is governed by the Apache 2.0
     3  // license that can be found in the LICENSE file.
     4  
     5  package embedbin
     6  
     7  import (
     8  	"encoding/binary"
     9  	"errors"
    10  	"io"
    11  
    12  	"github.com/cespare/xxhash"
    13  )
    14  
    15  const magic uint32 = 0xec90a479
    16  const headersz = 20
    17  
    18  var (
    19  	errNoFooter = errors.New("binary contains no footer")
    20  
    21  	bin = binary.LittleEndian
    22  )
    23  
    24  func writeFooter(w io.Writer, offset int64) (int, error) {
    25  	var p [headersz]byte
    26  	bin.PutUint64(p[:8], uint64(offset))
    27  	bin.PutUint32(p[8:12], magic)
    28  	bin.PutUint64(p[12:20], xxhash.Sum64(p[:12]))
    29  	return w.Write(p[:])
    30  }
    31  
    32  func readFooter(r io.ReaderAt, size int64) (offset int64, err error) {
    33  	if size < headersz {
    34  		return 0, errNoFooter
    35  	}
    36  	var p [headersz]byte
    37  	_, err = r.ReadAt(p[:], size-headersz)
    38  	if err != nil {
    39  		return 0, err
    40  	}
    41  	if bin.Uint32(p[8:12]) != magic {
    42  		return 0, errNoFooter
    43  	}
    44  	offset = int64(bin.Uint64(p[:8]))
    45  	if xxhash.Sum64(p[:12]) != bin.Uint64(p[12:20]) {
    46  		return 0, ErrCorruptedImage
    47  	}
    48  	return
    49  }