github.com/grailbio/base@v0.0.11/fatbin/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 fatbin
     6  
     7  import (
     8  	"encoding/binary"
     9  	"errors"
    10  	"io"
    11  
    12  	"github.com/cespare/xxhash"
    13  )
    14  
    15  const (
    16  	magic    uint32 = 0x5758ba2c
    17  	headersz        = 20
    18  )
    19  
    20  var (
    21  	errNoFooter = errors.New("binary contains no footer")
    22  
    23  	bin = binary.LittleEndian
    24  )
    25  
    26  func writeFooter(w io.Writer, offset int64) (int, error) {
    27  	var p [headersz]byte
    28  	bin.PutUint64(p[:8], uint64(offset))
    29  	bin.PutUint32(p[8:12], magic)
    30  	bin.PutUint64(p[12:20], xxhash.Sum64(p[:12]))
    31  	return w.Write(p[:])
    32  }
    33  
    34  func readFooter(r io.ReaderAt, size int64) (offset int64, err error) {
    35  	if size < headersz {
    36  		return 0, errNoFooter
    37  	}
    38  	var p [headersz]byte
    39  	_, err = r.ReadAt(p[:], size-headersz)
    40  	if err != nil {
    41  		return 0, err
    42  	}
    43  	if bin.Uint32(p[8:12]) != magic {
    44  		return 0, errNoFooter
    45  	}
    46  	offset = int64(bin.Uint64(p[:8]))
    47  	if xxhash.Sum64(p[:12]) != bin.Uint64(p[12:20]) {
    48  		return 0, ErrCorruptedImage
    49  	}
    50  	return
    51  }