github.com/meulengracht/snapd@v0.0.0-20210719210640-8bde69bcc84e/osutil/digest.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2016 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 osutil
    21  
    22  import (
    23  	"crypto"
    24  	"io"
    25  	"os"
    26  )
    27  
    28  const (
    29  	hashDigestBufSize = 2 * 1024 * 1024
    30  )
    31  
    32  // FileDigest computes a hash digest of the file using the given hash.
    33  // It also returns the file size.
    34  func FileDigest(filename string, hash crypto.Hash) ([]byte, uint64, error) {
    35  	f, err := os.Open(filename)
    36  	if err != nil {
    37  		return nil, 0, err
    38  	}
    39  	defer f.Close()
    40  	h := hash.New()
    41  	size, err := io.CopyBuffer(h, f, make([]byte, hashDigestBufSize))
    42  	if err != nil {
    43  		return nil, 0, err
    44  	}
    45  	return h.Sum(nil), uint64(size), nil
    46  }