github.com/u-root/u-root@v7.0.1-0.20200915234505-ad7babab0a8e+incompatible/cmds/exp/crc/crc.go (about)

     1  // Copyright 2019 the u-root Authors. All rights reserved
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Prints crc checksum of a file.
     6  //
     7  // Synopsis:
     8  //     crc OPTIONS [FILE]
     9  //
    10  // Description:
    11  //     One of the crc types must be specified. If there is no file, stdin is
    12  //     read.
    13  //
    14  // Options:
    15  //     -f: CRC function to use. May be one of the following:
    16  //         crc32-ieee:       CRC-32 IEEE standard (default)
    17  //         crc32-castognoli: CRC-32 Castognoli standard
    18  //         crc32-koopman:    CRC-32 Koopman standard
    19  //         crc64-ecma:       CRC-64 ECMA standard
    20  //         crc64-iso:        CRC-64 ISO standard
    21  package main
    22  
    23  import (
    24  	"flag"
    25  	"fmt"
    26  	"hash"
    27  	"hash/crc32"
    28  	"hash/crc64"
    29  	"io"
    30  	"log"
    31  	"os"
    32  )
    33  
    34  var function = flag.String("f", "crc32-ieee", "CRC function")
    35  
    36  func main() {
    37  	flag.Parse()
    38  
    39  	functions := map[string]hash.Hash{
    40  		"crc32-ieee":       crc32.New(crc32.MakeTable(crc32.IEEE)),
    41  		"crc32-castognoli": crc32.New(crc32.MakeTable(crc32.Castagnoli)),
    42  		"crc32-koopman":    crc32.New(crc32.MakeTable(crc32.Koopman)),
    43  		"crc64-ecma":       crc64.New(crc64.MakeTable(crc64.ECMA)),
    44  		"crc64-iso":        crc64.New(crc64.MakeTable(crc64.ISO)),
    45  	}
    46  
    47  	h, ok := functions[*function]
    48  	if !ok {
    49  		expected := ""
    50  		for k := range functions {
    51  			expected += " " + k
    52  		}
    53  		log.Fatalf("invalid function %q, expected one of:%s", *function, expected)
    54  	}
    55  
    56  	var r io.Reader
    57  	switch flag.NArg() {
    58  	case 0:
    59  		r = os.Stdin
    60  	case 1:
    61  		f, err := os.Open(flag.Arg(0))
    62  		if err != nil {
    63  			log.Fatal(err)
    64  		}
    65  		defer f.Close()
    66  		r = f
    67  	default:
    68  		log.Fatal("expected 0 or 1 positional args")
    69  	}
    70  
    71  	if _, err := io.Copy(h, r); err != nil {
    72  		log.Fatal(err)
    73  	}
    74  	fmt.Printf("%x\n", h.Sum([]byte{}))
    75  }