Hash 値を計算するパッケージを作ってみた

package hash

import (
    "crypto"
    "io"
    "strings"

    "github.com/pkg/errors"
)

var (
    //ErrNoImplement is error "no implementation"
    ErrNoImplement = errors.New("no implementation")
)

//Value returns hash value string from io.Reader
func Value(r io.Reader, alg crypto.Hash) ([]byte, error) {
    if !alg.Available() {
        return nil, errors.Wrap(ErrNoImplement, "error "+algoString(alg))
    }
    h := alg.New()
    io.Copy(h, r)
    return h.Sum(nil), nil
}

v, err := hash.Value(bytes.NewBuffer([]byte("")), crypto.SHA1)
if err != nil {
    return
}
fmt.Printf("%x\n", v)
// Output:
// da39a3ee5e6b4b0d3255bfef95601890afd80709

// Hash is the common interface implemented by all hash functions.
type Hash interface {
    // Write (via the embedded io.Writer interface) adds more data to the running hash.
    // It never returns an error.
    io.Writer

    // Sum appends the current hash to b and returns the resulting slice.
    // It does not change the underlying hash state.
    Sum(b []byte) []byte

    // Reset resets the Hash to its initial state.
    Reset()

    // Size returns the number of bytes Sum will return.
    Size() int

    // BlockSize returns the hash's underlying block size.
    // The Write method must be able to accept any amount
    // of data, but it may operate more efficiently if all writes
    // are a multiple of the block size.
    BlockSize() int
}

package main

import (
    _ "crypto/md5"
    _ "crypto/sha1"
    _ "crypto/sha256"
    _ "crypto/sha512"

    _ "golang.org/x/crypto/blake2b"
    _ "golang.org/x/crypto/blake2s"
    _ "golang.org/x/crypto/md4"
    _ "golang.org/x/crypto/ripemd160"
    _ "golang.org/x/crypto/sha3"
)

$ hash -h
Usage:
  hash [flags] [binary file]

Flags:
  -a, --algo string      hash algorithm (default "sha256")
  -c, --compare string   compare hash value
  -h, --help             help for hash

$ hash -a sha1 empty.txt
da39a3ee5e6b4b0d3255bfef95601890afd80709

$ cat empty.txt | hash -a sha1
da39a3ee5e6b4b0d3255bfef95601890afd80709

$ hash -a sha1 empty.txt -c da39a3ee5e6b4b0d3255bfef95601890afd80709
matched

034f8cf6c225fde51aa025376df12450832f111b39050a7ec451a9ec2ce2cb54  release/dep-windows-amd64

$ hash dep-windows-amd64 -c 034f8cf6c225fde51aa025376df12450832f111b39050a7ec451a9ec2ce2cb54
matched