/
score.go
78 lines (66 loc) · 2.13 KB
/
score.go
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// Copyright 2012 Aaron Jacobs. All Rights Reserved.
// Author: aaronjjacobs@gmail.com (Aaron Jacobs)
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package blob
import (
"crypto/sha1"
"encoding/hex"
"fmt"
"regexp"
)
// A Score is the identifier for a blob previously stored by a blob store. It
// consists of a 20-byte SHA-1 hash of the blob's contents, so that with high
// probability two blobs have the same contents if and only if they have the
// same score.
const ScoreLength = 20
type Score [ScoreLength]byte
// Compute the score for the supplied blob. This is primarily intended for use
// by blob store implementations; most users should obtain scores through calls
// to a blob store's Store method.
func ComputeScore(b []byte) (s Score) {
h := sha1.New()
h.Write(b)
slice := h.Sum(nil)
if len(slice) != ScoreLength {
panic(
fmt.Sprintf(
"Expected %d bytes for SHA-1; got %d",
ScoreLength,
len(slice)))
}
copy(s[:], slice)
return
}
var hexScoreRegexp = regexp.MustCompile(
fmt.Sprintf("^[0-9a-f]{%d}$", hex.EncodedLen(ScoreLength)))
// Parse the output of Score.Hex.
func ParseHexScore(hexScore string) (s Score, err error) {
// Is this a legal hex score?
if !hexScoreRegexp.MatchString(hexScore) {
err = fmt.Errorf("Not a legal hex score: %s", hexScore)
return
}
// Decode.
n, err := hex.Decode(s[:], []byte(hexScore))
if n != ScoreLength || err != nil {
err = fmt.Errorf("Unexpected hex.Decode output: %v %v", n, err)
return
}
return
}
// Return a fixed-width hex version of the score's hash, suitable for using
// e.g. as a filename.
func (s Score) Hex() string {
return fmt.Sprintf("%x", s)
}