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id.go
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id.go
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// Copyright (c) 2016-2017 Tigera, Inc. All rights reserved.
//
// 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 hashutils
import (
"crypto/sha256"
"encoding/base64"
)
const shortenedPrefix = "_"
// GetLengthLimitedID returns an ID that consists of the given prefix and, either the given suffix,
// or, if that would exceed the length limit, a cryptographic hash of the suffix, truncated to the
// required length.
func GetLengthLimitedID(fixedPrefix, suffix string, maxLength int) string {
prefixLen := len(fixedPrefix)
suffixLen := len(suffix)
totalLen := prefixLen + suffixLen
if totalLen > maxLength || (totalLen == maxLength && suffix[0:1] == shortenedPrefix) {
// Either it's just too long, or it's exactly the right length but it happens to
// start with the character that we use to denote a shortened string, which could
// result in a clash. Hash the value and truncate...
hasher := sha256.New()
hasher.Write([]byte(suffix))
hash := base64.RawURLEncoding.EncodeToString(hasher.Sum(nil))
charsLeftForHash := maxLength - 1 - prefixLen
return fixedPrefix + shortenedPrefix + hash[0:charsLeftForHash]
}
// No need to shorten.
return fixedPrefix + suffix
}