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// Copyright (C) 2016 Opsmate, Inc.
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License, v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
//
// This software is distributed WITHOUT A WARRANTY OF ANY KIND.
// See the Mozilla Public License for details.
//
// From: https://github.com/SSLMate/certspotter/blob/master/identifiers.go
// Minor tweaks to get a SanitizeDNSName function for ASCII names only.
package sanitize
import (
"fmt"
"strings"
)
// Try to canonicalize/sanitize the DNS name:
//
// 1. Trim leading and trailing whitespace
// 2. Trim trailing dots
// 3. Trim http:// and https:// prefix
// 4. Convert to lower case
// 5. Error if the DNS labels are not composed of ASCII characters 32-126 or "\t"
//
// Please note that the above is not necessarily a good filter for real CT
// monitoring (this is why we're not applying it in the collect stage). It is
// also not a good filter for getting rid of non-domain names like "funny str".
// It is however simple to understand ("printable ascii chars"), and should be
// good enough for the purpose of assembling a SANs data set from CT logs.
func SanitizeDNSName(value string) (string, error) {
value = trimHttpPrefixString(strings.ToLower(trimTrailingDots(strings.TrimSpace(value))))
if !isASCIIString([]byte(value)) {
return "", fmt.Errorf("not an ascii string: %x", []byte(value))
}
labels := strings.Split(value, ".")
for _, label := range labels {
if !isSaneDNSLabel(label) {
return "", fmt.Errorf("process label %x", []byte(label))
}
}
return strings.Join(labels, "."), nil
}
func trimTrailingDots(value string) string {
length := len(value)
for length > 0 && value[length-1] == '.' {
length--
}
return value[0:length]
}
func trimHttpPrefixString(value string) string {
if strings.HasPrefix(value, "http://") {
return value[7:]
} else if strings.HasPrefix(value, "https://") {
return value[8:]
} else {
return value
}
}
func isASCIIString(value []byte) bool {
for _, b := range value {
if b > 127 {
return false
}
}
return true
}
func isSaneDNSLabel(label string) bool {
for _, ch := range label {
if !isSaneDNSLabelChar(ch) {
return false
}
}
return true
}
func isSaneDNSLabelChar(ch rune) bool {
return ch == '\t' || (ch >= 32 && ch <= 126)
}
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