Measure how often DNS hostnames aren't in preferred name form.

net/dns/dns_util.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_DNS_DNS_UTIL_H_
 #define NET_DNS_DNS_UTIL_H_
 
 #include <string>
 
 #include "base/strings/string_piece.h"
 #include "base/time/time.h"
 #include "net/base/net_export.h"
 #include "net/base/network_change_notifier.h"
 
 namespace net {
 
 class AddressList;
 
 // DNSDomainFromDot - convert a domain string to DNS format. From DJB's
 // public domain DNS library.
 //
 //   dotted: a string in dotted form: "www.google.com"
 //   out: a result in DNS form: "\x03www\x06google\x03com\x00"
 NET_EXPORT_PRIVATE bool DNSDomainFromDot(const base::StringPiece& dotted,
                                          std::string* out);
 
 // Checks that a hostname is valid. Simple wrapper around DNSDomainFromDot.
 NET_EXPORT_PRIVATE bool IsValidDNSDomain(const base::StringPiece& dotted);
 
+// Returns true if the character is valid in a DNS hostname label, whether in
+// the first position or later in the label.
+//
+// This function asserts a looser form of the restrictions in RFC 1123 (section

[Ryan Sleevi, 2017/03/22 00:16:07]

https://tools.ietf.org/html/rfc7719#section-2 is meant to be the clarifying
document about whose rules matter :) And include the link back to 1123 (under
"Host name")

[palmer, 2017/03/22 01:03:33]

Done.

+// 2.1): hostnames can include characters a-z, A-Z, 0-9, -, and _, and any of
+// those characters (except -) are legal in the first position. The looser rules
+// are necessary to support service records (initial _), and non-compliant but
+// attested hostnames that include _. These looser rules also allow Punycode and
+// hence IDN.
+//
+// TODO(palmer): In the future, when we can remove support for invalid names,
+// this can be a private implementation detail of |DNSDomainFromDot|, and need
+// not be NET_EXPORT_PRIVATE.
+NET_EXPORT_PRIVATE bool IsValidLabelCharacter(char c, bool is_first_char);

[Ryan Sleevi, 2017/03/22 00:16:07]

pedantry: IsValidHostLabelCharacter? Since other labels can and do exceed the
host record (implied A/AAAA, such as SRVNames)

[palmer, 2017/03/22 01:03:34]

Done.

+
 // DNSDomainToString converts a domain in DNS format to a dotted string.
 // Excludes the dot at the end.
 NET_EXPORT_PRIVATE std::string DNSDomainToString(
     const base::StringPiece& domain);
 
 #if !defined(OS_NACL)
 NET_EXPORT_PRIVATE
 base::TimeDelta GetTimeDeltaForConnectionTypeFromFieldTrialOrDefault(
     const char* field_trial_name,
     base::TimeDelta default_delta,
@@ skipping 15 matching lines @@
 };
 
 // Compares two AddressLists to see how similar or different their addresses
 // are. (See |AddressListDeltaType| for details of exactly what's checked.)
 AddressListDeltaType FindAddressListDeltaType(const AddressList& a,
                                               const AddressList& b);
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_UTIL_H_