discovery/dnssd/public/dns_sd_instance.cc

// Copyright 2019 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.

#include "discovery/dnssd/public/dns_sd_instance.h"

#include <algorithm>
#include <cctype>
#include <utility>
#include <vector>

#include "util/osp_logging.h"

namespace openscreen {
namespace discovery {
namespace {

// Maximum number of octets allowed in a single domain name label.
constexpr size_t kMaxLabelLength = 63;

bool IsValidUtf8(const std::string& string) {
  for (size_t i = 0; i < string.size(); i++) {
    if (string[i] >> 5 == 0x06) {  // 110xxxxx 10xxxxxx
      if (i + 1 >= string.size() || string[++i] >> 6 != 0x02) {
        return false;
      }
    } else if (string[i] >> 4 == 0x0E) {  // 1110xxxx 10xxxxxx 10xxxxxx
      if (i + 2 >= string.size() || string[++i] >> 6 != 0x02 ||
          string[++i] >> 6 != 0x02) {
        return false;
      }
    } else if (string[i] >> 3 == 0x1E) {  // 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
      if (i + 3 >= string.size() || string[++i] >> 6 != 0x02 ||
          string[++i] >> 6 != 0x02 || string[++i] >> 6 != 0x02) {
        return false;
      }
    } else if ((string[i] & 0x80) != 0x0) {  // 0xxxxxxx
      return false;
    }
  }
  return true;
}

bool HasControlCharacters(const std::string& string) {
  for (auto ch : string) {
    if ((ch >= 0x0 && ch <= 0x1F /* Ascii control characters */) ||
        ch == 0x7F /* DEL character */) {
      return true;
    }
  }
  return false;
}

}  // namespace

DnsSdInstance::DnsSdInstance(std::string instance_id,
                             std::string service_id,
                             std::string domain_id,
                             DnsSdTxtRecord txt,
                             uint16_t port,
                             std::vector<Subtype> subtypes)
    : instance_id_(std::move(instance_id)),
      service_id_(std::move(service_id)),
      domain_id_(std::move(domain_id)),
      txt_(std::move(txt)),
      port_(port),
      subtypes_(std::move(subtypes)) {
  OSP_DCHECK(IsInstanceValid(instance_id_))
      << instance_id_ << " is an invalid instance id";
  OSP_DCHECK(IsServiceValid(service_id_))
      << service_id_ << " is an invalid service id";
  OSP_DCHECK(IsDomainValid(domain_id_))
      << domain_id_ << " is an invalid domain";
  for (const Subtype& subtype : subtypes_) {
    OSP_DCHECK(IsSubtypeValid(subtype)) << subtype << " is an invalid subtype";
  }

  std::sort(subtypes_.begin(), subtypes_.end());
}

DnsSdInstance::DnsSdInstance(const DnsSdInstance& other) = default;

DnsSdInstance::DnsSdInstance(DnsSdInstance&& other) = default;

DnsSdInstance::~DnsSdInstance() = default;

DnsSdInstance& DnsSdInstance::operator=(const DnsSdInstance& rhs) = default;

DnsSdInstance& DnsSdInstance::operator=(DnsSdInstance&& rhs) = default;

// static
bool IsInstanceValid(const std::string& instance) {
  // According to RFC6763, Instance names must:
  // - Be encoded in Net-Unicode (which required UTF-8 formatting).
  // - NOT contain ASCII control characters
  // - Be no longer than 63 octets.

  return instance.size() <= kMaxLabelLength &&
         !HasControlCharacters(instance) && IsValidUtf8(instance);
}

// static
bool IsServiceValid(const std::string& service) {
  // According to RFC6763, the service name "consists of a pair of DNS labels".
  // "The first label of the pair is an underscore character followed by the
  // Service Name" and "The second label is either '_tcp' [...] or '_udp'".
  // According to RFC6335 Section 5.1, the Service Name section must:
  //   Contain from 1 to 15 characters.
  // - Only contain A-Z, a-Z, 0-9, and the hyphen character.
  // - Contain at least one letter.
  // - NOT begin or end with a hyphen.
  // - NOT contain two adjacent hyphens.
  if (service.size() > 21 || service.size() < 7) {  // Service name size + 6.
    return false;
  }

  const std::string protocol = service.substr(service.size() - 5);
  if (protocol != "._udp" && protocol != "._tcp") {
    return false;
  }

  if (service[0] != '_' || service[1] == '-' ||
      service[service.size() - 6] == '-') {
    return false;
  }

  bool last_char_hyphen = false;
  bool seen_letter = false;
  for (size_t i = 1; i < service.size() - 5; i++) {
    if (service[i] == '-') {
      if (last_char_hyphen) {
        return false;
      }
      last_char_hyphen = true;
    } else if (std::isalpha(service[i])) {
      last_char_hyphen = false;
      seen_letter = true;
    } else if (std::isdigit(service[i])) {
      last_char_hyphen = false;
    } else {
      return false;
    }
  }

  return seen_letter;
}

// static
bool IsDomainValid(const std::string& domain) {
  // As RFC6763 Section 4.1.3 provides no validation requirements for the domain
  // section, the following validations are used:
  // - All labels must be no longer than 63 characters
  // - Total length must be no more than 256 characters
  // - Must be encoded using valid UTF8
  // - Must not include any ASCII control characters

  if (domain.size() > 255) {
    return false;
  }

  size_t label_start = 0;
  for (size_t next_dot = domain.find('.'); next_dot != std::string::npos;
       next_dot = domain.find('.', label_start)) {
    if (next_dot - label_start > kMaxLabelLength) {
      return false;
    }
    label_start = next_dot + 1;
  }

  return !HasControlCharacters(domain) && IsValidUtf8(domain);
}

// static
bool IsSubtypeValid(const DnsSdInstance::Subtype& subtype) {
  // As specified in RFC6763 section 9.1, all subtypes may be arbitrary bit
  // data. Despite this, this implementation has chosen to limit valid subtypes
  // to only UTF8 character strings. Therefore, the subtype must:
  // - Be encoded in Net-Unicode (which required UTF-8 formatting).
  // - NOT contain ASCII control characters
  // - Be no longer than 63 octets.
  // - Be of length one label.
  return subtype.size() <= kMaxLabelLength &&
         subtype.find('.') == std::string::npos &&
         !HasControlCharacters(subtype) && IsValidUtf8(subtype);
}

bool operator<(const DnsSdInstance& lhs, const DnsSdInstance& rhs) {
  if (lhs.port_ != rhs.port_) {
    return lhs.port_ < rhs.port_;
  }

  int comp = lhs.instance_id_.compare(rhs.instance_id_);
  if (comp != 0) {
    return comp < 0;
  }

  comp = lhs.service_id_.compare(rhs.service_id_);
  if (comp != 0) {
    return comp < 0;
  }

  comp = lhs.domain_id_.compare(rhs.domain_id_);
  if (comp != 0) {
    return comp < 0;
  }

  if (lhs.subtypes_.size() != rhs.subtypes_.size()) {
    return lhs.subtypes_.size() < rhs.subtypes_.size();
  }

  for (size_t i = 0; i < lhs.subtypes_.size(); i++) {
    comp = lhs.subtypes_[i].compare(rhs.subtypes_[i]);
    if (comp != 0) {
      return comp < 0;
    }
  }

  return lhs.txt_ < rhs.txt_;
}

}  // namespace discovery
}  // namespace openscreen