client/mdns_utils.cpp

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * 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.
 */

#include "client/mdns_utils.h"

#include <android-base/strings.h>

namespace mdns {

// <Instance>.<Service>.<Domain>
std::optional<MdnsInstance> mdns_parse_instance_name(std::string_view name) {
    CHECK(!name.empty());

    // Return the whole name if it doesn't fall under <Instance>.<Service>.<Domain> or
    // <Instance>.<Service>
    bool has_local_suffix = false;
    // Strip the local suffix, if any
    {
        std::string local_suffix = ".local";
        local_suffix += android::base::EndsWith(name, ".") ? "." : "";

        if (android::base::ConsumeSuffix(&name, local_suffix)) {
            if (name.empty()) {
                return std::nullopt;
            }
            has_local_suffix = true;
        }
    }

    std::string transport;
    // Strip the transport suffix, if any
    {
        std::string add_dot = (!has_local_suffix && android::base::EndsWith(name, ".")) ? "." : "";
        std::array<std::string, 2> transport_suffixes{"._tcp", "._udp"};

        for (const auto& t : transport_suffixes) {
            if (android::base::ConsumeSuffix(&name, t + add_dot)) {
                if (name.empty()) {
                    return std::nullopt;
                }
                transport = t.substr(1);
                break;
            }
        }

        if (has_local_suffix && transport.empty()) {
            return std::nullopt;
        }
    }

    if (!has_local_suffix && transport.empty()) {
        return std::make_optional<MdnsInstance>(name, "", "");
    }

    // Split the service name from the instance name
    auto pos = name.rfind(".");
    if (pos == 0 || pos == std::string::npos || pos == name.size() - 1) {
        return std::nullopt;
    }

    return std::make_optional<MdnsInstance>(name.substr(0, pos), name.substr(pos + 1), transport);
}

}  // namespace mdns