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RTPS通信使用的socket和端口

article 2024/11/23 5:35:37

RTPS通信使用的socket和端口

概述

在FastRTPS中，无论SenderResource还是，ReceiverResource，其内部会依赖NetworkFactory创建socket，每个socket都需要绑定socket才能正常使用。

一般来说，一个RTPSParticipant中创建的RTPSReader/RTPSWriter都是共用一组socket资源的，而这些socket的端口的值一般是RTPSParticipant的domainid和participantid相关的。

上层应用可以指定创建的RTPSParticipant用于元数据和业务数据通信的单播地址/组播地址，但是无法指定通信的端口，端口是RTPS中根据规则进行计算分配的。

下面主要是梳理一下一个RTPSParticipant会创建哪些socket，每一类socket绑定的端口规则是怎样的。

创建的socket

通过阅读RTPSReader,RTPSWriter,StatelessWriter,StatelessReader,StatefulWriter以及StatefulReader的代码可以发现，这些endpoint类是只负责处理数据，管理匹配的对端endpoint，而发送和接收数据都是依赖内部的history对象的。history中的数据则是依赖了下层的ReceiverResource和SenderResource，而ReceiverResource和SenderResource是依赖了更下层Transport中的各种ChannelResource来进行网络数据通信的，每个ChannelResource中包含了用于地层数据通信的socket对象

发送

发送的Socket在SenderResource中创建，有如下几个创建的时机点

1. 创建RTPSParticipant设置qos的时候

DomainParticipantImpl::set_qos
	RTPSParticipant::update_attributes
		RTPSParticipantImpl::update_attributes
			createSenderResources(元数据组播地址)
			createSenderResources(元数据单播地址)
			createSenderResources(业务数据单播地址)
				NetworkFactory::build_send_resources
					UDPTransportInterface::OpenOutputChannel
					UDPTransportInterface::OpenAndBindUnicastOutputSocket
					UDPTransportInterface::createUDPSocket

2. StatelessWriter匹配到对端Reader

StatelessWriter::matched_reader_add
	StatelessWriter::update_reader_info
		RTPSParticipantImpl::createSenderResources

3. StatefulWriter匹配到对端Reader

StatefulWriter::matched_reader_add
	StatefulWriter::update_reader_info
		RTPSParticipantImpl::createSenderResources

4. StatefulReader匹配到对端Writer（需要创建SenderResource用于发送ACKNACK消息）

StatefulReader::matched_writer_add
	RTPSParticipantImpl::createSenderResources

接收

接收的Socket在ReceiverResource中创建，

元数据组播地址绑定的端口

https://gitee.com/zzl0109/Fast-DDS/blob/master/include/fastdds/rtps/common/PortParameters.h

    inline uint32_t getMulticastPort(
            uint32_t domainId) const
    {
        uint32_t port = portBase + domainIDGain * domainId + offsetd0;
		...
		return port;
	}

元数据单播地址绑定的端口

https://gitee.com/zzl0109/Fast-DDS/blob/master/include/fastdds/rtps/common/PortParameters.h

inline uint32_t getUnicastPort(
            uint32_t domainId,
            uint32_t RTPSParticipantID) const
    {
        uint32_t port = portBase + domainIDGain * domainId + offsetd1   + participantIDGain * RTPSParticipantID;
		...
		return port;
	}

业务数据单播地址绑定端口

https://gitee.com/zzl0109/Fast-DDS/blob/master/src/cpp/rtps/participant/RTPSParticipantImpl.cpp

...
RTPSParticipantImpl::RTPSParticipantImpl(
	...
    // 上层应用未指定单播和组播地址
    if (m_att.defaultUnicastLocatorList.empty() && m_att.defaultMulticastLocatorList.empty())
    {
        get_default_unicast_locators();
        internal_default_locators_ = true;
		        EPROSIMA_LOG_INFO(RTPS_PARTICIPANT,
                m_att.getName() << " Created with NO default Unicast Locator List, adding Locators:"
                                << m_att.defaultUnicastLocatorList);
    }
	else
    {
        // Locator with port 0, calculate port.  指定了地址，通过计算分配端口
        std::for_each(m_att.defaultUnicastLocatorList.begin(), m_att.defaultUnicastLocatorList.end(),
                [&](Locator_t& loc)
                {   // 端口通过calculate_well_known_port计算
                    m_network_Factory.fill_default_locator_port(domain_id_, loc, m_att, false);
                });
        m_network_Factory.NormalizeLocators(m_att.defaultUnicastLocatorList);

        std::for_each(m_att.defaultMulticastLocatorList.begin(), m_att.defaultMulticastLocatorList.end(),
                [&](Locator_t& loc)
                {   // 端口通过calculate_well_known_port计算
                    m_network_Factory.fill_default_locator_port(domain_id_, loc, m_att, true);
                });
    }
	...
}

...

void RTPSParticipantImpl::get_default_unicast_locators()
{
    m_network_Factory.getDefaultUnicastLocators(domain_id_, m_att.defaultUnicastLocatorList, m_att);
    m_network_Factory.NormalizeLocators(m_att.defaultUnicastLocatorList);
}

...

https://gitee.com/zzl0109/Fast-DDS/blob/master/src/cpp/rtps/network/NetworkFactory.cpp

bool NetworkFactory::getDefaultUnicastLocators(
        uint32_t domain_id,
        LocatorList_t& locators,
        const RTPSParticipantAttributes& m_att) const
{
    bool result = false;
    for (auto& transport : mRegisteredTransports)
    {
        result |= transport->getDefaultUnicastLocators(locators, calculate_well_known_port(domain_id, m_att, false));
    }
    return result;
}

bool NetworkFactory::fill_default_locator_port(
        uint32_t domain_id,
        Locator_t& locator,
        const RTPSParticipantAttributes& m_att,
        bool is_multicast) const
{
    bool result = false;
    for (auto& transport : mRegisteredTransports)
    {
        if (transport->IsLocatorSupported(locator))
        {   // 端口通过calculate_well_known_port计算
            result |= transport->fillUnicastLocator(locator, calculate_well_known_port(domain_id, m_att, is_multicast));
        }
    }
    return result;
}

uint16_t NetworkFactory::calculate_well_known_port(
        uint32_t domain_id,
        const RTPSParticipantAttributes& att,
        bool is_multicast) const
{

    uint32_t port = att.port.portBase +
            att.port.domainIDGain * domain_id +
            (is_multicast ?
            att.port.offsetd2 :
            att.port.offsetd3 + att.port.participantIDGain * att.participantID);

    if (port > 65535)
    {
       	...  // error log
        exit(EXIT_FAILURE);
    }

    return static_cast<uint16_t>(port);
}