一、mediasoup之router的创建过程

        每一个worker代表一个nodejs主进程，通过nodejs的spawn 方法创建一个c++子进程,主进程与子进程之间通过unix socket进行通信，nodejs代码中的channel就是对unix socket的一个封装。

      通过channel的request方法发送 “worker.createRouter”指令，并附加参数routerId,到c++子进程，查看worker.ts代码的createRouter方法：

const internal = { routerId: uuidv4() };

await this.#channel.request('worker.createRouter', internal);

        channel的request方法中把指令包装为{ id, method, internal, data } 的JSON格式的数据，

id：请求id.每次请求递增

method: 即为“worker.createRouter”指令

internal: 此处为 ｛routerId｝

data: 此处为null

然后通过producerSocket发送给c++层面，看如下代码：

/**
	 * @private
	 */
	async request(method: string, internal?: object, data?: any): Promise<any>
	{
		this.#nextId < 4294967295 ? ++this.#nextId : (this.#nextId = 1);

		const id = this.#nextId;

		logger.debug('request() [method:%s, id:%s]', method, id);

		if (this.#closed)
			throw new InvalidStateError('Channel closed');

		const request = { id, method, internal, data };
		const payload = JSON.stringify(request);

		if (Buffer.byteLength(payload) > MESSAGE_MAX_LEN)
			throw new Error('Channel request too big');

		// This may throw if closed or remote side ended.
		this.#producerSocket.write(
			Buffer.from(Uint32Array.of(Buffer.byteLength(payload)).buffer));
		this.#producerSocket.write(payload);
        ........后面省略   
    }

        在c++层面ChannelRequest.cpp代码中，定义了指令到方法id之间的映射关系std::unordered_map：

	std::unordered_map<std::string, ChannelRequest::MethodId> ChannelRequest::string2MethodId =
	{
		{ "worker.close",                                ChannelRequest::MethodId::WORKER_CLOSE                                     },
..................
		{ "worker.createRouter",                         ChannelRequest::MethodId::WORKER_CREATE_ROUTER  
......................
}

从中可以看出createRouter对应的方法MethodId为  ChannelRequest::MethodId::WORKER_CREATE_ROUTER 。我们再看一下MethodId的定义如下，可以看出WORKER_CREATE_ROUTER的值为 5 ：

class ChannelRequest
{
	public:
		enum class MethodId
		{
			WORKER_CLOSE = 1,
			WORKER_DUMP,
			WORKER_GET_RESOURCE_USAGE,
			WORKER_UPDATE_SETTINGS,
			WORKER_CREATE_ROUTER,
            ................
        }
};

C++层面在void ConsumerSocket::UserOnUnixStreamRead()中收到消息时，在子类方法ChannelSocket::OnConsumerSocketMessage中对JOSN格式的消息进行解析，并创建ChannelRequest::ChannelRequest类实例，实例中就包含了解析后的{ id, method, internal, data }数据，看下ChannelRequest的成员变量：

	public:
		// Passed by argument.
		Channel::ChannelSocket* channel{ nullptr };
		uint32_t id{ 0u }; 
		std::string method;
		MethodId methodId;
		json internal;
		json data;
		// Others.
		bool replied{ false };

        最后通过c++层面的 Worker::OnChannelRequest对消息进行处理:

inline void Worker::OnChannelRequest(Channel::ChannelSocket* /*channel*/, Channel::ChannelRequest* request)
{
    switch (request->methodId)
	{
        ....................
        case Channel::ChannelRequest::MethodId::WORKER_CREATE_ROUTER:
		{
			std::string routerId;

			try
			{
				SetNewRouterIdFromInternal(request->internal, routerId);
			}
			catch (const MediaSoupError& error)
			{
				MS_THROW_ERROR("%s [method:%s]", error.buffer, request->method.c_str());
			}

			auto* router = new RTC::Router(routerId);

			this->mapRouters[routerId] = router;

			MS_DEBUG_DEV("Router created [routerId:%s]", routerId.c_str());

			request->Accept();

			break;
		}
        ...........................
    }
// Any other request must be delivered to the corresponding Router.
	default:
		{
			try
			{
				RTC::Router* router = GetRouterFromInternal(request->internal);

				router->HandleRequest(request);
			}
			catch (const MediaSoupTypeError& error)
			{
				MS_THROW_TYPE_ERROR("%s [method:%s]", error.buffer, request->method.c_str());
			}
			catch (const MediaSoupError& error)
			{
				MS_THROW_ERROR("%s [method:%s]", error.buffer, request->method.c_str());
			}

			break;
		}
}

其中我们看到了 auto* router = new RTC::Router(routerId); 即是创建了一个router. 

最后通过调用request->Accept(); 向nodejs主进程发送响应消息：

void ChannelRequest::Accept()
{
		MS_TRACE();

		MS_ASSERT(!this->replied, "request already replied");

		this->replied = true;

		json jsonResponse = json::object();

		jsonResponse["id"]       = this->id;
		jsonResponse["accepted"] = true;

		this->channel->Send(jsonResponse);
}