Mediasoup Js和 C++ 管道通信的过程

整体分为两部分

1、 js对c++读写消息，_consumerSocket和producerSocket

2、c++对js读写消息，c++收到都是底层都是通过libuv的uv_read_start和uv_write

目录

一、js接收c++数据

二、js主动调用c++，通过producerSocket.write

三、C++底层读取JS数据

四、c++写数据给js，主要两种形式

---

一、js接收c++数据

channel.js 构造函数注册监听器
this._consumerSocket.on('data', (buffer) => {})

//真正的处理有效数据其实在processMessage

processMessage(msg) {
        // If a response, retrieve its associated request.
        if (msg.id) {
            const sent = this.#sents.get(msg.id);
            if (!sent) {
                logger.error('received response does not match any sent request [id:%s]', msg.id);
                return;
            }
            if (msg.accepted) {
                logger.debug('request succeeded [method:%s, id:%s]', sent.method, sent.id);
                sent.resolve(msg.data);
            }
        else if (msg.targetId && msg.event) {
            setImmediate(() => this.emit(String(msg.targetId), msg.event, msg.data));
        }

上层需要回调response就带msg.id
不带id属于事件通知，最终会调用 this.emit(msg.targetId, msg.event, msg.data);  发送出去

二、js主动调用c++，通过producerSocket.write

async request(method, handlerId, data) {
        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 errors_1.InvalidStateError('Channel closed');
        }
        const request = `${id}:${method}:${handlerId}:${JSON.stringify(data)}`;
        if (Buffer.byteLength(request) > 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(request)).buffer));
        this.#producerSocket.write(request);
        //构建response的callback，添加id，在processMessage进行回调
        return new Promise((pResolve, pReject) => {
            const sent = {
                id: id,
                method: method,
                resolve: (data2) => {
                    if (!this.#sents.delete(id)) {
                        return;
                    }
                    pResolve(data2);
                },
                reject: (error) => {
                    if (!this.#sents.delete(id)) {
                        return;
                    }
                    pReject(error);
                },
                close: () => {
                    pReject(new errors_1.InvalidStateError('Channel closed'));
                }
            };
            // Add sent stuff to the map.
            this.#sents.set(id, sent);
        });

三、C++底层读取JS数据

C++与js的读写就是通过
libuv的uv_read_start和uv_write

以下分析worker进程从启动，到处理信令消息的流程

main方法 ,run_worker方法，运行worker进程

worker.cpp 
1、run_worker 建数据通道,创建c++socket

 channel = new Channel::ChannelSocket(consumerChannelFd, producerChannelFd);　　

class ChannelSocket : public ConsumerSocket::Listener
class ConsumerSocket : public ::UnixStreamSocket

底层读取数据
void ConsumerSocket::UserOnUnixStreamRead()
    {
        MS_TRACE_STD();

        // Be ready to parse more than a single message in a single chunk.
        while (true)
        {
            if (IsClosed())
                return;

            size_t readLen = this->bufferDataLen - this->msgStart;
            char* msgStart = nullptr;
            size_t msgLen;
            int nsRet = netstring_read(　　//读取数据
              reinterpret_cast(this->buffer + this->msgStart), readLen, &msgStart, &msgLen);
         }
}

给bufferDataLen进行赋值
inline void UnixStreamSocket::OnUvRead(
        this->bufferDataLen += static_cast(nread);
）

    err = uv_read_start(
          reinterpret_cast(this->uvHandle),
          static_cast(onAlloc),
          static_cast(onRead));


2、解析为Json数据，转为request进行分发
    void ChannelSocket::OnConsumerSocketMessage(ConsumerSocket* /*consumerSocket*/, char* msg, size_t msgLen)
    {
    
            auto* request = new Channel::ChannelRequest(this, msg, msgLen);
    }


3、worker.cpp中HandleRequest方法
inline void Worker::HandleRequest(Channel::ChannelRequest* request)
{
    MS_TRACE();

    MS_DEBUG_DEV(
      "Channel request received [method:%s, id:%" PRIu32 "]", request->method.c_str(), request->id);

    INFO("[cxf]req id str:", (int)request->methodId, ":", request->method);

    switch (request->methodId)
    {
        case Channel::ChannelRequest::MethodId::WORKER_CLOSE:
        {
            if (this->closed)
                return;

            MS_DEBUG_DEV("Worker close request, stopping");

            Close();

            break;
        }

        case Channel::ChannelRequest::MethodId::WORKER_DUMP:
        {
            json data = json::object();

            FillJson(data);

            request->Accept(data);

            break;
        }

四、c++写数据给js，主要两种形式

1、Accept返回response
2、给上层发送通知：使用Notifier类
 

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

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

        this->replied = true;

        std::string response("{\"id\":");

        response.append(std::to_string(this->id));
        response.append(",\"accepted\":true}");

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

    inline void ChannelSocket::SendImpl(const uint8_t* payload, uint32_t payloadLen)
    {
    
        if (this->channelWriteFn)
        {
            this->channelWriteFn(payload, payloadLen, this->channelWriteCtx);
        }
        else
        {
            std::memcpy(this->writeBuffer, &payloadLen, sizeof(uint32_t));

            if (payloadLen != 0)
            {
                std::memcpy(this->writeBuffer + sizeof(uint32_t), payload, payloadLen);
            }

            size_t len = sizeof(uint32_t) + payloadLen;

            this->producerSocket->Write(this->writeBuffer, len);
        }
    }


void UnixStreamSocket::Write(const uint8_t* data, size_t len)
{


    uv_buf_t buffer = uv_buf_init(reinterpret_cast(const_cast(data)), len);
    int written     = uv_try_write(reinterpret_cast(this->uvHandle), &buffer, 1);

    // All the data was written. Done.
    if (written == static_cast(len))
    {
        return;
    }
    // Cannot write any data at first time. Use uv_write().
    else if (written == UV_EAGAIN || written == UV_ENOSYS)
    {
        // Set written to 0 so pendingLen can be properly calculated.
        written = 0;
    }
    // Any other error.
    else if (written < 0)
    {
        MS_ERROR_STD("uv_try_write() failed, trying uv_write(): %s", uv_strerror(written));

        // Set written to 0 so pendingLen can be properly calculated.
        written = 0;
    }

    const size_t pendingLen = len - written;
    auto* writeData         = new UvWriteData(pendingLen);

    writeData->req.data = static_cast(writeData);
    std::memcpy(writeData->store, data + written, pendingLen);

    buffer = uv_buf_init(reinterpret_cast(writeData->store), pendingLen);

    const int err = uv_write
    }


2、给上层发送通知
Notifier类在run_worker函数里初始化
Channel::ChannelNotifier::ClassInit(channel);

  void ChannelNotifier::Emit(const std::string& targetId, const char* event)　　//和下面区别就在于是否有数据，与Accept响应相似
    {
        MS_TRACE();

        MS_ASSERT(ChannelNotifier::channel, "channel unset");

        json jsonNotification = json::object();

        jsonNotification["targetId"] = targetId;
        jsonNotification["event"]    = event;

        ChannelNotifier::channel->Send(jsonNotification);
    }


举例
inline void WebRtcTransport::OnIceServerCompleted(const RTC::IceServer* /*iceServer*/)　　//状态发生变化,回調使用
    {
        MS_TRACE();

        MS_DEBUG_TAG(ice, "ICE completed");

        // Notify the Node WebRtcTransport.
        json data = json::object();

        data["iceState"] = "completed";　　//设置Json数据

        Channel::ChannelNotifier::Emit(this->id, "icestatechange", data);　　//状态发送变化，上传通知到JS层
      }