爲什麼zmq_stream客戶端需要recv四次才能獲取實際數據？

Question

端口9070是簡單的HTTP服務器（無ZMQ TCP）
我有一個問題：

1. 爲什麼第二recv的是0？它來自哪裏？

感謝您的幫助

void test_stream_to_tcp() 
{ 
    uint8_t id [256]; 
    size_t id_size = 256; 
    uint8_t buffer [256]; 
    void *ctx = zmq_ctx_new(); 
    void *client = zmq_socket (ctx, ZMQ_STREAM); 
    int rc = 0; 
    rc = zmq_connect (client, "tcp://localhost:9070"); 
    rc = zmq_getsockopt (client, ZMQ_IDENTITY, id, &id_size); 
    rc = zmq_send (client, id, id_size, ZMQ_SNDMORE); 
    rc = zmq_send (client, "GET /\n\n", 7, 0); 
    assert (rc == 7); 
    rc = zmq_recv (client, buffer, 256, 0); 
    cout <<"first recv "<< buffer << "rc = "<< rc<<endl; 
    rc = zmq_recv (client, buffer, 256, 0); 
    cout <<"second recv "<< buffer<< "rc = "<< rc<<endl; 
    rc = zmq_recv (client, buffer, 256, 0); 
    cout <<"third recv "<< buffer<< "rc = "<< rc<<endl; 
    rc = zmq_recv (client, buffer, 256, 0); 
    buffer[rc] = '\0'; 
    cout <<"forth recv "<< buffer<< "rc = "<< rc<<endl; 
} 

Answer 1

我得到它，在ZMQ :: stream_engine_t ::插上 原始套接字，發送初始長度爲0的消息給應用程序，以便它知道有同行連接的。