c - ZeroMQ 示例的网络诊断

Question

我正在尝试实现 ZeroMQ 以使 Raspberry Pi 3(Raspbian Stretch)上的应用程序与通过有线或 WLAN 连接链接的单独机器(在本例中为 Windows 7 64 位操作系统)上的应用程序进行通信。

我已经在两台机器上使用 C 库接口(interface)编译了 ZeroMQ(在 Windows 上使用 Cygwin)和 Hello World 示例(我稍微修改了它以打印指针值以向我保证这些函数正在“工作”)。两台机器都已连接(在这种情况下通过有线以太网链路和路由器)并且连接良好(我通过 Xrdp 或 SSH 从 PC 链接到 RPi OK)。

我遇到的问题是客户端/服务器 ZeroMQ 程序似乎并没有“看到”对方，即使它们看起来确实有效，我的问题是:我应该采取哪些第一步来调查为什么会发生这种情况？是否有任何命令行或 GUI 工具可以帮助我找出导致阻塞的原因？ (比如端口事件监视器什么的？)。

我对网络知之甚少，所以在您的回复中，我认为我是所有套接字/服务方面的新手。 RPi(服务器)上的源代码是:

// ZeroMQ Test Server
// Compile with
// gcc -o zserver zserver.c -lzmq

#include <zmq.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>

int main (void)
{
    void *context=NULL,*responder=NULL;
    int rc=1;

    //  Socket to talk to clients
    context = zmq_ctx_new ();
printf("Context pointer = %p\n",context);
    responder = zmq_socket (context, ZMQ_REP);
printf("Responder pointer = %p\n",responder);
    rc = zmq_bind (responder, "tcp://*:5555");
printf("rc = %d\n",rc);

    assert (rc == 0);

    while (1) {
        char buffer [10];
        zmq_recv (responder, buffer, 10, 0);
        printf ("Received Hello\n");
        sleep (1);          //  Do some 'work'
        zmq_send (responder, "World", 5, 0);
    }
    return 0;
}

PC(Cygwin)客户端上的源代码为:

// ZeroMQ Test Client
// Compile with:
// gcc -o zclient zclient.c -L/usr/local/lib -lzmq

#include <zmq.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>

int main (void)
{
  void *context=NULL,*requester=NULL;

    printf ("Connecting to hello world server\n");
    context = zmq_ctx_new ();
printf("Context pointer = %p\n",context);
    requester = zmq_socket (context, ZMQ_REQ);
printf("Requester pointer = %p\n",requester);
    zmq_connect (requester, "tcp://localhost:5555");

    int request_nbr;
    for (request_nbr = 0; request_nbr != 10; request_nbr++) {
        char buffer [10];
        printf ("Sending Hello %d\n", request_nbr);
        zmq_send (requester, "Hello", 5, 0);
        zmq_recv (requester, buffer, 10, 0);
        printf ("Received World %d\n", request_nbr);
    }
    zmq_close (requester);
    zmq_ctx_destroy (context);
    return 0;
}

在 RPi LX 终端上，我运行服务器并得到以下信息:

Context pointer = 0xefe308
Responder pointer = 0xf00e08
rc = 0

在 Cygwin Bash shell 上，我运行客户端并得到这个:

Connecting to hello world server
Context pointer = 0x60005ab90
Requester pointer = 0x60005f890
Sending Hello 0

...他们都卡在那里——一个在听，另一个在发送，但彼此都不回应。
任何线索如何开始对此进行调查将不胜感激。

Answer 1

+1 使用显式 zmq_close() 进行护理和 zmq_ctx_term()资源释放...
如果这是第一次使用 ZeroMQ，
在深入了解更多细节之前，不妨先看看“ZeroMQ Principles in less than Five Seconds”

Q : What are the first steps I should take to investigate why this is happening?

视线测试作为 零步 在这里没有意义。
全部 localhost -放置的接口(interface)很难不“看到”彼此。

接下来，测试为 第一步调用 { .bind() | .connect() } - 使用显式地址的方法，如 tcp://127.0.0.1:56789 (以避免 * -通配符和 localhost -符号名称翻译的扩展)

随时准备阅读/评估 API 提供的 errno ZeroMQ 不断报告有关最后一个 ZeroMQ API 操作导致错误状态的信息。

最好阅读 ZeroMQ 原生 API 文档，该文档在各个版本之间都得到了很好的维护，以充分了解 API 设计的信令/消息元平面的舒适性。

Mea Culpa:LoS 肯定不是由 O/P 代码建立的:

树莓派 .bind() -s 在它的本地 I/F 上(否则不能)

电脑 .connect() -s 不是 与 RPi 相同，但 PC 的本地 I/F

电脑 .connect( "tcp://<address_of_RPi>:5555" )会成功的 (使用与 Xrdp 或 SSH 相同的 IP 地址连接到 RPi，或者可以在 ~$ ip address 之后从 RPi CLI 终端显式读取一个并将该地址用于 PC 端客户端代码)

两个不相交的 ZeroMQ AccessPoint -s 有零方式如何通信，一旦没有从 A 到 B 的传输“线”

// Zero MQ Test Server
// Compile with
// gcc -o zserver zserver.c -lzmq

#include <zmq.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>

int main (void)
{
    void *context=NULL,*responder=NULL;
    int rc=1;

    //  Socket to talk to clients
    context = zmq_ctx_new ();                  printf("Context pointer = %p\n",context);
    responder = zmq_socket (context, ZMQ_REP); printf("Responder pointer = %p\n",responder);
    rc = zmq_bind (responder, "tcp://*:5555"); printf("rc = %d\n",rc);
/* ----------------------------------^^^^^^------------RPi interface-----------*/
    assert (rc == 0);

    while (1) {
        char buffer [10];
        zmq_recv (responder, buffer, 10, 0);   printf("Received Hello\n");
        sleep (1);                         //  Do some 'work'
        zmq_send (responder, "World", 5, 0);
    }
    return 0;
}

PC(Cygwin)客户端上的源代码为:

// ZeroMQ Test Client
// Compile with:
// gcc -o zclient zclient.c -L/usr/local/lib -lzmq

#include <zmq.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>

int main (void)
{
    void *context=NULL,*requester=NULL;
                                               printf("Connecting to hello world server\n");
    context = zmq_ctx_new ();                  printf("Context pointer = %p\n",context);
    requester = zmq_socket (context, ZMQ_REQ); printf("Requester pointer = %p\n",requester);
    zmq_connect (requester, "tcp://localhost:5555");
/*---------------------------------^^^^^^^^^^^^^^---------PC-local-interface------*/
    int request_nbr;
    for (request_nbr = 0; request_nbr != 10; request_nbr++) {
        char buffer [10];                      printf("Sending Hello %d\n", request_nbr);
        zmq_send (requester, "Hello", 5, 0);
        zmq_recv (requester, buffer, 10, 0);   printf("Received World %d\n", request_nbr);
    }
    zmq_close (requester);
    zmq_ctx_destroy (context);
    return 0;
}

可能还想阅读更多有关 ZeroMQ 相关主题的内容 here

结语:

O/P 中报告的故障实际上被掩盖了，并且仍然隐藏在 API 检测不到的情况下。 ZeroMQ 允许一个 接入点 有 0+ 运输级 -同时连接，给定正确的语法和满足其他条件。

调用 zmq_connect( reguester, "tcp://<address-not-intended-but-correct>:<legal-port>" ) 将导致法律上公平的状态，并且不会报告任何已定义和记录的可能错误状态的案例，因为所有此类案例都没有真正发生:

EINVAL
The endpoint supplied is invalid.

EPROTONOSUPPORT
The requested transport protocol is not supported.

ENOCOMPATPROTO
The requested transport protocol is not compatible with the socket type.

ETERM
The ØMQ context associated with the specified socket was terminated.

ENOTSOCK
The provided socket was invalid.

EMTHREAD
No I/O thread is available to accomplish the task.

有机会至少不知何故- “检测” 麻烦在于强制执行另一种异常/错误，但推迟到 { zmq_recv() | zmq_recv() } 的调用中。以非阻塞形式，这些可能会变成报告 EAGAIN或者可能是 EFSM因为没有完成端到端重新确认的 ZMTP 协议(protocol)握手(在远程 RPi-server-side 的 PC-localhost-port 上没有任何交易对手)。这也需要预先设置 zmq_setsockopt( responder, ZMQ_IMMEDIATE, 1 )和其他配置细节。

下一个，在 ZeroMQ v4.+ 中，有机会通过一个相当复杂的实例化策略 int zmq_socket_monitor (void *socket, char *endpoint, int events); 使用“检查套接字”来检查 AccessPoint 内部报告的事件的子集。通过 连接到接入点的内部inproc:// 运输级~这里 "inproc://myPCsocketAccessPOINT_monitor" 像这样:

rc = zmq_socket_monitor( responder,                               // AccessPoint to monitor
                        "inproc://myPCsocketAccessPOINT_monitor", // symbolinc name
                         ZMQ_ALL_EVENTS                           // scope of Events
                         );

这样创建的内部监控“inspection-socket”接下来可能会得到 zmq_connect() -ed喜欢:

void             *my_end_of_monitor_socket = zmq_socket ( context, ZMQ_PAIR );
rc = zmq_connect( my_end_of_monitor_socket,               // local-end PAIR-socket AccessPoint
                 "inproc://myPCsocketAccessPOINT_monitor" // symbolic name
                  );

最后，我们可以使用它来读取一系列事件(并采取相应的行动):

int event = get_monitor_event( my_end_of_monitor_socket, NULL, NULL );
if (event == ZMQ_EVENT_CONNECT_DELAYED) { ...; }
if (event == ... ) { ...; }

使用琐碎的 get_monitor_event() 作为工具像这样，它处理一些读取和解释多部分消息的内部规则，这些消息是从附加到接入点的实例化“内部”监视器中排序而来的:

// Read one event off the monitor socket; return value and address
// by reference, if not null, and event number by value. Returns -1
// in case of error.

static int
get_monitor_event ( void *monitor, int *value, char **address )
{
// First frame in message contains event number and value
   zmq_msg_t msg;
   zmq_msg_init (&msg);
   if (zmq_msg_recv (&msg, monitor, 0) == -1) return -1; // Interrupted, presumably
   assert (zmq_msg_more (&msg));

   uint8_t *data = (uint8_t *) zmq_msg_data (&msg);
   uint16_t event = *(uint16_t *) (data);

   if (value) *value = *(uint32_t *) (data + 2);

// Second frame in message contains event address
   zmq_msg_init (&msg);
   if (zmq_msg_recv (&msg, monitor, 0) == -1) return -1; // Interrupted, presumably
   assert (!zmq_msg_more (&msg));

   if (address) {
      uint8_t *data = (uint8_t *) zmq_msg_data (&msg);
      size_t size = zmq_msg_size (&msg);
      *address = (char *) malloc (size + 1);
      memcpy (*address, data, size);
      (*address)[size] = 0;
   }
   return event;
}

可以监控哪些内部 API 事件？

从 v4.2 API 的状态开始，有一组“内部”-monitor(able) internal-API-events:

ZMQ_EVENT_CONNECTED
The socket has successfully connected to a remote peer. The event value is the file descriptor (FD) of the underlying network socket. Warning: there is no guarantee that the FD is still valid by the time your code receives this event.
ZMQ_EVENT_CONNECT_DELAYED
A connect request on the socket is pending. The event value is unspecified.
ZMQ_EVENT_CONNECT_RETRIED
A connect request failed, and is now being retried. The event value is the reconnect interval in milliseconds. Note that the reconnect interval is recalculated at each retry.
ZMQ_EVENT_LISTENING
The socket was successfully bound to a network interface. The event value is the FD of the underlying network socket. Warning: there is no guarantee that the FD is still valid by the time your code receives this event.
ZMQ_EVENT_BIND_FAILED
The socket could not bind to a given interface. The event value is the errno generated by the system bind call.
ZMQ_EVENT_ACCEPTED
The socket has accepted a connection from a remote peer. The event value is the FD of the underlying network socket. Warning: there is no guarantee that the FD is still valid by the time your code receives this event.
ZMQ_EVENT_ACCEPT_FAILED
The socket has rejected a connection from a remote peer. The event value is the errno generated by the accept call.
ZMQ_EVENT_CLOSED
The socket was closed. The event value is the FD of the (now closed) network socket.
ZMQ_EVENT_CLOSE_FAILED
The socket close failed. The event value is the errno returned by the system call. Note that this event occurs only on IPC transports.
ZMQ_EVENT_DISCONNECTED
The socket was disconnected unexpectedly. The event value is the FD of the underlying network socket. Warning: this socket will be closed.
ZMQ_EVENT_MONITOR_STOPPED
Monitoring on this socket ended.
ZMQ_EVENT_HANDSHAKE_FAILED
The ZMTP security mechanism handshake failed. The event value is unspecified.

NOTE: in DRAFT state, not yet available in stable releases.
ZMQ_EVENT_HANDSHAKE_SUCCEED

NOTE: as new events are added, the catch-all value will start returning them. An application that relies on a strict and fixed sequence of events must not use ZMQ_EVENT_ALL in order to guarantee compatibility with future versions.
Each event is sent as two frames. The first frame contains an event number (16 bits), and an event value (32 bits) that provides additional data according to the event number. The second frame contains a string that specifies the affected TCP or IPC endpoint.