libwebsockets在接收后写入所有活动连接

Question

我正在摆弄一个libwebsocket教程，试图使它在通过给定协议从连接接收到消息后，向实现该协议的所有活动连接发送响应。我已经使用了函数libwebsocket_callback_all_protocol，但是它并没有按照我的想法从它的名字中执行我认为应该做的事情(我不太确定它在文档中做了什么)。

目标是打开两个网页，当其中一个网页发送信息时，结果将传递给两个网页。下面是我的代码-你会看到libwebsocket_callback_all_protocol是在main中调用的(我想它目前什么都不做...)：

#include <stdio.h>
#include <stdlib.h>
#include <libwebsockets.h>
#include <string.h>

static int callback_http(struct libwebsocket_context * this,
                         struct libwebsocket *wsi,
                         enum libwebsocket_callback_reasons reason, void *user,
                         void *in, size_t len)
{
    return 0;
}

static int callback_dumb_increment(struct libwebsocket_context * this,
                                   struct libwebsocket *wsi,
                                   enum libwebsocket_callback_reasons reason,
                                   void *user, void *in, size_t len)
{

    switch (reason) {
        case LWS_CALLBACK_ESTABLISHED: // just log message that someone is connecting
            printf("connection established\n");
            break;
        case LWS_CALLBACK_RECEIVE: { // the funny part
            // create a buffer to hold our response
            // it has to have some pre and post padding. You don't need to care
            // what comes there, libwebsockets will do everything for you. For more info see
            // http://git.warmcat.com/cgi-bin/cgit/libwebsockets/tree/lib/libwebsockets.h#n597
            unsigned char *buf = (unsigned char*) malloc(LWS_SEND_BUFFER_PRE_PADDING + len +
                                                         LWS_SEND_BUFFER_POST_PADDING);

            int i;

            // pointer to `void *in` holds the incomming request
            // we're just going to put it in reverse order and put it in `buf` with
            // correct offset. `len` holds length of the request.
            for (i=0; i < len; i++) {
                buf[LWS_SEND_BUFFER_PRE_PADDING + (len - 1) - i ] = ((char *) in)[i];
            }

            // log what we recieved and what we're going to send as a response.
            // that disco syntax `%.*s` is used to print just a part of our buffer
            // http://stackoverflow.com/questions/5189071/print-part-of-char-array
            printf("received data: %s, replying: %.*s\n", (char *) in, (int) len,
                 buf + LWS_SEND_BUFFER_PRE_PADDING);

            // send response
            // just notice that we have to tell where exactly our response starts. That's
            // why there's `buf[LWS_SEND_BUFFER_PRE_PADDING]` and how long it is.
            // we know that our response has the same length as request because
            // it's the same message in reverse order.
            libwebsocket_write(wsi, &buf[LWS_SEND_BUFFER_PRE_PADDING], len, LWS_WRITE_TEXT);

            // release memory back into the wild
            free(buf);
            break;
        }
        default:
            break;
    }


    return 0;
}

static struct libwebsocket_protocols protocols[] = {
    /* first protocol must always be HTTP handler */
    {
        "http-only",   // name
        callback_http, // callback
        0,              // per_session_data_size
        0
    },
    {
        "dumb-increment-protocol", // protocol name - very important!
        callback_dumb_increment,   // callback
        0,                          // we don't use any per session data
        0

    },
    {
        NULL, NULL, 0, 0   /* End of list */
    }
};

int main(void) {
    // server url will be http://localhost:9000
    int port = 9000;
    const char *interface = NULL;
    struct libwebsocket_context *context;
    // we're not using ssl
    const char *cert_path = NULL;
    const char *key_path = NULL;
    // no special options
    int opts = 0;

    // create libwebsocket context representing this server
    struct lws_context_creation_info info;
    memset(&info, 0, sizeof info);   

    info.port = port;
    info.iface = interface;
    info.protocols = protocols;
    info.extensions = libwebsocket_get_internal_extensions();
    info.ssl_cert_filepath = cert_path;
    info.ssl_private_key_filepath = key_path;
    info.gid = -1;
    info.uid = -1;
    info.options = opts;
    info.user = NULL;
    info.ka_time = 0;
    info.ka_probes = 0;
    info.ka_interval = 0;

    /*context = libwebsocket_create_context(port, interface, protocols,
                                          libwebsocket_get_internal_extensions,
                                          cert_path, key_path, -1, -1, opts);
   */
    context = libwebsocket_create_context(&info);
    if (context == NULL) {
        fprintf(stderr, "libwebsocket init failed\n");
        return -1;
    }

    libwebsocket_callback_all_protocol(&protocols[1], LWS_CALLBACK_RECEIVE);

    printf("starting server...\n");

    // infinite loop, to end this server send SIGTERM. (CTRL+C)
    while (1) {
        libwebsocket_service(context, 50);
        // libwebsocket_service will process all waiting events with their
        // callback functions and then wait 50 ms.
        // (this is a single threaded webserver and this will keep our server
        // from generating load while there are not requests to process)
    }

    libwebsocket_context_destroy(context);

    return 0;
}

Answer 1

我也有同样的问题，LWS_CALLBACK_ESTABLISHED上的libwebsocket_write生成了一些随机的段错误，所以使用邮件列表的libwebsocket开发者Andy Green告诉我正确的方法是使用libwebsocket_callback_on_writable_all_protocol，文件test-server/test-server.c在库源代码中显示了使用示例。

libwebsocket_callback_on_writable_all_protocol(libwebsockets_get_protocol(wsi))

它可以很好地通知所有实例，但它只在所有连接的实例中调用write方法，并不定义要发送的数据。您需要自己管理数据。样例源文件test-server.c显示了执行此操作的样例环形缓冲区。

http://ml.libwebsockets.org/pipermail/libwebsockets/2015-January/001580.html

希望能有所帮助。

Answer 2

根据我从文档中快速获取的信息，为了向所有客户端发送消息，您应该做的是将客户端连接时可以访问的struct libwebsocket * wsi存储在某个位置(以向量、哈希图、数组等形式存储)。

然后，当您收到一条消息并希望广播它时，只需在所有wsi *实例上调用libwebsocket_write。

不管怎样，这就是我要做的。