libwebsockets libwebsockets-webserver.c hacking

Posted 2020-09-22 zengjf

/**********************************************************************************
 *                libwebsockets libwebsockets-webserver.c hacking
 * 说明：
 *     找点libwesockets的资料看看，主要是为后续使用做准备。
 *
 *                                           2017-6-9 深圳 龙华樟坑村 曾剑锋
 *********************************************************************************/

一、参考文档：
    1. libwebsockets如何使用？
        https://www.zhihu.com/question/57474416
    2. libwebsockets: Simple HTTP server
        https://medium.com/@martin.sikora/libwebsockets-simple-http-server-2b34c13ab540
    3. martinsik/libwebsockets-webserver.c
        https://gist.github.com/martinsik/3216369
    4. martinsik/index.html
        https://gist.github.com/martinsik/3654228

二、代码解读：
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>
    #include <libwebsockets.h>
    
    
    // 浏览器websocket访问的回调函数
    static int callback_http(struct libwebsocket_context *context,
                             struct libwebsocket *wsi,
                             enum libwebsocket_callback_reasons reason, void *user,
                             void *in, size_t len)
    {
        
        switch (reason) {
            // 头文件链接描述，出了作为Server会喷出一行连接建立以外，这里不进行任何处理
            // http://git.warmcat.com/cgi-bin/cgit/libwebsockets/tree/lib/libwebsockets.h#n260
            case LWS_CALLBACK_CLIENT_WRITEABLE:
                printf("connection established\n");
                
            // 头文件链接描述
            // http://git.warmcat.com/cgi-bin/cgit/libwebsockets/tree/lib/libwebsockets.h#n281
            case LWS_CALLBACK_HTTP: {
                char *requested_uri = (char *) in;
                printf("requested URI: %s\n", requested_uri);       // 喷出访问的URL
                
                // uri为"/"访问，直接给出hello world
                if (strcmp(requested_uri, "/") == 0) {
                    void *universal_response = "Hello, World!";
                    // http://git.warmcat.com/cgi-bin/cgit/libwebsockets/tree/lib/libwebsockets.h#n597
                    libwebsocket_write(wsi, universal_response,
                                       strlen(universal_response), LWS_WRITE_HTTP);
                    break;
    
                } else {
                    // try to get current working directory
                    char cwd[1024];
                    char *resource_path;
                    
                    if (getcwd(cwd, sizeof(cwd)) != NULL) {
                        // allocate enough memory for the resource path
                        // 动态分配路径存储空间
                        resource_path = malloc(strlen(cwd) + strlen(requested_uri));
                        
                        // join current working direcotry to the resource path
                        // 合成资源路径
                        sprintf(resource_path, "%s%s", cwd, requested_uri);
                        printf("resource path: %s\n", resource_path);
                        
                        // 获取文件扩展名
                        char *extension = strrchr(resource_path, ‘.‘);
                        char *mime;
                        
                        // choose mime type based on the file extension
                        // 设置扩展类型
                        if (extension == NULL) {
                            mime = "text/plain";
                        } else if (strcmp(extension, ".png") == 0) {
                            mime = "image/png";
                        } else if (strcmp(extension, ".jpg") == 0) {
                            mime = "image/jpg";
                        } else if (strcmp(extension, ".gif") == 0) {
                            mime = "image/gif";
                        } else if (strcmp(extension, ".html") == 0) {
                            mime = "text/html";
                        } else if (strcmp(extension, ".css") == 0) {
                            mime = "text/css";
                        } else {
                            mime = "text/plain";
                        }
                        
                        // by default non existing resources return code 400
                        // for more information how this function handles headers
                        // see it‘s source code
                        // http://git.warmcat.com/cgi-bin/cgit/libwebsockets/tree/lib/parsers.c#n1896
                        libwebsockets_serve_http_file(wsi, resource_path, mime);
                        
                    }
                }
                
                // close connection
                // 关闭连接
                libwebsocket_close_and_free_session(context, wsi,
                                                    LWS_CLOSE_STATUS_NORMAL);
                break;
            }
            default:
                printf("unhandled callback\n");
                break;
        }
        
        return 0;
    }
    
    /* list of supported protocols and callbacks */
    // 配置协议以及其回调函数
    static struct libwebsocket_protocols protocols[] = {
        /* first protocol must always be HTTP handler */
        
        {
            "http-only",    /* name */
            callback_http,  /* callback */
            0               /* per_session_data_size */
        },
        {
            NULL, NULL, 0   /* End of list */
        }
        
    };
    
    int main(void) {
        // server url will be http://localhost:7681
        int port = 8080;
        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
        // 创建上下文
        context = libwebsocket_create_context(port, interface, protocols,
                                              libwebsocket_internal_extensions,
                                              cert_path, key_path, -1, -1, opts);
        
        if (context == NULL) {
            fprintf(stderr, "libwebsocket init failed\n");
            return -1;
        }
        
        printf("starting server...\n");
        
        // infinite loop, the only option to end this serer is
        // by sending 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 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;
    }