一、问题引入

通过 Tinyhttpd：运行测试【1】 和 抓包分析【2】，基本完成了对程序的功能测试和通信原理。此时可以进一步对源码进行分析，本文不考虑代码一行一行的分析，仅对关键部分代码解析。

二、解决过程

2-1 main()函数

主函数主要创建http的监听套接字，等待客户端的连接。一旦有新客户端连接http，则创建一个新线程与客户端通信，而主线程（即main函数）继续等待客户端的连接。

int main(void)
{
    int server_sock = -1;
    u_short port = 10080;
    int client_sock = -1;
    struct sockaddr_in client_name;
    socklen_t  client_name_len = sizeof(client_name);
    pthread_t newthread;

    server_sock = startup(&port);
    printf("httpd running on port %d\n", port);

    while (1)
    {
        client_sock = accept(server_sock,(struct sockaddr *) &client_name, &client_name_len);
        if (client_sock == -1)
            error_die("accept");
        /* accept_request(&client_sock); */
        if (pthread_create(&newthread , NULL, (void *)accept_request, (void *)(intptr_t)client_sock) != 0)
            perror("pthread_create");
    }
    close(server_sock);

    return(0);
}

2-2 startup()函数

如果熟悉套接字编程，那么肯定对上面的代码肯定很眼熟。该函数的功能就是服务器在指定端口创建监听套接字。但同时对监听的端口做了冗余处理，若指定的端口为0，则动态的申请一个端口号。

int startup(u_short *port)
{
    int httpd = 0;
    int on = 1;
    struct sockaddr_in name;

    httpd = socket(PF_INET, SOCK_STREAM, 0);
    if (httpd == -1)
        error_die("socket");
    memset(&name, 0, sizeof(name));
    name.sin_family = AF_INET;
    name.sin_port = htons(*port);
    name.sin_addr.s_addr = htonl(INADDR_ANY);
    if ((setsockopt(httpd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on))) < 0)  /* set port reuse */
    {  
        error_die("setsockopt failed");
    }
    if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
        error_die("bind");
    if (*port == 0)  /* if dynamically allocating a port */
    {
        socklen_t namelen = sizeof(name);
        if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
            error_die("getsockname");
        *port = ntohs(name.sin_port);
    }
    if (listen(httpd, 5) < 0)
        error_die("listen");
    return(httpd);
}

2-3 accept_request()函数

该线程回调函数是整个程序最核心、最关键的部分，它包含了如何解析客户端发送的http request和服务区根据客户端的请求如何发送http respond。

void accept_request(void *arg)
{
    int client = (intptr_t)arg;
    char buf[1024];
    size_t numchars;
    char method[255];
    char url[255];
    char path[512];
    size_t i, j;
    struct stat st;
    int cgi = 0;      /* becomes true if server decides this is a CGI
                       * program */
    char *query_string = NULL;

    numchars = get_line(client, buf, sizeof(buf));
    i = 0; j = 0;
    while (!ISspace(buf[i]) && (i < sizeof(method) - 1))
    {
        method[i] = buf[i];
        i++;
    }
    j=i;
    method[i] = '\0';

    if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
    {
        unimplemented(client);
        return;
    }

    if (strcasecmp(method, "POST") == 0)
        cgi = 1;

    i = 0;
    while (ISspace(buf[j]) && (j < numchars))
        j++;
    while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < numchars))
    {
        url[i] = buf[j];
        i++; j++;
    }
    url[i] = '\0';

    if (strcasecmp(method, "GET") == 0)
    {
        query_string = url;
        while ((*query_string != '?') && (*query_string != '\0'))
            query_string++;
        if (*query_string == '?')
        {
            cgi = 1;
            *query_string = '\0';
            query_string++;
        }
    }

    sprintf(path, "htdocs%s", url);
    if (path[strlen(path) - 1] == '/')
        strcat(path, "index.html");
    if (stat(path, &st) == -1) {
        while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
            numchars = get_line(client