tinyhttpd 是一个不到 500 行的超轻量型 Http Server很适合初学者，帮助我们快速掌握unix socket编程 和 http请求流程。看完所有源码，真的感觉有很大收获，无论是 unix 的编程，还是 GET/POST 的 Web 处理流程，都清晰了不少。

直接从github下载

注释源码如下：

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <sys/stat.h>
#include <pthread.h>
#include <sys/wait.h>
#include <stdlib.h>
#define ISspace(x) isspace((int)(x))
#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"
// 从套接字监听HTTP请求
void accept_request(int);
// 返回错误请求代码
void bad_request(int);
// 读取服务器上的文件到套接字
void cat(int, FILE *);
// 执行cgi发生错误
void cannot_execute(int);
// 吧错误信息写到perror并退出
void error_die(const char *);
// 执行cgi
void execute_cgi(int, const char *, const char *, const char *);
// 读取一行套接字
int get_line(int, char *, int);
// 把http响应头写到套接字
void headers(int, const char *);
// 找不到文件
void not_found(int);
// 调用cat把吴福气文件返回客户端
void serve_file(int, const char *);
// 初始化http server
int startup(u_short *);
// 返回给浏览器表明收到的 HTTP 请求所用的 method 不被支持
void unimplemented(int);
/**********************************************************************/
/* A request has caused a call to accept() on the server port to
 * return.  Process the request appropriately.
 * Parameters: the socket connected to the client */
/**********************************************************************/
void accept_request(int client)
{
    char buf[1024];
    int 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;
    /* 读取一行数据 */
    numchars = get_line(client, buf, sizeof(buf));
    printf("buf:%s\n", buf);
    i = 0; j = 0;
    /* 将数据 复制到method中，直到空格或长度超过 */
    while (!ISspace(buf[j]) && (i < sizeof(method) - 1))
    {
        method[i] = buf[j];
        i++; j++;
    }
    method[i] = '\0';
    printf("method:%s\n", method);
    /* 如果不是GET请求 或 POST请求 */
    if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
    {
        /* 返回请求类型不支持到客户端 */
        printf("uniplemented");
        unimplemented(client);
        return;
    }
    /*如果是POST请求 则执行cgi */
    if (strcasecmp(method, "POST") == 0)
        cgi = 1;

    i = 0;
    /* 转到下一个空格后的数据*/
    /* 跳过空格  */ 
    while (ISspace(buf[j]) && (j < sizeof(buf)))
        j++;
    /* 获取url */
    while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))
    {
        url[i] = buf[j];
        i++; j++;
    }
    url[i] = '\0';
    if (strcasecmp(method, "GET") == 0)
    {
        query_string = url;
        /* 获取url参数 */
        while ((*query_string != '?') && (*query_string != '\0'))
            query_string++;
        /* 如果有参数 ，执行cgi*/
        if (*query_string == '?')
        {
            cgi = 1;
            /* 跳过？*/
            *query_string = '\0';
            query_string++;
        }
    }
    /* 生成文件地址path */
    sprintf(path, "htdocs%s", url);
    printf("%s", path);
    /* 如果url为 / 这访问 index.html*/
    if (path[strlen(path) - 1] == '/')
        strcat(path, "index.html");
    /* 打开path文件*/
    if (stat(path, &st) == -1) {
        /* 打开文件失败 */
        while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
            numchars = get_line(client, buf, sizeof(buf));
        /* 返回403 错误 */
        not_found(client);
    }
    else /* 打开文件成功 */
    {
        if ((st.st_mode & S_IFMT) == S_IFDIR)
            strcat(path, "/index.html");
        if ((st.st_mode & S_IXUSR) ||
            (st.st_mode & S_IXGRP) ||
            (st.st_mode & S_IXOTH)    )
            cgi = 1;
        if (!cgi) /* 发送文件内容到客户端 */
            serve_file(client, path);
        else /* 执行cgi */
            execute_cgi(client, path, method, query_string);
        }

    close(client);
}

/**********************************************************************/
/* Inform the client that a request it has made has a problem.
 * Parameters: client socket */
/**********************************************************************/
void bad_request(int client)
{
    char buf[1024];

    sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "Content-type: text/html\r\n");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "\r\n");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "<P>Your browser sent a bad request, ");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "such as a POST without a Content-Length.\r\n");
    send(client, buf, sizeof(buf), 0);
}

/**********************************************************************/
/* Put the entire contents of a file out on a socket.  This function
 * is named after the UNIX "cat" command, because it might have been
 * easier just to do something like pipe, fork, and exec("cat").
 * Parameters: the client socket descriptor
 *             FILE pointer for the file to cat */
/**********************************************************************/
void cat(int client, FILE *resource)
{
    char buf[1024];
    /* 读取文件内容到buf */
    fgets(buf, sizeof(buf), resource);
    /* 读取玩所有内容并发送到客户端 */
    while (!feof(resource))
    {
        send(client, buf, strlen(buf), 0);
        fgets(buf, sizeof(buf), resource);
    }
}

/**********************************************************************/
/* Inform the client that a CGI script could not be executed.
 * Parameter: the client socket descriptor. */
/**********************************************************************/
void cannot_execute(int client)
{
    char buf[1024];

    sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-type: text/html\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<P>Error prohibited CGI execution.\r\n");
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Print out an error message with perror() (for system errors; based
 * on value of errno, which indicates system call errors) and exit the
 * program indicating an error. */
/**********************************************************************/
void error_die(const char *sc)
{
    /* 打印错误信息 */
    perror(sc);
    exit(1);
}

/**********************************************************************/
/*CGI(Common Gateway Interface 通用网关接口)
 * 作用：
 *  提取用户提交的表单信息
 *  处理表单信息
 *  输出，返回html响应*/

/* Execute a CGI script.  Will need to set environment variables as
 * appropriate.
 * Parameters: client socket descriptor
 *             path to the CGI script */
/**********************************************************************/
void execute_cgi(int client, const char *path,
                 const char *method, const char *query_string)
{
    char buf[1024];
    int cgi_output[2];
    int cgi_input[2];
    pid_t pid;
    int status;
    int i;
    char c;
    int numchars = 1;
    int content_length = -1;
    
    buf[0] = 'A'; buf[1] = '\0';
    if (strcasecmp(method, "GET") == 0)
        while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
            numchars = get_line(client, buf, sizeof(buf));
    else    /* POST */
    {
        numchars = get_line(client, buf, sizeof(buf));
        while ((numchars > 0) && strcmp("\n", buf))
        {
            buf[15] = '\0';
            if (strcasecmp(buf, "Content-Length:") == 0)
                content_length = atoi(&(buf[16]));
            numchars = get_line(client, buf, sizeof(buf));
        }
        if (content_length == -1) 
        {
            bad_request(client);
            return;
        }
    }   
    
    sprintf(buf, "HTTP/1.0 200 OK\r\n");
    send(client, buf, strlen(buf), 0);
    
    if (pipe(cgi_output) < 0) 
    {
        cannot_execute(client);
        return;
    }
    if (pipe(cgi_input) < 0) 
    {
        cannot_execute(client);
        return;
    }
    
    if ( (pid = fork()) < 0 ) 
    {
        cannot_execute(client);
        return;
    }
    if (pid == 0)  /* child: CGI script */
    {
        char meth_env[255];
        char query_env[255];
        char length_env[255];
            
        dup2(cgi_output[1], 1);
        dup2(cgi_input[0], 0);
        close(cgi_output[0]);
        close(cgi_input[1]);
        sprintf(meth_env, "REQUEST_METHOD=%s", method);
        putenv(meth_env);
        if (strcasecmp(method, "GET") == 0) 
        {
            sprintf(query_env, "QUERY_STRING=%s", query_string);
            putenv(query_env);
        }
        else {   /* POST */
            sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
            putenv(length_env);
        }
        execl(path, path, NULL);
        exit(0);
    } else {    /* parent */
        close(cgi_output[1]);
        close(cgi_input[0]);
        if (strcasecmp(method, "POST") == 0)
            for (i = 0; i < content_length; i++) 
            {
                recv(client, &c, 1, 0);
                write(cgi_input[1], &c, 1);
            }
        while (read(cgi_output[0], &c, 1) > 0)
        send(client, &c, 1, 0);
                
        close(cgi_output[0]);
        close(cgi_input[1]);
        waitpid(pid, &status, 0);
    }
}

/**********************************************************************/
/* Get a line from a socket, whether the line ends in a newline,
 * carriage return, or a CRLF combination.  Terminates the string read
 * with a null character.  If no newline indicator is found before the
 * end of the buffer, the string is terminated with a null.  If any of
 * the above three line terminators is read, the last character of the
 * string will be a linefeed and the string will be terminated with a
 * null character.
 * Parameters: the socket descriptor
 *             the buffer to save the data in
 *             the size of the buffer
 * Returns: the number of bytes stored (excluding null) */
/**********************************************************************/
int get_line(int sock, char *buf, int size)
{
    int i = 0;
    char c = '\0';
    int n;
    
    /* 循环读取直到长度超过size或者读到了行末 */
    while ((i < size - 1) && (c != '\n'))
    {
        /* 获取客户端发送的数据 （获取 1 个字符存放在c中)，
         * flag = 0 从tcp buffer 中复制数据并将它从tcp buffer,
         * 中移除*/
        n = recv(sock, &c, 1, 0);
        /* DEBUG printf("%02X\n", c); */
        if (n > 0)/* 读取到了数据 */
        {
            if (c == '\r')/*如果是行末 读取下一行 */
            {
                /* msg_peek 仅把tcp buffer中的数据督导buf中，
                 * 并不会把读取的数据从tcpbuffer中移除，再次
                 * 调用时任然读取到的时这个数据 */
                n = recv(sock, &c, 1, MSG_PEEK);
                /* DEBUG printf("%02X\n", c); */
                if ((n > 0) && (c == '\n'))
                    /* 如果接收到的是 \r\n则将\n从tcp buffer中移除 */
                    recv(sock, &c, 1, 0);
                else
                    c = '\n';
            }
            buf[i] = c;
            i++;
        }
        else
            c = '\n';
    }
    buf[i] = '\0';
    
    /* 返回读取到的个数 */
    return(i);
}

/**********************************************************************/
/* Return the informational HTTP headers about a file. */
/* Parameters: the socket to print the headers on
 *             the name of the file */
/**********************************************************************/
void headers(int client, const char *filename)
{
    char buf[1024];
    (void)filename;  /* could use filename to determine file type */

    strcpy(buf, "HTTP/1.0 200 OK\r\n");
    send(client, buf, strlen(buf), 0);
    strcpy(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/html\r\n");
    send(client, buf, strlen(buf), 0);
    strcpy(buf, "\r\n");
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Give a client a 404 not found status message. */
/**********************************************************************/
void not_found(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<BODY><P>The server could not fulfill\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "your request because the resource specified\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "is unavailable or nonexistent.\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</BODY></HTML>\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Send a regular file to the client.  Use headers, and report
 * errors to client if they occur.
 * Parameters: a pointer to a file structure produced from the socket
 *              file descriptor
 *             the name of the file to serve */
/**********************************************************************/
void serve_file(int client, const char *filename)
{
    FILE *resource = NULL;
    int numchars = 1;
    char buf[1024];

    buf[0] = 'A'; buf[1] = '\0';
    while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
        numchars = get_line(client, buf, sizeof(buf));

    resource = fopen(filename, "r");
    if (resource == NULL)
        not_found(client);
    else
    {
        /* 向客户端发送 header和内容*/
        headers(client, filename);
        cat(client, resource);
    }
    fclose(resource);
}

/**********************************************************************/
/* This function starts the process of listening for web connections
 * on a specified port.  If the port is 0, then dynamically allocate a
 * port and modify the original port variable to reflect the actual
 * port.
 * Parameters: pointer to variable containing the port to connect on
 * Returns: the socket */
/**********************************************************************/
int startup(u_short *port)
{
    int httpd = 0; /* 文件描述符*/
    struct sockaddr_in name;

    httpd = socket(PF_INET, SOCK_STREAM, 0);
    /* 出错处理 */
    if (httpd == -1)
        error_die("socket");
    /* 清0 */
    memset(&name, 0, sizeof(name));
    name.sin_family = AF_INET;
    name.sin_port = htons(*port);
    name.sin_addr.s_addr = htonl(INADDR_ANY); /* 全网 */
    
    if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
        error_die("bind");
    
    if (*port == 0)  /* 如果端口为0 则申请一个临时端口 */
    {
        int 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);
}

/**********************************************************************/
/* Inform the client that the requested web method has not been
 * implemented.
 * Parameter: the client socket */
/**********************************************************************/
void unimplemented(int client)
{
    char buf[1024];

    sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/html\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</TITLE></HEAD>\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</BODY></HTML>\r\n");
    send(client, buf, strlen(buf), 0);
}
/**********************************************************************/
int main(int argc, char argv[])
{
    int server_sock = -1;
    u_short port = 0;
    int client_sock = -1;
    struct sockaddr_in client_name;
    int client_name_len = sizeof(client_name);
    pthread_t newthread;
    server_sock = startup(&port);
    printf("httpd running on port %d\n", port);
    while (1)
    {
        /* 开始阻塞接受 */
        client_sock = accept(server_sock,
                           (struct sockaddr *)&client_name,
                           &client_name_len);
        if (client_sock == -1)
            error_die("accept");
        /* 收到客户端连接，创建一个线程处理连接 */
        if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0)
            perror("pthread_create");
    }
    close(server_sock);
    return(0);
}