tinyhttpd ------ C 语言实现最简单的 HTTP 服务器

工作流程：

1>服务器启动，在指定端口或随机选取端口绑定httpd服务。

2>收到一个http请求时(其实就是listen端口accept的时候)，派生一个线程运行accept_request函数。

3>取出http请求中method(get或post)和url,对于get方法，如果有携带参数，则query_string指针指向url中?后面的get参数。

4>格式化url到path数组，表示浏览器请求的文件路径，在tinyhttpd中服务器文件是在htdocs文件夹下。当url以/结尾，或者url是个目录，则默认在path中加上index.thml，表示访问主页。

5>如果文件路径合法，对于无参数的get请求，直接输出服务器文件到浏览器，即用http格式写到套接字上，跳到(10)。其他情况(带参数get，post方法，url为科执行文件)，则调用execute_cgi函数执行cgi脚本。

6>读取整个http请求并丢弃，如果是post则找出content-length，把http状态码200写到套接字里面。

7>建立两个管道，cgi_input和cgi_output,并fork一个子进程。

8>在子进程中，把stdout重定向到cgi_output的写入端，把stdin重定向到cgi_input的读取端，关闭cgi_input的写入端和cgi_output的读取端，是指request_method的环境变量，get的话设置query_string的环境变量，post的话设置content-length的环境变量，这些环境变量都是为了给cgi脚本调用，接着用execl运行cgi程序。

9>在父进程中，关闭cgi_input的读取端和cgi_output的写入端，如果post的话，把post数据写入到cgo_input，已被重定向到stdin读取cgi_output的管道输出到客户端，等待子进程结束。

10>关闭与浏览器的链接，完成一次http请求与回应，因为http是无连接的。

/* J. David's webserver */
/* This is a simple webserver.
 * Created November 1999 by J. David Blackstone.
 * CSE 4344 (Network concepts), Prof. Zeigler
 * University of Texas at Arlington
 */
/* This program compiles for Sparc Solaris 2.6.
 * To compile for Linux:
 *  1) Comment out the #include <pthread.h> line.
 *  2) Comment out the line that defines the variable newthread.
 *  3) Comment out the two lines that run pthread_create().
 *  4) Uncomment the line that runs accept_request().
 *  5) Remove -lsocket from the Makefile.
 */
#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
"

void accept_request(int);
//处理从套接字上监听到的一个HTTP请求，在这里可以很大一部分的体现服务器处理请求的流程
void bad_request(int);
//返回给客户端这是个错误请求，HTTP状态码是400 BAD REQUEST
void cat(int, FILE *);
//读取服务器上某个文件写到socket套接字
void cannot_execute(int);
//主要执行在处理cgi程序的处理，也是个主要函数
void error_die(const char *);
//把错误信息写到perror并退出
void execute_cgi(int, const char *, const char *, const char *);
//运行cgi程序的处理，也是哥主函数
int get_line(int, char *, int);
//读取套接字的一行，把回车换行等情况都统一为换行符结束
void headers(int, const char *);
//把HTTP相应头写到套接字
void not_found(int);
//主要处理找不到请求的文件时的情况
void serve_file(int, const char *);
//调用cat把服务器文件返回给浏览器
int startup(u_short *);
//初始化httpd服务，包括建立套接字，绑定端口，进行监听等
void unimplemented(int);
//返回给浏览器表示接收到的http请求所用的method不被支持

/**********************************************************************/
/* 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;

    numchars = get_line(client, buf, sizeof(buf));
    //读取 client端发送的数据并且 返回的参数是 numchars
    i = 0;
    j = 0;
    while (!ISspace(buf[j]) && (i < sizeof(method) - 1))
    {
        method[i] = buf[j];
        i++;
        j++;
    }
    //得到传递的参数是post 还是get方法 还是其他
    method[i] = '';

    if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
    {
    //回给浏览器表明收到的 HTTP 请求所用的 method 不被支持
        unimplemented(client);
        return;
    }

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

    i = 0;
    //http请求行格式是 method urI http-version
    while (ISspace(buf[j]) && (j < sizeof(buf)))
        j++;
    while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))
    {
        url[i] = buf[j]; //包含请求行中的URI
        i++;
        j++;
    }
    url[i] = '';
    ///获取发送数据中的URI
    if (strcasecmp(method, "GET") == 0)
    {
    //get方法 是将参数传递在URI中的？后面如果元素多用&进行链接
        query_string = url;
        while ((*query_string != '?') && (*query_string != ''))
            query_string++;
         // get 请求？ 后面为参数
     if (*query_string == '?')
        {
            cgi = 1;
            *query_string = '';
            query_string++;
        }
    }
    //格式url存储在path数组 并且html存储在 htdocs文件中
    sprintf(path, "htdocs%s", url);
    if (path[strlen(path) - 1] == '/')
        strcat(path, "index.html");  //字符串进行衔接 + index.html
   //stat函数 根据path路径 获取文件内容 存储在 st 结构体中  成功返回0 错误返回-1
    if (stat(path, &st) == -1)
    {
        while ((numchars > 0) && strcmp("
", buf))  /* read & discard headers */
            numchars = get_line(client, buf, sizeof(buf));
        not_found(client);
    }
    else
    {
        if ((st.st_mode & S_IFMT) == S_IFDIR)
            strcat(path, "/index.html");
        //文件的权限 属主 属组 其它 三种任一个拥有执行权
    if ((st.st_mode & S_IXUSR) ||
                (st.st_mode & S_IXGRP) ||
                (st.st_mode & S_IXOTH)    )
            cgi = 1;
    //调用cat 把服务器文件返回给浏览器  post方法或者拥有执行权限
        if (!cgi)
            serve_file(client, path);
        else
            execute_cgi(client, path, method, query_string)
    //运行cgi程序的处理，也是个主要函数
    }

    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
");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "Content-type: text/html
");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "
");
    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.
");
    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 */
/**********************************************************************/
//读取服务器上的某个文件 写到socket套接字上
void cat(int client, FILE *resource)
{
    char buf[1024];

    fgets(buf, sizeof(buf), resource);
    //检测流上的文件结束符  如果文件结束，则返回非0值，否则返回0，文件结束符只能被clearerr()清除。
    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
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-type: text/html
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<P>Error prohibited CGI execution.
");
    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)
{
    perror(sc);
    exit(1);
}

/**********************************************************************/
/* Execute a CGI script.  Will need to set environment variables as
 * appropriate.
 * Parameters: client socket descriptor
 *             path to the CGI script */
/**********************************************************************/

//运行cgi程序  也是个主函数
void execute_cgi(int client, const char *path,
                 const char *method, const char *query_string)
{
    //在父进程中，关闭cgi_input的读入端和cgi_output的写入端，如果post的话
    //把post数据写入到cgi_input，已被重定向到stdin，读取cgi_output的管道
    //输出到客户端，该管道输入是stdout，接着关闭所有管道，等待子进程结束。
    
    char buf[1024];
    int cgi_output[2];
    int cgi_input[2];
    //cgi_output[1] cgi_input[1] 为输入端
    //cgi_input[0] cgi_output[0] 为输出端
    pid_t pid;
    int status;
    int i;
    char c;
    int numchars = 1;
    int content_length = -1;

    buf[0] = 'A';
    buf[1] = '';
    //读入请求头
    if (strcasecmp(method, "GET") == 0)
        while ((numchars > 0) && strcmp("
", buf))  /* read & discard headers */
            numchars = get_line(client, buf, sizeof(buf));
    else    /* POST */
    {
        numchars = get_line(client, buf, sizeof(buf));
        while ((numchars > 0) && strcmp("
", buf))
        {
            buf[15] = '';
            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
");
    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];
    //把stdout重定向到cgi_output的写入端
        dup2(cgi_output[1], 1);
    //把stdin重定向到cgi_input的读入端
        dup2(cgi_input[0], 0);
    //关闭cgi_output的读入端 和 cgi_input的 写入端
        close(cgi_output[0]);
        close(cgi_input[1]);
    //设置request_method的环境变量
        sprintf(meth_env, "REQUEST_METHOD=%s", method);
        putenv(meth_env);
        if (strcasecmp(method, "GET") == 0)
        {
        //设置query_string的环境变量
            sprintf(query_env, "QUERY_STRING=%s", query_string);
            putenv(query_env);
        }
        else     /* POST */
        {
        //设置content_length的环境变量
            sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
            putenv(length_env);
        }
        //用execl运行cgi程序
    execl(path, path, NULL);
        exit(0);
    }
    else        /* parent */
    {
        close(cgi_output[1]);
        close(cgi_input[0]);
        //关闭cgi_output的 写入端 和 cgi_input的读取端
    if (strcasecmp(method, "POST") == 0)
       //接受post的数据
            for (i = 0; i < content_length; i++)
            {
                recv(client, &c, 1, 0);
                write(cgi_input[1], &c, 1);
                //讲post数据写入cgi_input，并且重定向到stdin中
             }
    //读取cgi_output的管道输出到客户端，该管道输入时stdout
        while (read(cgi_output[0], &c, 1) > 0)
            send(client, &c, 1, 0);
    //关闭管道
        close(cgi_output[0]);
        close(cgi_input[1]);
        //等待子进程
    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 = '';
    int n;

    while ((i < size - 1) && (c != '
'))
    {
        //每次接受一个字符
    n = recv(sock, &c, 1, 0);
        /* DEBUG printf("%02X
", c); */
        if (n > 0)
        {
            if (c == '
')
            {
                n = recv(sock, &c, 1, MSG_PEEK);
                /* DEBUG printf("%02X
", c); */
                if ((n > 0) && (c == '
'))
                    recv(sock, &c, 1, 0);
                else
                    c = '
';
            }
            buf[i] = c;
            i++;
        }
        else
            c = '
';
    }
    buf[i] = '';

    return(i);
}

/**********************************************************************/
/* Return the informational HTTP headers about a file. */
/* Parameters: the socket to print the headers on
 *             the name of the file */
/**********************************************************************/
//http 响应体
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
");//响应的状态行
    send(client, buf, strlen(buf), 0);
    strcpy(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/html
"); //响应头
    send(client, buf, strlen(buf), 0);
    strcpy(buf, "
");        //响应正文段
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Give a client a 404 not found status message. */
/**********************************************************************/
void not_found(int client)
{
    //客户端发送的请求无法实现
    char buf[1024];
   //响应行
    sprintf(buf, "HTTP/1.0 404 NOT FOUND
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    //响应头
    sprintf(buf, "Content-Type: text/html
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "
");
    //响应头和响应正文段之间有一个空行 表示响应行结束
    send(client, buf, strlen(buf), 0);
    //响应正文段 text/html
    sprintf(buf, "<HTML><TITLE>Not Found</TITLE>
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<BODY><P>The server could not fulfill
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "your request because the resource specified
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "is unavailable or nonexistent.
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</BODY></HTML>
");
    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] = '';
    while ((numchars > 0) && strcmp("
", buf))  /* read & discard headers */
        numchars = get_line(client, buf, sizeof(buf));

    resource = fopen(filename, "r");
    if (resource == NULL)
        not_found(client);
    else
    {
        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 allo        //响应正文段cate 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;
    struct sockaddr_in name;
    //建立套接字
    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);
    //绑定端口和ip
    if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
        error_die("bind");
    if (*port == 0)  /* if dynamically allocating a port */
    {
        int namelen = sizeof(name);
        if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
            error_die("getsockname");
        *port = ntohs(name.sin_port);
    }
    //监听
    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)
{
    //发回响应信息  http的请求方法不被接受
    char buf[1024];
    //返回501 错误 未实现 (Not implemented)是指Web 服务器不理解或不支持发送给它的 HTTP 数据流中找到的 HTTP 方法
    sprintf(buf, "HTTP/1.0 501 Method Not Implemented
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/html
");//响应头
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "
");
    send(client, buf, strlen(buf), 0); //响应正文段
    sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</TITLE></HEAD>
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<BODY><P>HTTP request method not supported.
");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</BODY></HTML>
");
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/

int main(void)
{
    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
", port);

    while (1)
    {
        client_sock = accept(server_sock,
                             (struct sockaddr *)&client_name,
                             &client_name_len);
        //建立链接
    if (client_sock == -1)
            error_die("accept");
        /* accept_request(client_sock); */
        //多线程进行控制
    if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0)
            perror("pthread_create");
    }

    close(server_sock);

    return(0);
}