实现简易http服务器

tinyhttpd工作流程

核心函数说明

• startup: 绑定监听套接字
• accept_request 每次收到请求，创建一个线程来处理接收到的请求
• serve_file 接读取文件返回给请求的http客户端
• execute_cgi 执行cgi文件

注意事项

index.html必须没有执行权限，否则看不到内容，并且会产生Program received signal SIGPIPE, Broken pipe，因为程序中如果有可执行权限会当cgi脚本处理。 所以假如html有执行权限先把它去除了，chmod 600 index.html

color.cgi、date.cgi必须要有执行权限，chmod 755 *.cgi

操作

在项目文件目录下执行make

在浏览器中输入 127.0.0.1:port

测试color.cgi

测试index2.html

测试date.cgi

httpd.c

/* 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 <unistd.h>
##include <arpa/inet.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"

/**
 * 每次收到请求，创建一个线程来处理接收到的请求
 * 把client_sock转成地址作为参数传入pthread_create
 */
void accept_request(void *arg);

/**
 * 错误请求
 */
void bad_request(int);

/**
 * 读取文件
 */
void cat(int, FILE *);

/**
 * 无法执行
 */
void cannot_execute(int);

/**
 * 错误输出
 */
void error_die(const char *);

/**
 * 执行cig脚本
 */
void execute_cgi(int, const char *, const char *, const char *);

/**
 * 得到一行数据，只要发现c为\n，就认为是一行结束，如果读到\r，在用MSG_PEEK的方式读入一个字符，如果是\n，从socket用读出
 * 如果是下个字符则不处理，将c置为\n，结束。如果读到的数据为0中断，或者小于0，也视为结束，c置为\n
 */
int get_line(int, char *, int);

/**
 * 返回httpd头
 */
void headers(int, const char *);

/**
 * 没有发现文件
 */
void not_found(int);

/**
 * 如果不是CGI文件，直接读取文件返回给请求的http客户端
 */
void server_file(int, const char *);

/**
 * 开启tcp连接，绑定端口等操作
 */
int startup(u_short *);

/**
 * 如果不是Get或者Post，就报方法没有实现
 */
void unimplemented(int);

// Http请求，后续主要是处理这个头
//
// GET / HTTP/1.1
// Host: 192.168.0.23:47310
// Connection: keep-alive
// Upgrade-Insecure-Requests: 1
// User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36
// Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*; q = 0.8
// Accept - Encoding: gzip, deflate, sdch
// Accept - Language : zh - CN, zh; q = 0.8
// Cookie: __guid = 179317988.1576506943281708800.1510107225903.8862; monitor_count = 5
//

// POST / color1.cgi HTTP / 1.1
// Host: 192.168.0.23 : 47310
// Connection : keep - alive
// Content - Length : 10
// Cache - Control : max - age = 0
// Origin : http ://192.168.0.23:40786
// Upgrade - Insecure - Requests : 1
// User - Agent : Mozilla / 5.0 (Windows NT 6.1; WOW64) AppleWebKit / 537.36 (KHTML, like Gecko) Chrome / 55.0.2883.87 Safari / 537.36
// Content - Type : application / x - www - form - urlencoded
// Accept : text / html, application / xhtml + xml, application / xml; q = 0.9, image / webp, */*;q=0.8
// Referer: http://192.168.0.23:47310/
// Accept-Encoding: gzip, deflate
// Accept-Language: zh-CN,zh;q=0.8
// Cookie: __guid=179317988.1576506943281708800.1510107225903.8862; monitor_count=281
// Form Data
// color=gray

/**********************************************************************/
/* 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(void *arg) {
    // socket
    int client = (intptr_t) arg;
    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;
    // 根据上面的Get请求，可以看到这边就是取第一行
    // 这边都是在处理第一条http信息
    // "GET / HTTP/1.1\n"
    numchars = get_line(client, buf, sizeof(buf));
    i = 0; j = 0;

    // 第一行字符串提取Get
    while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) {
        method[i] = buf[j];
        i++; j++;
    }

    // 结束
    method[i] = '\0';

    // 判断是Get还是Post
    if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) {
        unimplemented(client);
        return ;
    }

    // 如果是POST，cgi置为1
    if (strcasecmp(method, "POST") == 0) {
        cgi = 1;
    }

    i = 0;
    // 跳过空格
    while (ISspace(buf[j]) && (j < sizeof(buf))) {
        j++;
    }

     //得到 "/"   注意：如果你的http的网址为http://192.168.0.23:47310/index.html
     //               那么你得到的第一条http信息为GET /index.html HTTP/1.1，那么
     //               解析得到的就是/index.html
    while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf))) {
        url[i] = buf[j];
        i++; j++;
    }
    url[i] = '\0';

    // 判断Get请求
    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++;
        }
    }

    // 路径
    sprintf(path, "htdocs%s", url);

    // 默认地址，解析道的路径如果是/，则自动加上index.html
    if (path[strlen(path) - 1] == '/') {
        strcat(path, "index.html");
    }

    // 获得文件信息
    if (stat(path, &st) == -1) {
        // 把所有http信息读出然后丢弃
        while ((numchars > 0) && strcmp("\n", buf)) { /* read & discard headers */
            numchars = get_line(client, buf, sizeof(buf));
        }
        // 没有找到
        not_found(client);
    } else {
        if ((st.st_mode & S_IFMT) == S_IFDIR) {
            strcat(path, "/index.html");
        }
        // 如果你的文件默认是有执行全县的，自动解析成cgi程序，如果有执行权限但是不能执行，会接受到报错信号
        if ((st.st_mode & S_IXUSR) 
            (st.st_mode & S_IXGRP) 
            (st.st_mode & S_IXOTH)  ) {
            cgi = 1;
        }
        if (!cgi) {
            // 接读取文件返回给请求的http客户端
            server_file(client, path);
        } else {
            // 执行cgi文件
            execute_cgi(client, path, method, query_string);
        }
        // 执行完毕关闭socket
    }
    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/1.0 500 BAD REQUEST\r\n");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "Content-type: test/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 */
/**********************************************************************/

// 得到文件内容，发送
void cat(int client, FILE *resource) {
    char buf[1024];

    fgets(buf, sizeof(buf), resource);
    // 循环读
    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) {
    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 */
/**********************************************************************/
void execute_cgi(int client, const char *path,
                        const char *method, const char *query_string) {
    // 缓冲区
    char buf[1024];

    // 2根管道
    int cgi_output[2];
    int cgi_input[2];

    // 进程pid和状态
    pid_t pid;
    int status;

    int i;
    char c;

    // 读取的字符数
    int numchars = 1;

    // http的content_length
    int content_length = -1;

    // 默认字符
    buf[0] = 'A'; buf[1] = '\0';

    // 忽略大小写比较字符串
    if (strcasecmp(method, "GET") == 0) {
        // 读取数据，把整个header都读掉，以为Get写死了直接读取index.html，没有必要分析余下的http信息了
        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)) {
            // 如果是POST请求，就需要得到Content-Length，Content-Length：这个字符串一共长15位，所以
            // 取出头部一句后，将第16位设置结束符，进行比较
            // 第16位置为结束
            buf[15] = '\0';
            if (strcasecmp(buf, "Content-Length:") == 0) {
                // 内存从第17位开始就是长度，将17位开始的所有字符串转成整数就是content-length
                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);

    // 建立output管道
    if (pipe(cgi_output) < 0) {
        cannot_execute(client);
        return ;
    }

    // 建立input管道
    if (pipe(cgi_input) < 0) {
        cannot_execute(client);
        return ;
    }

    //       fork后管道都复制了一份，都是一样的
    //       子进程关闭2个无用的端口，避免浪费             
    //       ×<------------------------->1    output
    //       0<-------------------------->×   input

    //       父进程关闭2个无用的端口，避免浪费             
    //       0<-------------------------->×   output
    //       ×<------------------------->1    input
    //       此时父子进程已经可以通信

    // fork进程，子进程用于执行CGI
    // 父进程用于收数据以及发送子进程处理的回复数据
    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];

        // 子进程输出重定向到output管道的1端
        dup2(cgi_output[1], 1);
        // 子进程输入重定向到input管道的0端
        dup2(cgi_input[0], 0);

        // 关闭无用管道
        close(cgi_output[0]);
        close(cgi_input[1]);

        // CGI环境变量
        sprintf(meth_env, "REQUEST_METHOD=%s", method);
        putenv(meth_env);
        if (strcasecmp(method, "GET") == 0) {
            sprintf(query_env, "REQUEST_STRING=%s", query_string);
            putenv(query_env);
        } else { /* POST */
            sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
            putenv(length_env);
        }
        // 替换执行path
        execl(path, path, NULL);
        // int m = execl(path, path, NULL);
        // 如果path有问题，例如将html网页改成可执行的，但是执行后m为-1
        // 退出子进程，管道被破坏，但是父进程还在往里面写东西，触发Program received signal SIGPIPE, Broken pipe.
        exit(0);
    } else { /* parent */
        // 关闭无用管道
        close(cgi_output[1]);
        close(cgi_input[0]);

        if (strcasecmp(method, "POST") == 0) {
            for (i = 0; i < content_length; i++) {
                // 得到post请求数据，写到input管道中，供子进程使用
                recv(client, &c, 1, 0);
                write(cgi_input[1], &c, 1);
            }
        }

        // 从output管道读到子进程处理后的信息，然后send出去
        while (read(cgi_output[0], &c, 1) > 0) {
            send(client, &c, 1, 0);
        }

        // 完成操作后关闭管道
        close(cgi_output[0]);
        close(cgi_input[1]);

        // 等待子进程返回
        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) */
/**********************************************************************/

//得到一行数据,只要发现c为\n,就认为是一行结束，如果读到\r,再用MSG_PEEK的方式读入一个字符，如果是\n，从socket用读出
//如果是下个字符则不处理，将c置为\n，结束。如果读到的数据为0中断，或者小于0，也视为结束，c置为\n
int get_line(int sock, char *buf, int size) {
    int i = 0;
    char c = '\0';
    int n;

    while ((i < size - 1) && (c != '\n')) {
        n = recv(sock, &c, 1, 0);
        /* DEBUG printf("%02X\n", c); */
        if (n > 0) {
            if (c == '\r') {
                // 偷窥一个字节，如果是\n就读走
                n = recv(sock, &c, 1, MSG_PEEK);
                /* DEBUG printf("%02X\n", c); */
                if ((n > 0) && (c == '\n')) {
                    recv(sock, &c, 1, 0);
                } else {
                    //不是\n（读到下一行的字符）或者没读到，置c为\n 跳出循环,完成一行读取
                    c = '\n';
                }
            }
            buf[i] = c;
            i++;
        } else {
            c = '\n';
        }
    }
    buf[i] = '\0';

    return (i);
}

/**********************************************************************/
/* Return the informational HTTP headers about a file. */
/* Parameters: the socket to print the headers on
 *             the name of the file */
/**********************************************************************/

// 加入http的headers
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. */
/**********************************************************************/

//如果资源没有找到得返回给客户端下面的信息
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 */
/**********************************************************************/

//如果不是CGI文件，直接读取文件返回给请求的http客户端
void server_file(int client, const char *filename) {
    FILE *resource = NULL;
    int numchars = 1;
    char buf[1024];

    // 默认字符
    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 {
        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;
    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);
    // 绑定socket
    if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0) {
        error_die("bind");
    }
    // 如果端口没有设置，提供个随机端口
    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);
    }
    // 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 */
/**********************************************************************/

//如果方法没有实现，就返回此信息
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(void) {
    int server_sock = -1;
    u_short port = 0;
    int client_sock = -1;
    struct sockaddr_in client_name;

    // 这边要为socklen_t类型
    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) {
        // 接受请求，函数原型
        // ##include <sys/types.h>
        // ##include <sys/socket.h>
        // int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
        client_sock = accept(server_sock, (struct sockaddr *)&client_name, &client_name_len);
        if (client_sock == -1) {
            error_die("accept");
        }
        /* accept_request(client_sock) */

        // 每次收到请求，创建一个线程来处理接收到的请求
        // 把client_sock转成地址作为参数传入pthread_create
        if (pthread_create(&newthread, NULL, (void *)accept_request, (void *)(intptr_t)client_sock) != 0) {
            perror("pthread_create");
        }
    }
    close(server_sock);

    return 0;
}

simpleclient.c

##include <stdio.h>
##include <sys/types.h>
##include <sys/socket.h>
##include <netinet/in.h>
##include <arpa/inet.h>
##include <unistd.h>
##include <stdlib.h>

int main(int argc, char *argv[]) {
    int sockfd;
    int len;
    struct sockaddr_in address;
    int result;
    char ch = 'A';

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = inet_addr("127.0.0.1");
    address.sin_port = htons(9734);
    len = sizeof(address);
    result = connect(sockfd, (struct sockaddr *)&address, len);

    if (result == -1) {
        perror("oops: client1");
        exit(1);
    }
    write(sockfd, &ch, 1);
    read(sockfd, &ch, 1);
    printf("char from server = %c\n", ch);
    close(sockfd);
    exit(0);
}

本文作者：jujimeizuo
本文地址： https://blog.jujimeizuo.cn/2022/11/09/tinyhttpd/
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