6-2-web-writev.c

#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>

#define BUFFER_SIZE 1024

/*定义两种HTTP状态码和状态信息*/
static const char *status_line[2] = {"200 OK","500 Internal server error"};

int main(int argc, const char *argv[])
{
    if (argc <= 3) 
    {
        fprintf(stderr, "usage: %s ip_address port_number filename\n", basename(argv[0]));
        return 1;
    }
    const char *ip = argv[1];
    int port       = atoi(argv[2]);
    
    /*将目标文件作为程序的第三个参数传入*/
    const char *file_name = argv[3];

    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    inet_pton(AF_INET, ip, &address.sin_addr);
    address.sin_port   = htons(port);

    int sock = socket(PF_INET, SOCK_STREAM, 0);
    assert(sock >=0 );

    int ret = bind(sock, (struct sockaddr *)&address, sizeof(address));
    assert(ret != -1);

    ret = listen(sock, 5);
    assert(ret != -1);

    struct sockaddr_in client;
    socklen_t client_addrlength = sizeof(client);
    int connfd = accept(sock, (struct sockaddr *)&client, &client_addrlength);
    if (connfd < 0) 
    {
        fprintf(stderr, "accept error, errno:%d, strerr:%s\n", errno, strerror(errno));
    }
    else
    {
        /*用于保存HTTP应答的状态行、头部字段和一个空行的缓存区*/
        char header_buf[BUFFER_SIZE];
        memset(header_buf, '\0', sizeof(header_buf));

        /*用于存放目标文件内容的应该用程序缓存*/
        char *file_buf = NULL;
        /*用于获取目标文件的属性，比如是否为目录， 文件大小等*/
        struct stat file_stat;
        /*记录目标文件是否是有效文件*/
        bool valid = true;
        /*缓存区header_buf目前已经使用了多少字节的空间*/
        int len = 0;
        if (stat(file_name, &file_stat) < 0) /*目标文件不存在*/
        {
            valid = false;
        }
        else
        {
            if (S_ISDIR(file_stat.st_mode)) //目标文件是一个目录
            {
                valid = false;
            }
            else if (file_stat.st_mode & S_IROTH) /*当前用户有读取目标文件爱你的权限*/
            {
                /*动态分配缓存区file_buf,
                 * 并指定其大小为目标的大小file_stat.st_size加1,
                 * 然后将目标文件读入缓存区file_buf中*/
                int fd = open(file_name, O_RDONLY);
                file_buf = new char[file_stat.st_size + 1];
                memset(file_buf, '\0', file_stat.st_size + 1);
                if (read(fd, file_buf, file_stat.st_size) < 0) 
                {
                    valid = false;
                }
            }
            else
            {
                valid = false;
            }
        }

        /*如果目标文件有效， 则发送正常的HTTP应答 */
        if (valid) 
        {
            /*下面部分内容将HTTP应答的状态行、
             * “Content-Length”头部字段和一个空行依次加入header_buf中
             * */
            ret = snprintf(header_buf, BUFFER_SIZE - 1, "%s %s\r\n",
                    "HTTP/1.1", status_line[0]);
            len += ret;
            ret = snprintf(header_buf + len, BUFFER_SIZE - 1 - len,
                    "Content-Length: %lld\r\n", (long long)file_stat.st_size);
            /*利用writev将header_buf和file_buf的内容一并写出 */
            struct iovec iv[2];
            iv[0].iov_base = header_buf;
            iv[0].iov_len  = strlen(header_buf);
            iv[1].iov_base = file_buf;
            iv[1].iov_len  = file_stat.st_size;
            ret = writev(connfd, iv, 2);
        }
        else /*如果目标文件无效， 则通知客户端服务器发生了“内部错误”*/
        {
            ret = snprintf(header_buf, BUFFER_SIZE - 1, "%s %s\r\n",
                    "HTTP/1.1", status_line[1]);
            len += ret;
            ret = snprintf(header_buf + len, BUFFER_SIZE - 1 - len, "%s", "\r\n");
            send(connfd, header_buf, strlen(header_buf), 0);
        }
        close(connfd);
        if(file_buf)  //没有分配空间就不需要释放
            delete [] file_buf;
    }

    close(sock);
    return 0;
}