c - 在C中通过http将图像发送到浏览器

Question

A 是 C 的新手，我正在尝试用 C 实现 Web 服务器。我可以成功地将 .txt 和 .html 文件发送到浏览器。但是，我无法发送任何图像，尽管我有正确的内容类型 header ，可以识别图像是 .jpg。这是我用来查找内容类型的函数:

char *find_content_type (char *filename) {
    char *p;  // pointer to the type found
    int i;
    char buf1[MAXFILENAME]; // used to store the extension of the file
    char buf2[MAXFILENAME];

    p = (char *)malloc(30);
    strcpy(buf1, filename);
    printf("name of file requested: %s \n", buf1);

    /* find the extension: */
    for (i = 0; i<strlen(buf1); i++) {
        if ( buf1[i] == '.' ) {
            strcpy(buf2, &buf1[i]);
        }
    }
    /* find the type: */
    if ( strcmp(buf2, ".html") == 0 || strcmp (buf2, ".hml") == 0) {
        strcpy (buf2, "Content-Type: text/html \r\n");
    }

    else if ( strcmp(buf2, ".txt") == 0) {
        strcpy (buf2, "Content-Type: text/plain \r\n");
    }

    else if ( strcmp(buf2, ".jpg") == 0 || strcmp (buf2, ".jpeg") == 0) {
        strcpy (buf2, "Content-Type: image/jpeg \r\n");
    }

    else if ( strcmp(buf2, ".gif") == 0) {
        strcpy (buf2, "Content-Type: image/gif \r\n");
    }

    else {
        strcpy (buf2, "Content-Type: application/octet-stream \r\n");
    }

     p = buf2;
    printf ("content-type: %s\n", p);
    //return "Content-type: image/jpeg\r\n";
    return p;
}

我有一个函数可以解析请求并返回一个指向所请求文件名称的指针。在 main 中我只接受请求并写入浏览器，所有数据解析和响应构造都在 main 之外。下面的函数形成将发送到浏览器的响应:

char * response_generator (char *filename) {
    char *p; // pointer to the whole response
    char *content_type; // pointer to the content type
    char data [MAXLEN], data2[MAXLEN - 100], data3 [MAXLEN - 200];
    /* vars needed for finding the length of the file */
    struct stat filestat;
    FILE *fp;
    int fd;
    off_t size;
    char filesize[6], name[30]; 

    strcpy (name, filename);
    if ( ((fd = open (filename, O_RDONLY)) < -1) || (fstat(fd, &filestat) < 0) ) {
        printf ("Error in measuring the size of the file");
    }
    if (filename == NULL) {
        // I have measured the length of my 400.html file
        strcpy (data, "HTTP/1.1 400 Bad Request\r\nContent-Length: 327\r\nContent-Type: text/html\r\n");
        fp = fopen ("400index.html", "r");
    }
    sprintf (filesize, "%d", filestat.st_size); // put the file size of buffer, so we can add it to the response header

    fp = fopen (name, "r");
    if (fp == NULL || strcmp (name,"404") == 0 ) {
         // I have measured the length of my 404.html file
         strcpy (data, "HTTP/1.1 404 Not Found\r\nContent-Length: 165\r\nContent-Type: text/html\r\n");
        fp = fopen ("404index.html", "r");
    }
    else if (fp != NULL) {
        strcpy (data, "HTTP/1.1 200 OK\r\nContent-Length: ");
        /* content-length: */
        strcat (data, filesize);
        strcat (data, "\r\n");
        /* content-type: */
        strcpy (data2, find_content_type (name));
        printf ("content-type: %s\n", find_content_type (name));
        strcat (data, data2);
    }

    else {
        // I have measured the length of my 500.html file
        strcpy (data, "HTTP/1.1 500 Internal Server Error\r\nContent-Length: 190\r\nContent-Type: text/html\r\n");
        fp = fopen ("500index.html", "r");
    }      

    strcat (data, "Connection: keep-alive\r\n\r\n");
    fread (data3, sizeof(char), filestat.st_size + 150, fp); /* read the file in a data buffer: */
    strcat (data, data3);
    data[strlen(data)] = '\0';
    p = data;
    fclose(fp);
    return p;
}

它的功能又长又重，但正如我提到的，当我必须发送图像时，它似乎可以正常工作。当我打印要在终端上发送的请求时，我得到的是:

 HTTP/1.1 200 OK
 Content-Length: 49657
 Content-Type: image/jpeg 
 Connection: keep-alive

 ÿØÿà

如果你有任何想法，请告诉我我做错了什么。谢谢!

Answer 1

我设法修复了它。有很多问题。首先，我删除了所有 (str*())，因为如评论中所述，它们并不意味着处理二进制数据。我删除了不必要的缓冲区数量。现在我有两个:第一个用于存储响应 header ，可以安全地在其上使用 strcat/strcpy 等。我一收到标题响应就将其写入浏览器。第二个缓冲区包含浏览器请求的文件的数据。我从文件中读取它后立即将它写入服务器，因此我避免了任何可能导致问题的操作。这是我的 response_generator 代码:

void response_generator (int conn_fd, char *filename) {

    /* vars needed for finding the length of the file */
    struct stat filestat;
    FILE *fp;
    int fd;
    char header_buff [HEADER_LEN];
    char file_buff [MAXLEN];
    char filesize[7];//, name[30]; 

    if ( ((fd = open (filename, O_RDONLY)) < -1) || (fstat(fd, &filestat) < 0) ) {
        printf ("Error in measuring the size of the file");
}

    if (filename == NULL) {
        // I have measured the length of my 400.html file
        strcpy (header_buff, "HTTP/1.1 400 Bad Request\r\nContent-Length: 327\r\nContent-Type: text/html\r\n");
        fp = fopen ("400index.html", "r");
    }

    sprintf (filesize, "%zd", filestat.st_size); // put the file size of buffer, so we can add it to the response header
    fp = fopen (filename, "r");
    if (fp == NULL) {
    printf ("fp is null or filename = 404\n");
        // I have measured the length of my 404.html file
        strcpy (header_buff, "HTTP/1.1 404 Not Found\r\nContent-Length: 165\r\nContent-Type: text/html\r\n");
        fp = fopen ("404index.html", "r");
    }

    else if (fp != NULL) {
        strcpy (header_buff, "HTTP/1.1 200 OK\r\nContent-Length: ");
        /* content-length: */
        strcat (header_buff, filesize);
        strcat (header_buff, "\r\n");
        /* content-type: */
        strcat (header_buff, find_content_type (filename));
        printf ("%s\n", find_content_type (filename));
    }

    else {
        // I have measured the length of my 500.html file
        strcpy (header_buff, "HTTP/1.1 500 Internal Server Error\r\nContent-Length: 190\r\nContent-Type: text/html\r\n");
        fp = fopen ("500index.html", "r");
    }        

    strcat (header_buff, "Connection: keep-alive\r\n\r\n");
    write (conn_fd, header_buff, strlen(header_buff));

    fread (file_buff, sizeof(char), filestat.st_size + 1, fp);
    fclose(fp);
    write (conn_fd, file_buff, filestat.st_size);

    close (conn_fd);
}

非常感谢您对我的问题的评论，他们确实帮助我修复了这段代码。