在C中通过http发送图像到浏览器

Question

A 是 C 的新手，我正在尝试用 C 实现一个 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标头，可以识别图像是 .jpg。\n这是我用来查找内容类型的函数：

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char *find_content_type (char *filename) {\n    char *p;  // pointer to the type found\n    int i;\n    char buf1[MAXFILENAME]; // used to store the extension of the file\n    char buf2[MAXFILENAME];\n\n    p = (char *)malloc(30);\n    strcpy(buf1, filename);\n    printf("name of file requested: %s \\n", buf1);\n\n    /* find the extension: */\n    for (i = 0; i<strlen(buf1); i++) {\n        if ( buf1[i] == \'.\' ) {\n            strcpy(buf2, &buf1[i]);\n        }\n    }\n    /* find the type: */\n    if ( strcmp(buf2, ".html") == 0 || strcmp (buf2, ".hml") == 0) {\n        strcpy (buf2, "Content-Type: text/html \\r\\n");\n    }\n\n    else if ( strcmp(buf2, ".txt") == 0) {\n        strcpy (buf2, "Content-Type: text/plain \\r\\n");\n    }\n\n    else if ( strcmp(buf2, ".jpg") == 0 || strcmp (buf2, ".jpeg") == 0) {\n        strcpy (buf2, "Content-Type: image/jpeg \\r\\n");\n    }\n\n    else if ( strcmp(buf2, ".gif") == 0) {\n        strcpy (buf2, "Content-Type: image/gif \\r\\n");\n    }\n\n    else {\n        strcpy (buf2, "Content-Type: application/octet-stream \\r\\n");\n    }\n\n     p = buf2;\n    printf ("content-type: %s\\n", p);\n    //return "Content-type: image/jpeg\\r\\n";\n    return p;\n}\n

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我有一个函数可以解析请求并返回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：

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char * response_generator (char *filename) {\n    char *p; // pointer to the whole response\n    char *content_type; // pointer to the content type\n    char data [MAXLEN], data2[MAXLEN - 100], data3 [MAXLEN - 200];\n    /* vars needed for finding the length of the file */\n    struct stat filestat;\n    FILE *fp;\n    int fd;\n    off_t size;\n    char filesize[6], name[30]; \n\n    strcpy (name, filename);\n    if ( ((fd = open (filename, O_RDONLY)) < -1) || (fstat(fd, &filestat) < 0) ) {\n        printf ("Error in measuring the size of the file");\n    }\n    if (filename == NULL) {\n        // I have measured the length of my 400.html file\n        strcpy (data, "HTTP/1.1 400 Bad Request\\r\\nContent-Length: 327\\r\\nContent-Type: text/html\\r\\n");\n        fp = fopen ("400index.html", "r");\n    }\n    sprintf (filesize, "%d", filestat.st_size); // put the file size of buffer, so we can add it to the response header\n\n    fp = fopen (name, "r");\n    if (fp == NULL || strcmp (name,"404") == 0 ) {\n         // I have measured the length of my 404.html file\n         strcpy (data, "HTTP/1.1 404 Not Found\\r\\nContent-Length: 165\\r\\nContent-Type: text/html\\r\\n");\n        fp = fopen ("404index.html", "r");\n    }\n    else if (fp != NULL) {\n        strcpy (data, "HTTP/1.1 200 OK\\r\\nContent-Length: ");\n        /* content-length: */\n        strcat (data, filesize);\n        strcat (data, "\\r\\n");\n        /* content-type: */\n        strcpy (data2, find_content_type (name));\n        printf ("content-type: %s\\n", find_content_type (name));\n        strcat (data, data2);\n    }\n\n    else {\n        // I have measured the length of my 500.html file\n        strcpy (data, "HTTP/1.1 500 Internal Server Error\\r\\nContent-Length: 190\\r\\nContent-Type: text/html\\r\\n");\n        fp = fopen ("500index.html", "r");\n    }      \n\n    strcat (data, "Connection: keep-alive\\r\\n\\r\\n");\n    fread (data3, sizeof(char), filestat.st_size + 150, fp); /* read the file in a data buffer: */\n    strcat (data, data3);\n    data[strlen(data)] = \'\\0\';\n    p = data;\n    fclose(fp);\n    return p;\n}\n

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它的功能相当长且繁重，但正如我提到的，当我必须发送图像时，它似乎可以很好地工作。当我打印要在终端上发送的请求时，我得到的是：

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 HTTP/1.1 200 OK\n Content-Length: 49657\n Content-Type: image/jpeg \n Connection: keep-alive\n\n \xc3\xbf\xc3\x98\xc3\xbf\xc3\xa0\n

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如果您有任何想法，请告诉我我做错了什么。谢谢你！

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Answer 1

我设法修复它。存在多个问题。首先，我删除了所有 (str*())，因为，正如评论中提到的，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标头，可以安全地在其上使用 strcat/strcpy 等。我一收到标头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。我从文件中读取数据后立即将其写入服务器，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。