Sending images over http to browser in C

Question

A am new to C and I am trying to implement a web server in C. I can successfully send .txt and .html files to the browser. However, I can't send any images, although I have correct content-type header which recognises that the image is .jpg. Here is the function I use to find the content-type:

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;
}

I have function which parses the request and returns a pointer to the name of the file requested. In main I only accept requests and write to the browser, all data parsing and response constructing is outside main. The function below forms the response which will be sent to the browser:

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;
}

It is pretty long and heavy function, but it seems to work fine apart when I have to send images, as I mentioned. When I print the request to be send on the terminal what I get is:

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

 ÿØÿà

If you have any idea, please tell me what I am doing wrong. Thank you!

Answer 1

I managed to fix it. There were multiple problems. First, I removed all (str*()), because, as mentioned on the comments, they ARE NOT meant to deal with binary data. I removed the unnecessary number of buffers. Now I have two: the first one is for storing the response headers, it is safe to use strcat/strcpy, etc on it. I write to the browser the header response as soon as I have them. The second buffer contains the data of the file that the browser requested. I write it to the server immediately after I have read it from the file, so I avoid any manipulations that might cause problems. Here is my code for the response_generator:

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);
}

Thanks very much for the comments on my problem, they really helped me in fixing this piece of code.