C sockets，jpeg 图像无法正确显示

Question

I'm learning about sockets and Im in the process of creating a socket server which can serve html files, as well as images in the jpeg format. Based on other similar posts I've found, I can't deduce what I'm doing wrong. I use fseek and ftell to get the size of the image, and then I use fread to read those bytes into a malloc 'ed character array, which I then send back. What am I doing wrong?

code for dealing with jpeg files:

else if (!strcmp(getFileExtension(fname), "jpg") || !strcmp(getFileExtension(fname), "jpeg"))
      {
        printf("got a jpeg request\n");
        FILE *fp = fopen(fname, "rb");

        if (fp == NULL)
        {
          perror("Error opening .jpg/.jpeg file");
          status = 500;
          ret = toStr(status);
          statusMessage = " Internal Server Error\n";
          body = "<h1>Server encountered error trying to open jpeg file</h1>";
          mode = html;
          goto shutdown;
        }

        // seek to end of file and get
        // length of the file to read
        fseek(fp, 0, SEEK_END);
        bodySize = ftell(fp);
        printf("file is %d bytes\n", bodySize);

        // seek back to beginning of file
        fseek(fp, 0, SEEK_SET);
        // allocate and read len amt of bytes
        char *data = malloc(bodySize);
        fread(data, sizeof(char), bodySize, fp);
        fclose(fp);

        status = 200;
        ret = toStr(status);
        statusMessage = " OK\n";
        body = data;
        mode = jpeg;
        goto shutdown;
    }

my shutdown code, which simply sets the headers, status codes, etc. The jpeg file data should be within the body variable

    // cleanup and closing
    shutdown:
      // send just the headers first
      size = strlen(header) + strlen(ret) + strlen(statusMessage) + strlen(mode) + 1;
      reply = (char *)malloc(size);
      reply[size - 1] = '\0';
      snprintf(reply, size, "%s%s%s%s", header, ret, statusMessage, mode);
      printf("\n%s\n\n", reply);
      send(new_sd, reply, size, 0);

      // send just body
      if (!strcmp(mode, jpeg)) // jpeg uses bodySize
      {
        printf("body size (%d):\n%s\n", bodySize, body);
        send(new_sd, body, bodySize, 0);
      }
      else // non jpeg uses strlen
      {
        printf("body size (%d):\n%s\n", (int)strlen(body), body);
        send(new_sd, body, strlen(body), 0);
      }

      shutdown(new_sd, SHUT_RDWR);
      close(new_sd);
      exit(0);

Here is my server response to the browser(client):

Answer 1

Nothing stands out to me in terms of the socket code. Instead of this being a socket (only) issue, maybe it is (also) a protocol issue? Possibly a non-compliance issue with the HTTP/1.1 ( RFC 7230 +)? neither Content-Length nor Transfer-Encoding specified? bad line endings? (status line would normally end with OK\r\n not OK\n\n)

Answer 2

shouldn't use snprintf with %s for binary data like jpeg bytes, I believe %s terminates at null byte (0x00) which makes the binary file corrupt.

Also strlen(body) won't work either as strlen will also terminate at null byte (0x00) giving bad length for the jpeg data.

Try memcpy instead.

Open the file with this mode "rb+"

Simple pseudo-code (might not compile)

int jpegDataSize = len;
char* jpegdata = data;
reply_size = strlen(HEADER) + strlen(ret) + strlen(statusMessage) + strlen(mode) + jpegDataSize + 1; //can't use strlen for jpeg because it's binary
reply = (char *)malloc(reply_size);
memcpy(&reply[0], HEADER, strlen(HEADER));
memcpy(&reply[strlen(HEADER)], ret, strlen(ret));
memcpy(&reply[strlen(ret)], statusMessage, strlen(statusMessage));
memcpy(&reply[strlen(statusMessage)], mode, strlen(mode));
memcpy(&reply[strlen(mode)], jpegdata, jpegDataSize); //avoid strlen(jpegdata)
reply[reply_size - 1] = '\0';
printf("\n-------------------------------------\nresponse is (%d): \n%s\n\n", reply_size, reply); //can't use strlen (because jpegdata is binary)
send(new_sd, reply, reply_size, 0); //can't use strlen because jpegdata is binary.
shutdown(new_sd, SHUT_RDWR);
close(new_sd);
exit(0);

Answer 3

Turns out there is no logistical issue to my edited post's code. The problem was that in the shutdown code, when I send the HTTP header reply, I used size as the length for the reply, when I should have used strlen(reply) or size - 1 for send(new_sd, reply, size, 0) .