如何在服务器端（在我的特定情况下）验证用户请求？

Question

In my client server application, the client request the camera server to send one or more images with some given resolution (width x height). I have hard-coded the resolution.

Let's say the camera is not capable of taking that specified size of the image the user requests. In that case, the server has to deal with that request and take the appropriate action (eg let the user know that the size is invalid, or input again). Can someone give me any hints how do I implement that? Or if someone could clue me with any better way of doing it than I am doing it right now. I may not need any code (if someone can answer with it, its fine), I just require a theoretical explanation. Thanks for your attention.

My working code [If complete code is necessary, please ask for it]:

Client:

   printf("chose resolution\nsmall = 1 \nmedium = 2 \nlarge = 3 \nelse defualt\n  ");
    cin >> res;
    if (res == 1) {
        char rr[10] = { "160x120" };
        strcat(RES, rr); // store the rr (160x120) into RES
    }   else if (res == 2) {
        char rr[10] = { "640x480" };
        strcat(RES, rr);
    }   else if (res == 3) {
        char rr[10] = { "1024x768" };
        strcat(RES, rr);
    }
    else {
        char rr[10] = { "320x200" };
        strcat(RES, rr);
    }

Server:

for (;;) {

            recv(sock_CONNECTION,fps_res, sizeof(fps_res),NULL);

            stream = capture_open_stream(IMAGE_JPEG, fps_res);

            for(;;)
            {
            int Sbytes=0;
            frame        = capture_get_frame(stream);
            data = capture_frame_data(frame);

            int size = capture_frame_size(frame);

            send(sock_CONNECTION,(char*)&size,sizeof(int),NULL);
            Sbytes=send(sock_CONNECTION,data, size, NULL);


            capture_frame_free(frame);

            if(Sbytes<0){

            break;

            }

            }
            exit(0);

    }

Answer 1

Get the size of the frame after this line of code and compare with client frame. And also check whether you have received a frame or not based original request from client.

int size = capture_frame_size(frame);

after the above line of code check whether you have received the frame based on original request. If not send a error message to client that frame with requested resolution is not available.

Please let me know if not yet clear.