WEBVTT 00:05.070 --> 00:10.620 So let me show you the demonstration of client and server program so you can see the two windows on 00:10.620 --> 00:15.390 the screen on the left hand side that is in the left window. 00:15.420 --> 00:21.900 I will execute the server process and on the right window I will execute the client process. 00:22.320 --> 00:28.560 So you can see in this directory we have two files server and client dot C, So we will compile these 00:28.560 --> 00:35.640 two files and we will create executable of the server and client process and we will execute each of 00:35.640 --> 00:36.120 them. 00:36.330 --> 00:39.060 So let us compile the server dot c file. 00:39.900 --> 00:44.640 So GCC minus g server dot c minus O server. 00:45.060 --> 00:49.200 So this is the command that you should use to compile your server program. 00:49.350 --> 00:52.230 So it has created a server executable. 00:52.230 --> 01:01.380 You can simply execute this file that is executable so you can see that your server has started and 01:01.380 --> 01:07.740 the first thing the server does is to create master socket file descriptor and the server has successfully 01:07.740 --> 01:13.560 invoked the bind system call and now your server is now waiting on the Accept system call. 01:14.370 --> 01:20.400 So remember the Accept system call is a blocking system call and therefore the execution do not proceed 01:20.430 --> 01:26.220 beyond accept system call until the server receives the connection initiation request from a client. 01:26.250 --> 01:31.890 So at this point of time our server process is actually blocked on accept system call. 01:32.340 --> 01:40.020 Now, on the right hand side, I will compile the client program and I will execute the client program 01:40.020 --> 01:42.210 on the right window. 01:43.710 --> 01:45.990 So compile the client program 01:49.680 --> 01:57.330 so it will create a client executable and now simply execute the client executable. 01:57.330 --> 02:04.200 So when you execute the client program, you can see that the something happens on the server side. 02:04.800 --> 02:12.940 So the moment you execute the client program, the client has created a socket file descriptor, the 02:12.940 --> 02:17.320 client created the communication file descriptor that is data socket. 02:17.380 --> 02:24.160 And the second thing that the client immediately does is to send the connection initiation request to 02:24.160 --> 02:30.910 the server using correct system call so you can see that our server has actually accepted the connection 02:30.910 --> 02:36.820 from the client and now the server is actually waiting for the actual data from the client. 02:37.330 --> 02:38.050 That is. 02:38.050 --> 02:44.860 Now our server has moved to data exchange or data communication phase with the client. 02:44.860 --> 02:50.920 And on the right hand side you can see that the client is now asking the user to send an integer number 02:50.920 --> 02:51.850 to the server. 02:52.660 --> 02:54.460 So let us send one. 02:55.390 --> 03:03.280 You can see on the left hand side that our server process has actually accepted the value one that is 03:03.280 --> 03:06.100 sent by the client and. 03:06.730 --> 03:10.150 It is now waiting for the next data item from the client. 03:12.160 --> 03:16.540 So the client will send two, three, four and let's say five. 03:17.350 --> 03:22.720 So you can see that all these values that is sent by the client is now. 03:23.670 --> 03:30.300 Has now been accepted by the server and the server internally has computed the summation of all these 03:30.300 --> 03:37.440 values, but the server will send back the result to the client only when the client sends zero to the 03:37.440 --> 03:38.100 server. 03:38.550 --> 03:42.150 So let us enter the value zero and see what happens. 03:42.300 --> 03:48.900 So we can see that our client has received the summation of the values that it has sent to the server. 03:49.680 --> 03:56.940 And also the thing to note here is that our client process has now terminated because after receiving 03:56.940 --> 04:02.730 the result from the server, we actually close the connection in the client program. 04:05.730 --> 04:12.060 Whereas on the server side you can see that a server after receiving the value zero from the client 04:12.060 --> 04:14.940 has actually sent the final result. 04:14.940 --> 04:19.290 That is the final summation of all the values it had received from the client. 04:19.650 --> 04:25.920 And after sending back the result to the client or server process, actually closed the connection with 04:25.920 --> 04:27.270 that particular client. 04:27.570 --> 04:36.720 And after that, as we discussed, our server process goes back to the outer infinite loop. 04:37.430 --> 04:43.730 And it get blocked itself on the accept system call that is it is now waiting for the new connection 04:43.730 --> 04:49.580 initiation request from the new client and is now ready to repeat the entire cycle again with the new 04:49.580 --> 04:55.910 client so we can execute the client executable again and again. 04:55.910 --> 05:02.030 You can see that the server that the server has now accepted the connection with this new client again 05:02.030 --> 05:09.380 and it is now again waiting for the integer values from the client and the same process repeats. 05:10.900 --> 05:16.810 And now if I enter zero, you can see that our client process has again received the result. 05:18.050 --> 05:19.580 So this goes on. 05:21.230 --> 05:21.800 Right. 05:21.800 --> 05:27.080 So our client server program is working fine as expected. 05:27.650 --> 05:31.250 But there is one flaw in this client server communication. 05:31.550 --> 05:38.630 And that flaw is that our server process can actually entertain only one client at a time. 05:40.970 --> 05:46.850 To demonstrate this drawback, let us say that we have started the client, right? 05:46.850 --> 05:50.720 And now this client is sending its data items to the server. 05:52.770 --> 05:53.520 Right. 05:53.520 --> 06:00.570 So our separate process at this point of time is now waiting or blocked on the read system call that 06:00.570 --> 06:03.930 is, it is waiting for the next data item from the client. 06:05.340 --> 06:13.650 Now, in the next window on the client side, if I start a new client, that is you can execute a same 06:13.650 --> 06:16.380 client executable in the separate window. 06:16.470 --> 06:24.060 It is as good as some new client has come up and it also wants to get connected with the same server. 06:24.330 --> 06:25.230 So. 06:25.230 --> 06:34.770 So executing the client executable in different windows on your machine is as good as like multiple 06:34.770 --> 06:37.620 clients wants to communicate with the same server. 06:38.250 --> 06:46.470 So you can see that the moment I execute the new client, you can see that our server process has not 06:46.470 --> 06:48.720 responded to this new client. 06:49.590 --> 06:58.240 And if the new client send its data items to the server and after that, if it sends zero, you can 06:58.240 --> 06:59.170 see that. 07:00.450 --> 07:03.150 It has not received any result from the server. 07:03.850 --> 07:08.230 In fact, the server process has not responded to this new client at all. 07:08.800 --> 07:15.910 The reason is that our server process has to be blocked on the accept system call in order to establish 07:15.910 --> 07:17.560 the connection with the new client. 07:17.710 --> 07:23.980 But at this point of time our server process is not blocked on accept system call, but it is blocked 07:23.980 --> 07:25.360 on the read system call. 07:25.720 --> 07:32.170 So our server process is actually waiting for the data item from the first client. 07:32.950 --> 07:43.600 So as long as our server is in a data exchange or data communication state with the first client, any 07:43.600 --> 07:48.760 other client in the system cannot participate in communication with the server. 07:49.690 --> 07:56.860 In a nutshell or in brief, our server process is actually able to handle only one client at a time. 07:57.280 --> 08:00.670 It cannot handle multiple clients at the same time. 08:01.860 --> 08:04.350 So this is the drawback of this server design. 08:04.350 --> 08:11.220 And in our next discussion of client server socket programming, we will try to improve the design of 08:11.220 --> 08:17.130 the server such that our server process will be able to handle multiple clients at the same time. 08:17.790 --> 08:19.740 So you should download this source code. 08:19.740 --> 08:26.310 As I have already mentioned, the path and how to download the source code, compile and execute these 08:26.310 --> 08:29.910 files on your machine and try to analyze what is going on. 08:30.600 --> 08:33.240 And please do not copy paste my code. 08:33.240 --> 08:35.490 Write your own codes from scratch. 08:35.820 --> 08:40.110 It will give you a fair confidence and build your knowledge thoroughly. 08:40.110 --> 08:45.300 If you write each and every line of code by yourself instead of copy pasting my code. 08:46.810 --> 08:48.950 So see you in the next section. 08:48.970 --> 08:49.870 Thank you.