WEBVTT 00:00.740 --> 00:04.460 Hey, everyone, and welcome back to the Knowledge Portal Video series. 00:04.490 --> 00:09.260 Now, today we will be speaking about partial get request. 00:09.260 --> 00:15.890 So let's get started with a very similar example that we have been discussing since past few lectures. 00:16.400 --> 00:18.320 So you have a client. 00:18.320 --> 00:21.770 So consider this as a web browser or a Telnet. 00:22.100 --> 00:28.460 And on the right hand side you have a web server which has a file called as documentary dot mp4. 00:29.000 --> 00:37.580 Now, when a client makes a request to the web server of type, get so you have a get request on the 00:37.580 --> 00:44.750 documentary.mp for what a web server will do is that it will fetch the entire file and send it back 00:44.750 --> 00:46.100 to the client. 00:46.940 --> 00:56.600 Now what happens if a client wants to see only first five minutes or first let's assume 20s of documentary 00:56.810 --> 01:03.340 and before the client does not really want to see the entire content, just first 20s of the content. 01:03.360 --> 01:06.890 So what client will do along with the get request? 01:06.900 --> 01:09.180 This is the first mandatory step. 01:09.480 --> 01:14.900 Client will also specify that I want to watch only first 20s. 01:14.910 --> 01:19.320 So this is what client will specify to the web server. 01:19.650 --> 01:30.270 Now web server in response will say that here is the first 20s of the data and instead of sending the 01:30.270 --> 01:36.060 entire file, web server will send only partial part of that specific file. 01:36.750 --> 01:45.390 Now, if you look into the response header, you have Http 1.1 and instead of 200, okay, you have 01:45.420 --> 01:47.510 206 partial content. 01:47.520 --> 01:55.020 So this header specifies that the content which is being sent is only partial and it is not the entire 01:55.020 --> 01:55.620 file. 01:55.950 --> 01:59.220 So this is about the partial get request. 01:59.460 --> 02:09.120 So going back to a theoretical perspective, partial get method is used to retrieve only specific content 02:09.120 --> 02:11.400 instead of the entire file. 02:11.550 --> 02:17.490 So if you look into the example over here, you have get request followed by movie dot mp4. 02:17.700 --> 02:29.040 You have the http 1.1 protocol host is Dexter labs in and range is bytes 0 to 1 024. 02:29.070 --> 02:36.790 This basically means only send me the first 1024 bytes of the movie dot mp4. 02:36.810 --> 02:44.100 So once the web server receives this request, instead of sending the entire file, it was it will just 02:44.100 --> 02:50.520 send the first 1024 bytes of the file which is being requested. 02:50.730 --> 02:58.770 Now, one important thing to remember over here is that the partial get was introduced in the Http protocol 02:58.770 --> 03:00.410 version 1.1. 03:00.420 --> 03:06.370 So if you try to do it with 1.0 or 0.9, this will not work. 03:06.390 --> 03:09.080 It got introduced in 1.1. 03:09.090 --> 03:13.980 So if you want to have a partial get, you need to use Http 1.1. 03:13.980 --> 03:16.410 So one important thing to remember. 03:16.620 --> 03:19.290 So this is about the theoretical part. 03:19.320 --> 03:24.900 Let's go to our favorite lab section so that we can actually see on how this really works. 03:26.160 --> 03:27.420 So what I'll do. 03:27.450 --> 03:33.270 I'll type Dexter dot Labs dot in and I'll type partial dot txt. 03:34.890 --> 03:41.440 So if you see over here, the response has content numbers from 1 to 100. 03:41.460 --> 03:46.650 So these are all the numbers which is present in this partial dot txt file. 03:47.280 --> 03:55.770 Now, instead of using classic telnet this time we'll be using one more client which is very famous 03:55.770 --> 03:56.790 called as curl. 03:57.390 --> 03:59.130 So if you do a curl. 03:59.820 --> 04:07.010 Let's say Dexter dot labs dot n slash partial dot txt. 04:08.870 --> 04:10.820 Curl will give you a similar output. 04:10.820 --> 04:15.470 So you see, you got numbers from 1 to 100. 04:15.690 --> 04:22.220 Now Curl is very famous for its flexibility and customization features that it offers. 04:22.400 --> 04:28.400 So I can actually print out the response headers only. 04:28.790 --> 04:35.900 So if you do a hyphen I it will only print out the response headers and not the entire file. 04:35.930 --> 04:41.900 So let me show you on how that actually works so that it becomes much more clear. 04:42.170 --> 04:48.680 Let me start the Wireshark capture and I'll fire up the curl. 04:49.160 --> 04:50.940 So you got the response. 04:50.960 --> 04:54.740 Now I'll stop the Wireshark packet capture. 04:54.740 --> 04:59.480 And this is the request which was made, which is get slash partial dot txt on. 05:00.090 --> 05:01.030 1.1. 05:01.050 --> 05:05.520 So I'll right click here and I'll follow the http stream. 05:07.120 --> 05:12.970 So if you look into the request which curl automatically created. 05:12.970 --> 05:19.240 So whenever you type this command, whenever you type, this command curl will automatically formulate 05:19.270 --> 05:20.800 a get request for us. 05:20.830 --> 05:28.750 However, in case of Telnet, ideally we had seen on how we can write a get request manually. 05:29.230 --> 05:35.830 So curl created a request a get method for partial dot txt. 05:36.100 --> 05:42.000 The protocol is http 1.1 and the host is Dexter Labs dot n. 05:42.280 --> 05:43.810 And this request. 05:43.810 --> 05:49.270 This entire request was sent to the web server listening on Dexter Labs. 05:50.740 --> 05:59.080 Once the web server received this request, it responded back with the Http 1.1 200. 05:59.080 --> 05:59.410 Okay. 05:59.650 --> 06:00.520 200. 06:00.520 --> 06:00.820 Okay. 06:00.850 --> 06:05.410 Means the request that was sent by the curl was successfully processed. 06:05.410 --> 06:07.550 And this is the reason why you have 200. 06:07.550 --> 06:08.120 Okay. 06:08.750 --> 06:10.730 Followed by the other headers. 06:10.730 --> 06:16.850 It also tells us what is the version of web server which is being listened, which is nginx in our case 06:17.900 --> 06:20.170 after this response headers. 06:20.180 --> 06:22.400 So these are called as the request headers. 06:22.400 --> 06:24.440 These are called as the response headers. 06:24.680 --> 06:32.840 After this response headers, the web server which is Nginx, responded with the actual content of the. 06:34.110 --> 06:35.880 Bicycle dot txt file. 06:37.410 --> 06:48.780 So when you do a curl hyphen i what will really happen is that curl will only give us these particular 06:48.780 --> 06:49.290 headers. 06:49.320 --> 06:51.870 It will not send us the content. 06:51.870 --> 06:54.960 Which of the file which was been requested. 06:54.960 --> 06:56.940 Only the response headers. 06:56.940 --> 06:59.670 And you might ask do I really need response headers? 06:59.670 --> 07:01.350 And the answer is very well. 07:01.440 --> 07:07.560 So let's print the response headers and see on what kind of information it provides. 07:07.740 --> 07:14.220 Now, the first information it provides is whether the request was executed successfully or not. 07:14.220 --> 07:19.530 And since the response headers is 200, okay, it means that this request was successfully executed. 07:19.680 --> 07:22.890 Then you have the server which is Nginx. 07:23.040 --> 07:31.020 Now, next important header that will be discussing is the content type which says text slash plain, 07:31.170 --> 07:40.300 which basically says that this file, the partial dot txt or file is of type text. 07:40.810 --> 07:44.320 Then it tells about the content length. 07:44.350 --> 07:51.730 It says that the file which is being requested is of of size 292 bytes. 07:51.730 --> 07:57.460 So we can actually find the size of the file even without requesting it. 07:57.460 --> 07:58.870 This is very important. 07:59.440 --> 07:59.890 Okay. 08:00.730 --> 08:08.650 292 bytes and the last important header is the exit ranges which is of type byte. 08:08.800 --> 08:16.900 Now this is very this specific header is very important when it comes to partial get requests because 08:16.900 --> 08:21.870 this signifies which ranges does the server accept. 08:21.880 --> 08:26.410 So let's let me show you so that it will become much more clear. 08:26.410 --> 08:29.350 So I'll do a curl hyphen hyphen header. 08:31.390 --> 08:43.680 I'll say range range would be bytes 0 to 24 Dexter dot labs dot n slash partial dot txt. 08:44.160 --> 08:55.530 So now what this specifies is that curl will send a get request with a header range and the range is 08:55.530 --> 08:57.000 bytes 0 to 20. 08:57.030 --> 09:04.800 That means just I just need the first 20 bytes of the partial dot txt file. 09:04.800 --> 09:07.380 So this is what it really signifies. 09:07.650 --> 09:18.030 So if I press enter you will see instead of entire file it is only sending me the first 20 bytes of 09:18.030 --> 09:20.370 the partial dot txt file. 09:20.790 --> 09:22.440 So let's do one thing. 09:22.440 --> 09:27.600 Let's fire up the wireshark so that we can see the request headers. 09:31.120 --> 09:31.500 Okay. 09:31.510 --> 09:32.620 And 09:35.170 --> 09:35.830 I'll press. 09:35.830 --> 09:37.990 And you got the first 20 bytes. 09:38.410 --> 09:41.170 So now if I'll stop over here. 09:41.860 --> 09:43.930 Let's go a bit down. 09:44.890 --> 09:46.540 This is our stream. 09:46.540 --> 09:48.250 I'll do a follow Http stream. 09:48.460 --> 09:56.710 So now if you'll see, when we entered this command, when we entered the Curl command, we also specified 09:56.710 --> 10:01.360 a an additional header which it should send to a web server. 10:01.360 --> 10:03.040 And this is the header. 10:03.160 --> 10:05.560 Now Curl will add that header. 10:05.560 --> 10:14.260 So if you see over here, Curl has added one more header called as range with bytes 0 to 20 and this 10:14.260 --> 10:17.740 is what the hyphen hyphen header command actually does. 10:19.330 --> 10:27.550 After this specific request was sent, the Nginx server sent a Http response. 10:27.550 --> 10:30.230 You see 206 partial content. 10:30.230 --> 10:34.490 That means the content that is being sent is of partial type. 10:34.490 --> 10:36.230 It is not the entire file. 10:36.770 --> 10:42.170 Along with that, it tells the content length of the new content which was being sent. 10:42.170 --> 10:52.880 And in the content range header you will see byte is 0 to 20 slash to 92, which signifies out of 292 10:52.880 --> 10:55.130 bytes of the partial dot txt. 10:55.430 --> 11:03.020 Only the bytes ranging from 0 to 20 have been sent back to the client. 11:03.740 --> 11:12.650 Now you can actually modify these value as well, so I can put 20 to 40. 11:15.530 --> 11:18.890 And now you see accordingly you get the information. 11:18.890 --> 11:27.380 Now, this is a commonly used in a downloading website, like there are various websites where you download 11:27.380 --> 11:34.490 files from, and some of these websites will not allow you to resume file for free users. 11:34.490 --> 11:38.900 However, some websites will allow to resume files for free users. 11:39.380 --> 11:49.000 So how they actually do it is that let's assume I'm a free user and I have downloaded content from 0 11:49.000 --> 11:54.920 to 20 bytes, so this much amount of content got downloaded and my internet got disconnected. 11:55.280 --> 12:05.870 So after my internet resumed again, I would ideally want to download file from 20, say, let's say 12:05.870 --> 12:10.190 from 20 to the last byte, which is let's assume to 90. 12:10.340 --> 12:19.320 However, since I'm a free user, what the downloading website does is it will not allow you or it will 12:19.320 --> 12:22.410 not respond with the range header. 12:22.410 --> 12:28.230 It will ask you to start downloading from the absolute zero. 12:28.590 --> 12:34.260 However, for premium users who have paid money, it will allow the range header. 12:34.260 --> 12:40.770 And if you want to resume your downloading from the 21st byte, that will be possible. 12:40.770 --> 12:49.650 So this is how the file downloading websites can block free users from resuming the operations. 12:49.950 --> 12:51.240 So this is it. 12:51.240 --> 12:52.470 About this lecture. 12:52.470 --> 12:58.170 I hope the partial Http get method is understood by you. 12:58.260 --> 13:03.570 And again, if you have any doubts, suggestions, questions, feel free to connect us at Twitter, 13:03.570 --> 13:08.460 Facebook or LinkedIn or mail us at instructors at the Rate Labs dot n. 13:08.490 --> 13:09.690 Thanks for watching.