WEBVTT 00:04.950 --> 00:10.500 So guys, continuing from the previous lecture video, here is one more example of the Tlv. 00:10.920 --> 00:15.480 Now here you can see that each Tlv can carry multiple values. 00:15.480 --> 00:16.170 Right? 00:16.170 --> 00:18.660 So while passing this tlv buffer. 00:18.690 --> 00:26.190 Now note that the contiguous chunk of memory which contains all the tlvs packed together is called tlv 00:26.190 --> 00:26.810 buffer. 00:26.820 --> 00:31.770 So these portion of memory is nothing, but it is called tlv buffer. 00:31.770 --> 00:32.520 Right. 00:32.520 --> 00:36.720 And it is contiguous straight flat chunk of memory. 00:37.370 --> 00:39.260 Now, how would you know that? 00:39.260 --> 00:43.700 Whether there are two units of values present in the value part of this Tlv. 00:44.210 --> 00:45.530 It's simple. 00:45.650 --> 00:53.120 You know that the type of the Tlv is one, and by definition whenever the type of the Tlv is one, it 00:53.120 --> 01:00.370 means that the data type of the value is a string as well as the length of one unit of data is 32 bytes. 01:00.380 --> 01:03.450 So here the length is specified as 64 bytes. 01:03.470 --> 01:09.500 When you divide this length value by one unit of data, you will get two, right? 01:09.500 --> 01:12.980 So 64 divided by 32 is equal to two. 01:13.010 --> 01:21.710 It simply means that the the value portion of this Tlv contains two strings, each of 32 bytes. 01:22.160 --> 01:26.570 And the same applies to the second Tlv as well as the third tlv. 01:27.170 --> 01:34.310 So this is how you read the Tlv by dividing the length of the value portion of this tlv by the size 01:34.310 --> 01:37.470 of one unit of data of this tlv. 01:37.830 --> 01:42.660 Now let us try to write a program regarding how would you parse this tlv? 01:42.930 --> 01:43.530 Right. 01:43.530 --> 01:49.460 So for example, let us suppose that I give you a pointer which points to the very start of this tlv 01:49.470 --> 01:52.830 buffer and the total size of this buffer. 01:52.830 --> 01:55.920 Let's say that it is 222 bytes. 01:57.220 --> 02:00.310 So how were you going to read the type field of this Tlv? 02:00.880 --> 02:06.970 You can read the type field of the Tlv by simply type casting the first byte of this tlv buffer into 02:06.970 --> 02:13.090 the unsigned int eight byte of data type and the length of the first tlv. 02:13.120 --> 02:17.650 You can obtained by incrementing the pointer of the tlv buffer by one. 02:17.680 --> 02:21.820 That is, you are reading one byte of the data starting from this pointer. 02:21.820 --> 02:22.570 Right? 02:22.570 --> 02:29.230 So it's a simple pointer arithmetic and the number of units which is packed in the value field of this 02:29.230 --> 02:33.070 Tlv can be obtained by dividing the total length of the Tlv. 02:33.100 --> 02:37.750 That is this value by the size of the unit data of this Tlv. 02:37.990 --> 02:43.900 So you can always write a function which takes an argument the type of the tlv and depending on the 02:43.900 --> 02:48.490 type of the Tlv, you can always return the size of unit data of this tlv. 02:49.000 --> 02:49.840 Right. 02:49.870 --> 02:56.830 So here you can see that I'm simply dividing the total length of this tlv by the size of unit data of 02:56.930 --> 02:57.560 this tlv. 02:57.800 --> 02:58.400 Right. 02:58.400 --> 03:03.540 So in this case I will get the number of units which is packed in this tlv value. 03:03.560 --> 03:05.960 So in this case it will return to. 03:06.580 --> 03:13.300 And following that, I can simply read the first name and then I can start a loop depending on the number 03:13.300 --> 03:19.980 of units and I can read all the names which are packaged in this value part of this. 03:19.990 --> 03:21.610 Tlv Right. 03:22.410 --> 03:28.980 And once we have read all the values which are present in the value part of this Tlv, we need to start 03:28.980 --> 03:30.990 reading the next Tlv from the beginning. 03:30.990 --> 03:37.470 So the TLB buffer pointer which was pointing to the start of the Tlv needs to be adjusted to the to 03:37.470 --> 03:39.360 point to the start of the second tlv. 03:39.600 --> 03:46.710 It is for this reason that we will increment the tlv buffer by size equal to the length of this tlv. 03:47.430 --> 03:52.230 And also you have to consider the tlv overhead also, which is two bytes. 03:53.040 --> 03:56.580 And after that we can start reading on to the next. 03:57.000 --> 04:02.130 Because our tlv buffer now points to the start of the second tlv right. 04:02.160 --> 04:09.810 So always you need to take a caution that you don't overshoot the TLB buffer and track how much buffer 04:09.810 --> 04:14.910 you have scanned so far, starting from the beginning to the end of the Tlv buffer. 04:14.910 --> 04:15.540 Right. 04:15.570 --> 04:21.300 Don't overshoot the tlv buffer, otherwise it will lead to memory, corruption or segmentation fault. 04:21.390 --> 04:24.340 So there is an assignment following this lecture video. 04:24.340 --> 04:25.780 Please do the assignment. 04:25.780 --> 04:32.230 In that assignment we will going to develop an easy way to parse the Tlv without having to worry about 04:32.230 --> 04:36.490 jumping the pointer from here to there within a buffer.