1 00:00:00,500 --> 00:00:06,380 So this time around, we want to change this button, which currently just displays a search form to 2 00:00:06,380 --> 00:00:07,980 search for availability. 3 00:00:08,390 --> 00:00:15,500 We want to change that so that it behind the scenes sends a request to the server to check for availability. 4 00:00:15,950 --> 00:00:19,070 And the server will send back a Jason response. 5 00:00:19,070 --> 00:00:21,140 And Jason will talk about more in just a moment. 6 00:00:21,470 --> 00:00:24,210 But it stands for JavaScript object notation. 7 00:00:24,740 --> 00:00:27,620 We wanted to do that without ever leaving this page. 8 00:00:27,620 --> 00:00:31,110 So we don't have to do a full page reload, which will make things ever so much faster. 9 00:00:31,700 --> 00:00:34,220 So we're going to do this in a series of steps. 10 00:00:34,220 --> 00:00:39,800 And the first step, which will cover in this lecture is actually to create a handler that this form 11 00:00:39,800 --> 00:00:40,270 will call. 12 00:00:40,280 --> 00:00:42,690 We're not going to call that until the next lecture, but we're going to call it. 13 00:00:43,280 --> 00:00:45,710 So first of all, let's think about what the what we're going to do. 14 00:00:45,710 --> 00:00:51,230 We want to call this form and we want it to send back a response in the form of Jason. 15 00:00:51,920 --> 00:00:55,190 Now, you may never have encountered Jason, and it's not that difficult. 16 00:00:55,640 --> 00:01:00,440 Here's an example of a JSON file, and this is exactly the format I want to send back. 17 00:01:00,890 --> 00:01:04,730 So Jason is wrapped in curly brackets like this. 18 00:01:05,000 --> 00:01:10,970 And here is the parameter name or the value name, and here's the value that's that's associated with 19 00:01:10,970 --> 00:01:11,380 OK. 20 00:01:11,810 --> 00:01:17,570 So obviously if we send a request to search for dates, that handler should take the dates, should 21 00:01:17,570 --> 00:01:21,800 look at them and decide whether or not the room is available on the dates in question. 22 00:01:22,010 --> 00:01:28,220 If it is available, it should set OK to true and then give a message like available or if they're not 23 00:01:28,220 --> 00:01:32,420 available it should say OK is equal to false and send a message not available. 24 00:01:32,600 --> 00:01:34,310 And that's just for an example. 25 00:01:34,310 --> 00:01:40,670 If we wanted to have a third parameter like something else, well, we just give it a name followed 26 00:01:40,670 --> 00:01:41,480 by a colon. 27 00:01:41,480 --> 00:01:44,840 The name is in quotation marks and then some value, which might be 100 in this case. 28 00:01:44,840 --> 00:01:45,670 But we're not going to do that. 29 00:01:45,980 --> 00:01:50,060 We're going to go with a straight to to the values that we have to set here. 30 00:01:50,490 --> 00:01:50,860 All right. 31 00:01:50,870 --> 00:01:55,970 So let's go back to our code, which is way over here and go and let's stop the application if it's 32 00:01:55,970 --> 00:01:58,400 running and we're going to create a new handler. 33 00:01:58,490 --> 00:02:03,500 So I'll create the handler first and I'm going to give this a name and I'll put it near post availability. 34 00:02:03,500 --> 00:02:09,170 Now, just for the purposes of this exercise, I'm going to make this handler, which I'm going to call 35 00:02:09,290 --> 00:02:17,270 availability, JSON like that, and then I'll change my comment and change my comment here to say that 36 00:02:17,270 --> 00:02:25,550 it handles request for availability and sends Jason response. 37 00:02:26,120 --> 00:02:28,880 OK, and I don't want to do any of this stuff in here. 38 00:02:29,480 --> 00:02:30,440 So there's my handler. 39 00:02:30,620 --> 00:02:32,300 OK, and I better spell request. 40 00:02:32,300 --> 00:02:32,540 Right. 41 00:02:33,740 --> 00:02:34,710 So that's my name. 42 00:02:34,760 --> 00:02:39,170 Let's go back to our roots file and create a route to that which I'll put right here and I'm going to 43 00:02:39,170 --> 00:02:43,420 put these all on there and online through my own block just so things are a little clearer. 44 00:02:44,270 --> 00:02:49,070 So we have this one that I just duplicated is going to be calling a different U. 45 00:02:49,070 --> 00:02:50,480 URL, obviously. 46 00:02:50,480 --> 00:02:52,160 Otherwise it will never match this route. 47 00:02:52,760 --> 00:02:53,810 And I'll call this Jason. 48 00:02:54,500 --> 00:02:57,230 And the handler is going to call is availability Jason. 49 00:02:57,500 --> 00:03:01,070 So I now have a link between what I'm going to make this a get for right now. 50 00:03:01,070 --> 00:03:08,090 We'll change it back to post later when someone makes a get request to this URL slash search dash availability 51 00:03:08,090 --> 00:03:12,140 destination, it calls this handler and I'll get there right here. 52 00:03:13,100 --> 00:03:14,180 Now, what am I going to do in here? 53 00:03:14,300 --> 00:03:16,310 I don't want to build a Web page. 54 00:03:16,340 --> 00:03:18,200 I can't send back straight text. 55 00:03:18,350 --> 00:03:21,080 I actually want to build a Jason request. 56 00:03:21,560 --> 00:03:28,460 And the nice thing about this is that Go makes it remarkably easy to generate JSON and we do it by defining 57 00:03:28,460 --> 00:03:31,000 our own type or using a type if we haven't already. 58 00:03:31,010 --> 00:03:36,560 I want to call this JSON response and I'm going to leave it lowercase because I'm never going to use 59 00:03:36,560 --> 00:03:39,290 this outside of this package, the handler's package. 60 00:03:39,650 --> 00:03:41,390 So it's a JSON response. 61 00:03:41,390 --> 00:03:42,200 It is a struct. 62 00:03:42,200 --> 00:03:44,740 And we just describe what we want our Jason to look like. 63 00:03:45,350 --> 00:03:50,150 Now, if you go back to that Jason file that I was showing you a minute ago, we have two values, OK? 64 00:03:50,150 --> 00:03:50,870 And message. 65 00:03:51,200 --> 00:03:57,470 Well, we can't use those as names because one of the rules, if you want to export a Jason a struct 66 00:03:57,470 --> 00:04:01,450 to JSON is that the member names have to start with a capital letter. 67 00:04:01,460 --> 00:04:03,200 They have to be exported, in other words. 68 00:04:03,350 --> 00:04:04,550 So I'll call mine, OK? 69 00:04:04,970 --> 00:04:11,540 And it's going to be of type bool for Boolean and then the next one is actually message. 70 00:04:11,570 --> 00:04:14,690 So I'll just call that message and that's just going to hold a string. 71 00:04:15,500 --> 00:04:17,240 Now that is not enough. 72 00:04:17,240 --> 00:04:18,380 Technically speaking it is. 73 00:04:18,380 --> 00:04:25,190 But you need to get in the habit of actually explicitly telling go what you want to use as the values 74 00:04:25,190 --> 00:04:26,390 in the JSON response. 75 00:04:27,080 --> 00:04:32,570 Any time that I'm populating the value of OK, I want it to return in JSON. 76 00:04:32,570 --> 00:04:34,850 So I've got back to around all of this. 77 00:04:35,210 --> 00:04:42,380 That's the little button just above the tab on my keyboard, subarctic gesso and to say for JSON, then 78 00:04:42,380 --> 00:04:47,660 a colon, then in double quotes what you want the value to be called or that feel to be called in JSON. 79 00:04:47,660 --> 00:04:54,680 I don't want it to be called OC lowercase the same way for message for Jason Colon, in quotes I wanted 80 00:04:54,680 --> 00:04:56,180 to call message all lowercase. 81 00:04:56,690 --> 00:04:59,930 Now if I don't specify, these go will do its best. 82 00:05:00,340 --> 00:05:04,690 Well, that probably should be a lower case, OK, this probably should be a lower case message, but 83 00:05:04,690 --> 00:05:05,560 I'm not going to do that. 84 00:05:05,570 --> 00:05:08,380 I'm not going to trust it because I'm not sure that's going to stay there. 85 00:05:08,980 --> 00:05:10,180 Maybe five years from now. 86 00:05:10,180 --> 00:05:12,970 The go authors will decide to change the way that they're doing that. 87 00:05:13,270 --> 00:05:15,570 It's unlikely, but why take the chance? 88 00:05:15,580 --> 00:05:17,610 It's very easy to specify those right now. 89 00:05:18,190 --> 00:05:25,510 So I've created a struct type called JSON Response, and the convention engo is to when you're creating 90 00:05:25,510 --> 00:05:29,860 a struct like this or a type like this that you're only going to use in a couple of places, put it 91 00:05:29,860 --> 00:05:32,580 as close as possible to the code that uses it. 92 00:05:32,620 --> 00:05:33,620 That way, it's easy to find. 93 00:05:34,180 --> 00:05:35,620 So in my function, what am I going to do? 94 00:05:35,640 --> 00:05:37,840 Well, right now I want to define a response. 95 00:05:37,840 --> 00:05:39,670 What am I going to send back when I say response? 96 00:05:39,670 --> 00:05:41,170 I'm not talking about response writer. 97 00:05:41,470 --> 00:05:44,020 I'm talking about what I'm going to push to that response. 98 00:05:44,020 --> 00:05:44,200 Right. 99 00:05:44,290 --> 00:05:51,970 So it's not are I'll just call it resp and I will assign that the value of type JSON response and I'm 100 00:05:51,970 --> 00:05:55,180 going to use the shorthand to create and populate the struct at once. 101 00:05:55,630 --> 00:06:01,840 Jason responses my type and in curly brackets I'm going to say, OK, true. 102 00:06:01,840 --> 00:06:11,440 Right now I'm going to set my message to a male with an exclamation mark and a format that good. 103 00:06:11,440 --> 00:06:12,960 OK, so I've created that value. 104 00:06:13,390 --> 00:06:16,810 Now I need to convert that to Jason and send it back. 105 00:06:16,810 --> 00:06:19,120 And here's the the magic that is go. 106 00:06:19,900 --> 00:06:22,090 I'm going to create a response from that. 107 00:06:22,090 --> 00:06:26,710 I'm going to call the response out and it might create an error when I try to create this. 108 00:06:26,710 --> 00:06:30,430 So I'll trap for an error because this is what I'm going to call actually returns to values. 109 00:06:30,670 --> 00:06:31,660 And you'll see that in a moment. 110 00:06:32,050 --> 00:06:35,920 And I'm going to call the built in package that's part of the standard library called Jason. 111 00:06:36,790 --> 00:06:44,080 And in JSON, I'm going to call the method mercial, but I'm going to call the method Marshall the method 112 00:06:44,080 --> 00:06:46,870 mercial indent, which is a little more complex. 113 00:06:46,870 --> 00:06:49,240 I just want to format things so that we can see them properly. 114 00:06:49,240 --> 00:06:52,180 And as you can see here, this takes an interface. 115 00:06:52,180 --> 00:06:53,290 So it takes some value. 116 00:06:53,290 --> 00:06:58,240 Well, my struct is an interface because everything's at least the interface can go a prefix which I'll 117 00:06:58,240 --> 00:07:02,200 leave empty and whether or not what I'm going to indented by just to make it readable. 118 00:07:02,830 --> 00:07:07,360 So I'll choose Mercial indent and I'm going to pass it out. 119 00:07:07,900 --> 00:07:12,820 No prefix and I want to indented by one, two, three, four, five spaces. 120 00:07:13,190 --> 00:07:18,160 OK then of course because I'm possibly throwing an error, I should check for that. 121 00:07:18,160 --> 00:07:22,270 So I'll see if error is not equal to nil then do something. 122 00:07:22,270 --> 00:07:23,200 And what do I want to do. 123 00:07:23,200 --> 00:07:26,890 I'll just log the print line error which is sufficient for our purposes right now. 124 00:07:27,760 --> 00:07:29,380 Otherwise what am I going to do? 125 00:07:29,380 --> 00:07:34,930 I am going to send my my information directly to the response writer and we did that already. 126 00:07:35,440 --> 00:07:44,980 We can just call the W don't write and pass it out because out is already not out here. 127 00:07:44,980 --> 00:07:47,350 This should be resp because it doesn't exist. 128 00:07:48,220 --> 00:07:49,480 Out is already. 129 00:07:49,570 --> 00:07:52,150 If you look at this, Marshall Indebt throws back. 130 00:07:53,560 --> 00:07:59,500 A slice of bites, and that's exactly what we need to pass to the writer, that's almost enough and 131 00:07:59,500 --> 00:08:02,130 chances are that'll work in the vast majority of cases. 132 00:08:02,500 --> 00:08:09,130 But the last thing I want to do is I need to create a header that tells the Web browser that's receiving 133 00:08:09,130 --> 00:08:09,880 my response. 134 00:08:10,030 --> 00:08:11,710 What kind of response? 135 00:08:11,710 --> 00:08:13,200 I'm sending it now. 136 00:08:13,270 --> 00:08:17,560 Whenever whenever you call a Web page, you are automatically getting a header sent back to you by the 137 00:08:17,560 --> 00:08:20,380 server that says this is of typed text HTML. 138 00:08:20,740 --> 00:08:27,190 But I want to send a type of application JSON, which is the standard header for JSON files, and I 139 00:08:27,190 --> 00:08:34,990 just do that before I call my write, I call W header and that has a method called set and I'm going 140 00:08:34,990 --> 00:08:36,360 to set that to two things. 141 00:08:36,370 --> 00:08:38,700 The first thing is what am I sending and what kind of header is this? 142 00:08:38,710 --> 00:08:42,230 It has to be exactly like this content dash type. 143 00:08:42,760 --> 00:08:45,460 So this is telling the browser, here's the kind of content you're going to get. 144 00:08:45,670 --> 00:08:48,610 And the second argument is just application driessen. 145 00:08:49,570 --> 00:08:55,510 So when I do this, when I call this now, because if you look back at my roots file, if I call this 146 00:08:55,510 --> 00:08:58,960 using a get request, which will change to post before too long. 147 00:08:58,960 --> 00:09:00,610 But right now I just want to make sure it works. 148 00:09:02,080 --> 00:09:05,770 This route matches this path or this this handler. 149 00:09:05,920 --> 00:09:11,170 And all that does is say here's my JSON type that I'm going to be using this way to find a struct type 150 00:09:11,170 --> 00:09:12,430 that I'm going to be using shortly. 151 00:09:12,790 --> 00:09:17,590 I create that struct type in a variable called response. 152 00:09:17,800 --> 00:09:21,790 It has OK for its first member, it has a message for a second member. 153 00:09:22,120 --> 00:09:24,050 Then I say, Marschall this to Jason. 154 00:09:24,280 --> 00:09:29,230 So this intenta this Marschall and it actually looks at the struct type for this and says, do you have 155 00:09:29,230 --> 00:09:31,420 any tags up here that tell me what to call those fields? 156 00:09:31,420 --> 00:09:31,950 And Jason. 157 00:09:31,960 --> 00:09:32,800 Oh yes you do. 158 00:09:33,280 --> 00:09:35,260 All right then it creates that. 159 00:09:35,260 --> 00:09:41,560 Then I write that result as a content type application, JSON right to the Web browser. 160 00:09:41,590 --> 00:09:43,690 So let's say let's put one more thing in here as well. 161 00:09:44,060 --> 00:09:52,600 We'll just write a log print line, log print line and I will print out the value of about now. 162 00:09:52,600 --> 00:09:58,060 I could pass it bytes, but if you actually do that, you'll see a whole bunch of codes on your terminal 163 00:09:58,060 --> 00:09:59,650 window that aren't going to be meaningful. 164 00:09:59,960 --> 00:10:04,460 So I'm going to cast this to type string just so it looks quite readable. 165 00:10:04,840 --> 00:10:05,280 All right. 166 00:10:05,860 --> 00:10:07,630 So let's start our application. 167 00:10:09,160 --> 00:10:11,160 Go run command slash web slash. 168 00:10:11,170 --> 00:10:11,830 Start out, go. 169 00:10:14,010 --> 00:10:20,820 Everything compiled, let's go over to our Web browser and let's change the URL up here from what it 170 00:10:20,820 --> 00:10:23,220 is right now to what do we call it in the rules file? 171 00:10:23,250 --> 00:10:28,750 I better go make sure in route's I called it search availability JSON. 172 00:10:29,070 --> 00:10:33,890 I saw a copy, that whole thing, including the slash, go back to my web browser wherever it is. 173 00:10:33,900 --> 00:10:34,470 There it is. 174 00:10:35,850 --> 00:10:39,690 And paste it in here and see what we get. 175 00:10:40,290 --> 00:10:45,280 And what I get in Firefox is I get a nice rendering of what the JSON looks like. 176 00:10:45,300 --> 00:10:49,830 So this says here the little tab in Firefox, Chrome is probably a little different and it shows me 177 00:10:49,830 --> 00:10:52,140 OK is such a true and message it set available. 178 00:10:52,150 --> 00:10:55,650 I can look at the raw data and that will show me the actual message itself. 179 00:10:55,920 --> 00:10:57,720 OK, true message available. 180 00:10:57,720 --> 00:10:58,230 Perfect. 181 00:10:58,590 --> 00:11:04,470 And the headers are I look at that, it says the header types are the response headers are application 182 00:11:04,470 --> 00:11:05,070 JSON. 183 00:11:05,070 --> 00:11:07,680 So everything worked exactly as it should. 184 00:11:07,920 --> 00:11:12,410 And if I go back to my go terminal, I wrote that to the terminal window. 185 00:11:12,510 --> 00:11:14,810 So everything seems to work absolutely beautiful. 186 00:11:15,630 --> 00:11:23,000 Now, if I stop the application and go back to my handler and change that defaults wherever it is where 187 00:11:23,020 --> 00:11:30,390 my handlers, their handlers change this from true to false, start the application back up. 188 00:11:32,970 --> 00:11:38,070 And go back to my terminal or my Web browser and reload it now, it should give me the same header file, 189 00:11:38,220 --> 00:11:42,190 but it should give OK thought, OK, this works exactly the way that I want it to. 190 00:11:42,750 --> 00:11:48,870 So in the next lecture, we'll turn this back into a post request and we'll actually build the JavaScript 191 00:11:48,870 --> 00:11:57,990 necessary to send an example or an Ajax request from our client, the Web browser to the server and 192 00:11:57,990 --> 00:12:02,160 listen for the response and take some action based upon the response we get from the server. 193 00:12:02,430 --> 00:12:06,110 And we'll take care of that in the next lecture or possibly next to lectures, but we'll get it done.