1 00:00:03,930 --> 00:00:06,395 In the previous lecture, 2 00:00:06,395 --> 00:00:14,130 we learned about the essentials of networking including details of the HTTP protocol. 3 00:00:14,130 --> 00:00:20,805 Now, we'll look at how Node can be used to construct an HTTP server. 4 00:00:20,805 --> 00:00:28,420 This is where the core HTTP module that is built into Node comes to our aid. 5 00:00:28,420 --> 00:00:33,820 In addition, we will look at a couple of other core Node modules that are useful for 6 00:00:33,820 --> 00:00:40,390 building an HTTP server from using Node. 7 00:00:40,390 --> 00:00:42,730 So, how do we make use of the Node HTTP module? 8 00:00:42,730 --> 00:00:50,045 As I mentioned, the HTTP module is one of the core modules that are built into the Node. 9 00:00:50,045 --> 00:00:53,275 So, this is a core networking module that supports 10 00:00:53,275 --> 00:00:58,475 a high-performance foundation for HTTP stack. 11 00:00:58,475 --> 00:01:02,440 So using the module within our Node application requires 12 00:01:02,440 --> 00:01:06,430 us to import the module into our application. 13 00:01:06,430 --> 00:01:12,190 So this is what we do by saying const HTTP = require and, 14 00:01:12,190 --> 00:01:15,120 the name of the module HTTP there. 15 00:01:15,120 --> 00:01:17,260 Now, once the module is imported, 16 00:01:17,260 --> 00:01:24,330 then this HTTP module supports a createServer function which takes, 17 00:01:24,330 --> 00:01:29,500 as a parameter, a function that acts as 18 00:01:29,500 --> 00:01:32,890 a callback function for the createServer module and 19 00:01:32,890 --> 00:01:37,240 this function has two parameters : request and response. 20 00:01:37,240 --> 00:01:40,120 The request is the request message that comes in from 21 00:01:40,120 --> 00:01:44,380 the client side and we can parse the request message and then extract 22 00:01:44,380 --> 00:01:48,010 a lot of information from the request message and use it to make 23 00:01:48,010 --> 00:01:51,850 decisions on how we construct the response message corresponding to that. 24 00:01:51,850 --> 00:01:56,665 The response message is constructed using the second parameter here, the res, 25 00:01:56,665 --> 00:02:01,855 on which we can construct the various header values for 26 00:02:01,855 --> 00:02:08,830 our HTTP response message and also the body of the HTTP response message. 27 00:02:08,830 --> 00:02:10,120 Now, to start the server, 28 00:02:10,120 --> 00:02:11,725 once you create the server, 29 00:02:11,725 --> 00:02:16,030 then you would say server.listen and then supply the port number 30 00:02:16,030 --> 00:02:20,420 and the host name for the server and that will start up our server. 31 00:02:20,420 --> 00:02:27,520 We'll look at some details in the examples exercise that follows this lecture. 32 00:02:27,520 --> 00:02:32,770 As I mentioned, the incoming request message information is available 33 00:02:32,770 --> 00:02:38,130 through the req parameter that the function takes in the createServer method. 34 00:02:38,130 --> 00:02:40,480 So, the req or request, 35 00:02:40,480 --> 00:02:42,460 if you want to give it full name, 36 00:02:42,460 --> 00:02:46,120 you can call it as a request but in general we have found that in 37 00:02:46,120 --> 00:02:50,425 examples we used req to represent the request message. 38 00:02:50,425 --> 00:02:57,462 It supports on the Javascript object properties like the header, 39 00:02:57,462 --> 00:03:02,225 the body and also various information that can be extracted, 40 00:03:02,225 --> 00:03:09,350 the URL and the method that has been requested by that client site. 41 00:03:09,350 --> 00:03:13,240 And, in response, you construct the response using 42 00:03:13,240 --> 00:03:18,424 the response Javascript object which supports that setHeader function, 43 00:03:18,424 --> 00:03:23,570 the statusCode function which can be set to the status code of the response message. 44 00:03:23,570 --> 00:03:26,235 And then you would write the message saying 45 00:03:26,235 --> 00:03:29,440 res.write and you would end the message by saying 46 00:03:29,440 --> 00:03:35,785 res.end and that takes the final part of the body for the message. 47 00:03:35,785 --> 00:03:40,225 The body may be either standard text or HTML or 48 00:03:40,225 --> 00:03:47,369 any other information that you want to enclose inside the body of that reply message. 49 00:03:47,369 --> 00:03:49,780 But once the res.end is called, 50 00:03:49,780 --> 00:03:54,460 the reply is sent back to the client from the HTTP server. 51 00:03:54,460 --> 00:03:59,185 Two other core modules that are useful for us 52 00:03:59,185 --> 00:04:04,295 when we're constructing the Node HTTP server is the Node path module. 53 00:04:04,295 --> 00:04:09,145 The path module enables us to specify the path to a file and then 54 00:04:09,145 --> 00:04:14,375 examine whether the file exists or examine more details about a file. 55 00:04:14,375 --> 00:04:17,620 For example, the extension of the file, 56 00:04:17,620 --> 00:04:19,185 name and so on. 57 00:04:19,185 --> 00:04:22,000 So, the path module can be used within 58 00:04:22,000 --> 00:04:26,360 our application by requiring the path module as shown here. 59 00:04:26,360 --> 00:04:28,360 And then, this supports methods, 60 00:04:28,360 --> 00:04:29,990 like for example, path.resolve, 61 00:04:29,990 --> 00:04:33,940 which will convert a relative path into 62 00:04:33,940 --> 00:04:38,620 an absolute path that the entire path to the file. 63 00:04:38,620 --> 00:04:43,930 You can also check the extension name for the file by calling the 64 00:04:43,930 --> 00:04:47,830 path.extname function and supply the file path that will 65 00:04:47,830 --> 00:04:52,640 examine the extension of the filename. 66 00:04:52,640 --> 00:04:55,870 Similarly, the file system module, 67 00:04:55,870 --> 00:04:57,970 again a core module in Node, 68 00:04:57,970 --> 00:05:00,670 will enable us to read and write 69 00:05:00,670 --> 00:05:04,805 files that exist in the local file system on the computer. 70 00:05:04,805 --> 00:05:08,725 So the file system modules can be used within 71 00:05:08,725 --> 00:05:13,480 our Node application by requiring it as shown here. 72 00:05:13,480 --> 00:05:16,765 And then, these file system modules supports many methods 73 00:05:16,765 --> 00:05:21,460 including a method for checking whether the file exists in the local file system or not. 74 00:05:21,460 --> 00:05:24,190 So the fs.exists will take 75 00:05:24,190 --> 00:05:28,165 the filePath as the first parameter and the second parameter is 76 00:05:28,165 --> 00:05:35,530 a callback function which will come back with a parameter which we can name it as exists. 77 00:05:35,530 --> 00:05:38,410 This parameter, exists, will be true if the file 78 00:05:38,410 --> 00:05:43,595 exists and will be false if the file does not exist within the local file system. 79 00:05:43,595 --> 00:05:50,390 Similarly, you can read from the file by creating a read stream given the file path. 80 00:05:50,390 --> 00:05:53,585 So you can say fs.createReadStream and 81 00:05:53,585 --> 00:05:58,240 the filePath and this can be piped in to the response message. 82 00:05:58,240 --> 00:06:01,175 So the file will be read in from the file 83 00:06:01,175 --> 00:06:05,290 given by the filePath and then the contents will be put 84 00:06:05,290 --> 00:06:13,220 into the body of the response message by calling a chained function as shown here. 85 00:06:13,220 --> 00:06:17,920 So, these are some examples of some core Node modules that will be very 86 00:06:17,920 --> 00:06:23,710 useful when we are constructing a HTTP server using Node. 87 00:06:23,710 --> 00:06:29,223 Now, that we understand some details about the HTTP server and how it can be constructed, 88 00:06:29,223 --> 00:06:30,690 let's go to the exercise, 89 00:06:30,690 --> 00:06:36,880 where we will construct a simple Node HTTP server which first will serve up 90 00:06:36,880 --> 00:06:41,950 some basic information and then after that we'll serve up files 91 00:06:41,950 --> 00:06:48,170 that exist in a public folder in our project.