w1_2_Node_Http

Node and HTTP
-------------
The HTTP Protocol
------------------
* Client and server
--------------------
-> Web applications are not stand-alone, they require communication with the server in the backend (cloud);
-> The communication between the client and the server is facilitated by the HTTP Protocol;

|       |                                                  | ----cloud---           |
|Browser| <------------Client-server communication ------->| server <-----> database|
|       |       HTTP with REST API                         |                        |

Networking Alphabet Soup
-----------------------
a. HTTP
b. URL
c. JSON
d. XML
e. SOAP
f. REST
g. GET
h. PUT
i. POST
j. DELETE
-----------------------------------------------
-> Client -Server Communication
------------------------------------
* Network operations cause unexpected delays;
* Applications must be written recognizing the asynchronous nature of the communication;(Data is not instantaneously available);
--------------------------------------------------
Hypertext Transfer Protocol (HTTP)
-----------------------------------
-> Client-server communication protocol, used for exchanging documents between client and server;
-> Allows retrieving interlinked text documents (hypertext) - World Wide Web;
-> HTTP Verbs
--------------
a. HEAD
b. GET
c. POST
d. PUT
e. DELETE
f. TRACE
g. OPTIONS
h. CONNECT, etc

        --------------GET/PUT/POST/DELETE--request-------------> 
Browser                                                          Web server
        <--------Response----------------------------------------
        
 HTTP Request Message
 --------------------
 (Client -> Server) - contains three major parts
 -----------------------------------------------------------------------------------------
        Request Line (details of the request message)| Method URL Version ; GET /index.html HTTP/1.1
 ------------------------------------------------------------------------------------------
        Headers
        (carries additional information)             | Header Field Name : Value
                                                     | Header Field Name : Value
                                                     .... 
                                                     host: localhost:3000
 -------------------------------------------------------------------------------------------
        Blank Line
 --------------------------------------------------------------------------------------------
        
        (optional)     
        Body
        (contains data sent from client   (body content) (HTML/XML, BASE64 (binary - ascii/text) - server - binary)
        to server, if any)
                
 ---------------------------------------------------------------------------------------------
 --------------------------------------------------------------------------------------------------------------------------------
 HTTP Response Message
 -------------------------------------------------------------------------------------------------
         Status Line | HTTP/1.1 200 OK
 -------------------------------------------------------------------------------------------------
         
         
         Headers         |Connection: keep-alive
                         |Content-Type: text/html

 -------------------------------------------------------------------------------------------------
          Blank Line
 -------------------------------------------------------------------------------------------------


        Response Data | <html> .........</html>
        
 -----------------------------------------------------------------------------------------------------
 -> Server may send back data in a specific format:
 a. extensible Markup Language (XML)
 b. Javascript Object Notation (JSON)
 ---------------------------------------------------------------------------------------------------------------------------
  Response Codes
  -----------------------
  code  Meaning
  -----------
  200   OK
  201   Created
  301   Moved permanently
  304   Not Modified
  400   Bad Request
  401   Unauthorized
  403   Forbidden
  404   Not Found
  422   Unprocessable Entry
  500   Internal Server Error
  505   HTTP version Not Supported
 -----------------------------------------------------------------------------------------------------------------------------
  Node and the HTTP Module
  --------------------------
  * Node HTTP Module
  -----------------
  -> Core networking module supporting a high performance foundation for a HTTP stack;
  -> Using the module: var http = require('http');
  -> Creating a server: var server = http.createServer(function(req, res){.....});//req.header, req.body; res.setHeader, res.statusCode;
  -> Starting the server: server.listen(port,...);
  
  ---------------------------------------------------------------------------------------------------------------------------------
  I. path module -> enables to specify the path to various files, it creates path based on the native operating system of the
  machine on which the code is running;
  
  II. fs (file system) -> checks if file exists; reads file;