Now, talking about the web, multiple protocols are used to communicate. <\/strong>Primarily for end users the most important and visible protocols are HTTP and HTTPS. Though\u00a0there are many other protocols as well, but HTTP and HTTPS protocols cater to most of the population.<\/p>\n HTTP is hypertext transfer protocol. As we all know, computers work in a language of 1\u2019s and 0\u2019s i.e. Binary language.<\/p>\n Let\u2019s say I want to write \u2018a\u2019. Now, if 0 stands for \u2018a\u2019, 1 stands for \u2018b\u2019, and 01 stands for \u2018c\u2019, I can infer that a combination of 0\u2019s and 1\u2019s can construct a word as well. In this case, the text is already constructed and is being sent on the wire. Here, what is being transferred is text (in form of bytes). I am emphasising on \u2018text\u2019 because this text is interpreted by the browser and the moment browser interprets it, it becomes hypertext, and the protocol that transfers the text is referred to as hypertext transfer protocol \u2013 HTTP.<\/em><\/p>\n NOTE: Hyper is also a prefix, from the Greek\u00a0hyper-<\/em>\u00a0meaning over, above, or excessive, used in such terms as\u00a0hypertext\u00a0(text that extends to point to or include other text).<\/p>\n Basically, HTTP is a TCP\/IP based communication protocol, that is used to deliver data (HTML files, image files, query results, etc.) on the World Wide Web. This is an Application Layer protocol. The default port is TCP 80, but other ports can be used as well. It provides a standardized way for computers to communicate with each other. HTTP specification specifies how clients’ request data will be constructed and sent to the server, and how the servers respond to these requests.<\/p>\n There are three basic features that make HTTP a simple but powerful protocol:<\/p>\n * HTTP\/1.0 uses a new connection for each request\/response exchange, where as HTTP uses a\u00a0<major>.<minor><\/strong>\u00a0numbering scheme to indicate versions of the protocol.<\/p>\n Here is the general syntax of specifying HTTP version number: Example <\/p>\n When you log into your site, your login credentials are easy to intercept if not encrypted with HTTPS. The “password” field may show only circles in your Web browser, but\u00a0your actual password is transmitted “in the clear” across the Internet for anyone to see. So, sending data on internet over HTTP is like sending item from courier without security. Criminals can access that traffic in several ways, including monitoring WiFi connections, having an inside position at an Internet service provider or backbone network, or by hacking into routers across the Internet so they can watch the traffic that flows across them.<\/p>\n So, new protocol introduced to handle valuable sensitive data. This protocol is known as SSL (Secured Socket Layer).<\/p>\n HTTPS= HTTP + SSL (HTTP protocol working in tandem with SSL)<\/p>\n So, what is SSL? Before we understand SSL, first we need to understand Cryptography.<\/p>\n It is basically a science of hiding information. It\u2019s a method of storing and transmitting data in a form so that only those for whom it is intended can read and process it.<\/p>\n In fig 4.2, we have a text \u201cHello World\u201d that is being encrypted by algorithm and the output text after the encryption is called cipher\/encrypted text as sown in above diagram.<\/p>\n Sometimes encryption needs a key to encrypt data. Data encrypted via key can be send to respective consumer who can decrypt to its normal form via same kay, here it is called semantic\u00a0key that is used for both encryption and decryptions.<\/p>\n So, one key can be shared among all the users but this is situation like all the houses have lock and each have key and any one can open any\u2019s lock. So, cryptography come to rescue again. In cryptography, there is a way to encrypt with one key and decrypt with another key.<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n Coming back around SSL Protocol, so following steps happens when a data is send to serve.<\/p>\n The purpose of Finish message is, confirmation that all the previous message not conferred \/ tempered. At this point SSL handshake is complete. The client sends Semantic secret key to server for encryption and decryption.<\/p>\n So, after that actual message shared by browser to the server and this way our data is secured via HTTPS over internet.<\/p>\n HTTP requests and HTTP responses use a generic message format of RFC 822 for transferring the required data. This generic message format consists of the following four items.<\/p>\n A start-line will have the following generic syntax: <\/p>\n We will discuss Request-Line and Status-Line while discussing HTTP Request and HTTP Response messages respectively. For now, let’s see the examples of start line in case of request and response: HTTP header fields provide required information about the request or response, or about the object sent in the message body.<\/p>\n Syntax of the header field is as follow <\/p>\n The above image is explaining all the components of the request. Following is separate example of GET and POST.<\/p>\n Here we are not sending any request data to the server because we are fetching a plain HTML page from the server. Connection is a general-header, and the rest of the headers are request headers.<\/p>\n The following example shows how to send form data to the server using request message body:<\/p>\n Here the given URL\u00a0\/cgi-bin\/process.cgi<\/em>\u00a0will be used to process the passed data and accordingly, a response will be returned. Here\u00a0content-type<\/strong>\u00a0tells the server that the passed data is a simple web form data and\u00a0length<\/strong>\u00a0will be the actual length of the data put in the message body.<\/p>\n After receiving and interpreting a request message, a server responds with an HTTP response message: Following is an example of HTTP response message showing error condition when the web server encountered a wrong HTTP version in the given HTTP request: <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n HTTP status codes are extensible and HTTP applications are not required to understand the meaning of all registered status codes. A list of all the status codes has been given in a status code topic defined down the line of document<\/p>\n The set of common methods for HTTP\/1.1 is defined below and this set can be expanded based on requirements. These method names are case sensitive and they must be used in uppercase.<\/p>\n A GET request retrieves data from a web server by specifying parameters in the URL portion of the request. This is the main method used for document retrieval. The following example makes use of GET method to fetch hello.htm: The server response against the above GET request will be as follows: <\/p>\n The POST method is used when you want to send some data to the server, for example, file update, form data, etc. The following example makes use of POST method to send a form data to the server, which will be processed by a process.cgi and finally a response will be returned: The server side script process.cgi processes the passed data and sends the following response: As I described above status code in brief, now we are going to see all the codes with its description. Status code play role in response and the browser or user behaves according to the status code received from the server. <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n 1XX Information:<\/strong> 2XX Information:<\/strong> <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n 3XX Information:<\/strong><\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n 4XX Information:<\/strong> <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n 5XX Information<\/strong><\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n HTTP allows servers to redirect a client request to a different location. Although, this will usually result in another network round trip, it has some useful applications:<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n How redirection happens actually that I show in pictorial form as below:<\/p>\n <\/p>\n The above picture shows, how redirection happens on behalf of status code. All of these status codes require the URL of the redirect target to be given in the Location: header of the HTTP response.<\/p>\n All of these status codes require the URL of the redirect target to be given in the Location: header of the HTTP response.<\/p>\n A HTTP<\/a> response with the 301 “moved permanently” redirect looks like this: <\/p>\n <\/p>\n <\/p>\n <\/p>\n \u00a0<\/strong><\/p>\n To understand what is cross domain, let\u2019s understand Ajax request. Suppose you need to populate states on the selection of country and you don\u2019t want to reload the page again for each request. So what we do is we send a silent request (i.e. Ajax request) from back ground and get the particular contain and using the help of JavaScript and reloads the only the stat\u2019s dropdown. SO it get loaded and page doesn\u2019t get refreshed. So suppose A.com want to read data from B.com and both are different servers. Pulling data form another domain is called cross domain.<\/p>\n Following are the pictorial representation of the cross domain request. The following will show what all the steps happens when we send the request cross domain.<\/p>\n <\/p>\n <\/p>\n Preflight \/ Preflight requests<\/strong><\/p>\n An example:<\/strong><\/p>\n When performing certain types of cross-domain AJAX requests, modern browsers that support CORS will insert an extra “preflight” request to determine whether they have permission to perform the action.<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\nNow, what does HTTP mean?<\/h3>\n
HTTP Overview<\/h3>\n
Basic Features<\/h4>\n
\n
\nHTTP\/1.1 connection may be used for one or more request\/response exchanges.<\/p>\nHTTP Version<\/h4>\n
\n![\"h1\"](\"https:\/\/www.innovationm.com\/blog\/wp-content\/uploads\/2016\/10\/h1.png\")
<\/a><\/p>\n
\n<\/a><\/p>\nHTTPS<\/h3>\n
Why we need HTTPS?<\/h4>\n
What is Cryptography?<\/h4>\n
<\/a><\/p>\n
\nFig 4.2<\/p>\n<\/a><\/p>\nCommunication between browser and server<\/h4>\n
\n
\n443 (default port for HTTPS) over transport layer.<\/li>\nMessage Format<\/h3>\n
\n
\u00a0Message Start-Line<\/h4>\n
\n<\/a><\/p>\n<\/a><\/p>\n<\/h4>\n
Header Fields<\/h4>\n
<\/a><\/p>\nHTTP Request message
<\/a><\/h4>\nGET Request example
<\/a><\/h4>\nPost Request example
<\/a><\/h4>\n<\/a><\/p>\n<\/a><\/p>\n<\/a>The following example shows an HTTP response message displaying error condition when the web server could not find the requested page:<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\nHTTP \u2013 Methods<\/h3>\n
<\/a><\/p>\nGET Method<\/h3>\n
<\/a><\/p>\n<\/a><\/p>\nPOST Method<\/h3>\n
<\/a><\/p>\n<\/a><\/p>\nHTTP – Status Codes<\/h3>\n
<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\nRedirection<\/h3>\n
\n
<\/a><\/p>\n<\/a><\/p>\nExample HTTP response for a 301 redirect<\/h4>\n
<\/a><\/p>\nCross Domain<\/strong><\/h3>\n
<\/a><\/p>\n\n
Preflight Request:
<\/a><\/h4>\nPreflight Response:<\/h4>\n