What does http stand for

What is HTTP?

HTTP stands for Hyper Text Transfer Protocol

WWW is about communication between web clients and servers

Communication between client computers and web servers is done by sending HTTP Requests and receiving HTTP Responses

World Wide Web Communication

The World Wide Web is about communication between web clients and web servers.

Clients are often browsers (Chrome, Edge, Safari), but they can be any type of program or device.

Servers are most often computers in the cloud.

HTTP Request / Response

Communication between clients and servers is done by requests and responses:

The HTTP Request Circle

A typical HTTP request / response circle:

All browsers have a built-in XMLHttpRequest Object (XHR).

XHR is a JavaScript object that is used to transfer data between a web browser and a web server.

XHR is often used to request and receive data for the purpose of modifying a web page.

Despite the XML and Http in the name, XHR is used with other protocols than HTTP, and the data can be of many different types like HTML, CSS, XML, JSON, and plain text.

The XHR Object is a Web Developers Dream, because you can:

The XHR Object is the underlying concept of AJAX and JSON:

An overview of HTTP

HTTP is a protocol for fetching resources such as HTML documents. It is the foundation of any data exchange on the Web and it is a client-server protocol, which means requests are initiated by the recipient, usually the Web browser. A complete document is reconstructed from the different sub-documents fetched, for instance, text, layout description, images, videos, scripts, and more.

Clients and servers communicate by exchanging individual messages (as opposed to a stream of data). The messages sent by the client, usually a Web browser, are called requests and the messages sent by the server as an answer are called responses.

Designed in the early 1990s, HTTP is an extensible protocol which has evolved over time. It is an application layer protocol that is sent over TCP, or over a TLS-encrypted TCP connection, though any reliable transport protocol could theoretically be used. Due to its extensibility, it is used to not only fetch hypertext documents, but also images and videos or to post content to servers, like with HTML form results. HTTP can also be used to fetch parts of documents to update Web pages on demand.

Components of HTTP-based systems

HTTP is a client-server protocol: requests are sent by one entity, the user-agent (or a proxy on behalf of it). Most of the time the user-agent is a Web browser, but it can be anything, for example, a robot that crawls the Web to populate and maintain a search engine index.

Each individual request is sent to a server, which handles it and provides an answer called the response. Between the client and the server there are numerous entities, collectively called proxies, which perform different operations and act as gateways or caches, for example.

In reality, there are more computers between a browser and the server handling the request: there are routers, modems, and more. Thanks to the layered design of the Web, these are hidden in the network and transport layers. HTTP is on top, at the application layer. Although important for diagnosing network problems, the underlying layers are mostly irrelevant to the description of HTTP.

Client: the user-agent

The user-agent is any tool that acts on behalf of the user. This role is primarily performed by the Web browser, but it may also be performed by programs used by engineers and Web developers to debug their applications.

The browser is always the entity initiating the request. It is never the server (though some mechanisms have been added over the years to simulate server-initiated messages).

To display a Web page, the browser sends an original request to fetch the HTML document that represents the page. It then parses this file, making additional requests corresponding to execution scripts, layout information (CSS) to display, and sub-resources contained within the page (usually images and videos). The Web browser then combines these resources to present the complete document, the Web page. Scripts executed by the browser can fetch more resources in later phases and the browser updates the Web page accordingly.

A Web page is a hypertext document. This means some parts of the displayed content are links, which can be activated (usually by a click of the mouse) to fetch a new Web page, allowing the user to direct their user-agent and navigate through the Web. The browser translates these directions into HTTP requests, and further interprets the HTTP responses to present the user with a clear response.

The Web server

On the opposite side of the communication channel is the server, which serves the document as requested by the client. A server appears as only a single machine virtually; but it may actually be a collection of servers sharing the load (load balancing), or a complex piece of software interrogating other computers (like cache, a DB server, or e-commerce servers), totally or partially generating the document on demand.

A server is not necessarily a single machine, but several server software instances can be hosted on the same machine. With HTTP/1.1 and the Host header, they may even share the same IP address.

Proxies

Between the Web browser and the server, numerous computers and machines relay the HTTP messages. Due to the layered structure of the Web stack, most of these operate at the transport, network or physical levels, becoming transparent at the HTTP layer and potentially having a significant impact on performance. Those operating at the application layers are generally called proxies. These can be transparent, forwarding on the requests they receive without altering them in any way, or non-transparent, in which case they will change the request in some way before passing it along to the server. Proxies may perform numerous functions:

Basic aspects of HTTP

HTTP is simple

HTTP is generally designed to be simple and human readable, even with the added complexity introduced in HTTP/2 by encapsulating HTTP messages into frames. HTTP messages can be read and understood by humans, providing easier testing for developers, and reduced complexity for newcomers.

HTTP is extensible

Introduced in HTTP/1.0, HTTP headers make this protocol easy to extend and experiment with. New functionality can even be introduced by a simple agreement between a client and a server about a new header’s semantics.

HTTP is stateless, but not sessionless

HTTP is stateless: there is no link between two requests being successively carried out on the same connection. This immediately has the prospect of being problematic for users attempting to interact with certain pages coherently, for example, using e-commerce shopping baskets. But while the core of HTTP itself is stateless, HTTP cookies allow the use of stateful sessions. Using header extensibility, HTTP Cookies are added to the workflow, allowing session creation on each HTTP request to share the same context, or the same state.

HTTP and connections

A connection is controlled at the transport layer, and therefore fundamentally out of scope for HTTP. HTTP doesn’t require the underlying transport protocol to be connection-based; it only requires it to be reliable, or not lose messages (at minimum, presenting an error in such cases). Among the two most common transport protocols on the Internet, TCP is reliable and UDP isn’t. HTTP therefore relies on the TCP standard, which is connection-based.

Before a client and server can exchange an HTTP request/response pair, they must establish a TCP connection, a process which requires several round-trips. The default behavior of HTTP/1.0 is to open a separate TCP connection for each HTTP request/response pair. This is less efficient than sharing a single TCP connection when multiple requests are sent in close succession.

In order to mitigate this flaw, HTTP/1.1 introduced pipelining (which proved difficult to implement) and persistent connections: the underlying TCP connection can be partially controlled using the Connection header. HTTP/2 went a step further by multiplexing messages over a single connection, helping keep the connection warm and more efficient.

Experiments are in progress to design a better transport protocol more suited to HTTP. For example, Google is experimenting with QUIC which builds on UDP to provide a more reliable and efficient transport protocol.

What can be controlled by HTTP

This extensible nature of HTTP has, over time, allowed for more control and functionality of the Web. Cache and authentication methods were functions handled early in HTTP history. The ability to relax the origin constraint, by contrast, was only added in the 2010s.

Here is a list of common features controllable with HTTP:

HTTP flow

When a client wants to communicate with a server, either the final server or an intermediate proxy, it performs the following steps:

If HTTP pipelining is activated, several requests can be sent without waiting for the first response to be fully received. HTTP pipelining has proven difficult to implement in existing networks, where old pieces of software coexist with modern versions. HTTP pipelining has been superseded in HTTP/2 with more robust multiplexing requests within a frame.

HTTP Messages

HTTP messages, as defined in HTTP/1.1 and earlier, are human-readable. In HTTP/2, these messages are embedded into a binary structure, a frame, allowing optimizations like compression of headers and multiplexing. Even if only part of the original HTTP message is sent in this version of HTTP, the semantics of each message is unchanged and the client reconstitutes (virtually) the original HTTP/1.1 request. It is therefore useful to comprehend HTTP/2 messages in the HTTP/1.1 format.

There are two types of HTTP messages, requests and responses, each with its own format.

Requests

An example HTTP request:

Requests consist of the following elements:

Responses

An example response:

Responses consist of the following elements:

APIs based on HTTP

The most commonly used API based on HTTP is the XMLHttpRequest API, which can be used to exchange data between a user agent and a server. The modern Fetch API provides the same features with a more powerful and flexible feature set.

Another API, server-sent events, is a one-way service that allows a server to send events to the client, using HTTP as a transport mechanism. Using the EventSource interface, the client opens a connection and establishes event handlers. The client browser automatically converts the messages that arrive on the HTTP stream into appropriate Event objects. Then it delivers them to the event handlers that have been registered for the events’ type if known, or to the onmessage event handler if no type-specific event handler was established.

Conclusion

HTTP is an extensible protocol that is easy to use. The client-server structure, combined with the ability to add headers, allows HTTP to advance along with the extended capabilities of the Web.

Though HTTP/2 adds some complexity by embedding HTTP messages in frames to improve performance, the basic structure of messages has stayed the same since HTTP/1.0. Session flow remains simple, allowing it to be investigated and debugged with a simple HTTP message monitor.

What Does HTTP Stand For?

HyperText Transfer Protocol simply HTTP is a protocol designed to transfer web resources like HTML, Video, Audio, Picture, etc. over the web between client and server. HTTP can be used by different applications but the most popular one is a web browser where the user simply navigates or surf on web pages.

World Wide Web (WWW) aka Web

World Wide Web is created in 1990 in order to share information in different formats over the world. Because of its structure, it is called the web which is worldwide which can be accessed all over the world to the other world parts. HTTP works over WWW and acts as a part of WWW.

HyperText Markup Language (HTML)

HyperText Markup Language or HTML is a markup language designed to create web pages with different elements. HTML provides different web pages as markup code and some image, audio, video, etc. HTTP’s main duty is the transmission of the HTML content.

Uniform Resource Locator (URL)

Uniform Resource Locator or URL is the path for a given resource which is generally a web page. URL is used inside the HTTP requests in order to specify single or multiple resources and web pages.

HyperText Transfer Protocol (HTTP)

HyperText Transfer Protocol or HTTP is used to transfer HTML and related resources between clients and servers by using the URLs. HyperText means a text which contains some special data which is web page elements and contents. HTTP is a simple text protocol that uses ASCII and some encoding in order to represent data in ASCI or Unicode format. HTTP also provides some attributes which are defined below. HTTP uses the TCP port 80. There are different web servers which provide HTTP server function like Apache, Nginx, IIS, etc.

HTTP Standard

HTTP Attributes

HTTP provides some attributes, features, and behaviors. Here we will list some of the most popular.

HTTP Status Codes

The HTTP request answered with status code which provides information about the request action. The status codes of HTTP are categorized into the following parts.

Secure HTTP with HTTPS

What is HTTP, Structure of HTTP Request and Response?

Whether you are a user or a website owner, the one word you might come across when browsing is HTTP. It is important to get the basics of HTTP to understand how Internet works and the details sent and received between your browser and the web server. Here is a beginners guide to HTTP attempting to explain the basics.

A Beginners Guide to HTTP

We have explained the following topics in this guide:

1. What is HTTP?

HTTP stands for H yper T ext T ransfer P rotocol. This is a basis for data communication in the internet. The data communication starts with a request sent from a client and ends with the response received from a web server.

The symbolic representation of a HTTP communication process is shown in the below picture:

The web browser is called as a User Agent and other example of a user agent is the crawlers of search engines like Googlebot.

2. HTTP Request Structure from Client

A simple request message from a client computer consists of the following components:

All the lines should end with a carriage return and line feed. The empty line should only contains carriage return and line feed without any spaces.

3. HTTP Response Structure from Web Server

A simple response from the server contains the following components:

All the lines in the server response should end with a carriage return and line feed. Similar to request, the empty line in a response also should only have carriage return and line feed without any spaces.

4. Example of HTTP Session

Let us take an example that you want to open a page “home.html” from the site “yoursite.com”. Below is how the request from the client browser should look like to get a “home.html” page from “yoursite.com”.

The response from the web server should look like below:

Chunked transfer encoding is a method in which the server responds with a data in chunks and this used in place of Content-Length header. The communication is stopped when a zero length of chunk is received and this method is used in HTTP Version 1.1.

5. What is that HTTPS?

Now you understand HTTP then what is that HTTPS? HTTPS is the secured HTTP protocol required to send and receive information securely over internet. Nowadays it is mandatory for all websites to have HTTPS protocol to have secured internet. Browsers like Google Chrome will show an alert with “Not Secure” message in the address bar if the site is not served over HTTPS.

Besides the security and encryption, the communication structure of HTTPS protocol remains same as HTTP protocol as explained above.

Warning: We do not recommend using confidential information like credit card details on HTTP sites. Ensure the financial transactions happens through HTTPS protocol.

6. How to Check HTTP Request and Response on Chrome?

Well, it’s time to practical. Let us take Google Chrome the popular browser, but the process remains same in all other browsers to view the details.

You can see the details of request and responses as exactly we have explained in the above sections. The “Headers” tab will show you the details of HTTP header information for request and response for the selected item.

7. HTTP Header Checker Tool

Similar to Chrome, there are also many other free tools available to check the response code received in HTTP headers. For example, go to this HTTP header checker tool, enter any of the URL you wanted to check and click the submit button.

You will see the complete details of the header like below:

8. Troubleshooting with HTTP Status Codes

There are many reasons, a request from browser will not get required response from web server. In such failure cases, the response information from the web server is important for troubleshooting. The status codes returned by the server can be seen in Chrome Developer Tools section clearly. In the above screenshot, line 4 – HTTP/1.1 200 OK code indicates the server successfully returned the requested resource without any problem. You can get these detail using HTTP header check tool as explained above.

The three digits code returned from the server is called HTTP status code, though some people refer it as error code though it is not an error. It is merely a status response and helps you to find the reason for the communication failure. Remember that the communication failure can also happen due to the browser and computer problems like local network issues. In these cases, modern browsers like Chrome will show browser errors like “err_network_changed“, “err_internet_disconnected“, etc.

9. Details of HTTP Status Codes

The HTTP status codes are developed as per the Internet standards defined by Internet Engineering Task Force (IETF). They are classified into five different categories as below:

9.1. Informational Series – 1xx

These are the informational codes send by the server indicating that the request is received from the client successfully and the same is under processing at the server end. This is a provisional response from the server normally contains only the status line and optional headers and is terminated with an empty line. Learn more about each 1xx status codes in detail.

9.2. Success Series – 2xx

These are the success codes send by the server indicating that the request is received and processed successfully. Learn more about each 2xx status codes in detail.

9.3. Redirection – 3xx

These are the status codes for redirection. When a user agent (a web browser or a crawler) requesting URL1 is redirected to another resource URL2 then 2xx codes are returned as a response. These codes are not seen in the browser window since browsers are auto redirected to another URL. Learn more about each 3xx status codes in detail.

9.4. Client Errors – 4xx

These are the errors from the client side which the server could not resolve. Simple and well known example is a “404 – Page Not Found” error displayed in the browser window when an unavailable URL is requested by the browser. Learn more about each 4xx status codes in detail.

9.5. Server Errors Series – 5xx

When a web server can’t fulfill a valid request from a client it sends a 5xx error code in the response. An example is “504 – Gateway Timeout” error where the web server1 is acting as a proxy to get a response from another web server2 but failed to receive a timely response. Learn more about each 5xx status codes in detail.

10. Download HTTP Status Codes Guide

You can download the complete HTTP status codes guide for offline reference and learn more about each code in detail.

Final Words

We recommend all Internet users and website owners learn the basic concepts of HTTP. This will really help in troubleshooting the connection failure related issues. Hope we have covered all required details for a beginner level user in this guide. If you see any important details are missed, just drop in a comment. We will try to update this guide for the benefit of all readers.

What is HTTP?

Every website address begins with “http://” (or “https://”). This refers to the HTTP protocol, which your web browser uses to request a website. In the following, we will introduce the concept of HTTP, explain the differences between the versions, and indicate what other concepts are related to HTTP.

What does HTTP mean?

HTTP stands for “Hypertext Transfer Protocol.” It was developed by Tim Berners-Lee at CERN (Switzerland) alongside other concepts that laid the basis for the world wide web, such as HTML and URI. While HTML (Hypertext Markup Language) defines the structure and layout of a website, HTTP controls how the page is transferred from the server to the client. The third concept URL (Uniform Resource Locator) defines how a resource (e.g. a website) must be addressed on the web.

So, what does the term “hypertext,” used in the abbreviations HTTP and HTML, actually mean? It refers to a concept we are all familiar with: linking files. Hyperlinks are placed on websites and lead to other pages.

What is the purpose of HTTP?

If you enter an internet address in your web browser and a website is displayed shortly thereafter, your browser has communicated with the web server via HTTP. Figuratively speaking, HTTP is the language your web browser uses to speak with the web server in order to inform it of a request.

How does HTTP work?

The easiest way to explain how HTTP works is by looking at an example of how a website is requested:

Diagram of the HTTP protocol communication process

When is HTTP used?

Originally, HTTP was only used to request an HTML document from a web server. Today, the protocol has many different uses:

What are the different HTTP versions?

The original version: HTTP/1

The history of HTTP began in 1989 when Tim Berners-Lee and his team at CERN developed the world wide web. The original version of HTTP was labeled version 0.9 and called the “One-Line Protocol.” It could only request one HTML file from a server.

All the server did was send the corresponding file. Therefore, this protocol version could only handle HTML files.

In 1996, the Internet Engineering Task Force (IETF) documented version HTTP/1 in the non-binding informational memo RFC 1945. A new header was introduced which could specify both the client request and the server response more precisely. One new header introduced was the “content type” header which made it possible to transfer files other than HTML files. The following is a short summary of this HTTP version’s features:

The first official standard: HTTP/1.1

In 1997, version HTTP/1.1 was published, as documented in the informational memo RFC 2068. It became the first official standard and is still being used today. It offered some important innovations in comparison to HTTP/1:

An urgently needed update: HTTP/2

Over the years, websites have become larger and more complex. To load a modern website in your browser, the browser will need to request several megabytes of data and send up to several hundred HTTP requests. Since HTTP/1.1 requires requests over a connection to be processed one after the other, the more complex the website is, the longer it will take to load the page.

In response, Google developed a new experimental protocol called SPDY (pronounced “speedy”). This was met with great interest by the developer community and finally led to the release of the protocol version HTTP/2 in 2015. This new standard introduced the following non-comprehensive list of innovations, all of which are intended to speed up the loading time of websites:

HTTP/2 was able to establish itself quickly, particularly with websites with a lot of traffic which switched over shortly. According to W3Techs, currently (as of January 2020) around 42% of websites use HTTP/2.