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. 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.
Features:
There are three basic features that make HTTP a simple but powerful protocol:
HTTP is connectionless: The HTTP client, i.e., a browser initiates an HTTP request and after a request is made, the client waits for the response. The server processes the request and sends a response back after which client disconnect the connection. So client and server knows about each other during current request and response only. Further requests are made on new connection like client and server are new to each other.
HTTP is media independent: It means, any type of data can be sent by HTTP as long as both the client and the server know how to handle the data content. It is required for the client as well as the server to specify the content type using appropriate MIME-type.
HTTP is stateless: As mentioned above, HTTP is connectionless and it is a direct result of HTTP being a stateless protocol. The server and client are aware of each other only during a current request. Afterwards, both of them forget about each other. Due to this nature of the protocol, neither the client nor the browser can retain information between different requests across the web pages.
Architecture:
The HTTP protocol is a request/response protocol based on the client/server based architecture where web browsers, robots and search engines, etc. act like HTTP clients, and the Web server acts as a server.
Client
The HTTP client sends a request to the server in the form of a request method, URI, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible body content over a TCP/IP connection.
Server
The HTTP server responds with a status line, including the message's protocol version and a success or error code, followed by a MIME-like message containing server information, entity meta information, and possible entity-body content.
Components of HTTP based system
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.
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:
caching (the cache can be public or private, like the browser cache)
filtering (like an antivirus scan or parental controls)
load balancing (to allow multiple servers to serve different requests)
authentication (to control access to different resources)
logging (allowing the storage of historical information)
Uniform Resource Locator (URL)
A client that wants to access the document in an internet needs an address and to facilitate the access of documents, the HTTP uses the concept of Uniform Resource Locator (URL). The Uniform Resource Locator (URL) is a standard way of specifying any kind of information on the internet. The URL defines four parts: method, host computer, port, and path.
Method: The method is the protocol used to retrieve the document from a server. For example, HTTP.
Host: The host is the computer where the information is stored, and the computer is given an alias name. Web pages are mainly stored in the computers and the computers are given an alias name that begins with the characters "www". This field is not mandatory.
Port: The URL can also contain the port number of the server, but it's an optional field. If the port number is included, then it must come between the host and path and it should be separated from the host by a colon.
Path: Path is the pathname of the file where the information is stored. The path itself contain slashes that separate the directories from the subdirectories and files.
Advantages:
1. Addressing
HTTP uses advanced scheme of addressing. It assigns IP address with recognizable names so that it can be identified easily in the World Wide Web. Compared to the standard procedure of IP address with a series of numbers, using this the public can easily engage with the internet.
2. Flexibility
Whenever there are additional capabilities needed by an application, HTTP has the capability to download extensions or plugins and display the relevant data. These can include Flash players and Acrobat reader.
3. Security
In HTTP each files is downloaded from an independent connection and then gets closed. Due to this no more than one single element of a webpage gets transferred. Therefore, the chance of interception during transmission is minimized here.
4. Latency
Only when the connection is established, the handshaking process will take place in HTTP. Hence, there will be no handshaking procedure following a request. This significantly reduces latency in the connection.
5. Accessibility
When the page is loaded for the first time, all of the HTTP pages gets stored inside the internet caches known as the page cache. Therefore, once the page is visited again, the content is loaded quickly.
Disadvantages:
1. Data Integrity
Since there are no any encryption methods used in HTTP, there are chances of someone altering the content. That is the reason why HTTP is considered to be an insecure method prone to data integrity.
2. Data Privacy
Privacy is another problem faced in a HTTP connection. If any hacker manages to intercept the request they can view all the content present in the web page. Besides that they can also gather confidential informations such as the username and the password.
3. Server Availability
Even if HTTP receives all the data that it needs, clients does not take measures to close the connection. Therefore, during this time period, server will not be present.
4. Administrative Overhead
For transmitting a web page, a HTTP needs to create multiple connections. This causes administrative overhead in the connection.
5. IoT Device Support
HTTP uses more number of system resources which leads to more power consumption. Since IoT device today contain wireless sensor networks, it is not suitable to use HTTP.
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