Top 25 HTTP Interview Questions and Answers

HTTP Interview Questions

Mostly asked important HTTP Interview Questions are described below:

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1) What is HTTP?

HTTP stands for 'Hypertext Transfer Protocol'. HTTP is such a type of networking protocol that is used for distributed, collaborative, hypermedia information systems. It is known as the foundation of data communication for WWW (World Wide Web) which means that it transfers the data (such as images, audio, video, text, etc.) on WWW.  It helps in the transmission of hypertext from the client-end to the server-end.

2) What are the HTTP Request Messages?

HTTP requests are the messages generated by the client (a user) to initiate an action on the server.
The request message consists of the following:

I) Request Line – It starts with a method token followed by the Request URI (Uniform Resource Identifier), protocol version, and ending with <CR><LF> (a carriage return followed by a line feed). The elements are separated by using the SP characters. The syntax can be defined as:

Request-Line = Method SP Request-URI SP HTTP-Version <CR><LF>
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Note: The request line and headers must all end with <CR><LF>. The empty line must contain only <CR><LF> without whitespace.

II) The Resource identified by a request

III) Request Header Fields – These allow the client to process additional information to the server like the request and the client itself. These fields react as request modifiers, with semantics similar to the parameters on a programming language method invocation.

3) What is mean by URI?

URI stands for the 'Uniform Resource Identifier'. It is used to define the identity of something on the web. It can also be used to represent a piece of an URL.

4) What are the request methods available in HTTP?

Following are the request methods available in HTTP:

GETGET method requests a representation of the specified resource. It retrieves information from the origin server or a proxy caching server from specified URI.

HEADHEAD method is almost similar to the GET method. Unlike the GET method, the HEAD method does not retrieve the response body. It only retrieves information written in response headers.

POSTPOST request transfers the data to the server. The data is included in the body of the request. It can create a new resource or update the existing one or both.

PUTPUT method uploads the entire representation of the specified resource. It replaces existing representations of the target resource with the uploaded content.

DELETEDELETE method deletes the specified resource. It removes all the existing representations of the target resource, provided by the URI.

CONNECTCONNECT method establishes a tunnel to the server, which is identified by the provided URI.

TRACETRACE method performs a message loop-back test along the path to the target resource.

OPTIONSOPTION method describes the available communication options or HTTP methods that the server supports for the specified URL. It can also be used to check the functionality of a web server.

PATCHPATCH method is used to apply the partial modification.

5) What are the safe methods?

Some of the request methods are known as safe methods. For example- HEAD GET, OPTIONS, and TRACE. It is because they are only intended to retrieve the information from the server and do not change the state of the origin server.

6) What do you understand by idempotent methods?

The methods PUT and DELETE are known as idempotent methods. It is because multiple identical requests have the same effect as a single request. Other methods such as HEAD, GET, OPTIONS, and TRACE should also be idempotent as HTTP is a stateless protocol.

7) What do you understand by an HTTP request and HTTP response?

Whenever a user interacts with the web-based features of any browser, the HTTP request is generated by the browser. For example, assume that you click on any hyperlink. The browser will send a series of ‘HTTP GET’ requests to get the content from that specific hyperlink. It will try to get all the information required to render the page. These HTTP requests are transmitted to the origin server or a proxy caching server, and the server further generates an HTTP response. HTTP responses are answers to the HTTP requests made by the browser. An HTTP response can also inform a user if any error occurs while processing an HTTP request. 

An HTTP response includes Status-Line, Response Header Fields or a series of HTTP headers, and a 3Message Body.

8) How does a typical HTTP request and response request look?

An HTTP request is a series of lines containing text data that follow the HTTP protocol. A general HTTP GET request might look like this:

GET /welcome_user.txt HTTP/1.1
User-Agent: curl/7.63.0 libcurl/7.63.0 OpenSSL/1.1.l zlib/1.2.11
Accept-Language: en
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The HTTP GET requests are generated by the user's browser and sent across the internet.
As soon as the origin server receives an HTTP request, it generates an HTTP response back to the user’s browser. A general HTTP response request might look like this:

HTTP/1.1 200 OK
Date: Wed, 08 Jan 2020 12:14:39 GMT
Server: Apache
Last-Modified: Mon, 20 Jan 2020 11:17:01 GMT
Accept-Ranges: bytes
Content-Length: 13
Vary: Accept-Encoding
Content-Type: text/plain

Welcome, user!
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This is how an HTTP request and response request process work.

9) Is HTTP secure? Also, give a reason?

HTTP is not considered as a secure connection. It is because HTTP requests are sent to an origin server or proxy server in plain text, just the same whatever user has entered into the form or input field of the browser's web page. This can be risky in cases where a user enters sensitive data via a webpage or web application.  The sensitive data might include any password, debit-credit card details, or any other personal information.

Therefore, if a website is using an HTTP, then anyone who is monitoring the session can read the text sent or received over HTTP.

10) What do you understand by a Status Code?

The HTTP status code is a standard response code that is issued by the server whenever a client generates a request to the server. In HTTP/1.0 or later, the starting line of the HTTP response is known as the status line. It includes a 3 digits numeric status code (e.g., “404”) and a textual reason phrase (such as “Not Found"). It is used to describe the reason why the web page or other resource could not be loaded properly. The first digit of the HTTP status code specifies one of the five standard classes of responses. The other two digits do not have any role in specification or categorization.

There are usually two types of groups for HTTP status code error:
4xx Client Error
5xx Server Error

11) Describe Persistent connections.

In HTTP/0.99 and 1.0, the connection is terminated after a single request or response pair. In HTTP/1.1, a new mechanism was involved to keep it alive, where an existing connection could be used again for more than one request.

12) Describe header fields present in HTTP.

HTTP headers fields allow the client to process additional information to the server like the request and the client itself. These fields react as request modifiers, with semantics similar to the parameters on a programming language method invocation.

Following are the header fields available in HTTP:

General Headerapplicable for both the request and response message.
Request Headercontains information for the request message.
Response Headercontains the response header information that is sent by the webserver.
Entity Headercontains information about the body of the entity.

13) What is HTTP cURL?

HTTP cURL is a command-line tool. This tool is available on all major operating systems.

14) Define 100 Continue response code in HTTP.

It defines that the client should continue with the request. The interim response notifies the client that the request’s initial part is retrieved successfully.

15) Define 200 OK response code in HTTP.

It defines that the request was successful.

16) Define 201 Created response code in HTTP.

It defines that the request was successful and a resource was created. It also ensures the success of a PUT or POST request.

17) Define 300 Multiple Choices responses code in HTTP.

It defines that multiple options are available for the resource and the client may choose accordingly.

18) Define 400 Bad Request response code in HTTP.

It defines that the server could not understand the request or request was malformed. It generally happens with PUT and POST requests, when the data does not pass the validation or is in invalid syntax.

19) Define the 401 Unauthorized response code in HTTP.

It defines that a user has to perform the authentication before accessing the resource.

20) Define 405 Method Not Allowed response code in HTTP.

It defines that the applied HTTP method is not supported by this resource. For example, if a resource allows the GET method, a user cannot request the POST method to get this resource.

21) Define the 408 Request Timeout response code in HTTP.

It defines that the request has taken a longer time than the server was prepared to wait.

22) Define the 409 Conflict response code in HTTP.

It defines that there is a conflict in request. For example, a client uses PUT request to create the same resource twice.

23) Define 500 Internal Server Error response code in HTTP.

It defines that the server has encountered a situation, where failure occurs due to some unanticipated incident on the server-side.

24) How will you explain secure HTTP?

The HTTPS (Hypertext Transfer Protocol Secure) is a secure version of HTTP. In this protocol, the transmission of data over the WWW is secured and encrypted. It also decrypts the HTTP page or page request that is retrieved by the web-server.

25) Explain an HTTP session.

An HTTP session is defined as the series of network-based request and response transactions. First, an HTTP client initiates a request which further forms a TCP (Transmission Control Protocol) to a specific port on a host (in most cases, port 80). An HTTP server working for that specific port waits for a request message from the client-side. As soon as the server receives the message, the server responds back a status line (e.g., "HTTP/1.1 200 OK"), and a message of its own. In case of any error, the server sends an error message and other necessary information. The entire session is known as an HTTP session.

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