The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, and hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web. Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text.

• The term HTTP was coined by Ted Nelson.
• The standard port for HTTP connections is port 80.
• HTTP/0.9 was the first version of the HTTP, and was introduced in 1991.
• HTTP/1.0 is specified in RFC 1945, and was introduced in 1996.
• HTTP/1.1 is specified in RFC 2616, and was officially released in January 1997.

HTTPS

Short for Hypertext Transfer Protocol Secure, HTTPS is a protocol which uses HTTP on a connection encrypted by transport-layer security. HTTPS is used to protect transmitted data from eavesdropping. It is the default protocol for conducting financial transactions on the web, and can protect a website’s users from censorship by a government or an ISP.

• HTTPS uses port 443 to transfer its information.
• HTTPS is first used in HTTP/1.1 and is defined in RFC 2616.

 

HTTP status codes

Below is a listing of HTTP status codes currently defined by Computer Hope. These codes enable a client accessing another computer or device over HTTP to know how to proceed or not proceed. For example, 404 tells the browser the request does not exist on the server.

1xx – 2xx	3xx – 4xx	5xx
100 101 102 200 201 202 204 205 206 207	301 302 304 400 401 402 403 404 405 406 407 408 409 410 413 414 416	500 501 503 505

 

Status Code Definitions

   Each Status-Code is described below, including a description of which
   method(s) it can follow and any metainformation required in the
   response.

9.1 Informational 1xx

   This class of status code indicates a provisional response,
   consisting only of the Status-Line and optional headers, and is
   terminated by an empty line. HTTP/1.0 does not define any 1xx status
   codes and they are not a valid response to a HTTP/1.0 request.
   However, they may be useful for experimental applications which are
   outside the scope of this specification.

9.2 Successful 2xx

   This class of status code indicates that the client's request was
   successfully received, understood, and accepted.

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   200 OK

   The request has succeeded. The information returned with the
   response is dependent on the method used in the request, as follows:

   GET    an entity corresponding to the requested resource is sent
          in the response;

   HEAD   the response must only contain the header information and
          no Entity-Body;

   POST   an entity describing or containing the result of the action.

   201 Created

   The request has been fulfilled and resulted in a new resource being
   created. The newly created resource can be referenced by the URI(s)
   returned in the entity of the response. The origin server should
   create the resource before using this Status-Code. If the action
   cannot be carried out immediately, the server must include in the
   response body a description of when the resource will be available;
   otherwise, the server should respond with 202 (accepted).

   Of the methods defined by this specification, only POST can create a
   resource.

   202 Accepted

   The request has been accepted for processing, but the processing
   has not been completed. The request may or may not eventually be
   acted upon, as it may be disallowed when processing actually takes
   place. There is no facility for re-sending a status code from an
   asynchronous operation such as this.

   The 202 response is intentionally non-committal. Its purpose is to
   allow a server to accept a request for some other process (perhaps
   a batch-oriented process that is only run once per day) without
   requiring that the user agent's connection to the server persist
   until the process is completed. The entity returned with this
   response should include an indication of the request's current
   status and either a pointer to a status monitor or some estimate of
   when the user can expect the request to be fulfilled.

   204 No Content

   The server has fulfilled the request but there is no new
   information to send back. If the client is a user agent, it should
   not change its document view from that which caused the request to

Redirection 3xx

   This class of status code indicates that further action needs to be
   taken by the user agent in order to fulfill the request. The action
   required may be carried out by the user agent without interaction
   with the user if and only if the method used in the subsequent
   request is GET or HEAD. A user agent should never automatically
   redirect a request more than 5 times, since such redirections usually
   indicate an infinite loop.

   300 Multiple Choices

   This response code is not directly used by HTTP/1.0 applications,
   but serves as the default for interpreting the 3xx class of
   responses.

   The requested resource is available at one or more locations.
   Unless it was a HEAD request, the response should include an entity
   containing a list of resource characteristics and locations from
   which the user or user agent can choose the one most appropriate.
   If the server has a preferred choice, it should include the URL in
   a Location field; user agents may use this field value for
   automatic redirection.

   301 Moved Permanently

   The requested resource has been assigned a new permanent URL and
   any future references to this resource should be done using that
   URL. Clients with link editing capabilities should automatically
   relink references to the Request-URI to the new reference returned
   by the server, where possible.

   The new URL must be given by the Location field in the response.
   Unless it was a HEAD request, the Entity-Body of the response
   should contain a short note with a hyperlink to the new URL.

   If the 301 status code is received in response to a request using
   the POST method, the user agent must not automatically redirect the
   request unless it can be confirmed by the user, since this might
   change the conditions under which the request was issued.

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       Note: When automatically redirecting a POST request after
       receiving a 301 status code, some existing user agents will
       erroneously change it into a GET request.

   302 Moved Temporarily

   The requested resource resides temporarily under a different URL.
   Since the redirection may be altered on occasion, the client should
   continue to use the Request-URI for future requests.

   The URL must be given by the Location field in the response. Unless
   it was a HEAD request, the Entity-Body of the response should
   contain a short note with a hyperlink to the new URI(s).

   If the 302 status code is received in response to a request using
   the POST method, the user agent must not automatically redirect the
   request unless it can be confirmed by the user, since this might
   change the conditions under which the request was issued.

       Note: When automatically redirecting a POST request after
       receiving a 302 status code, some existing user agents will
       erroneously change it into a GET request.

   304 Not Modified

   If the client has performed a conditional GET request and access is
   allowed, but the document has not been modified since the date and
   time specified in the If-Modified-Since field, the server must
   respond with this status code and not send an Entity-Body to the
   client. Header fields contained in the response should only include
   information which is relevant to cache managers or which may have
   changed independently of the entity's Last-Modified date. Examples
   of relevant header fields include: Date, Server, and Expires. A
   cache should update its cached entity to reflect any new field
   values given in the 304 response.

Client Error 4xx

   The 4xx class of status code is intended for cases in which the
   client seems to have erred. If the client has not completed the
   request when a 4xx code is received, it should immediately cease
   sending data to the server. Except when responding to a HEAD request,
   the server should include an entity containing an explanation of the
   error situation, and whether it is a temporary or permanent
   condition. These status codes are applicable to any request method.

      Note: If the client is sending data, server implementations on TCP
      should be careful to ensure that the client acknowledges receipt
      of the packet(s) containing the response prior to closing the
      input connection. If the client continues sending data to the
      server after the close, the server's controller will send a reset
      packet to the client, which may erase the client's unacknowledged
      input buffers before they can be read and interpreted by the HTTP
      application.

   400 Bad Request

   The request could not be understood by the server due to malformed
   syntax. The client should not repeat the request without
   modifications.

   401 Unauthorized

   The request requires user authentication. The response must include
   a WWW-Authenticate header field (Section 10.16) containing a
   challenge applicable to the requested resource. The client may
   repeat the request with a suitable Authorization header field
   (Section 10.2). If the request already included Authorization
   credentials, then the 401 response indicates that authorization has
   been refused for those credentials. If the 401 response contains
   the same challenge as the prior response, and the user agent has
   already attempted authentication at least once, then the user
   should be presented the entity that was given in the response,
   since that entity may include relevant diagnostic information. HTTP
   access authentication is explained in Section 11.

   403 Forbidden

   The server understood the request, but is refusing to fulfill it.
   Authorization will not help and the request should not be repeated.
   If the request method was not HEAD and the server wishes to make
   public why the request has not been fulfilled, it should describe
   the reason for the refusal in the entity body. This status code is
   commonly used when the server does not wish to reveal exactly why
   the request has been refused, or when no other response is
   applicable.

   404 Not Found

   The server has not found anything matching the Request-URI. No
   indication is given of whether the condition is temporary or
   permanent. If the server does not wish to make this information
   available to the client, the status code 403 (forbidden) can be
   used instead.

Server Error 5xx

   Response status codes beginning with the digit "5" indicate cases in
   which the server is aware that it has erred or is incapable of
   performing the request. If the client has not completed the request
   when a 5xx code is received, it should immediately cease sending data
   to the server. Except when responding to a HEAD request, the server
   should include an entity containing an explanation of the error
   situation, and whether it is a temporary or permanent condition.
   These response codes are applicable to any request method and there
   are no required header fields.

   500 Internal Server Error

   The server encountered an unexpected condition which prevented it
   from fulfilling the request.

   501 Not Implemented

   The server does not support the functionality required to fulfill
   the request. This is the appropriate response when the server does
   not recognize the request method and is not capable of supporting
   it for any resource.

   502 Bad Gateway

   The server, while acting as a gateway or proxy, received an invalid
   response from the upstream server it accessed in attempting to
   fulfill the request.

   503 Service Unavailable

   The server is currently unable to handle the request due to a
   temporary overloading or maintenance of the server. The implication
   is that this is a temporary condition which will be alleviated
   after some delay.

       Note: The existence of the 503 status code does not imply
       that a server must use it when becoming overloaded. Some
       servers may wish to simply refuse the connection.

Why is http called a stateless protocol?

HTTP is a Stateless Protocol. HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands that came before it. This is the main reason that it is difficult to implement Web sites that react intelligently to user input.

What is meant by HTTP server?

A web server is a computer system that processes requests via HTTP, the basic network protocol used to distribute information on the World Wide Web. The term can refer to the entire system, or specifically to the software that accepts and supervises the HTTP requests.

What are the different HTTP methods?

The primary or most-commonly-used HTTP verbs (or methods, as they are properly called) are POST, GET, PUT, PATCH, and DELETE. These correspond to create, read, update, and delete (or CRUD) operations, respectively.

What is a GET request?

POST and GET are two HTTP request methods. GET is usually intended to retrieve some data, and is expected to be idempotent (repeating the query does not have any side-effects) and can only send limited amounts of parameter data to the