What is HTTP

Hypertext Transfer Protocol (HTTP) is the method used to transfer or convey information on the World Wide Web. It is a patented open internet protocol whose original purpose was to provide a way to publish and receive HTML pages.

HTTP is a request/response protocol between clients and servers. The originating client, such as a web browser, spider, or other end-user tool, is referred to as the user agent.

The destination server, which stores or creates resources such as HTML files and images, is called the origin server. In between the user agent and origin server may be several intermediaries, such as proxies, gateways, and tunnels.

An HTTP client initiates a request by establishing a Transmission Control Protocol (TCP) connection to a particular port on a remote host (port 80 by default)

An HTTP server listening on that port waits for the client to send a Request Message.

Upon receiving the request, the server sends back a status line, such as "HTTP/1.1 200 OK", and a message of its own, the body of which is perhaps the requested file, an error message, or some other information.

HTTP Status Codes

Here is a list of frequently-used HTTP status codes:

1xx Informational

Request received, continuing process.

• 100: Continue
• 101: Switching Protocols

2xx Success

The action was successfully received, understood, and accepted.

• 200: OK
• 201: Created
• 202: Accepted
• 203: Non-Authoritative Information
• 204: No Content
• 205: Reset Content
• 206: Partial Content

3xx Redirection

Further action must be taken in order to complete the request.

• 300: Multiple Choices
• 301: Moved Permanently
• 302: Moved Temporarily (HTTP/1.0)
• 302: Found (HTTP/1.1)
• 303: See Other (HTTP/1.1)
• 304: Not Modified
• 305: Use Proxy
• 306: (no longer used, but reserved)
• 307: Temporary Redirect

4xx Client Error

The request contains bad syntax or cannot be fulfilled.

• 400: Bad Request
• 401: Unauthorized
• 402: Payment Required
• 403: Forbidden
• 404: Not Found
• 405: Method Not Allowed
• 406: Not Acceptable
• 407: Proxy Authentication Required
• 408: Request Timeout
• 409: Conflict
• 410: Gone
• 411: Length Required
• 412: Precondition Failed
• 413: Request Entity Too Large
• 414: Request-URI Too Long
• 415: Unsupported Media Type
• 416: Requested Range Not Satisfiable
• 417: Expectation Failed

5xx Server Error

The server failed to fulfill an apparently valid request.

• 500: Internal Server Error
• 501: Not Implemented
• 502: Bad Gateway
• 503: Service Unavailable
• 504: Gateway Timeout
• 505: HTTP Version Not Supported
• 509: Bandwidth Limit Exceeded