HTTP POST Request Method

What is HTTP?

The Hypertext Transfer Protocol (HTTP) is designed to support communication between clients (browser or application) and web servers. HTTP is designed to send information in a format that both the client and the server can understand. HTTP works as a stateless request-response protocol between the client and the web server. HTTP is based on several request methods, or "verbs", including the HTTP POST and HTTP GET request methods, and several others. Web browsers usually only use HTTP GET and HTTP POST, but RESTful desktop and mobile applications use many others. Sending data to the server over HTTP can be done using several HTTP request methods. The HTTP POST request method is one of them. The HTTP POST method asks the web server to accept the data contained in the body of the message. The data type in the HTTP POST body is indicated by the Content-Type header.

What is the HTTP POST request method used for?

The HTTP POST method is used to create or add a resource on the server. Typically, the POST request adds a new resource to the server, while the PUT request replaces an existing resource on the server. For example, the HTTP POST request method is used by browsers when submitting HTML form data to the server or when submitting data using jQuery/AJAX requests. Unlike GET and HEAD requests, the HTTP POST requests may change the server state.

How do I send data using the HTTP POST request method?

To send data using the HTTP POST method, you must include the data in the body of the HTTP POST message and specify the MIME type of the data with a Content-Type header. Below is an example of an HTTP POST request to send JSON data to the server.

The size and data type for HTTP POST requests is not limited. But you must specify the data type in the Content-Type header and the data size in the Content-Length header fields. The HTTP POST requests can also send data to the server using the URL parameters. In this case, you are limited to the maximum size of the URL, which is about 2000 characters (it depends on the browser).

The HTTP POST method is not idempotent, which means that sending an identical POST request multiple times may additionally affect the state or cause further side effects (eg. on financial transactions).

HTTP POST Request Example

The following HTTP POST request example demonstrates sending a POST request to the server. In this example, the 'Content-Type: application/json' request header indicates the media type of the resource, and the 'Content-Length: 85' request header indicates the size of the data in the request body.

HTTP POST Request Example Run Example
POST /echo/post/json HTTP/1.1
Authorization: Bearer mt0dgHmLJMVQhvjpNXDyA83vA_PxH23Y
Accept: application/json
Content-Type: application/json
Content-Length: 85
Host: reqbin.com

{
"Id": 12345,
"Customer": "John Smith",
"Quantity": 1,
"Price": 10.00
}

And the server response to our request.

Server Response to HTTP POST Request
HTTP/1.1 200 OK
Content-Length: 19
Content-Type: application/json

{"success":"true"}


Some notes on HTTP POST requests:
  • POST requests are never cached
  • POST requests do not remain in the browser history
  • POST requests cannot be bookmarked

HTTP POST vs GET

GET POST
Browser BACK button/Reload Harmless Data will be re-submitted (the browser should alert the user that the data are about to be re-submitted)
Bookmarked Can be bookmarked Cannot be bookmarked
Cached Can be cached Not cached
History Parameters remain in browser history Parameters are not saved in browser history
Restrictions on data length Yes, when sending data, the GET method adds the data to the URL; and the length of a URL is limited (maximum URL length is 2048 characters) No restrictions
Restrictions on data type Only ASCII characters allowed No restrictions. Binary data is also allowed
Security GET is less secure compared to HTTP POST because data sent is part of the URL. Never use GET when sending passwords or other sensitive information!
Visibility Data is visible to everyone in the URL Data is not displayed in the URL

HTTP POST vs PUT

The fundamental difference between the HTTP POST and PUT requests is reflected in the different meaning of the Request-URI. The URI in a POST request identifies the resource that will handle the enclosed entity. In contrast; the URI in a PUT request identifies the entity enclosed with the request. Practically speaking, POST is used to append a resource to an existing collection, while PUT is used to update an existing resource.
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