What is HTTP?
The Hypertext Transfer Protocol (HTTP) is designed to enable communications between clients and servers.
HTTP works as a request-response protocol between a client and server.
A web browser may be the client, and an application on a computer that hosts a web site may be the server.
HTTP Methods:
Two commonly used methods for a request-response between a client and server are: GET and POST.
The GET method
The GET method is used to retrieve information from a specified URI and is assumed to be a safe, repeatable operation by browsers, caches and other HTTP aware components. This means that the operation must have no side effects and GET requests can be re-issued without worrying about the consequences.
One downside of GET requests is that they can only supply data in the form of parameters encoded in the URI (known as a Query String) or as cookies in the cookie request header. Therefore, GET cannot be used for uploading files or other operations that require large amounts of data to be sent to the server.
The POST method
The POST method is used for operations that have side effects and cannot be safely repeated. For example, transferring money from one bank account to another has side effects and should not be repeated without explicit approval by the user.
The POST request message has a content body that is normally used to send parameters and data. Unlike using the request URI or cookies, there is no upper limit on the amount of data that can be sent and POST must be used if files or other variable length data has to be sent to the server.
Compare GET vs. POST
The following table compares the two HTTP methods: GET and POST.
| GET | POST | |
|---|---|---|
| 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 |
| Encoding type | application/x-www-form-urlencoded | application/x-www-form-urlencoded or multipart/form-data. Use multipart encoding for binary data |
| 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 POST because data sent is part of the URL
Never use GET when sending passwords or other sensitive information! |
POST is a little safer than GET because the parameters are not stored in browser history or in web server logs |
| Visibility | Data is visible to everyone in the URL | Data is not displayed in the URL |
Other HTTP Request Methods
The following table lists some other HTTP request methods:
| Method | Description |
|---|---|
| HEAD | Same as GET but returns only HTTP headers and no document body |
| PUT | Uploads a representation of the specified URI |
| DELETE | Deletes the specified resource |
| OPTIONS | Returns the HTTP methods that the server supports |
| CONNECT | Converts the request connection to a transparent TCP/IP tunnel |