Why do we need anything more than HTTP GET, PUT, P

Question

What is the practical benefit of using HTTP GET, PUT, DELETE, POST, HEAD? Why not focus on their behavioral benefits (safety and idempotency), forgetting their names, and use GET, PUT or POST depending on which behavior we want?

Why shouldn't we only use GET, PUT and POST (and drop HEAD, DELETE)?

Answer 1

POST has no guarantees of safety or idempotency. That's one reason for PUT and DELETE—both PUT and DELETE are idempotent (i.e., 1+N identical requests have the same end result as just 1 request).

PUT is used for setting the state of a resource at a given URI. When you send a POST request to a resource at a particular URI, that resource should not be replaced by the content. At most, it should be appended to. This is why POST isn't idempotent—in the case of appending POSTS, every request will add to the resource (e.g., post a new message to a discussion forum each time).

DELETE is used for making sure that a resource at a given URI is removed from the server. POST shouldn't normally be used for deleting except for the case of submitting a request to delete. Again, the URI of the resource you would POST to in that case shouldn't be the URI for the resource you want to delete. Any resource for which you POST to is a resource that accepts the POSTed data to append to itself, add to a collection, or to process in some other way.

HEAD is used if all you care about is the headers of a GET request and you don't want to waste bandwidth on the actual content. This is nice to have.

Answer 2

HEAD is really useful for determining what a given server's clock is set to (accurate to within the 1 second or the network round-trip time, whichever is greater). It's also great for getting Futurama quotes from Slashdot:

~$ curl -I slashdot.org
HTTP/1.1 200 OK
Date: Wed, 29 Oct 2008 05:35:13 GMT
Server: Apache/1.3.41 (Unix) mod_perl/1.31-rc4
SLASH_LOG_DATA: shtml
X-Powered-By: Slash 2.005001227
X-Fry: That's a chick show. I prefer programs of the genre: World's Blankiest Blank.
Cache-Control: private
Pragma: private
Connection: close
Content-Type: text/html; charset=iso-8859-1

For cURL, -I is the option for performing a HEAD request. To get the current date and time of a given server, just do

curl -I $server | grep ^Date

Answer 3

You could use only GET and POST but then you are losing out on some of the precision and clarity that PUT and DELETE bring. POST is a wildcard operation that could mean anything. PUT and DELETE's behaviour is very well defined. If you think of a resource management API then GET, PUT and DELETE probably cover 80%-90% of the required functionality. If you limit yourself to GET and POST then 40%-60% of your api is accessed using the poorly specified POST.

Answer 4

Why do we need more than POST? It allows data to flow both ways, so why would GET be needed? The answer is basically the same as for your question. By standardizing the basic expectations of the various methods other processes can better know what to do.

For example, intervening caching proxies can have a better chance of doing the correct thing.

Think about HEAD for instance. If the proxy server knows what HEAD means then it can process the result from a previous GET request to provide the proper answer to a HEAD request. And it can know that POST, PUT and DELETE should not be cached.

Answer 5

Not all hosters don't support PUT, DELETE.

I asked this question, in an ideal world we'd have all the verbs but....:

RESTful web services and HTTP verbs

Answer 6

The web server war from the earlier days probably caused it.

In HTTP 1.0 written in 1996, there were only GET, HEAD, and POST. But as you can see in Appendix D, vendors started to add their own things. So, to keep HTTP compatible, they were forced to make HTTP 1.1 in 1999.

However, HTTP/1.0 does not sufficiently take into consideration the effects of hierarchical proxies, caching, the need for persistent connections, or virtual hosts. In addition, the proliferation of incompletely-implemented applications calling themselves "HTTP/1.0" has necessitated a protocol version change in order for two communicating applications to determine each other's true capabilities.

This specification defines the protocol referred to as "HTTP/1.1". This protocol includes more stringent requirements than HTTP/1.0 in order to ensure reliable implementation of its features.