5 ms·

Actually there are two guarantees for GET: 1) It is a "safe" method. 2) It is an idempotent method. A safe method (GET/HEAD) should not modify server state.

Actually there are two guarantees for GET: 1) It is a "safe" method. 2) It is an idempotent method. A safe method (GET/HEAD) should not modify server state. "In particular, the convention has been established that the GET and HEAD methods SHOULD NOT have the significance of taking an action other than retrieval. " Whereas PUT & DELETE are also idempotent but not "safe". http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html

muaddirac 12y ago
Also from that RFC: > Naturally, it is not possible to ensure that the server does not generate side-effects as a result of performing a GET request; in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the side-effects, so therefore cannot be held accountable for them. I guess my point is that idempotence is the aspect that matters to clients - you can have side-effects if you really want, so long as the request can be safely repeated.
- meejah 12y ago
  ...and in fact, there's a popular use-case called "using memcached" that does have side-effects. That is, doing a GET on something absolutely changes the server "state" (in the sense that memcached might have a key added to it) but that should be invisible to the user. Of course, it's not actually-invisible: their next request might be a little bit faster.
  - dragonwriter 12y ago
    Its probably better to think of GET as not affecting the state of the resources within the API rather than not affecting the state of the server.
SilasX 12y ago
Safe implies idempotent. "Same effect from 0 or more actions" implies "Same effect from 1 or more actions".
- charonn0 12y ago
  All safe methods are idempotent, but not all idempotent methods are safe (e.g. PUT or DELETE.)
- marcosdumay 12y ago
  Safe means you can call it in any way you want. Like from a bot, or an accelerator plugin.

muaddirac 12y ago

Also from that RFC: > Naturally, it is not possible to ensure that the server does not generate side-effects as a result of performing a GET request; in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the side-effects, so therefore cannot be held accountable for them. I guess my point is that idempotence is the aspect that matters to clients - you can have side-effects if you really want, so long as the request can be safely repeated.

meejah 12y ago
...and in fact, there's a popular use-case called "using memcached" that does have side-effects. That is, doing a GET on something absolutely changes the server "state" (in the sense that memcached might have a key added to it) but that should be invisible to the user. Of course, it's not actually-invisible: their next request might be a little bit faster.
- dragonwriter 12y ago
  Its probably better to think of GET as not affecting the state of the resources within the API rather than not affecting the state of the server.

SilasX 12y ago

Safe implies idempotent. "Same effect from 0 or more actions" implies "Same effect from 1 or more actions".

charonn0 12y ago
All safe methods are idempotent, but not all idempotent methods are safe (e.g. PUT or DELETE.)
marcosdumay 12y ago
Safe means you can call it in any way you want. Like from a bot, or an accelerator plugin.