4 ms·

Idempotency in the context of HTTP requests isn't about the response you receive, but about the state of the resource on the server. You're supposed to be able

by Timon3 2y ago

Idempotency in the context of HTTP requests isn't about the response you receive, but about the state of the resource on the server. You're supposed to be able to call GET /{resource}/{id} any amount of times without the resource {id} being different at the end. You can't do the same for POST, as POST /{resource} could create a new entity with every call. A view counter also doesn't break this, as the view counter isn't the resource you're interacting with. As long as you're not modifying the resource on a `GET` call, the request is idempotent.

kbolino 2y ago
Strictly speaking, an inline view counter, which is incremented on each GET and included in the response, would break idempotence. Similarly, a PUT request that implicitly modifies a "last updated" field would also break idempotence. These are pretty minor violations, though, which arguably don't change any "semantics" of the response.
- Timon3 2y ago
  If the view counter is part of the resource itself, then yes, incrementing it on GET breaks the idempotence contract - but it should be obvious that by breaking idempotence, you're breaking idempotence. If it's part of the response without being part of the resource, you're not breaking idempotence - otherwise things like updating a JS library would also break idempotence, but it doesn't, since it's not part of the resource.
  - kbolino 2y ago
    Updating a JS library has nothing to do with idempotence. The JS libraries used in <script> tags by HTML pages are absolutely part of the resource. But they aren't changed by GET requests, they're (usually) changed by the site admin out-of-band. Idempotence is not immutability; the content of a resource can change between two identical GET requests, it just can't change because of those requests.
    - Timon3 2y ago
      > Updating a JS library has nothing to do with idempotence. The JS libraries used in <script> tags by HTML pages are absolutely part of the resource. No, they absolutely aren't, and this is a really important distinction. Not everything contained in the response is part of the resource. The resource is essentially the data living on the server. It doesn't matter what the response looks like or how it's formatted - as long as the same data is transferred, you're referring to the same resource (e.g. `/{resource}/{id}.html` and `/{resource}/{id}.json` can be different representations of the same resource). This means that changing ancillary response data, i.e. non-resource response data, doesn't change the resource, because it's not part of the resource. If you were correct, the resource would have to contain the JS libraries used. They would have to be part of the data model. Have you ever seen an application like that? Where all JS libraries, CSS files and so on are duplicated into every single resource, and updating the files means updating every single resource entry in your database? Where a JSON API also serves all the JS libraries used in the HTML representation of the resource? And mind you, we're not talking about a "HTML page builder" or something, but about any CRUD application. Usually these things live outside of the resources, in templates or similar.
      - kbolino 2y ago
        Ok, I think we're talking past each other a bit. If on index.html, the script src is "example-1.2.3.js" and you change it to "example-1.2.4.js" then yes, you have changed the resource identified by index.html. If instead you have a script src of "example.js" and you simply change the content served at example.js, this does not change the resource index.html. This rarely has anything to do with method idempotence, because these changes are usually made out-of-band (classically, by uploading new files to an FTP server).
        Timon3 2y ago
        No, this is simply not true. If you change "example-1.2.3.js" to "example-1.2.4.js" in the response to `/{resource}/{id}`, it does not change the underlying resource. The included script is simply a part of the representation of the resource, but it's not the resource itself. The representation of the resource can change without the resource itself changing. https://httpwg.org/specs/rfc9110.html#rfc.section.3.2 https://httpwg.org/specs/rfc9110.html#rfc.section.3.2 You can change "index.html" as much as you want to, as long as the resource it represents stays the same. "index.html" is not a resource, it's a representation of a resource. If you still disagree, please explain how "index.html" and "index.json" can be representations of the same resource.

by Timon3 2y ago

kbolino 2y ago

Strictly speaking, an inline view counter, which is incremented on each GET and included in the response, would break idempotence. Similarly, a PUT request that implicitly modifies a "last updated" field would also break idempotence. These are pretty minor violations, though, which arguably don't change any "semantics" of the response.

Timon3 2y ago
If the view counter is part of the resource itself, then yes, incrementing it on GET breaks the idempotence contract - but it should be obvious that by breaking idempotence, you're breaking idempotence. If it's part of the response without being part of the resource, you're not breaking idempotence - otherwise things like updating a JS library would also break idempotence, but it doesn't, since it's not part of the resource.
- kbolino 2y ago
  Updating a JS library has nothing to do with idempotence. The JS libraries used in <script> tags by HTML pages are absolutely part of the resource. But they aren't changed by GET requests, they're (usually) changed by the site admin out-of-band. Idempotence is not immutability; the content of a resource can change between two identical GET requests, it just can't change because of those requests.
  - Timon3 2y ago
    > Updating a JS library has nothing to do with idempotence. The JS libraries used in <script> tags by HTML pages are absolutely part of the resource. No, they absolutely aren't, and this is a really important distinction. Not everything contained in the response is part of the resource. The resource is essentially the data living on the server. It doesn't matter what the response looks like or how it's formatted - as long as the same data is transferred, you're referring to the same resource (e.g. `/{resource}/{id}.html` and `/{resource}/{id}.json` can be different representations of the same resource). This means that changing ancillary response data, i.e. non-resource response data, doesn't change the resource, because it's not part of the resource. If you were correct, the resource would have to contain the JS libraries used. They would have to be part of the data model. Have you ever seen an application like that? Where all JS libraries, CSS files and so on are duplicated into every single resource, and updating the files means updating every single resource entry in your database? Where a JSON API also serves all the JS libraries used in the HTML representation of the resource? And mind you, we're not talking about a "HTML page builder" or something, but about any CRUD application. Usually these things live outside of the resources, in templates or similar.
    - kbolino 2y ago
      Ok, I think we're talking past each other a bit. If on index.html, the script src is "example-1.2.3.js" and you change it to "example-1.2.4.js" then yes, you have changed the resource identified by index.html. If instead you have a script src of "example.js" and you simply change the content served at example.js, this does not change the resource index.html. This rarely has anything to do with method idempotence, because these changes are usually made out-of-band (classically, by uploading new files to an FTP server).
      - Timon3 2y ago
        No, this is simply not true. If you change "example-1.2.3.js" to "example-1.2.4.js" in the response to `/{resource}/{id}`, it does not change the underlying resource. The included script is simply a part of the representation of the resource, but it's not the resource itself. The representation of the resource can change without the resource itself changing. https://httpwg.org/specs/rfc9110.html#rfc.section.3.2 https://httpwg.org/specs/rfc9110.html#rfc.section.3.2 You can change "index.html" as much as you want to, as long as the resource it represents stays the same. "index.html" is not a resource, it's a representation of a resource. If you still disagree, please explain how "index.html" and "index.json" can be representations of the same resource.