What is the argument against caching data from a POST request?

Removing MediaWiki-extensions-Comments and Social-Tools tags because as far as I can see, this task is related to the External Data extension and not to the Comments extension and/or other extensions of the social tools family of MediaWiki extensions.

In T293248#7425990, @Yaron_Koren wrote:

What is the argument against caching data from a POST request?

At first, I presumed that a POST request is supposed to change the state of the server, so withholding an HTTP request by caching will not be correct.

Now that I have used POST variables for the first time in {{#get_web_data:}} (there is a patch waiting, BTW), I realised that {{#get_web_data:}} does not use POST request type, but abuses it, following the data source. Technically, a request is POST, effectively, it is GET. Unless I am unaware of some use cases that confirm my original hypothesis, now I thin that POST and GET requests should be treated equally regarding caching. This also will enable us to simplify the class hierarchy.

That makes sense - I don't think anyone should be (or is) using External Data to modify an outside system.

Then there is another question: now POST requests are tried only once, while GET requests can be re-tried several times. The reason was similar: POST requests are not necesserily idempotent. Perhas, this should be unified, too?

Maybe - there's probably no harm to doing that.

Change 789891 had a related patch set uploaded (by Alex Mashin; author: mashin):

[mediawiki/extensions/ExternalData@master] Simplify EDConnectorHttp hierarchy

https://gerrit.wikimedia.org/r/789891

Change 789891 merged by jenkins-bot:

[mediawiki/extensions/ExternalData@master] Simplify EDConnectorHttp hierarchy

https://gerrit.wikimedia.org/r/789891