I‘ve read many times that, when HTTP 400 error code (Bad request) is raised, the client should not repeat the request.

I‘m wondering, if the request couldn‘t be completed, why is it that important the client does not repeat the request? Even though repeating the request wouldn‘t help fixing the error, it seems to be very significant that the client doesn‘t re-send the malformed request.

Why is that?

CodePudding user response：

If a 400 bad request signifies that there was a client side issue, repeating the request would do nothing but waste the servers resources. Most of the time, a query param, header, or part of the body is incorrect, and the request needs to be physically changed to work. Some servers use 400 to show the request was recognized but not completed, but overall most cases need something to be physically changed. A 500 code shows that there was a SERVER side error, which is not the case here. A lot of the time, there will be a response body explaining the error along with the 400 code

The worst thing repeating the request will do is waste server resources since it’s not causing an error on the server, but is basically pointless in most cases to repeat.