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v-h example

In the image (taken from http/1 must die whitepaper) , James kettle says the parser discripency here is V-H .

Here is my argument, if i am wrong, let me know:

The first unmodified Host header, doesnt say anything.

2nd and 4th responses, give the same error, and most likely it is rejected by frontend, (i am assuming this, tell me if my assumption is wrong).

3rd response where we get 400 Bad Request, it might be from either frontend or backend, we are not so sure about this.

Then , how james is able to classify this discripency into : V-H ?

I would love to get detailed answer on this, and criticism on my thought process if any?

2nd v-h example

Here is the second example of V-H?

I think, 1st, 2nd & 4th responses isnt helpful in decided which discripency is it, tell me if i am wrong.

If you see the response of 3rd request, it says 200 ok , and i can say that, if we are getting 200ok, it must be from the backend system.