What is the Supported HTTP Header Size?
The supported http header size is 16K (4 slots)
In the scenario of header size is bigger than 16K:
(1) The request line can not be bigger than the size of one buffer (16K), if the client send a bigger header nginx returns error "Request URI too large" (414).
(2) The longest header line of request also must be not more than the size of one buffer (16K), otherwise the client get the error "Bad request" (400).