What is the Supported HTTP Header Size?
The supported HTTP header size is 16K (4 slots).
In the scenario when the header size is bigger than 16K:
(1) The request line cannot be bigger than the size of one buffer (16K), if the client sends 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 gets the error "Bad request" (400).