feat(request-transformer) change HTTP method of upstream request

[subnetmarco]

• Request-Transfomer: can change the HTTP method of the upstream request.

Issues resolved

Fix #1631.

[thibaultcha]

Reluctant to adding a new feature to 0.9.2. Should be targeted for 0.10.

[thibaultcha]

Such behavior should be configurable.

[thibaultcha]

All ngx methods are cached except this one. It should be too for consistency and efficiency.

[thibaultcha]

By convention our codebase returns nil on error. Some parts are not yet updated, but new code should comply.

[subnetmarco]

Think of this value as being stored into a is_valid property, that's why it's true or false.

local function check_method(value)
  if not value then return true end
  local method = value:upper()
  local ngx_method = ngx["HTTP_"..method]
  if not ngx_method then
    return false, method.." is not supported"
  end
  return true
end

local is_valid, err = check_method("hello")

Makes sense that the return value is boolean, with an optional error message into err.

[thibaultcha]

But that's not how this method is being used. It's passed to func, and it is a common Lua idiom when the second parameter is an error to return nil as the first one:

local ok, err = check_method("hello")
if not ok then

end

Returning false would make sense if, say, there was no error as the 2nd return value.

[thibaultcha]

Maybe HEAD too? Should probably be configurable as well.