kong.request.get_header will call openresty api ngx.req.get_headers , which every time it called, it created a lua table, and copy all key and value into the table, which cause all headers copy from c land to lua land.

Also, By default, ngx.req.get_headers copy 100 headers, so, it will not work as expect if size of request headers is great than 100.

so, why not kong implement kong.request.get_header by use $http_header variables?

And https://github.com/openresty/lua-nginx-module#ngxreqget_headers says:

why kong implement kong.request.get_header by use $http_header variables?

Thank you this is a good suggestion and we will consider it (feel free to open a pull request to change it!).

If we don't do this, at least we should consider putting a warning in kong.request.get_header 's docs.

Also, By default, ngx.req.get_headers copy 100 headers, so, it will not work as expect if size of request headers is great than 100.

The function signature is kong.request.get_headers([max_headers]) . The function documentation specifies what max_headers means cleanly. If someone expects more headers than that, they are trying to use the function without reading the docs first. I don't know what else we can do here.

why kong implement kong.request.get_header by use $http_header variables?

Thank you this is a good suggestion and we will consider it (feel free to open a pull request to change it!).

If we don't do this, at least we should consider putting a warning in kong.request.get_header 's docs.

Also, By default, ngx.req.get_headers copy 100 headers, so, it will not work as expect if size of request headers is great than 100.

The function signature is kong.request.get_headers([max_headers]) . The function documentation specifies what max_headers means cleanly. If someone expects more headers than that, they are trying to use the function without reading the docs first. I don't know what else we can do here.

Sorry, actually what I mean is the implementation of kong.request.get_header(name) call _REQUEST.get_headers without pass max_headers, so by default 100 is used. If the size of request header exceed 100, the header we want retrieve may not in the return table.

  function _REQUEST.get_header(name)
    check_phase(PHASES.request)
    if type(name) ~= "string" then
      error("header name must be a string", 2)
   -- the header specify by the `name` may not in the table, since only 100 headers return by _REQUEST.get_headers()
    local header_value = _REQUEST.get_headers()[name]  
    if type(header_value) == "table" then
      return header_value[1]
    return header_value