optimize: use the $http_content_type variable instead of ngx.req.get_headers()["content-type"]. thanks Soojin Nam for the patch in openresty#15.

Author: agentzh

lib/resty/upload.lua

@@ -7,6 +7,7 @@ local match = string.match
 local setmetatable = setmetatable
 local get_headers = ngx.req.get_headers
 local type = type
+local ngx_var = ngx.var
 -- local print = print
 
 
@@ -27,7 +28,7 @@ local state_handlers
 
 
 local function get_boundary()
- local header = get_headers()["content-type"]
+ local header = ngx_var.content_type
  if not header then
  return nil
  end