const_desc_fields = set(['Content-Length', 'Last-Modified', 'Pragma'])
const_ignore_fields = set([
	'Accept-Ranges', 'Age',
	'Cache-Control', 'Connection', 'Content-Type',
	'Date',
	'Expires',
	'Referer',
	'Server',
	'Via',
	'X-Cache', 'X-Cache-Lookup', 'X-Powered-By'
])

block_size = 4096

			if not my_path in index:
				info += '\nThis one is new.'
				reload = True
				record = {}
			else:
				# forcibly checking file if no file present
				if os.access(file_name, os.R_OK):
					info += '\nFull file found.'
					file_stat = os.stat(file_name)
				elif '_parts' in index[my_path] and os.access(temp_name, os.R_OK):
					info += '\nPartial file found.'
					file_stat = os.stat(temp_name)
				else:
					info += '\nFile not found or inaccessible.'
					index[my_path]['_parts'] = None
					reload = True
				record = index[my_path]

					request = 'http://' + config['root'] + self.path
					my_headers = {}
					for header in ('Cache-Control', 'Cookie', 'Referer', 'User-Agent'):
						if header in self.headers:
							my_headers[header] = self.headers[header]

					needed = None


					if '_parts' in record and record['_parts'] != None:
						if config['noparts'] or requested_ranges == None:
							needed = record['_parts']
						else:
							needed = record['_parts'] | requested_ranges
					elif not config['noparts']:
						needed = requested_ranges
					ranges = ()
					print('Missing ranges: {}, requested ranges: {}, needed ranges: {}.'.format(record['_parts'], requested_ranges, needed))
					if needed != None and len(needed) > 0:
						needed.rewind()
						while True:
							range = needed.pop()
							if range[0] == None:
								break
							ranges += '{}-{}'.format(range[0], range[1] - 1),
						my_headers['Range'] = 'bytes=' + ','.join(ranges)

					request = urllib.request.Request(request, headers = my_headers)

					with urllib.request.urlopen(request) as source:
						new_record = {}
						new_record['_parts'] = record['_parts']
						headers = source.info()

							# file is created at temporary location and moved in place only when download completes
							if not os.access(temp_name, os.R_OK):
								empty_name = config['dir'] + os.sep + '.tmp'
								with open(empty_name, 'w+b') as some_file:
									pass
								os.renames(empty_name, temp_name)
							temp_file = open(temp_name, 'r+b')
							if requested_ranges == None and needed == None:
								needed = new_record['_parts']
							needed.rewind()
							while True:
								(start, end) = needed.pop()
								if start == None:
									break
								stream_last = start
								old_record = new_record