text: from __future__ import unicode_literals
  
  import errno
  import os
  import socket
  import time
  import re
  
  from .common import FileDownloader
  from ..compat import compat_urllib_error
  from ..utils import (
      ContentTooShortError,
      encodeFilename,
      sanitize_open,
      sanitized_Request,
  )
  
  
  class HttpFD(FileDownloader):
      def real_download(self, filename, info_dict):
          url = info_dict['url']
          tmpfilename = self.temp_name(filename)
          stream = None
  
          # Do not include the Accept-Encoding header
          headers = {'Youtubedl-no-compression': 'True'}
          add_headers = info_dict.get('http_headers')
          if add_headers:
              headers.update(add_headers)
          basic_request = sanitized_Request(url, None, headers)
          request = sanitized_Request(url, None, headers)
  
          is_test = self.params.get('test', False)
  
          if is_test:
              request.add_header('Range', 'bytes=0-%s' % str(self._TEST_FILE_SIZE - 1))
  
          # Establish possible resume length
          if os.path.isfile(encodeFilename(tmpfilename)):
              resume_len = os.path.getsize(encodeFilename(tmpfilename))
          else:
              resume_len = 0
  
          open_mode = 'wb'
          if resume_len != 0:
              if self.params.get('continuedl', True):
                  self.report_resuming_byte(resume_len)
                  request.add_header('Range', 'bytes=%d-' % resume_len)
                  open_mode = 'ab'
              else:
                  resume_len = 0
  
          count = 0
          retries = self.params.get('retries', 0)
          while count <= retries:
              # Establish connection
              try:
                  data = self.ydl.urlopen(request)
                  # When trying to resume, Content-Range HTTP header of response has to be checked
                  # to match the value of requested Range HTTP header. This is due to a webservers
                  # that don't support resuming and serve a whole file with no Content-Range
                  # set in response despite of requested Range (see
                  # https://github.com/rg3/youtube-dl/issues/6057#issuecomment-126129799)
                  if resume_len > 0:
                      content_range = data.headers.get('Content-Range')
                      if content_range:
                          content_range_m = re.search(r'bytes (\d+)-', content_range)
                          # Content-Range is present and matches requested Range, resume is possible
                          if content_range_m and resume_len == int(content_range_m.group(1)):
                              break
                      # Content-Range is either not present or invalid. Assuming remote webserver is
                      # trying to send the whole file, resume is not possible, so wiping the local file
                      # and performing entire redownload
                      self.report_unable_to_resume()
                      resume_len = 0
                      open_mode = 'wb'
                  break
              except (compat_urllib_error.HTTPError, ) as err:
                  if (err.code < 500 or err.code >= 600) and err.code != 416:
                      # Unexpected HTTP error
                      raise
                  elif err.code == 416:
                      # Unable to resume (requested range not satisfiable)
                      try:
                          # Open the connection again without the range header
                          data = self.ydl.urlopen(basic_request)
                          content_length = data.info()['Content-Length']
                      except (compat_urllib_error.HTTPError, ) as err:
                          if err.code < 500 or err.code >= 600:
                              raise
                      else:
                          # Examine the reported length
                          if (content_length is not None and
                                  (resume_len - 100 < int(content_length) < resume_len + 100)):
                              # The file had already been fully downloaded.
                              # Explanation to the above condition: in issue #175 it was revealed that
                              # YouTube sometimes adds or removes a few bytes from the end of the file,
                              # changing the file size slightly and causing problems for some users. So
                              # I decided to implement a suggested change and consider the file
                              # completely downloaded if the file size differs less than 100 bytes from
                              # the one in the hard drive.
                              self.report_file_already_downloaded(filename)
                              self.try_rename(tmpfilename, filename)
                              self._hook_progress({
                                  'filename': filename,
                                  'status': 'finished',
                                  'downloaded_bytes': resume_len,
                                  'total_bytes': resume_len,
                              })
                              return True
                          else:
                              # The length does not match, we start the download over
                              self.report_unable_to_resume()
                              resume_len = 0
                              open_mode = 'wb'
                              break
              except socket.error as e:
                  if e.errno != errno.ECONNRESET:
                      # Connection reset is no problem, just retry
                      raise
  
              # Retry
              count += 1
              if count <= retries:
                  self.report_retry(count, retries)
  
          if count > retries:
              self.report_error('giving up after %s retries' % retries)
              return False
  
          data_len = data.info().get('Content-length', None)
  
          # Range HTTP header may be ignored/unsupported by a webserver
          # (e.g. extractor/scivee.py, extractor/bambuser.py).
          # However, for a test we still would like to download just a piece of a file.
          # To achieve this we limit data_len to _TEST_FILE_SIZE and manually control
          # block size when downloading a file.
          if is_test and (data_len is None or int(data_len) > self._TEST_FILE_SIZE):
              data_len = self._TEST_FILE_SIZE
  
          if data_len is not None:
              data_len = int(data_len) + resume_len
              min_data_len = self.params.get("min_filesize", None)
              max_data_len = self.params.get("max_filesize", None)
              if min_data_len is not None and data_len < min_data_len:
                  self.to_screen('\r[download] File is smaller than min-filesize (%s bytes < %s bytes). Aborting.' % (data_len, min_data_len))
                  return False
              if max_data_len is not None and data_len > max_data_len:
                  self.to_screen('\r[download] File is larger than max-filesize (%s bytes > %s bytes). Aborting.' % (data_len, max_data_len))
                  return False
  
          byte_counter = 0 + resume_len
          block_size = self.params.get('buffersize', 1024)
          start = time.time()
  
          # measure time over whole while-loop, so slow_down() and best_block_size() work together properly
          now = None  # needed for slow_down() in the first loop run
          before = start  # start measuring
          while True:
  
              # Download and write
              data_block = data.read(block_size if not is_test else min(block_size, data_len - byte_counter))
              byte_counter += len(data_block)
  
              # exit loop when download is finished
              if len(data_block) == 0:
                  break
  
              # Open destination file just in time
              if stream is None:
                  try:
                      (stream, tmpfilename) = sanitize_open(tmpfilename, open_mode)
                      assert stream is not None
                      filename = self.undo_temp_name(tmpfilename)
                      self.report_destination(filename)
                  except (OSError, IOError) as err:
                      self.report_error('unable to open for writing: %s' % str(err))
                      return False
  
                  if self.params.get('xattr_set_filesize', False) and data_len is not None:
                      try:
                          import xattr
                          xattr.setxattr(tmpfilename, 'user.ytdl.filesize', str(data_len))
                      except(OSError, IOError, ImportError) as err:
                          self.report_error('unable to set filesize xattr: %s' % str(err))
  
              try:
                  stream.write(data_block)
              except (IOError, OSError) as err:
                  self.to_stderr('\n')
                  self.report_error('unable to write data: %s' % str(err))
                  return False
  
              # Apply rate limit
              self.slow_down(start, now, byte_counter - resume_len)
  
              # end measuring of one loop run
              now = time.time()
              after = now
  
              # Adjust block size
              if not self.params.get('noresizebuffer', False):
                  block_size = self.best_block_size(after - before, len(data_block))
  
              before = after
  
              # Progress message
              speed = self.calc_speed(start, now, byte_counter - resume_len)
              if data_len is None:
                  eta = None
              else:
                  eta = self.calc_eta(start, time.time(), data_len - resume_len, byte_counter - resume_len)
  
              self._hook_progress({
                  'status': 'downloading',
                  'downloaded_bytes': byte_counter,
                  'total_bytes': data_len,
                  'tmpfilename': tmpfilename,
                  'filename': filename,
                  'eta': eta,
                  'speed': speed,
                  'elapsed': now - start,
              })
  
              if is_test and byte_counter == data_len:
                  break
  
          if stream is None:
              self.to_stderr('\n')
              self.report_error('Did not get any data blocks')
              return False
          if tmpfilename != '-':
              stream.close()
  
          if data_len is not None and byte_counter != data_len:
              raise ContentTooShortError(byte_counter, int(data_len))
          self.try_rename(tmpfilename, filename)
  
          # Update file modification time
          if self.params.get('updatetime', True):
              info_dict['filetime'] = self.try_utime(filename, data.info().get('last-modified', None))
  
          self._hook_progress({
              'downloaded_bytes': byte_counter,
              'total_bytes': byte_counter,
              'filename': filename,
              'status': 'finished',
              'elapsed': time.time() - start,
          })
  
          return True
  