docs: def parse(self, fp, headersonly=True):
          """Create a message structure from the data in a file."""
          feedparser = FeedParser(self._class)
          feedparser._set_headersonly()
  
          try:
              mp = mmap.mmap(fp.fileno(), 0, access=mmap.ACCESS_READ)
          except:
              mp = fp
  
          data = ""
  
          # While parsing the header we can convert to us-ascii?
          while True:
              line = mp.readline()
              data = data + line.decode("us-ascii")
              if line == b"\n":
                  break
          feedparser.feed(data) # mp[0:5000])
          return feedparser.close()