code: def FindPotentialURIs(self, file_obj):
      
      rfc822_format = ""  # will contain all lines not in legacy format
      uris_to_parse = []
  
      for line in utils.ReadFileBytesAsUnicode(file_obj).splitlines(True):
        # check if legacy style line - if it is then extract URL
        m = re.search(r"^\s*deb(?:-\S+)?(?:\s+\[[^\]]*\])*\s+(\S+)(?:\s|$)", line)
        if m:
          uris_to_parse.append(m.group(1))
        else:
          rfc822_format += line
  
      uris_to_parse.extend(self.ParseURIFromKeyValues(rfc822_format, ":", "uri"))
      return uris_to_parse
docs: Given a file, this will return all potenial APT source URIs.