text: # We use native strings for all the re patterns, to take advantage of string
  # formatting, and then convert to bytestrings when compiling the final re
  # objects.
  
  # https://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7230.html#whitespace
  #  OWS            = *( SP / HTAB )
  #                 ; optional whitespace
  OWS = r"[ \t]*"
  
  # https://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7230.html#rule.token.separators
  #   token          = 1*tchar
  #
  #   tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
  #                  / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
  #                  / DIGIT / ALPHA
  #                  ; any VCHAR, except delimiters
  token = r"[-!#$%&'*+.^_`|~0-9a-zA-Z]+"
  
  # https://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7230.html#header.fields
  #  field-name     = token
  field_name = token
  
  # The standard says:
  #
  #  field-value    = *( field-content / obs-fold )
  #  field-content  = field-vchar [ 1*( SP / HTAB ) field-vchar ]
  #  field-vchar    = VCHAR / obs-text
  #  obs-fold       = CRLF 1*( SP / HTAB )
  #                 ; obsolete line folding
  #                 ; see Section 3.2.4
  #
  # https://tools.ietf.org/html/rfc5234#appendix-B.1
  #
  #   VCHAR          =  %x21-7E
  #                  ; visible (printing) characters
  #
  # https://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7230.html#rule.quoted-string
  #   obs-text       = %x80-FF
  #
  # However, the standard definition of field-content is WRONG! It disallows
  # fields containing a single visible character surrounded by whitespace,
  # e.g. "foo a bar".
  #
  # See: https://www.rfc-editor.org/errata_search.php?rfc=7230&eid=4189
  #
  # So our definition of field_content attempts to fix it up...
  vchar_or_obs_text = r"[\x21-\xff]"
  field_vchar = vchar_or_obs_text
  field_content = r"{field_vchar}+(?:[ \t]+{field_vchar}+)*".format(**globals())
  
  # We handle obs-fold at a different level, and our fixed-up field_content
  # already grows to swallow the whole value, so ? instead of *
  field_value = r"({field_content})?".format(**globals())
  
  #  header-field   = field-name ":" OWS field-value OWS
  header_field = (
      r"(?P<field_name>{field_name})"
      r":"
      r"{OWS}"
      r"(?P<field_value>{field_value})"
      r"{OWS}"
      .format(**globals()))
  
  # https://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7230.html#request.line
  #
  #   request-line   = method SP request-target SP HTTP-version CRLF
  #   method         = token
  #   HTTP-version   = HTTP-name "/" DIGIT "." DIGIT
  #   HTTP-name      = %x48.54.54.50 ; "HTTP", case-sensitive
  #
  # request-target is complicated (see RFC 7230 sec 5.3) -- could be path, full
  # URL, host+port (for connect), or even "*", but in any case we are guaranteed
  # that it contains no spaces (see sec 3.1.1).
  method = token
  request_target = r"[^ ]+"
  http_version = r"HTTP/(?P<http_version>[0-9]\.[0-9])"
  request_line = (
      r"(?P<method>{method})"
      r" "
      r"(?P<target>{request_target})"
      r" "
      r"{http_version}"
      .format(**globals()))
  
  # https://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7230.html#status.line
  #
  #   status-line = HTTP-version SP status-code SP reason-phrase CRLF
  #   status-code    = 3DIGIT
  #   reason-phrase  = *( HTAB / SP / VCHAR / obs-text )
  status_code = r"[0-9]{3}"
  reason_phrase = r"([ \t]|{vchar_or_obs_text})*".format(**globals())
  status_line = (
      r"{http_version}"
      r" "
      r"(?P<status_code>{status_code})"
      # However, there are apparently a few too many servers out there that just
      # leave out the reason phrase:
      #   https://github.com/scrapy/scrapy/issues/345#issuecomment-281756036
      #   https://github.com/seanmonstar/httparse/issues/29
      # so make it optional. ?: is a non-capturing group.
      r"(?: (?P<reason>{reason_phrase}))?"
      .format(**globals()))
  
  HEXDIG = r"[0-9A-Fa-f]"
  # Actually
  #
  #      chunk-size     = 1*HEXDIG
  #
  # but we impose an upper-limit to avoid ridiculosity. len(str(2**64)) == 20
  chunk_size = r"({HEXDIG}){{1,20}}".format(**globals())
  # Actually
  #
  #     chunk-ext      = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
  #
  # but we aren't parsing the things so we don't really care.
  chunk_ext = r";.*"
  chunk_header = (
      r"(?P<chunk_size>{chunk_size})"
      r"(?P<chunk_ext>{chunk_ext})?"
      r"\r\n"
      .format(**globals()))
  