Source code for tornado.httputil

# Copyright 2009 Facebook
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

"""HTTP utility code shared by clients and servers.

This module also defines the `HTTPServerRequest` class which is exposed
via `tornado.web.RequestHandler.request`.

import calendar
import collections
import copy
import datetime
import email.utils
from http.client import responses
import http.cookies as Cookie
import numbers
import re
from ssl import SSLError
import time
import unicodedata
from urllib.parse import urlencode, urlparse, urlunparse, parse_qsl

from tornado.escape import native_str, parse_qs_bytes, utf8
from tornado.log import gen_log
from tornado.util import ObjectDict, unicode_type

# responses is unused in this file, but we re-export it to other files.
# Reference it so pyflakes doesn't complain.

import typing  # noqa: F401

# RFC 7230 section 3.5: a recipient MAY recognize a single LF as a line
# terminator and ignore any preceding CR.
_CRLF_RE = re.compile(r'\r?\n')

class _NormalizedHeaderCache(dict):
    """Dynamic cached mapping of header names to Http-Header-Case.

    Implemented as a dict subclass so that cache hits are as fast as a
    normal dict lookup, without the overhead of a python function

    >>> normalized_headers = _NormalizedHeaderCache(10)
    >>> normalized_headers["coNtent-TYPE"]
    def __init__(self, size):
        super(_NormalizedHeaderCache, self).__init__()
        self.size = size
        self.queue = collections.deque()

    def __missing__(self, key):
        normalized = "-".join([w.capitalize() for w in key.split("-")])
        self[key] = normalized
        if len(self.queue) > self.size:
            # Limit the size of the cache.  LRU would be better, but this
            # simpler approach should be fine.  In Python 2.7+ we could
            # use OrderedDict (or in 3.2+, @functools.lru_cache).
            old_key = self.queue.popleft()
            del self[old_key]
        return normalized

_normalized_headers = _NormalizedHeaderCache(1000)

[docs]class HTTPHeaders(collections.MutableMapping): """A dictionary that maintains ``Http-Header-Case`` for all keys. Supports multiple values per key via a pair of new methods, `add()` and `get_list()`. The regular dictionary interface returns a single value per key, with multiple values joined by a comma. >>> h = HTTPHeaders({"content-type": "text/html"}) >>> list(h.keys()) ['Content-Type'] >>> h["Content-Type"] 'text/html' >>> h.add("Set-Cookie", "A=B") >>> h.add("Set-Cookie", "C=D") >>> h["set-cookie"] 'A=B,C=D' >>> h.get_list("set-cookie") ['A=B', 'C=D'] >>> for (k,v) in sorted(h.get_all()): ... print('%s: %s' % (k,v)) ... Content-Type: text/html Set-Cookie: A=B Set-Cookie: C=D """ def __init__(self, *args, **kwargs): self._dict = {} # type: typing.Dict[str, str] self._as_list = {} # type: typing.Dict[str, typing.List[str]] self._last_key = None if (len(args) == 1 and len(kwargs) == 0 and isinstance(args[0], HTTPHeaders)): # Copy constructor for k, v in args[0].get_all(): self.add(k, v) else: # Dict-style initialization self.update(*args, **kwargs) # new public methods
[docs] def add(self, name, value): # type: (str, str) -> None """Adds a new value for the given key.""" norm_name = _normalized_headers[name] self._last_key = norm_name if norm_name in self: self._dict[norm_name] = (native_str(self[norm_name]) + ',' + native_str(value)) self._as_list[norm_name].append(value) else: self[norm_name] = value
[docs] def get_list(self, name): """Returns all values for the given header as a list.""" norm_name = _normalized_headers[name] return self._as_list.get(norm_name, [])
[docs] def get_all(self): # type: () -> typing.Iterable[typing.Tuple[str, str]] """Returns an iterable of all (name, value) pairs. If a header has multiple values, multiple pairs will be returned with the same name. """ for name, values in self._as_list.items(): for value in values: yield (name, value)
[docs] def parse_line(self, line): """Updates the dictionary with a single header line. >>> h = HTTPHeaders() >>> h.parse_line("Content-Type: text/html") >>> h.get('content-type') 'text/html' """ if line[0].isspace(): # continuation of a multi-line header if self._last_key is None: raise HTTPInputError("first header line cannot start with whitespace") new_part = ' ' + line.lstrip() self._as_list[self._last_key][-1] += new_part self._dict[self._last_key] += new_part else: try: name, value = line.split(":", 1) except ValueError: raise HTTPInputError("no colon in header line") self.add(name, value.strip())
[docs] @classmethod def parse(cls, headers): """Returns a dictionary from HTTP header text. >>> h = HTTPHeaders.parse("Content-Type: text/html\\r\\nContent-Length: 42\\r\\n") >>> sorted(h.items()) [('Content-Length', '42'), ('Content-Type', 'text/html')] .. versionchanged:: 5.1 Raises `HTTPInputError` on malformed headers instead of a mix of `KeyError`, and `ValueError`. """ h = cls() for line in _CRLF_RE.split(headers): if line: h.parse_line(line) return h
# MutableMapping abstract method implementations. def __setitem__(self, name, value): norm_name = _normalized_headers[name] self._dict[norm_name] = value self._as_list[norm_name] = [value] def __getitem__(self, name): # type: (str) -> str return self._dict[_normalized_headers[name]] def __delitem__(self, name): norm_name = _normalized_headers[name] del self._dict[norm_name] del self._as_list[norm_name] def __len__(self): return len(self._dict) def __iter__(self): return iter(self._dict) def copy(self): # defined in dict but not in MutableMapping. return HTTPHeaders(self) # Use our overridden copy method for the copy.copy module. # This makes shallow copies one level deeper, but preserves # the appearance that HTTPHeaders is a single container. __copy__ = copy def __str__(self): lines = [] for name, value in self.get_all(): lines.append("%s: %s\n" % (name, value)) return "".join(lines) __unicode__ = __str__
[docs]class HTTPServerRequest(object): """A single HTTP request. All attributes are type `str` unless otherwise noted. .. attribute:: method HTTP request method, e.g. "GET" or "POST" .. attribute:: uri The requested uri. .. attribute:: path The path portion of `uri` .. attribute:: query The query portion of `uri` .. attribute:: version HTTP version specified in request, e.g. "HTTP/1.1" .. attribute:: headers `.HTTPHeaders` dictionary-like object for request headers. Acts like a case-insensitive dictionary with additional methods for repeated headers. .. attribute:: body Request body, if present, as a byte string. .. attribute:: remote_ip Client's IP address as a string. If ``HTTPServer.xheaders`` is set, will pass along the real IP address provided by a load balancer in the ``X-Real-Ip`` or ``X-Forwarded-For`` header. .. versionchanged:: 3.1 The list format of ``X-Forwarded-For`` is now supported. .. attribute:: protocol The protocol used, either "http" or "https". If ``HTTPServer.xheaders`` is set, will pass along the protocol used by a load balancer if reported via an ``X-Scheme`` header. .. attribute:: host The requested hostname, usually taken from the ``Host`` header. .. attribute:: arguments GET/POST arguments are available in the arguments property, which maps arguments names to lists of values (to support multiple values for individual names). Names are of type `str`, while arguments are byte strings. Note that this is different from `.RequestHandler.get_argument`, which returns argument values as unicode strings. .. attribute:: query_arguments Same format as ``arguments``, but contains only arguments extracted from the query string. .. versionadded:: 3.2 .. attribute:: body_arguments Same format as ``arguments``, but contains only arguments extracted from the request body. .. versionadded:: 3.2 .. attribute:: files File uploads are available in the files property, which maps file names to lists of `.HTTPFile`. .. attribute:: connection An HTTP request is attached to a single HTTP connection, which can be accessed through the "connection" attribute. Since connections are typically kept open in HTTP/1.1, multiple requests can be handled sequentially on a single connection. .. versionchanged:: 4.0 Moved from ``tornado.httpserver.HTTPRequest``. """ def __init__(self, method=None, uri=None, version="HTTP/1.0", headers=None, body=None, host=None, files=None, connection=None, start_line=None, server_connection=None): if start_line is not None: method, uri, version = start_line self.method = method self.uri = uri self.version = version self.headers = headers or HTTPHeaders() self.body = body or b"" # set remote IP and protocol context = getattr(connection, 'context', None) self.remote_ip = getattr(context, 'remote_ip', None) self.protocol = getattr(context, 'protocol', "http") = host or self.headers.get("Host") or "" self.host_name = split_host_and_port([0] self.files = files or {} self.connection = connection self.server_connection = server_connection self._start_time = time.time() self._finish_time = None self.path, sep, self.query = uri.partition('?') self.arguments = parse_qs_bytes(self.query, keep_blank_values=True) self.query_arguments = copy.deepcopy(self.arguments) self.body_arguments = {} @property def cookies(self): """A dictionary of Cookie.Morsel objects.""" if not hasattr(self, "_cookies"): self._cookies = Cookie.SimpleCookie() if "Cookie" in self.headers: try: parsed = parse_cookie(self.headers["Cookie"]) except Exception: pass else: for k, v in parsed.items(): try: self._cookies[k] = v except Exception: # SimpleCookie imposes some restrictions on keys; # parse_cookie does not. Discard any cookies # with disallowed keys. pass return self._cookies
[docs] def full_url(self): """Reconstructs the full URL for this request.""" return self.protocol + "://" + + self.uri
[docs] def request_time(self): """Returns the amount of time it took for this request to execute.""" if self._finish_time is None: return time.time() - self._start_time else: return self._finish_time - self._start_time
[docs] def get_ssl_certificate(self, binary_form=False): """Returns the client's SSL certificate, if any. To use client certificates, the HTTPServer's `ssl.SSLContext.verify_mode` field must be set, e.g.:: ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH) ssl_ctx.load_cert_chain("foo.crt", "foo.key") ssl_ctx.load_verify_locations("cacerts.pem") ssl_ctx.verify_mode = ssl.CERT_REQUIRED server = HTTPServer(app, ssl_options=ssl_ctx) By default, the return value is a dictionary (or None, if no client certificate is present). If ``binary_form`` is true, a DER-encoded form of the certificate is returned instead. See SSLSocket.getpeercert() in the standard library for more details. """ try: return binary_form=binary_form) except SSLError: return None
def _parse_body(self): parse_body_arguments( self.headers.get("Content-Type", ""), self.body, self.body_arguments, self.files, self.headers) for k, v in self.body_arguments.items(): self.arguments.setdefault(k, []).extend(v) def __repr__(self): attrs = ("protocol", "host", "method", "uri", "version", "remote_ip") args = ", ".join(["%s=%r" % (n, getattr(self, n)) for n in attrs]) return "%s(%s)" % (self.__class__.__name__, args)
[docs]class HTTPInputError(Exception): """Exception class for malformed HTTP requests or responses from remote sources. .. versionadded:: 4.0 """ pass
[docs]class HTTPOutputError(Exception): """Exception class for errors in HTTP output. .. versionadded:: 4.0 """ pass
[docs]class HTTPServerConnectionDelegate(object): """Implement this interface to handle requests from `.HTTPServer`. .. versionadded:: 4.0 """
[docs] def start_request(self, server_conn, request_conn): """This method is called by the server when a new request has started. :arg server_conn: is an opaque object representing the long-lived (e.g. tcp-level) connection. :arg request_conn: is a `.HTTPConnection` object for a single request/response exchange. This method should return a `.HTTPMessageDelegate`. """ raise NotImplementedError()
[docs] def on_close(self, server_conn): """This method is called when a connection has been closed. :arg server_conn: is a server connection that has previously been passed to ``start_request``. """ pass
[docs]class HTTPMessageDelegate(object): """Implement this interface to handle an HTTP request or response. .. versionadded:: 4.0 """
[docs] def headers_received(self, start_line, headers): """Called when the HTTP headers have been received and parsed. :arg start_line: a `.RequestStartLine` or `.ResponseStartLine` depending on whether this is a client or server message. :arg headers: a `.HTTPHeaders` instance. Some `.HTTPConnection` methods can only be called during ``headers_received``. May return a `.Future`; if it does the body will not be read until it is done. """ pass
[docs] def data_received(self, chunk): """Called when a chunk of data has been received. May return a `.Future` for flow control. """ pass
[docs] def finish(self): """Called after the last chunk of data has been received.""" pass
[docs] def on_connection_close(self): """Called if the connection is closed without finishing the request. If ``headers_received`` is called, either ``finish`` or ``on_connection_close`` will be called, but not both. """ pass
[docs]class HTTPConnection(object): """Applications use this interface to write their responses. .. versionadded:: 4.0 """
[docs] def write_headers(self, start_line, headers, chunk=None): """Write an HTTP header block. :arg start_line: a `.RequestStartLine` or `.ResponseStartLine`. :arg headers: a `.HTTPHeaders` instance. :arg chunk: the first (optional) chunk of data. This is an optimization so that small responses can be written in the same call as their headers. :arg callback: a callback to be run when the write is complete. The ``version`` field of ``start_line`` is ignored. Returns a `.Future` if no callback is given. .. versionchanged:: 6.0 The ``callback`` argument was removed. """ raise NotImplementedError()
[docs] def write(self, chunk): """Writes a chunk of body data. The callback will be run when the write is complete. If no callback is given, returns a Future. .. versionchanged:: 6.0 The ``callback`` argument was removed. """ raise NotImplementedError()
[docs] def finish(self): """Indicates that the last body data has been written. """ raise NotImplementedError()
[docs]def url_concat(url, args): """Concatenate url and arguments regardless of whether url has existing query parameters. ``args`` may be either a dictionary or a list of key-value pairs (the latter allows for multiple values with the same key. >>> url_concat("", dict(c="d")) '' >>> url_concat("", dict(c="d")) '' >>> url_concat("", [("c", "d"), ("c", "d2")]) '' """ if args is None: return url parsed_url = urlparse(url) if isinstance(args, dict): parsed_query = parse_qsl(parsed_url.query, keep_blank_values=True) parsed_query.extend(args.items()) elif isinstance(args, list) or isinstance(args, tuple): parsed_query = parse_qsl(parsed_url.query, keep_blank_values=True) parsed_query.extend(args) else: err = "'args' parameter should be dict, list or tuple. Not {0}".format( type(args)) raise TypeError(err) final_query = urlencode(parsed_query) url = urlunparse(( parsed_url[0], parsed_url[1], parsed_url[2], parsed_url[3], final_query, parsed_url[5])) return url
[docs]class HTTPFile(ObjectDict): """Represents a file uploaded via a form. For backwards compatibility, its instance attributes are also accessible as dictionary keys. * ``filename`` * ``body`` * ``content_type`` """ pass
def _parse_request_range(range_header): """Parses a Range header. Returns either ``None`` or tuple ``(start, end)``. Note that while the HTTP headers use inclusive byte positions, this method returns indexes suitable for use in slices. >>> start, end = _parse_request_range("bytes=1-2") >>> start, end (1, 3) >>> [0, 1, 2, 3, 4][start:end] [1, 2] >>> _parse_request_range("bytes=6-") (6, None) >>> _parse_request_range("bytes=-6") (-6, None) >>> _parse_request_range("bytes=-0") (None, 0) >>> _parse_request_range("bytes=") (None, None) >>> _parse_request_range("foo=42") >>> _parse_request_range("bytes=1-2,6-10") Note: only supports one range (ex, ``bytes=1-2,6-10`` is not allowed). See [0] for the details of the range header. [0]: """ unit, _, value = range_header.partition("=") unit, value = unit.strip(), value.strip() if unit != "bytes": return None start_b, _, end_b = value.partition("-") try: start = _int_or_none(start_b) end = _int_or_none(end_b) except ValueError: return None if end is not None: if start is None: if end != 0: start = -end end = None else: end += 1 return (start, end) def _get_content_range(start, end, total): """Returns a suitable Content-Range header: >>> print(_get_content_range(None, 1, 4)) bytes 0-0/4 >>> print(_get_content_range(1, 3, 4)) bytes 1-2/4 >>> print(_get_content_range(None, None, 4)) bytes 0-3/4 """ start = start or 0 end = (end or total) - 1 return "bytes %s-%s/%s" % (start, end, total) def _int_or_none(val): val = val.strip() if val == "": return None return int(val)
[docs]def parse_body_arguments(content_type, body, arguments, files, headers=None): """Parses a form request body. Supports ``application/x-www-form-urlencoded`` and ``multipart/form-data``. The ``content_type`` parameter should be a string and ``body`` should be a byte string. The ``arguments`` and ``files`` parameters are dictionaries that will be updated with the parsed contents. """ if headers and 'Content-Encoding' in headers: gen_log.warning("Unsupported Content-Encoding: %s", headers['Content-Encoding']) return if content_type.startswith("application/x-www-form-urlencoded"): try: uri_arguments = parse_qs_bytes(native_str(body), keep_blank_values=True) except Exception as e: gen_log.warning('Invalid x-www-form-urlencoded body: %s', e) uri_arguments = {} for name, values in uri_arguments.items(): if values: arguments.setdefault(name, []).extend(values) elif content_type.startswith("multipart/form-data"): try: fields = content_type.split(";") for field in fields: k, sep, v = field.strip().partition("=") if k == "boundary" and v: parse_multipart_form_data(utf8(v), body, arguments, files) break else: raise ValueError("multipart boundary not found") except Exception as e: gen_log.warning("Invalid multipart/form-data: %s", e)
[docs]def parse_multipart_form_data(boundary, data, arguments, files): """Parses a ``multipart/form-data`` body. The ``boundary`` and ``data`` parameters are both byte strings. The dictionaries given in the arguments and files parameters will be updated with the contents of the body. .. versionchanged:: 5.1 Now recognizes non-ASCII filenames in RFC 2231/5987 (``filename*=``) format. """ # The standard allows for the boundary to be quoted in the header, # although it's rare (it happens at least for google app engine # xmpp). I think we're also supposed to handle backslash-escapes # here but I'll save that until we see a client that uses them # in the wild. if boundary.startswith(b'"') and boundary.endswith(b'"'): boundary = boundary[1:-1] final_boundary_index = data.rfind(b"--" + boundary + b"--") if final_boundary_index == -1: gen_log.warning("Invalid multipart/form-data: no final boundary") return parts = data[:final_boundary_index].split(b"--" + boundary + b"\r\n") for part in parts: if not part: continue eoh = part.find(b"\r\n\r\n") if eoh == -1: gen_log.warning("multipart/form-data missing headers") continue headers = HTTPHeaders.parse(part[:eoh].decode("utf-8")) disp_header = headers.get("Content-Disposition", "") disposition, disp_params = _parse_header(disp_header) if disposition != "form-data" or not part.endswith(b"\r\n"): gen_log.warning("Invalid multipart/form-data") continue value = part[eoh + 4:-2] if not disp_params.get("name"): gen_log.warning("multipart/form-data value missing name") continue name = disp_params["name"] if disp_params.get("filename"): ctype = headers.get("Content-Type", "application/unknown") files.setdefault(name, []).append(HTTPFile( # type: ignore filename=disp_params["filename"], body=value, content_type=ctype)) else: arguments.setdefault(name, []).append(value)
[docs]def format_timestamp(ts): """Formats a timestamp in the format used by HTTP. The argument may be a numeric timestamp as returned by `time.time`, a time tuple as returned by `time.gmtime`, or a `datetime.datetime` object. >>> format_timestamp(1359312200) 'Sun, 27 Jan 2013 18:43:20 GMT' """ if isinstance(ts, numbers.Real): pass elif isinstance(ts, (tuple, time.struct_time)): ts = calendar.timegm(ts) elif isinstance(ts, datetime.datetime): ts = calendar.timegm(ts.utctimetuple()) else: raise TypeError("unknown timestamp type: %r" % ts) return email.utils.formatdate(ts, usegmt=True)
RequestStartLine = collections.namedtuple( 'RequestStartLine', ['method', 'path', 'version'])
[docs]def parse_request_start_line(line): """Returns a (method, path, version) tuple for an HTTP 1.x request line. The response is a `collections.namedtuple`. >>> parse_request_start_line("GET /foo HTTP/1.1") RequestStartLine(method='GET', path='/foo', version='HTTP/1.1') """ try: method, path, version = line.split(" ") except ValueError: # # invalid request-line SHOULD respond with a 400 (Bad Request) raise HTTPInputError("Malformed HTTP request line") if not re.match(r"^HTTP/1\.[0-9]$", version): raise HTTPInputError( "Malformed HTTP version in HTTP Request-Line: %r" % version) return RequestStartLine(method, path, version)
ResponseStartLine = collections.namedtuple( 'ResponseStartLine', ['version', 'code', 'reason'])
[docs]def parse_response_start_line(line): """Returns a (version, code, reason) tuple for an HTTP 1.x response line. The response is a `collections.namedtuple`. >>> parse_response_start_line("HTTP/1.1 200 OK") ResponseStartLine(version='HTTP/1.1', code=200, reason='OK') """ line = native_str(line) match = re.match("(HTTP/1.[0-9]) ([0-9]+) ([^\r]*)", line) if not match: raise HTTPInputError("Error parsing response start line") return ResponseStartLine(, int(,
# _parseparam and _parse_header are copied and modified from python2.7's # The original 2.7 version of this code did not correctly support some # combinations of semicolons and double quotes. # It has also been modified to support valueless parameters as seen in # websocket extension negotiations, and to support non-ascii values in # RFC 2231/5987 format. def _parseparam(s): while s[:1] == ';': s = s[1:] end = s.find(';') while end > 0 and (s.count('"', 0, end) - s.count('\\"', 0, end)) % 2: end = s.find(';', end + 1) if end < 0: end = len(s) f = s[:end] yield f.strip() s = s[end:] def _parse_header(line): r"""Parse a Content-type like header. Return the main content-type and a dictionary of options. >>> d = "form-data; foo=\"b\\\\a\\\"r\"; file*=utf-8''T%C3%A4st" >>> ct, d = _parse_header(d) >>> ct 'form-data' >>> d['file'] == r'T\u00e4st'.encode('ascii').decode('unicode_escape') True >>> d['foo'] 'b\\a"r' """ parts = _parseparam(';' + line) key = next(parts) # decode_params treats first argument special, but we already stripped key params = [('Dummy', 'value')] for p in parts: i = p.find('=') if i >= 0: name = p[:i].strip().lower() value = p[i + 1:].strip() params.append((name, native_str(value))) params = email.utils.decode_params(params) params.pop(0) # get rid of the dummy again pdict = {} for name, value in params: value = email.utils.collapse_rfc2231_value(value) if len(value) >= 2 and value[0] == '"' and value[-1] == '"': value = value[1:-1] pdict[name] = value return key, pdict def _encode_header(key, pdict): """Inverse of _parse_header. >>> _encode_header('permessage-deflate', ... {'client_max_window_bits': 15, 'client_no_context_takeover': None}) 'permessage-deflate; client_max_window_bits=15; client_no_context_takeover' """ if not pdict: return key out = [key] # Sort the parameters just to make it easy to test. for k, v in sorted(pdict.items()): if v is None: out.append(k) else: # TODO: quote if necessary. out.append('%s=%s' % (k, v)) return '; '.join(out)
[docs]def encode_username_password(username, password): """Encodes a username/password pair in the format used by HTTP auth. The return value is a byte string in the form ``username:password``. .. versionadded:: 5.1 """ if isinstance(username, unicode_type): username = unicodedata.normalize('NFC', username) if isinstance(password, unicode_type): password = unicodedata.normalize('NFC', password) return utf8(username) + b":" + utf8(password)
def doctests(): import doctest return doctest.DocTestSuite()
[docs]def split_host_and_port(netloc): """Returns ``(host, port)`` tuple from ``netloc``. Returned ``port`` will be ``None`` if not present. .. versionadded:: 4.1 """ match = re.match(r'^(.+):(\d+)$', netloc) if match: host = port = int( else: host = netloc port = None return (host, port)
[docs]def qs_to_qsl(qs): """Generator converting a result of ``parse_qs`` back to name-value pairs. .. versionadded:: 5.0 """ for k, vs in qs.items(): for v in vs: yield (k, v)
_OctalPatt = re.compile(r"\\[0-3][0-7][0-7]") _QuotePatt = re.compile(r"[\\].") _nulljoin = ''.join def _unquote_cookie(str): """Handle double quotes and escaping in cookie values. This method is copied verbatim from the Python 3.5 standard library (http.cookies._unquote) so we don't have to depend on non-public interfaces. """ # If there aren't any doublequotes, # then there can't be any special characters. See RFC 2109. if str is None or len(str) < 2: return str if str[0] != '"' or str[-1] != '"': return str # We have to assume that we must decode this string. # Down to work. # Remove the "s str = str[1:-1] # Check for special sequences. Examples: # \012 --> \n # \" --> " # i = 0 n = len(str) res = [] while 0 <= i < n: o_match =, i) q_match =, i) if not o_match and not q_match: # Neither matched res.append(str[i:]) break # else: j = k = -1 if o_match: j = o_match.start(0) if q_match: k = q_match.start(0) if q_match and (not o_match or k < j): # QuotePatt matched res.append(str[i:k]) res.append(str[k + 1]) i = k + 2 else: # OctalPatt matched res.append(str[i:j]) res.append(chr(int(str[j + 1:j + 4], 8))) i = j + 4 return _nulljoin(res)