"""Exception classes for CherryPy. CherryPy provides (and uses) exceptions for declaring that the HTTP response should be a status other than the default "200 OK". You can ``raise`` them like normal Python exceptions. You can also call them and they will raise themselves; this means you can set an :class:`HTTPError` or :class:`HTTPRedirect` as the :attr:`request.handler`. .. _redirectingpost: Redirecting POST ================ When you GET a resource and are redirected by the server to another Location, there's generally no problem since GET is both a "safe method" (there should be no side-effects) and an "idempotent method" (multiple calls are no different than a single call). POST, however, is neither safe nor idempotent--if you charge a credit card, you don't want to be charged twice by a redirect! For this reason, *none* of the 3xx responses permit a user-agent (browser) to resubmit a POST on redirection without first confirming the action with the user: ===== ================================= =========== 300 Multiple Choices Confirm with the user 301 Moved Permanently Confirm with the user 302 Found (Object moved temporarily) Confirm with the user 303 See Other GET the new URI--no confirmation 304 Not modified (for conditional GET only--POST should not raise this error) 305 Use Proxy Confirm with the user 307 Temporary Redirect Confirm with the user ===== ================================= =========== However, browsers have historically implemented these restrictions poorly; in particular, many browsers do not force the user to confirm 301, 302 or 307 when redirecting POST. For this reason, CherryPy defaults to 303, which most user-agents appear to have implemented correctly. Therefore, if you raise HTTPRedirect for a POST request, the user-agent will most likely attempt to GET the new URI (without asking for confirmation from the user). We realize this is confusing for developers, but it's the safest thing we could do. You are of course free to raise ``HTTPRedirect(uri, status=302)`` or any other 3xx status if you know what you're doing, but given the environment, we couldn't let any of those be the default. Custom Error Handling ===================== .. image:: /refman/cperrors.gif Anticipated HTTP responses -------------------------- The 'error_page' config namespace can be used to provide custom HTML output for expected responses (like 404 Not Found). Supply a filename from which the output will be read. The contents will be interpolated with the values %(status)s, %(message)s, %(traceback)s, and %(version)s using plain old Python `string formatting `_. :: _cp_config = {'error_page.404': os.path.join(localDir, "static/index.html")} Beginning in version 3.1, you may also provide a function or other callable as an error_page entry. It will be passed the same status, message, traceback and version arguments that are interpolated into templates:: def error_page_402(status, message, traceback, version): return "Error %s - Well, I'm very sorry but you haven't paid!" % status cherrypy.config.update({'error_page.402': error_page_402}) Also in 3.1, in addition to the numbered error codes, you may also supply "error_page.default" to handle all codes which do not have their own error_page entry. Unanticipated errors -------------------- CherryPy also has a generic error handling mechanism: whenever an unanticipated error occurs in your code, it will call :func:`Request.error_response` to set the response status, headers, and body. By default, this is the same output as :class:`HTTPError(500) `. If you want to provide some other behavior, you generally replace "request.error_response". Here is some sample code that shows how to display a custom error message and send an e-mail containing the error:: from cherrypy import _cperror def handle_error(): cherrypy.response.status = 500 cherrypy.response.body = ["Sorry, an error occured"] sendMail('error@domain.com', 'Error in your web app', _cperror.format_exc()) class Root: _cp_config = {'request.error_response': handle_error} Note that you have to explicitly set :attr:`response.body ` and not simply return an error message as a result. """ from cgi import escape as _escape from sys import exc_info as _exc_info from traceback import format_exception as _format_exception from cherrypy._cpcompat import basestring, bytestr, iteritems, ntob, tonative, urljoin as _urljoin from cherrypy.lib import httputil as _httputil class CherryPyException(Exception): """A base class for CherryPy exceptions.""" pass class TimeoutError(CherryPyException): """Exception raised when Response.timed_out is detected.""" pass class InternalRedirect(CherryPyException): """Exception raised to switch to the handler for a different URL. This exception will redirect processing to another path within the site (without informing the client). Provide the new path as an argument when raising the exception. Provide any params in the querystring for the new URL. """ def __init__(self, path, query_string=""): import cherrypy self.request = cherrypy.serving.request self.query_string = query_string if "?" in path: # Separate any params included in the path path, self.query_string = path.split("?", 1) # Note that urljoin will "do the right thing" whether url is: # 1. a URL relative to root (e.g. "/dummy") # 2. a URL relative to the current path # Note that any query string will be discarded. path = _urljoin(self.request.path_info, path) # Set a 'path' member attribute so that code which traps this # error can have access to it. self.path = path CherryPyException.__init__(self, path, self.query_string) class HTTPRedirect(CherryPyException): """Exception raised when the request should be redirected. This exception will force a HTTP redirect to the URL or URL's you give it. The new URL must be passed as the first argument to the Exception, e.g., HTTPRedirect(newUrl). Multiple URLs are allowed in a list. If a URL is absolute, it will be used as-is. If it is relative, it is assumed to be relative to the current cherrypy.request.path_info. If one of the provided URL is a unicode object, it will be encoded using the default encoding or the one passed in parameter. There are multiple types of redirect, from which you can select via the ``status`` argument. If you do not provide a ``status`` arg, it defaults to 303 (or 302 if responding with HTTP/1.0). Examples:: raise cherrypy.HTTPRedirect("") raise cherrypy.HTTPRedirect("/abs/path", 307) raise cherrypy.HTTPRedirect(["path1", "path2?a=1&b=2"], 301) See :ref:`redirectingpost` for additional caveats. """ status = None """The integer HTTP status code to emit.""" urls = None """The list of URL's to emit.""" encoding = 'utf-8' """The encoding when passed urls are not native strings""" def __init__(self, urls, status=None, encoding=None): import cherrypy request = cherrypy.serving.request if isinstance(urls, basestring): urls = [urls] abs_urls = [] for url in urls: url = tonative(url, encoding or self.encoding) # Note that urljoin will "do the right thing" whether url is: # 1. a complete URL with host (e.g. "http://www.example.com/test") # 2. a URL relative to root (e.g. "/dummy") # 3. a URL relative to the current path # Note that any query string in cherrypy.request is discarded. url = _urljoin(cherrypy.url(), url) abs_urls.append(url) self.urls = abs_urls # RFC 2616 indicates a 301 response code fits our goal; however, # browser support for 301 is quite messy. Do 302/303 instead. See # http://www.alanflavell.org.uk/www/post-redirect.html if status is None: if request.protocol >= (1, 1): status = 303 else: status = 302 else: status = int(status) if status < 300 or status > 399: raise ValueError("status must be between 300 and 399.") self.status = status CherryPyException.__init__(self, abs_urls, status) def set_response(self): """Modify cherrypy.response status, headers, and body to represent self. CherryPy uses this internally, but you can also use it to create an HTTPRedirect object and set its output without *raising* the exception. """ import cherrypy response = cherrypy.serving.response response.status = status = self.status if status in (300, 301, 302, 303, 307): response.headers['Content-Type'] = "text/html;charset=utf-8" # "The ... URI SHOULD be given by the Location field # in the response." response.headers['Location'] = self.urls[0] # "Unless the request method was HEAD, the entity of the response # SHOULD contain a short hypertext note with a hyperlink to the # new URI(s)." msg = {300: "This resource can be found at %s.", 301: "This resource has permanently moved to %s.", 302: "This resource resides temporarily at %s.", 303: "This resource can be found at %s.", 307: "This resource has moved temporarily to %s.", }[status] msgs = [msg % (u, u) for u in self.urls] response.body = ntob("
\n".join(msgs), 'utf-8') # Previous code may have set C-L, so we have to reset it # (allow finalize to set it). response.headers.pop('Content-Length', None) elif status == 304: # Not Modified. # "The response MUST include the following header fields: # Date, unless its omission is required by section 14.18.1" # The "Date" header should have been set in Response.__init__ # "...the response SHOULD NOT include other entity-headers." for key in ('Allow', 'Content-Encoding', 'Content-Language', 'Content-Length', 'Content-Location', 'Content-MD5', 'Content-Range', 'Content-Type', 'Expires', 'Last-Modified'): if key in response.headers: del response.headers[key] # "The 304 response MUST NOT contain a message-body." response.body = None # Previous code may have set C-L, so we have to reset it. response.headers.pop('Content-Length', None) elif status == 305: # Use Proxy. # self.urls[0] should be the URI of the proxy. response.headers['Location'] = self.urls[0] response.body = None # Previous code may have set C-L, so we have to reset it. response.headers.pop('Content-Length', None) else: raise ValueError("The %s status code is unknown." % status) def __call__(self): """Use this exception as a request.handler (raise self).""" raise self def clean_headers(status): """Remove any headers which should not apply to an error response.""" import cherrypy response = cherrypy.serving.response # Remove headers which applied to the original content, # but do not apply to the error page. respheaders = response.headers for key in ["Accept-Ranges", "Age", "ETag", "Location", "Retry-After", "Vary", "Content-Encoding", "Content-Length", "Expires", "Content-Location", "Content-MD5", "Last-Modified"]: if key in respheaders: del respheaders[key] if status != 416: # A server sending a response with status code 416 (Requested # range not satisfiable) SHOULD include a Content-Range field # with a byte-range-resp-spec of "*". The instance-length # specifies the current length of the selected resource. # A response with status code 206 (Partial Content) MUST NOT # include a Content-Range field with a byte-range- resp-spec of "*". if "Content-Range" in respheaders: del respheaders["Content-Range"] class HTTPError(CherryPyException): """Exception used to return an HTTP error code (4xx-5xx) to the client. This exception can be used to automatically send a response using a http status code, with an appropriate error page. It takes an optional ``status`` argument (which must be between 400 and 599); it defaults to 500 ("Internal Server Error"). It also takes an optional ``message`` argument, which will be returned in the response body. See `RFC 2616 `_ for a complete list of available error codes and when to use them. Examples:: raise cherrypy.HTTPError(403) raise cherrypy.HTTPError("403 Forbidden", "You are not allowed to access this resource.") """ status = None """The HTTP status code. May be of type int or str (with a Reason-Phrase).""" code = None """The integer HTTP status code.""" reason = None """The HTTP Reason-Phrase string.""" def __init__(self, status=500, message=None): self.status = status try: self.code, self.reason, defaultmsg = _httputil.valid_status(status) except ValueError: raise self.__class__(500, _exc_info()[1].args[0]) if self.code < 400 or self.code > 599: raise ValueError("status must be between 400 and 599.") # See http://www.python.org/dev/peps/pep-0352/ # self.message = message self._message = message or defaultmsg CherryPyException.__init__(self, status, message) def set_response(self): """Modify cherrypy.response status, headers, and body to represent self. CherryPy uses this internally, but you can also use it to create an HTTPError object and set its output without *raising* the exception. """ import cherrypy response = cherrypy.serving.response clean_headers(self.code) # In all cases, finalize will be called after this method, # so don't bother cleaning up response values here. response.status = self.status tb = None if cherrypy.serving.request.show_tracebacks: tb = format_exc() response.headers['Content-Type'] = "text/html;charset=utf-8" response.headers.pop('Content-Length', None) content = ntob(self.get_error_page(self.status, traceback=tb, message=self._message), 'utf-8') response.body = content _be_ie_unfriendly(self.code) def get_error_page(self, *args, **kwargs): return get_error_page(*args, **kwargs) def __call__(self): """Use this exception as a request.handler (raise self).""" raise self class NotFound(HTTPError): """Exception raised when a URL could not be mapped to any handler (404). This is equivalent to raising :class:`HTTPError("404 Not Found") `. """ def __init__(self, path=None): if path is None: import cherrypy request = cherrypy.serving.request path = request.script_name + request.path_info self.args = (path,) HTTPError.__init__(self, 404, "The path '%s' was not found." % path) _HTTPErrorTemplate = ''' %(status)s

%(status)s

%(message)s

%(traceback)s
''' def get_error_page(status, **kwargs): """Return an HTML page, containing a pretty error response. status should be an int or a str. kwargs will be interpolated into the page template. """ import cherrypy try: code, reason, message = _httputil.valid_status(status) except ValueError: raise cherrypy.HTTPError(500, _exc_info()[1].args[0]) # We can't use setdefault here, because some # callers send None for kwarg values. if kwargs.get('status') is None: kwargs['status'] = "%s %s" % (code, reason) if kwargs.get('message') is None: kwargs['message'] = message if kwargs.get('traceback') is None: kwargs['traceback'] = '' if kwargs.get('version') is None: kwargs['version'] = cherrypy.__version__ for k, v in iteritems(kwargs): if v is None: kwargs[k] = "" else: kwargs[k] = _escape(kwargs[k]) # Use a custom template or callable for the error page? pages = cherrypy.serving.request.error_page error_page = pages.get(code) or pages.get('default') if error_page: try: if hasattr(error_page, '__call__'): return error_page(**kwargs) else: data = open(error_page, 'rb').read() return tonative(data) % kwargs except: e = _format_exception(*_exc_info())[-1] m = kwargs['message'] if m: m += "
" m += "In addition, the custom error page failed:\n
%s" % e kwargs['message'] = m return _HTTPErrorTemplate % kwargs _ie_friendly_error_sizes = { 400: 512, 403: 256, 404: 512, 405: 256, 406: 512, 408: 512, 409: 512, 410: 256, 500: 512, 501: 512, 505: 512, } def _be_ie_unfriendly(status): import cherrypy response = cherrypy.serving.response # For some statuses, Internet Explorer 5+ shows "friendly error # messages" instead of our response.body if the body is smaller # than a given size. Fix this by returning a body over that size # (by adding whitespace). # See http://support.microsoft.com/kb/q218155/ s = _ie_friendly_error_sizes.get(status, 0) if s: s += 1 # Since we are issuing an HTTP error status, we assume that # the entity is short, and we should just collapse it. content = response.collapse_body() l = len(content) if l and l < s: # IN ADDITION: the response must be written to IE # in one chunk or it will still get replaced! Bah. content = content + (ntob(" ") * (s - l)) response.body = content response.headers['Content-Length'] = str(len(content)) def format_exc(exc=None): """Return exc (or sys.exc_info if None), formatted.""" if exc is None: exc = _exc_info() if exc == (None, None, None): return "" import traceback return "".join(traceback.format_exception(*exc)) def bare_error(extrabody=None): """Produce status, headers, body for a critical error. Returns a triple without calling any other questionable functions, so it should be as error-free as possible. Call it from an HTTP server if you get errors outside of the request. If extrabody is None, a friendly but rather unhelpful error message is set in the body. If extrabody is a string, it will be appended as-is to the body. """ # The whole point of this function is to be a last line-of-defense # in handling errors. That is, it must not raise any errors itself; # it cannot be allowed to fail. Therefore, don't add to it! # In particular, don't call any other CP functions. body = ntob("Unrecoverable error in the server.") if extrabody is not None: if not isinstance(extrabody, bytestr): extrabody = extrabody.encode('utf-8') body += ntob("\n") + extrabody return (ntob("500 Internal Server Error"), [(ntob('Content-Type'), ntob('text/plain')), (ntob('Content-Length'), ntob(str(len(body)),'ISO-8859-1'))], [body])