HTTP request and response¶
Accessing and manipulating Zope's HTTP request and response objects programmatically.
- HTTP Request
- Accessing HTTP request outside context
- HTTP response
- Middleware-like hooks
- Transform chain
- Post-publication hook
- Custom redirect mappings
- Cross-origin resource sharing (CORS)
This chapter explains the basics of Zope HTTP requests and responses:
- request and response objects lifecycle;
- data which can be extracted from the request;
- data which can be placed on the response.
Unlike some other web frameworks, in Plone you do not explicitly create or return HTTP response objects. A HTTP request object always has a HTTP response object associated with it, and the response object is created as soon as the request hits the webserver.
The response is available for the whole lifetime of request processing. This effectively allows you to set and modify response headers at any point in the code.
The web server will affect how your HTTP objects are constructed.
All incoming HTTP requests are wrapped in Zope's
objects. This is a multi-mapping: it contains mappings for
environment variables, other variables, form data, and
cookies, but the keys of all these mappings can also be
looked up directly on the request object (i.e.
Usually your view function or instance will receive an HTTP request object, along with a traversed context, as its construction parameter.
You can access the request in your view:
from Products.Five.browser import BrowserView class SampleView(BrowserView): def __init__(self, context, request): # Each view instance receives context and request as construction parameters self.context = context self.request = request def __call__(self): # Entry point of request processing # Dump out incoming request variables print self.request.items()
The request method (GET or POST) can be read:
request["REQUEST_METHOD"] == "POST" # or "GET"
To get the requested URL:
>>> request["ACTUAL_URL"] 'http://localhost:8080/site'
To get the URL of the served object use the following (this might be different from the requested URL, since Plone does all kinds of default page and default view magic):
>>> request["URL"] 'http://m.localhost:8080/site/matkailijallefolder/@@frontpage'
URLs, as accessed above, do not contain query string.
The unparsed query string can be accessed.
E.g. if you go to
>>> self.request["QUERY_STRING"] 'something=foobar'
If the query string is not present in the HTTP request, it is an empty string.
You can also use the
dictionary to access parsed query string content.
The request URI path can be read from
request.path, which returns a list of path components.
is a virtual path, and has the site id component removed
reconstructed_path = "/".join(request.path)
Other possible headers:
('PATH_INFO', '/plonecommunity/Members') ('PATH_TRANSLATED', '/plonecommunity/Members')
What's the difference?
To get the variable which corresponds to
in e.g. PHP the following helps:
# Concatenate the user-visible URL and query parameters full_url = request.ACTUAL_URL + "?" + request.QUERY_STRING parsed = urlparse.urlsplit(full_url) # Extract path part and add the query if it existed uri = parsed if parsed: uri += "?" + parsed
For more information, see:
def get_ip(request): """ Extract the client IP address from the HTTP request in a proxy-compatible way. @return: IP address as a string or None if not available """ if "HTTP_X_FORWARDED_FOR" in request.environ: # Virtual host ip = request.environ["HTTP_X_FORWARDED_FOR"] elif "HTTP_HOST" in request.environ: # Non-virtualhost ip = request.environ["REMOTE_ADDR"] else: # Unit test code? ip = None return ip
For functional tests based on
method to add custom headers to a browser.
variables are available in
# http://yoursite.com/@@testview/?my_param_id=something print self.request.form["my_param_id"]
varibles are available in
print request.form.items() # Everything POST brought to us
There is no difference in accessing
The request body can be retrieved from the
object by using the get method with the key
print request.get('BODY') # Prints the content of the request body
HTTP headers are available through
referer = self.request.get_header("referer") # Page referer (the page from user came from) if referer == None: # referer will be none if it was missing pass
Dumping all headers:
for name, value in request.environ.items(): print "%s: %s" % (name, value)
A simple ZMI Python script to dump all HTTP request headers:
from StringIO import StringIO # Import a standard function, and get the HTML request and response objects. from Products.PythonScripts.standard import html_quote request = container.REQUEST response = request.response buffer = StringIO() response.setHeader("Content-type", "text/plain") for name, value in request.environ.items(): print >> buffer, "%s: %s" % (name, value) return buffer.getvalue()
print request.other.items() user_agent = request.other["HTTP_USER_AGENT"] user_agent = request.environ["HTTP_USER_AGENT"] # WSGI or Repoze server
Below is an example to get the HTTP server name in a safe manner, taking virtual hosting into account:
def get_hostname(request): """ Extract hostname in virtual-host-safe manner @param request: HTTPRequest object, assumed contains environ dictionary @return: Host DNS name, as requested by client. Lowercased, no port part. Return None if host name is not present in HTTP request headers (e.g. unit testing). """ if "HTTP_X_FORWARDED_HOST" in request.environ: # Virtual host host = request.environ["HTTP_X_FORWARDED_HOST"] elif "HTTP_HOST" in request.environ: # Direct client request host = request.environ["HTTP_HOST"] else: return None # separate to domain name and port sections host=host.split(":").lower() return host
It is possible to extract the Zope instance port from the request. This is useful e.g. for debugging purposes if you have multiple ZEO front ends running, and you want to identify them easily:
port = request.get("SERVER_PORT", None)
variable returns the port number as a string, not an
This port number is not the one visible to the external traffic (port 80, HTTP)
points to a view, method or template which was the last
item in the traversing chain to be called to render the
To extract the relevant content item from this information you can do e.g. in the after publication hook:
def find_context(request): """Find the context from the request http://stackoverflow.com/questions/10489544/getting-published-content-item-out-of-requestpublished-in-plone """ published = request.get('PUBLISHED', None) context = getattr(published, '__parent__', None) if context is None: context = request.PARENTS return context
- You might also want to filter out CSS etc. requests
Please note that
request[PUBLISHED]is set after language negotiation and authentication
- More complete example
and web environment variables are flat mapped to the
request object as a dictionary look up:
# Comes from POST request["input_username"] == request.form["input_username"] # Comes from environ request.get('HTTP_USER_AGENT') == request.environ["HTTP_USER_AGENT"]
There are often cases where you would like to get hold of the HTTP request object, but the underlying framework does not pass it to you. In these cases you have two ways to access the request object:
Use acquisition to get the request object from
the site root. When Plone site traversal starts, the
HTTP request is assigned to current site object as the
- Use https://pypi.python.org/pypi/five.globalrequest.
Example of getting the request using acquisition:
# context is any traversed Plone content item request = getattr(context, "REQUEST", None) if request is not None: # Do the normal flow ... else: # This code path was not initiated by an incoming web server request # Handle cases like # - command line scripts # - add-on installer # - code called during Zope start up # -etc. ...
Usually you do not return HTTP responses directly from your views. Instead, you modify the existing HTTP response object (associated with the request) and return the object which will be HTTP response payload.
The returned payload object can be:
- a string (str) 8-bit raw data; or
- an iterable: the response is streamed, instead of memory-buffered.
You can access the HTTP response if you know the request:
from Products.Five.browser import BrowserView class SampleView(BrowserView): def __init__(context, request): # Each view instance receives context and request as construction parameters self.context = context self.request = request def __call__(self): response = self.request.response return "<html><body>Hello world!</body></html>"
to set headers:
# The response is a dynamically generated image self.request.response.setHeader("Content-type", "image/jpeg") return image_data
header is used to set the filename of a download. It is
also used by Flash 10 to check whether Flash download is
Example of setting the download and downloadable filename:
response = self.request.response response.setHeader("Content-type", "text/x-vCard; charset=utf-8") response.setHeader("Content-Transfer-Encoding", "8bit") cd = 'attachment; filename=%s.vcf' % (context.id) response.setHeader('Content-Disposition', cd)
For more information, see:
to set HTTP return status ("404 Not Found",
"500 Internal Error", etc.).
lock=True, no further modification of the HTTPResponse status
are allowed, and will fail silently.
You might want to read or manipulate the response body in the post-publication hook.
The response body is not always a string or basestring: it can be a generator or iterable for blob data.
The body is available as the
You can change the body using setBody and locking it:
#lets empty the body and lock it response.setBody('', lock=True)
lock=True, no further modification of the HTTPResponse body are
allowed, and will fail silently.
# This will send a "302 Temporary Redirect" notification to the browser response.redirect(new_url) # This will send a "301 Permanent Redirect" notification to the browser response.redirect(new_url, status=301)
You can lock the status to not let other change the status later in the process
Plone does not have a middleware concept, as everything happens through traversal. Middleware behavior can be emulated with the before traverse hook. This hook can be installed on any persistent object in the traversing graph. The hook is persistent, so it is a database change and must be installed using custom GenericSetup Python code.
Before traverse hooks cannot create new HTTP responses, or return alternative HTTP responses. Only exception-like HTTP response modification is supported, e.g. HTTP redirects. If you need to rewrite the whole response, the post-publication hook must be used.
For more information, see:
Transform chain is a hook into repoze.zope2 that allows third party packages to register a sequence of hooks that will be allowed to modify the response before it is returned to the browser.
It is used e.g. by
The post-publication hook is run when:
- the context object has been traversed;
- after the view has been called and the view has rendered the response;
- before the response is sent to the browser;
- before the transaction is committed.
This is practical for caching purposes: it is the ideal place to determine and insert caching headers into the response.
Read more at the plone.postpublicationhook package page.
Below is an example how you use five.grok to install an event handler which checks in the site root for a TTW Python script and if such exist it asks it to provide a HTTP redirect.
This behavior allows you to write site-wide redirects easily
- In Python (thank god no Apache regular expressions)
- Redirects can access Plone content items
- You can easily have some redirects migrated from the old (non-Plone) sites
- no modifications needed for your site, just copy-paste
this to your Grok add-on folder. Remember to add
to Parameter list of the script on the script
""" Call a custom TTW script and allow it to handle redirects. Use Zope Management Interface to add a ``Script (Python)`` item named ``redirect_handler`` to your site root - you can edit this script in fly to change the redirects. * Redirect script must contain ``url`` in its parameter list """ import logging # Now we import things through the last decade... # Really old old stuff from zExceptions import Redirect # Really old stuff from Products.CMFCore.interfaces import ISiteRoot # Old stuff from zope.traversing.interfaces import IBeforeTraverseEvent # Modern stuff from five import grok logger = logging.getLogger("redirect") @grok.subscribe(ISiteRoot, IBeforeTraverseEvent) def check_redirect(site, event): """ Check if we have a custom redirect script in Zope application server root. If we do then call it and see if we get a redirect. The script itself is TTW Python script which may return string in the case of redirect or None if no redirect is needed. For more examples, check https://github.com/zopefoundation/Zope/blob/master/src/Zope2/App/tests/testExceptionHook.py """ request = event.request url = request["ACTUAL_URL"] if "no_redirect" in request.form: # Use no_redirect query parameter to disable this behavior in the case # you mess up with the redirect script return # Check if we have a redirect handler script in the site root if "redirect_handler" in site: try: # Call the script and get its output value = site.redirect_handler(url) except Exception, e: # No silent exceptions plz logger.error("Redirect exception for URL:" + url) logger.exception(e) return if value is not None and value.startswith("http"): # Trigger redirect, but only if the output value looks sane raise Redirect, value
Then an example
script added through ZMI. Remember to add
to the Parameter List field of TTW interface:
if "blaablaa" in url: return "http://webandmobile.mfabrik.com"
Or more complex example:
# Don't leak non-themed interface fom port 80 if ("manage.") in url and (not "8080" in url): return "http://manage.underconstruction.mfabrik.com:8080/LS" if url == "http://underconstruction.mfabrik.com/": return "http://underconstruction.mfabrik.com/special-front-page" # Redirect to the actual front page if url == "http://site.com/": return "http://www.site.com/special-front-page" if url == "http://www.site.com/": return "http://www.site.com/special-front-page" if url.startswith("http://underconstruction.mfabrik.com/"): return url.replace("underconstruction.mfabrik.com", "www.site.com") # Make sure that search engines and visitors access the site only using www. prefix if url.startswith("http://site.com/"): return url.replace("site.com", "www.site.com")
from zope.component import adapter, getUtility, getMultiAdapter from plone.postpublicationhook.interfaces import IAfterPublicationEvent from Products.CMFCore.interfaces import IContentish def get_contentish(object): """ Traverse acquisition upwards until we get contentish object used for the HTTP response. """ contentish = object while not IContentish.providedBy(contentish): if hasattr(contentish, "aq_parent"): contentish = contentish.aq_parent else: break return contentish # This must be referred in configure.zcml @adapter(Interface, IAfterPublicationEvent) def language_fixer(object, event): """ Redirect mobile users to mobile site using gomobile.mobile.interfaces.IRedirector. Note: Plone does not provide a good hook doing this before traversing, so we must do it in post-publication. This adds extra latency, but is doable. """ request = event.request response = request.response # object can be a page template, view, whichever happens to be at the very end of traversed acquisition chain context = get_contentish(object)