Added django.contrib.formtools, including the forced-preview application

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4164 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/formtools/preview.py

@@ -0,0 +1,160 @@
+"""
+Formtools Preview application.
+
+This is an abstraction of the following workflow:
+
+    "Display an HTML form, force a preview, then do something with the submission."
+
+Given a django.newforms.Form object that you define, this takes care of the
+following:
+
+    * Displays the form as HTML on a Web page.
+    * Validates the form data once it's submitted via POST.
+        * If it's valid, displays a preview page.
+        * If it's not valid, redisplays the form with error messages.
+    * At the preview page, if the preview confirmation button is pressed, calls
+      a hook that you define -- a done() method.
+
+The framework enforces the required preview by passing a shared-secret hash to
+the preview page. If somebody tweaks the form parameters on the preview page,
+the form submission will fail the hash comparison test.
+
+Usage
+=====
+
+Subclass FormPreview and define a done() method:
+
+    def done(self, request, clean_data):
+        # ...
+
+This method takes an HttpRequest object and a dictionary of the form data after
+it has been validated and cleaned. It should return an HttpResponseRedirect.
+
+Then, just instantiate your FormPreview subclass by passing it a Form class,
+and pass that to your URLconf, like so:
+
+    (r'^post/$', MyFormPreview(MyForm)),
+
+The FormPreview class has a few other hooks. See the docstrings in the source
+code below.
+
+The framework also uses two templates: 'formtools/preview.html' and
+'formtools/form.html'. You can override these by setting 'preview_template' and
+'form_template' attributes on your FormPreview subclass. See
+django/contrib/formtools/templates for the default templates.
+"""
+
+from django.conf import settings
+from django.core.exceptions import ImproperlyConfigured
+from django.http import Http404
+from django.shortcuts import render_to_response
+import cPickle as pickle
+import md5
+
+AUTO_ID = 'formtools_%s' # Each form here uses this as its auto_id parameter.
+
+class FormPreview(object):
+    preview_template = 'formtools/preview.html'
+    form_template = 'formtools/form.html'
+
+    # METHODS SUBCLASSES SHOULDN'T OVERRIDE ###################################
+
+    def __init__(self, form):
+        # form should be a Form class, not an instance.
+        self.form, self.state = form, {}
+
+    def __call__(self, request, *args, **kwargs):
+        stage = {'1': 'preview', '2': 'post'}.get(request.POST.get(self.unused_name('stage')), 'preview')
+        self.parse_params(*args, **kwargs)
+        try:
+            method = getattr(self, stage + '_' + request.method.lower())
+        except AttributeError:
+            raise Http404
+        return method(request)
+
+    def unused_name(self, name):
+        """
+        Given a first-choice name, adds an underscore to the name until it
+        reaches a name that isn't claimed by any field in the form.
+
+        This is calculated rather than being hard-coded so that no field names
+        are off-limits for use in the form.
+        """
+        while 1:
+            try:
+                f = self.form.fields[name]
+            except KeyError:
+                break # This field name isn't being used by the form.
+            name += '_'
+        return name
+
+    def preview_get(self, request):
+        "Displays the form"
+        f = self.form(auto_id=AUTO_ID)
+        return render_to_response(self.form_template, {'form': f, 'stage_field': self.unused_name('stage'), 'state': self.state})
+
+    def preview_post(self, request):
+        "Validates the POST data. If valid, displays the preview page. Else, redisplays form."
+        f = self.form(request.POST, auto_id=AUTO_ID)
+        context = {'form': f, 'stage_field': self.unused_name('stage'), 'state': self.state}
+        if f.is_valid():
+            context['hash_field'] = self.unused_name('hash')
+            context['hash_value'] = self.security_hash(request, f)
+            return render_to_response(self.preview_template, context)
+        else:
+            return render_to_response(self.form_template, context)
+
+    def post_post(self, request):
+        "Validates the POST data. If valid, calls done(). Else, redisplays form."
+        f = self.form(request.POST, auto_id=AUTO_ID)
+        if f.is_valid():
+            if self.security_hash(request, f) != request.POST.get(self.unused_name('hash')):
+                return self.failed_hash(request) # Security hash failed.
+            return self.done(request, f.clean_data)
+        else:
+            return render_to_response(self.form_template, {'form': f, 'stage_field': self.unused_name('stage'), 'state': self.state})
+
+    # METHODS SUBCLASSES MIGHT OVERRIDE IF APPROPRIATE ########################
+
+    def parse_params(self, *args, **kwargs):
+        """
+        Given captured args and kwargs from the URLconf, saves something in
+        self.state and/or raises Http404 if necessary.
+
+        For example, this URLconf captures a user_id variable:
+
+            (r'^contact/(?P<user_id>\d{1,6})/$', MyFormPreview(MyForm)),
+
+        In this case, the kwargs variable in parse_params would be
+        {'user_id': 32} for a request to '/contact/32/'. You can use that
+        user_id to make sure it's a valid user and/or save it for later, for
+        use in done().
+        """
+        pass
+
+    def security_hash(self, request, form):
+        """
+        Calculates the security hash for the given Form instance.
+
+        This creates a list of the form field names/values in a deterministic
+        order, pickles the result with the SECRET_KEY setting and takes an md5
+        hash of that.
+
+        Subclasses may want to take into account request-specific information
+        such as the IP address.
+        """
+        data = [(bf.name, bf.data) for bf in form] + [settings.SECRET_KEY]
+        # Use HIGHEST_PROTOCOL because it's the most efficient. It requires
+        # Python 2.3, but Django requires 2.3 anyway, so that's OK.
+        pickled = pickle.dumps(data, protocol=pickle.HIGHEST_PROTOCOL)
+        return md5.new(pickled).hexdigest()
+
+    def failed_hash(self, request):
+        "Returns an HttpResponse in the case of an invalid security hash."
+        return self.preview_post(request)
+
+    # METHODS SUBCLASSES MUST OVERRIDE ########################################
+
+    def done(self, request, clean_data):
+        "Does something with the clean_data and returns an HttpResponseRedirect."
+        raise NotImplementedError('You must define a done() method on your %s subclass.' % self.__class__.__name__)

django/contrib/formtools/templates/formtools/form.html

@@ -0,0 +1,15 @@
+{% extends "base.html" %}
+
+{% block content %}
+
+{% if form.errors %}<h1>Please correct the following errors</h1>{% else %}<h1>Submit</h1>{% endif %}
+
+<form action="" method="post">
+<table>
+{{ form }}
+</table>
+<input type="hidden" name="{{ stage_field }}" value="1" />
+<p><input type="submit" value="Submit" /></p>
+</form>
+
+{% endblock %}

django/contrib/formtools/templates/formtools/preview.html

@@ -0,0 +1,36 @@
+{% extends "base.html" %}
+
+{% block content %}
+
+<h1>Preview your submission</h1>
+
+<table>
+{% for field in form %}
+<tr>
+<th>{{ field.verbose_name }}:</th>
+<td>{{ field.data|escape }}</td>
+</tr>
+{% endfor %}
+</table>
+
+<p>Security hash: {{ hash_value }}</p>
+
+<form action="" method="post">
+{% for field in form %}{{ field.as_hidden }}
+{% endfor %}
+<input type="hidden" name="{{ stage_field }}" value="2" />
+<input type="hidden" name="{{ hash_field }}" value="{{ hash_value }}" />
+<p><input type="submit" value="Submit" /></p>
+</form>
+
+<h1>Or edit it again</h1>
+
+<form action="" method="post">
+<table>
+{{ form }}
+</table>
+<input type="hidden" name="{{ stage_field }}" value="1" />
+<p><input type="submit" value="Submit changes" /></p>
+</form>
+
+{% endblock %}

docs/add_ons.txt

@@ -48,6 +48,23 @@ See the `csrf documentation`_.
 
 .. _csrf documentation: http://www.djangoproject.com/documentation/csrf/
 
+formtools
+=========
+
+**New in Django development version**
+
+A set of high-level abstractions for Django forms (django.newforms).
+
+django.contrib.formtools.preview
+--------------------------------
+
+An abstraction of the following workflow:
+
+"Display an HTML form, force a preview, then do something with the submission."
+
+Full documentation for this feature does not yet exist, but you can read the
+code and docstrings in ``django/contrib/formtools/preview.py`` for a start.
+
 humanize
 ========