django-rest-framework/djangorestframework/emitters.py

"""Emitters are used to serialize a Resource's output into specific media types.
django-rest-framework also provides HTML and PlainText emitters that help self-document the API,
by serializing the output along with documentation regarding the Resource, output status and headers,
and providing forms and links depending on the allowed methods, emitters and parsers on the Resource. 
"""
from django.conf import settings
from django.template import RequestContext, loader
from django import forms

from djangorestframework.response import NoContent
from djangorestframework.utils import dict2xml, url_resolves

from urllib import quote_plus
import string
try:
    import json
except ImportError:
    import simplejson as json



# TODO: Rename verbose to something more appropriate
# TODO: NoContent could be handled more cleanly.  It'd be nice if it was handled by default,
#       and only have an emitter output anything if it explicitly provides support for that.

class BaseEmitter(object):
    """All emitters must extend this class, set the media_type attribute, and
    override the emit() function."""
    media_type = None

    def __init__(self, resource):
        self.resource = resource

    def emit(self, output=NoContent, verbose=False):
        """By default emit simply returns the ouput as-is.
        Override this method to provide for other behaviour."""
        if output is NoContent:
            return ''
        
        return output


class TemplateEmitter(BaseEmitter):
    """Provided for convienience.
    Emit the output by simply rendering it with the given template."""
    media_type = None
    template = None

    def emit(self, output=NoContent, verbose=False):
        if output is NoContent:
            return ''

        context = RequestContext(self.resource.request, output)
        return self.template.render(context)


class DocumentingTemplateEmitter(BaseEmitter):
    """Base class for emitters used to self-document the API.
    Implementing classes should extend this class and set the template attribute."""
    template = None

    def _get_content(self, resource, output):
        """Get the content as if it had been emitted by a non-documenting emitter.

        (Typically this will be the content as it would have been if the Resource had been
        requested with an 'Accept: */*' header, although with verbose style formatting if appropriate.)"""

        # Find the first valid emitter and emit the content. (Don't use another documenting emitter.)
        emitters = [emitter for emitter in resource.emitters if not isinstance(emitter, DocumentingTemplateEmitter)]
        if not emitters:
            return '[No emitters were found]'
        
        content = emitters[0](resource).emit(output, verbose=True)
        if not all(char in string.printable for char in content):
            return '[%d bytes of binary content]'
            
        return content
            

    def _get_form_instance(self, resource):
        """Get a form, possibly bound to either the input or output data.
        In the absence on of the Resource having an associated form then
        provide a form that can be used to submit arbitrary content."""
        # Get the form instance if we have one bound to the input
        form_instance = resource.form_instance

        # Otherwise if this isn't an error response
        # then attempt to get a form bound to the response object
        if not form_instance and resource.response.has_content_body:
            try:
                form_instance = resource.get_form(resource.response.raw_content)
                if form_instance:
                    form_instance.is_valid()
            except:
                form_instance = None
        
        # If we still don't have a form instance then try to get an unbound form
        if not form_instance:
            try:
                form_instance = self.resource.get_form()
            except:
                pass

        # If we still don't have a form instance then try to get an unbound form which can tunnel arbitrary content types
        if not form_instance:
            form_instance = self._get_generic_content_form(resource)
        
        return form_instance


    def _get_generic_content_form(self, resource):
        """Returns a form that allows for arbitrary content types to be tunneled via standard HTML forms
        (Which are typically application/x-www-form-urlencoded)"""

        # NB. http://jacobian.org/writing/dynamic-form-generation/
        class GenericContentForm(forms.Form):
            def __init__(self, resource):
                """We don't know the names of the fields we want to set until the point the form is instantiated,
                as they are determined by the Resource the form is being created against.
                Add the fields dynamically."""
                super(GenericContentForm, self).__init__()

                contenttype_choices = [(media_type, media_type) for media_type in resource.parsed_media_types]
                initial_contenttype = resource.default_parser.media_type

                self.fields[resource.CONTENTTYPE_PARAM] = forms.ChoiceField(label='Content Type',
                                                                            choices=contenttype_choices,
                                                                            initial=initial_contenttype)
                self.fields[resource.CONTENT_PARAM] = forms.CharField(label='Content',
                                                                      widget=forms.Textarea)

        # If either of these reserved parameters are turned off then content tunneling is not possible
        if self.resource.CONTENTTYPE_PARAM is None or self.resource.CONTENT_PARAM is None:
            return None

        # Okey doke, let's do it
        return GenericContentForm(resource)


    def emit(self, output=NoContent):
        content = self._get_content(self.resource, output)
        form_instance = self._get_form_instance(self.resource)

        if url_resolves(settings.LOGIN_URL) and url_resolves(settings.LOGOUT_URL):
            login_url = "%s?next=%s" % (settings.LOGIN_URL, quote_plus(self.resource.request.path))
            logout_url = "%s?next=%s" % (settings.LOGOUT_URL, quote_plus(self.resource.request.path))
        else:
            login_url = None
            logout_url = None

        template = loader.get_template(self.template)
        context = RequestContext(self.resource.request, {
            'content': content,
            'resource': self.resource,
            'request': self.resource.request,
            'response': self.resource.response,
            'form': form_instance,
            'login_url': login_url,
            'logout_url': logout_url,
        })
        
        ret = template.render(context)

        # Munge DELETE Response code to allow us to return content
        # (Do this *after* we've rendered the template so that we include the normal deletion response code in the output)
        if self.resource.response.status == 204:
            self.resource.response.status = 200

        return ret


class JSONEmitter(BaseEmitter):
    """Emitter which serializes to JSON"""
    media_type = 'application/json'

    def emit(self, output=NoContent, verbose=False):
        if output is NoContent:
            return ''
        if verbose:
            return json.dumps(output, indent=4, sort_keys=True)
        return json.dumps(output)


class XMLEmitter(BaseEmitter):
    """Emitter which serializes to XML."""
    media_type = 'application/xml'

    def emit(self, output=NoContent, verbose=False):
        if output is NoContent:
            return ''
        return dict2xml(output)


class DocumentingHTMLEmitter(DocumentingTemplateEmitter):
    """Emitter which provides a browsable HTML interface for an API.
    See the examples listed in the django-rest-framework documentation to see this in actions."""
    media_type = 'text/html'
    template = 'emitter.html'


class DocumentingXHTMLEmitter(DocumentingTemplateEmitter):
    """Identical to DocumentingHTMLEmitter, except with an xhtml media type.
    We need this to be listed in preference to xml in order to return HTML to WebKit based browsers,
    given their Accept headers."""
    media_type = 'application/xhtml+xml'
    template = 'emitter.html'


class DocumentingPlainTextEmitter(DocumentingTemplateEmitter):
    """Emitter that serializes the output with the default emitter, but also provides plain-text
    doumentation of the returned status and headers, and of the resource's name and description.
    Useful for browsing an API with command line tools."""
    media_type = 'text/plain'
    template = 'emitter.txt'