Synnefo

# vim: ts=4 sts=4 et ai sw=4 fileencoding=utf-8

#

# Copyright © 2010 Greek Research and Technology Network

#

from piston.resource import Resource as BaseResource

import re

_accept_re = re.compile(r'([^\s;,]+)(?:[^,]*?;\s*q=(\d*(?:\.\d+)?))?')

def parse_accept_header(value):

    """Parse an HTTP Accept header

    Returns an ordered by quality list of tuples (value, quality)

    """

    if not value:

        return []

    result = []

    for match in _accept_re.finditer(value):

        quality = match.group(2)

        if not quality:

            quality = 1

        else:

            quality = max(min(float(quality), 1), 0)

        result.append((match.group(1), quality))

    # sort by quality

    result.sort(key=lambda x: x[1])

    return result

# XXX: works as intended but not used since piston's XMLEmitter doesn't output

# XML according to our spec :(

class Resource(BaseResource):

    def determine_emitter(self, request, *args, **kwargs):

        """

        Override default emitter policy to account for Accept header

        emitter_format (.json or .xml suffix in URL) always takes precedence.

        After that, the Accept header is checked; if both JSON and XML are

        equally preferred, use JSON.

        If none of the two were provided, then use JSON as per the

        specification.

        """

        em = request.GET.get('format', 'xml')

        if 'emitter_format' in kwargs:

            em = kwargs.pop('emitter_format')

        elif 'HTTP_ACCEPT' in request.META:

            accepts = parse_accept_header(request.META['HTTP_ACCEPT'])

            for content_type, quality in accepts:

                if content_type == 'application/json':

                    break

                elif content_type == 'application/xml':

                    em = request.GET.get('format', 'xml')

                    break

        return em