1 files changed, 74 insertions, 0 deletions
diff --git a/djangorestframework/negotiation.py b/djangorestframework/negotiation.py
new file mode 100644
index 00000000..201d32ad
--- /dev/null
+++ b/djangorestframework/negotiation.py
@@ -0,0 +1,74 @@
+from djangorestframework import exceptions
+from djangorestframework.settings import api_settings
+from djangorestframework.utils.mediatypes import order_by_precedence
+
+
+class BaseContentNegotiation(object):
+    def negotiate(self, request, renderers, format=None, force=False):
+        raise NotImplementedError('.negotiate() must be implemented')
+
+
+class DefaultContentNegotiation(object):
+    settings = api_settings
+
+    def negotiate(self, request, renderers, format=None, force=False):
+        """
+        Given a request and a list of renderers, return a two-tuple of:
+        (renderer, media type).
+
+        If force is set, then suppress exceptions, and forcibly return a
+        fallback renderer and media_type.
+        """
+        try:
+            return self.unforced_negotiate(request, renderers, format)
+        except (exceptions.InvalidFormat, exceptions.NotAcceptable):
+            if force:
+                return (renderers[0], renderers[0].media_type)
+            raise
+
+    def unforced_negotiate(self, request, renderers, format=None):
+        """
+        As `.negotiate()`, but does not take the optional `force` agument,
+        or suppress exceptions.
+        """
+        # Allow URL style format override.  eg. "?format=json
+        format = format or request.GET.get(self.settings.URL_FORMAT_OVERRIDE)
+
+        if format:
+            renderers = self.filter_renderers(renderers, format)
+
+        accepts = self.get_accept_list(request)
+
+        # Check the acceptable media types against each renderer,
+        # attempting more specific media types first
+        # NB. The inner loop here isn't as bad as it first looks :)
+        #     Worst case is we're looping over len(accept_list) * len(self.renderers)
+        for media_type_set in order_by_precedence(accepts):
+            for renderer in renderers:
+                for media_type in media_type_set:
+                    if renderer.can_handle_media_type(media_type):
+                        return renderer, media_type
+
+        raise exceptions.NotAcceptable(available_renderers=renderers)
+
+    def filter_renderers(self, renderers, format):
+        """
+        If there is a '.json' style format suffix, filter the renderers
+        so that we only negotiation against those that accept that format.
+        """
+        renderers = [renderer for renderer in renderers
+                     if renderer.can_handle_format(format)]
+        if not renderers:
+            raise exceptions.InvalidFormat(format)
+        return renderers
+
+    def get_accept_list(self, request):
+        """
+        Given the incoming request, return a tokenised list of media
+        type strings.
+
+        Allows URL style accept override.  eg. "?accept=application/json"
+        """
+        header = request.META.get('HTTP_ACCEPT', '*/*')
+        header = request.GET.get(self.settings.URL_ACCEPT_OVERRIDE, header)
+        return [token.strip() for token in header.split(',')]