254 lines
11 KiB
Python
254 lines
11 KiB
Python
"""
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Middleware to serve assets.
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"""
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import logging
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import datetime
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from django.http import (
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HttpResponse, HttpResponseNotModified, HttpResponseForbidden,
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HttpResponseBadRequest, HttpResponseNotFound)
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from student.models import CourseEnrollment
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from contentserver.models import CourseAssetCacheTtlConfig
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from header_control import force_header_for_response
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from xmodule.assetstore.assetmgr import AssetManager
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from xmodule.contentstore.content import StaticContent, XASSET_LOCATION_TAG
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from xmodule.modulestore import InvalidLocationError
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from opaque_keys import InvalidKeyError
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from opaque_keys.edx.locator import AssetLocator
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from cache_toolbox.core import get_cached_content, set_cached_content
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from xmodule.modulestore.exceptions import ItemNotFoundError
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from xmodule.exceptions import NotFoundError
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# TODO: Soon as we have a reasonable way to serialize/deserialize AssetKeys, we need
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# to change this file so instead of using course_id_partial, we're just using asset keys
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log = logging.getLogger(__name__)
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HTTP_DATE_FORMAT = "%a, %d %b %Y %H:%M:%S GMT"
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class StaticContentServer(object):
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def is_asset_request(self, request):
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"""Determines whether the given request is an asset request"""
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return (
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request.path.startswith('/' + XASSET_LOCATION_TAG + '/')
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or
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request.path.startswith('/' + AssetLocator.CANONICAL_NAMESPACE)
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)
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def process_request(self, request):
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"""Process the given request"""
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if self.is_asset_request(request):
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# Make sure we can convert this request into a location.
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if AssetLocator.CANONICAL_NAMESPACE in request.path:
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request.path = request.path.replace('block/', 'block@', 1)
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try:
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loc = StaticContent.get_location_from_path(request.path)
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except (InvalidLocationError, InvalidKeyError):
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return HttpResponseBadRequest()
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# Try and load the asset.
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content = None
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try:
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content = self.load_asset_from_location(loc)
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except (ItemNotFoundError, NotFoundError):
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return HttpResponseNotFound()
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# Check that user has access to the content.
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if not self.is_user_authorized(request, content, loc):
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return HttpResponseForbidden('Unauthorized')
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# Figure out if the client sent us a conditional request, and let them know
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# if this asset has changed since then.
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last_modified_at_str = content.last_modified_at.strftime(HTTP_DATE_FORMAT)
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if 'HTTP_IF_MODIFIED_SINCE' in request.META:
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if_modified_since = request.META['HTTP_IF_MODIFIED_SINCE']
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if if_modified_since == last_modified_at_str:
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return HttpResponseNotModified()
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# *** File streaming within a byte range ***
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# If a Range is provided, parse Range attribute of the request
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# Add Content-Range in the response if Range is structurally correct
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# Request -> Range attribute structure: "Range: bytes=first-[last]"
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# Response -> Content-Range attribute structure: "Content-Range: bytes first-last/totalLength"
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# http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35
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response = None
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if request.META.get('HTTP_RANGE'):
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# If we have a StaticContent, get a StaticContentStream. Can't manipulate the bytes otherwise.
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if type(content) == StaticContent:
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content = AssetManager.find(loc, as_stream=True)
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header_value = request.META['HTTP_RANGE']
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try:
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unit, ranges = parse_range_header(header_value, content.length)
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except ValueError as exception:
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# If the header field is syntactically invalid it should be ignored.
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log.exception(
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u"%s in Range header: %s for content: %s", exception.message, header_value, unicode(loc)
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)
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else:
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if unit != 'bytes':
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# Only accept ranges in bytes
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log.warning(u"Unknown unit in Range header: %s for content: %s", header_value, unicode(loc))
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elif len(ranges) > 1:
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# According to Http/1.1 spec content for multiple ranges should be sent as a multipart message.
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# http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.16
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# But we send back the full content.
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log.warning(
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u"More than 1 ranges in Range header: %s for content: %s", header_value, unicode(loc)
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)
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else:
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first, last = ranges[0]
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if 0 <= first <= last < content.length:
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# If the byte range is satisfiable
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response = HttpResponse(content.stream_data_in_range(first, last))
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response['Content-Range'] = 'bytes {first}-{last}/{length}'.format(
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first=first, last=last, length=content.length
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)
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response['Content-Length'] = str(last - first + 1)
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response.status_code = 206 # Partial Content
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else:
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log.warning(
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u"Cannot satisfy ranges in Range header: %s for content: %s", header_value, unicode(loc)
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)
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return HttpResponse(status=416) # Requested Range Not Satisfiable
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# If Range header is absent or syntactically invalid return a full content response.
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if response is None:
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response = HttpResponse(content.stream_data())
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response['Content-Length'] = content.length
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# "Accept-Ranges: bytes" tells the user that only "bytes" ranges are allowed
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response['Accept-Ranges'] = 'bytes'
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response['Content-Type'] = content.content_type
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# Set any caching headers, and do any response cleanup needed. Based on how much
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# middleware we have in place, there's no easy way to use the built-in Django
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# utilities and properly sanitize and modify a response to ensure that it is as
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# cacheable as possible, which is why we do it ourselves.
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self.set_caching_headers(content, response)
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return response
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def set_caching_headers(self, content, response):
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"""
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Sets caching headers based on whether or not the asset is locked.
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"""
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is_locked = getattr(content, "locked", False)
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# We want to signal to the end user's browser, and to any intermediate proxies/caches,
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# whether or not this asset is cacheable. If we have a TTL configured, we inform the
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# caller, for unlocked assets, how long they are allowed to cache it. Since locked
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# assets should be restricted to enrolled students, we simply send headers that
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# indicate there should be no caching whatsoever.
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cache_ttl = CourseAssetCacheTtlConfig.get_cache_ttl()
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if cache_ttl > 0 and not is_locked:
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response['Expires'] = StaticContentServer.get_expiration_value(datetime.datetime.utcnow(), cache_ttl)
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response['Cache-Control'] = "public, max-age={ttl}, s-maxage={ttl}".format(ttl=cache_ttl)
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elif is_locked:
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response['Cache-Control'] = "private, no-cache, no-store"
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response['Last-Modified'] = content.last_modified_at.strftime(HTTP_DATE_FORMAT)
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# Force the Vary header to only vary responses on Origin, so that XHR and browser requests get cached
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# separately and don't screw over one another. i.e. a browser request that doesn't send Origin, and
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# caches a version of the response without CORS headers, in turn breaking XHR requests.
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force_header_for_response(response, 'Vary', 'Origin')
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@staticmethod
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def get_expiration_value(now, cache_ttl):
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"""Generates an RFC1123 datetime string based on a future offset."""
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expire_dt = now + datetime.timedelta(seconds=cache_ttl)
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return expire_dt.strftime(HTTP_DATE_FORMAT)
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def is_user_authorized(self, request, content, location):
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"""
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Determines whether or not the user for this request is authorized to view the given asset.
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"""
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is_locked = getattr(content, "locked", False)
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if not is_locked:
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return True
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if not hasattr(request, "user") or not request.user.is_authenticated():
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return False
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if not request.user.is_staff:
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deprecated = getattr(location, 'deprecated', False)
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if deprecated and not CourseEnrollment.is_enrolled_by_partial(request.user, location.course_key):
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return False
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if not deprecated and not CourseEnrollment.is_enrolled(request.user, location.course_key):
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return False
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return True
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def load_asset_from_location(self, location):
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"""
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Loads an asset based on its location, either retrieving it from a cache
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or loading it directly from the contentstore.
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"""
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# See if we can load this item from cache.
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content = get_cached_content(location)
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if content is None:
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# Not in cache, so just try and load it from the asset manager.
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try:
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content = AssetManager.find(location, as_stream=True)
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except (ItemNotFoundError, NotFoundError):
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raise
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# Now that we fetched it, let's go ahead and try to cache it. We cap this at 1MB
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# because it's the default for memcached and also we don't want to do too much
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# buffering in memory when we're serving an actual request.
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if content.length is not None and content.length < 1048576:
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content = content.copy_to_in_mem()
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set_cached_content(content)
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return content
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def parse_range_header(header_value, content_length):
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"""
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Returns the unit and a list of (start, end) tuples of ranges.
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Raises ValueError if header is syntactically invalid or does not contain a range.
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See spec for details: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35
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"""
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unit = None
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ranges = []
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if '=' in header_value:
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unit, byte_ranges_string = header_value.split('=')
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# Parse the byte ranges.
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for byte_range_string in byte_ranges_string.split(','):
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byte_range_string = byte_range_string.strip()
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# Case 0:
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if '-' not in byte_range_string: # Invalid syntax of header value.
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raise ValueError('Invalid syntax.')
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# Case 1: -500
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elif byte_range_string.startswith('-'):
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first = max(0, (content_length + int(byte_range_string)))
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last = content_length - 1
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# Case 2: 500-
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elif byte_range_string.endswith('-'):
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first = int(byte_range_string[0:-1])
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last = content_length - 1
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# Case 3: 500-999
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else:
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first, last = byte_range_string.split('-')
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first = int(first)
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last = min(int(last), content_length - 1)
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ranges.append((first, last))
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if len(ranges) == 0:
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raise ValueError('Invalid syntax')
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return unit, ranges
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