"""
Middleware to serve assets.
"""
import logging
from django.http import (
HttpResponse, HttpResponseNotModified, HttpResponseForbidden
)
from student.models import CourseEnrollment
from xmodule.assetstore.assetmgr import AssetManager
from xmodule.contentstore.content import StaticContent, XASSET_LOCATION_TAG
from xmodule.modulestore import InvalidLocationError
from opaque_keys import InvalidKeyError
from opaque_keys.edx.locator import AssetLocator
from cache_toolbox.core import get_cached_content, set_cached_content
from xmodule.modulestore.exceptions import ItemNotFoundError
from xmodule.exceptions import NotFoundError
# TODO: Soon as we have a reasonable way to serialize/deserialize AssetKeys, we need
# to change this file so instead of using course_id_partial, we're just using asset keys
log = logging.getLogger(__name__)
class StaticContentServer(object):
def process_request(self, request):
# look to see if the request is prefixed with an asset prefix tag
if (
request.path.startswith('/' + XASSET_LOCATION_TAG + '/') or
request.path.startswith('/' + AssetLocator.CANONICAL_NAMESPACE)
):
if AssetLocator.CANONICAL_NAMESPACE in request.path:
request.path = request.path.replace('block/', 'block@', 1)
try:
loc = StaticContent.get_location_from_path(request.path)
except (InvalidLocationError, InvalidKeyError):
# return a 'Bad Request' to browser as we have a malformed Location
response = HttpResponse()
response.status_code = 400
return response
# first look in our cache so we don't have to round-trip to the DB
content = get_cached_content(loc)
if content is None:
# nope, not in cache, let's fetch from DB
try:
content = AssetManager.find(loc, as_stream=True)
except (ItemNotFoundError, NotFoundError):
response = HttpResponse()
response.status_code = 404
return response
# since we fetched it from DB, let's cache it going forward, but only if it's < 1MB
# this is because I haven't been able to find a means to stream data out of memcached
if content.length is not None:
if content.length < 1048576:
# since we've queried as a stream, let's read in the stream into memory to set in cache
content = content.copy_to_in_mem()
set_cached_content(content)
else:
# NOP here, but we may wish to add a "cache-hit" counter in the future
pass
# Check that user has access to content
if getattr(content, "locked", False):
if not hasattr(request, "user") or not request.user.is_authenticated():
return HttpResponseForbidden('Unauthorized')
if not request.user.is_staff:
if getattr(loc, 'deprecated', False) and not CourseEnrollment.is_enrolled_by_partial(
request.user, loc.course_key
):
return HttpResponseForbidden('Unauthorized')
if not getattr(loc, 'deprecated', False) and not CourseEnrollment.is_enrolled(
request.user, loc.course_key
):
return HttpResponseForbidden('Unauthorized')
# convert over the DB persistent last modified timestamp to a HTTP compatible
# timestamp, so we can simply compare the strings
last_modified_at_str = content.last_modified_at.strftime("%a, %d-%b-%Y %H:%M:%S GMT")
# see if the client has cached this content, if so then compare the
# timestamps, if they are the same then just return a 304 (Not Modified)
if 'HTTP_IF_MODIFIED_SINCE' in request.META:
if_modified_since = request.META['HTTP_IF_MODIFIED_SINCE']
if if_modified_since == last_modified_at_str:
return HttpResponseNotModified()
# *** File streaming within a byte range ***
# If a Range is provided, parse Range attribute of the request
# Add Content-Range in the response if Range is structurally correct
# Request -> Range attribute structure: "Range: bytes=first-[last]"
# Response -> Content-Range attribute structure: "Content-Range: bytes first-last/totalLength"
# http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35
response = None
if request.META.get('HTTP_RANGE'):
# Data from cache (StaticContent) has no easy byte management, so we use the DB instead (StaticContentStream)
if type(content) == StaticContent:
content = AssetManager.find(loc, as_stream=True)
header_value = request.META['HTTP_RANGE']
try:
unit, ranges = parse_range_header(header_value, content.length)
except ValueError as exception:
# If the header field is syntactically invalid it should be ignored.
log.exception(
u"%s in Range header: %s for content: %s", exception.message, header_value, unicode(loc)
)
else:
if unit != 'bytes':
# Only accept ranges in bytes
log.warning(u"Unknown unit in Range header: %s for content: %s", header_value, unicode(loc))
elif len(ranges) > 1:
# According to Http/1.1 spec content for multiple ranges should be sent as a multipart message.
# http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.16
# But we send back the full content.
log.warning(
u"More than 1 ranges in Range header: %s for content: %s", header_value, unicode(loc)
)
else:
first, last = ranges[0]
if 0 <= first <= last < content.length:
# If the byte range is satisfiable
response = HttpResponse(content.stream_data_in_range(first, last))
response['Content-Range'] = 'bytes {first}-{last}/{length}'.format(
first=first, last=last, length=content.length
)
response['Content-Length'] = str(last - first + 1)
response.status_code = 206 # Partial Content
else:
log.warning(
u"Cannot satisfy ranges in Range header: %s for content: %s", header_value, unicode(loc)
)
return HttpResponse(status=416) # Requested Range Not Satisfiable
# If Range header is absent or syntactically invalid return a full content response.
if response is None:
response = HttpResponse(content.stream_data())
response['Content-Length'] = content.length
# "Accept-Ranges: bytes" tells the user that only "bytes" ranges are allowed
response['Accept-Ranges'] = 'bytes'
response['Content-Type'] = content.content_type
response['Last-Modified'] = last_modified_at_str
return response
def parse_range_header(header_value, content_length):
"""
Returns the unit and a list of (start, end) tuples of ranges.
Raises ValueError if header is syntactically invalid or does not contain a range.
See spec for details: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35
"""
unit = None
ranges = []
if '=' in header_value:
unit, byte_ranges_string = header_value.split('=')
# Parse the byte ranges.
for byte_range_string in byte_ranges_string.split(','):
byte_range_string = byte_range_string.strip()
# Case 0:
if '-' not in byte_range_string: # Invalid syntax of header value.
raise ValueError('Invalid syntax.')
# Case 1: -500
elif byte_range_string.startswith('-'):
first = max(0, (content_length + int(byte_range_string)))
last = content_length - 1
# Case 2: 500-
elif byte_range_string.endswith('-'):
first = int(byte_range_string[0:-1])
last = content_length - 1
# Case 3: 500-999
else:
first, last = byte_range_string.split('-')
first = int(first)
last = min(int(last), content_length - 1)
ranges.append((first, last))
if len(ranges) == 0:
raise ValueError('Invalid syntax')
return unit, ranges