diff --git a/openedx/core/djangoapps/contentserver/views.py b/openedx/core/djangoapps/contentserver/views.py index 7c40026415bb..096302f61d7d 100644 --- a/openedx/core/djangoapps/contentserver/views.py +++ b/openedx/core/djangoapps/contentserver/views.py @@ -62,261 +62,257 @@ def course_assets_view(request): HTTP_DATE_FORMAT = "%a, %d %b %Y %H:%M:%S GMT" -class StaticContentServer(): - """ - Serves course assets to end users. Colloquially referred to as "contentserver." - """ - def is_asset_request(self, request): - """Determines whether the given request is an asset request""" - # Don't change this without updating urls.py! See docstring of views.py. - return ( - request.path.startswith('/' + XASSET_LOCATION_TAG + '/') - or - request.path.startswith('/' + AssetLocator.CANONICAL_NAMESPACE) - or - StaticContent.is_versioned_asset_path(request.path) - ) - - # pylint: disable=too-many-statements - def process_request(self, request): - """Process the given request""" - asset_path = request.path - - if self.is_asset_request(request): # lint-amnesty, pylint: disable=too-many-nested-blocks - # Make sure we can convert this request into a location. - if AssetLocator.CANONICAL_NAMESPACE in asset_path: - asset_path = asset_path.replace('block/', 'block@', 1) - - # If this is a versioned request, pull out the digest and chop off the prefix. - requested_digest = None - if StaticContent.is_versioned_asset_path(asset_path): - requested_digest, asset_path = StaticContent.parse_versioned_asset_path(asset_path) - - # Make sure we have a valid location value for this asset. - try: - loc = StaticContent.get_location_from_path(asset_path) - except (InvalidLocationError, InvalidKeyError): - return HttpResponseBadRequest() - - # Attempt to load the asset to make sure it exists, and grab the asset digest - # if we're able to load it. - actual_digest = None +def is_asset_request(self, request): + """Determines whether the given request is an asset request""" + # Don't change this without updating urls.py! See docstring of views.py. + return ( + request.path.startswith('/' + XASSET_LOCATION_TAG + '/') + or + request.path.startswith('/' + AssetLocator.CANONICAL_NAMESPACE) + or + StaticContent.is_versioned_asset_path(request.path) + ) + +# pylint: disable=too-many-statements +def process_request(self, request): + """Process the given request""" + asset_path = request.path + + if self.is_asset_request(request): # lint-amnesty, pylint: disable=too-many-nested-blocks + # Make sure we can convert this request into a location. + if AssetLocator.CANONICAL_NAMESPACE in asset_path: + asset_path = asset_path.replace('block/', 'block@', 1) + + # If this is a versioned request, pull out the digest and chop off the prefix. + requested_digest = None + if StaticContent.is_versioned_asset_path(asset_path): + requested_digest, asset_path = StaticContent.parse_versioned_asset_path(asset_path) + + # Make sure we have a valid location value for this asset. + try: + loc = StaticContent.get_location_from_path(asset_path) + except (InvalidLocationError, InvalidKeyError): + return HttpResponseBadRequest() + + # Attempt to load the asset to make sure it exists, and grab the asset digest + # if we're able to load it. + actual_digest = None + try: + content = self.load_asset_from_location(loc) + actual_digest = getattr(content, "content_digest", None) + except (ItemNotFoundError, NotFoundError): + return HttpResponseNotFound() + + # If this was a versioned asset, and the digest doesn't match, redirect + # them to the actual version. + if requested_digest is not None and actual_digest is not None and (actual_digest != requested_digest): + actual_asset_path = StaticContent.add_version_to_asset_path(asset_path, actual_digest) + return HttpResponsePermanentRedirect(actual_asset_path) + + # Set the basics for this request. Make sure that the course key for this + # asset has a run, which old-style courses do not. Otherwise, this will + # explode when the key is serialized to be sent to NR. + safe_course_key = loc.course_key + if safe_course_key.run is None: + safe_course_key = safe_course_key.replace(run='only') + + set_custom_attribute('course_id', safe_course_key) + set_custom_attribute('org', loc.org) + set_custom_attribute('contentserver.path', loc.path) + + # Figure out if this is a CDN using us as the origin. + is_from_cdn = StaticContentServer.is_cdn_request(request) + set_custom_attribute('contentserver.from_cdn', is_from_cdn) + + # Check if this content is locked or not. + locked = self.is_content_locked(content) + set_custom_attribute('contentserver.locked', locked) + + # Check that user has access to the content. + if not self.is_user_authorized(request, content, loc): + return HttpResponseForbidden('Unauthorized') + + # Figure out if the client sent us a conditional request, and let them know + # if this asset has changed since then. + last_modified_at_str = content.last_modified_at.strftime(HTTP_DATE_FORMAT) + 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'): + # If we have a StaticContent, get a StaticContentStream. Can't manipulate the bytes otherwise. + if isinstance(content, StaticContent): + content = AssetManager.find(loc, as_stream=True) + + header_value = request.META['HTTP_RANGE'] try: - content = self.load_asset_from_location(loc) - actual_digest = getattr(content, "content_digest", None) - except (ItemNotFoundError, NotFoundError): - return HttpResponseNotFound() - - # If this was a versioned asset, and the digest doesn't match, redirect - # them to the actual version. - if requested_digest is not None and actual_digest is not None and (actual_digest != requested_digest): - actual_asset_path = StaticContent.add_version_to_asset_path(asset_path, actual_digest) - return HttpResponsePermanentRedirect(actual_asset_path) - - # Set the basics for this request. Make sure that the course key for this - # asset has a run, which old-style courses do not. Otherwise, this will - # explode when the key is serialized to be sent to NR. - safe_course_key = loc.course_key - if safe_course_key.run is None: - safe_course_key = safe_course_key.replace(run='only') - - set_custom_attribute('course_id', safe_course_key) - set_custom_attribute('org', loc.org) - set_custom_attribute('contentserver.path', loc.path) - - # Figure out if this is a CDN using us as the origin. - is_from_cdn = StaticContentServer.is_cdn_request(request) - set_custom_attribute('contentserver.from_cdn', is_from_cdn) - - # Check if this content is locked or not. - locked = self.is_content_locked(content) - set_custom_attribute('contentserver.locked', locked) - - # Check that user has access to the content. - if not self.is_user_authorized(request, content, loc): - return HttpResponseForbidden('Unauthorized') - - # Figure out if the client sent us a conditional request, and let them know - # if this asset has changed since then. - last_modified_at_str = content.last_modified_at.strftime(HTTP_DATE_FORMAT) - 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'): - # If we have a StaticContent, get a StaticContentStream. Can't manipulate the bytes otherwise. - if isinstance(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( - "%s in Range header: %s for content: %s", - str(exception), header_value, str(loc) + 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( + "%s in Range header: %s for content: %s", + str(exception), header_value, str(loc) + ) + else: + if unit != 'bytes': + # Only accept ranges in bytes + log.warning("Unknown unit in Range header: %s for content: %s", header_value, str(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( + "More than 1 ranges in Range header: %s for content: %s", header_value, str(loc) ) else: - if unit != 'bytes': - # Only accept ranges in bytes - log.warning("Unknown unit in Range header: %s for content: %s", header_value, str(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( - "More than 1 ranges in Range header: %s for content: %s", header_value, str(loc) + 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 + + set_custom_attribute('contentserver.ranged', True) 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 - - set_custom_attribute('contentserver.ranged', True) - else: - log.warning( - "Cannot satisfy ranges in Range header: %s for content: %s", - header_value, str(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 - - set_custom_attribute('contentserver.content_len', content.length) - set_custom_attribute('contentserver.content_type', content.content_type) - - # "Accept-Ranges: bytes" tells the user that only "bytes" ranges are allowed - response['Accept-Ranges'] = 'bytes' - response['Content-Type'] = content.content_type - response['X-Frame-Options'] = 'ALLOW' - - # Set any caching headers, and do any response cleanup needed. Based on how much - # middleware we have in place, there's no easy way to use the built-in Django - # utilities and properly sanitize and modify a response to ensure that it is as - # cacheable as possible, which is why we do it ourselves. - self.set_caching_headers(content, response) - - return response - - def set_caching_headers(self, content, response): - """ - Sets caching headers based on whether or not the asset is locked. - """ - - is_locked = getattr(content, "locked", False) - - # We want to signal to the end user's browser, and to any intermediate proxies/caches, - # whether or not this asset is cacheable. If we have a TTL configured, we inform the - # caller, for unlocked assets, how long they are allowed to cache it. Since locked - # assets should be restricted to enrolled students, we simply send headers that - # indicate there should be no caching whatsoever. - cache_ttl = CourseAssetCacheTtlConfig.get_cache_ttl() - if cache_ttl > 0 and not is_locked: - set_custom_attribute('contentserver.cacheable', True) - - response['Expires'] = StaticContentServer.get_expiration_value(datetime.datetime.utcnow(), cache_ttl) - response['Cache-Control'] = "public, max-age={ttl}, s-maxage={ttl}".format(ttl=cache_ttl) - elif is_locked: - set_custom_attribute('contentserver.cacheable', False) - - response['Cache-Control'] = "private, no-cache, no-store" - - response['Last-Modified'] = content.last_modified_at.strftime(HTTP_DATE_FORMAT) - - # Force the Vary header to only vary responses on Origin, so that XHR and browser requests get cached - # separately and don't screw over one another. i.e. a browser request that doesn't send Origin, and - # caches a version of the response without CORS headers, in turn breaking XHR requests. - force_header_for_response(response, 'Vary', 'Origin') - - @staticmethod - def is_cdn_request(request): - """ - Attempts to determine whether or not the given request is coming from a CDN. - - Currently, this is a static check because edx.org only uses CloudFront, but may - be expanded in the future. - """ - cdn_user_agents = CdnUserAgentsConfig.get_cdn_user_agents() - user_agent = request.META.get('HTTP_USER_AGENT', '') - if user_agent in cdn_user_agents: - # This is a CDN request. - return True + log.warning( + "Cannot satisfy ranges in Range header: %s for content: %s", + header_value, str(loc) + ) + return HttpResponse(status=416) # Requested Range Not Satisfiable - return False + # 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 - @staticmethod - def get_expiration_value(now, cache_ttl): - """Generates an RFC1123 datetime string based on a future offset.""" - expire_dt = now + datetime.timedelta(seconds=cache_ttl) - return expire_dt.strftime(HTTP_DATE_FORMAT) - - def is_content_locked(self, content): - """ - Determines whether or not the given content is locked. - """ - return bool(getattr(content, "locked", False)) - - def is_user_authorized(self, request, content, location): - """ - Determines whether or not the user for this request is authorized to view the given asset. - """ - if not self.is_content_locked(content): - return True - - if not hasattr(request, "user") or not request.user.is_authenticated: - return False + set_custom_attribute('contentserver.content_len', content.length) + set_custom_attribute('contentserver.content_type', content.content_type) + + # "Accept-Ranges: bytes" tells the user that only "bytes" ranges are allowed + response['Accept-Ranges'] = 'bytes' + response['Content-Type'] = content.content_type + response['X-Frame-Options'] = 'ALLOW' + + # Set any caching headers, and do any response cleanup needed. Based on how much + # middleware we have in place, there's no easy way to use the built-in Django + # utilities and properly sanitize and modify a response to ensure that it is as + # cacheable as possible, which is why we do it ourselves. + self.set_caching_headers(content, response) + + return response + +def set_caching_headers(self, content, response): + """ + Sets caching headers based on whether or not the asset is locked. + """ + + is_locked = getattr(content, "locked", False) + + # We want to signal to the end user's browser, and to any intermediate proxies/caches, + # whether or not this asset is cacheable. If we have a TTL configured, we inform the + # caller, for unlocked assets, how long they are allowed to cache it. Since locked + # assets should be restricted to enrolled students, we simply send headers that + # indicate there should be no caching whatsoever. + cache_ttl = CourseAssetCacheTtlConfig.get_cache_ttl() + if cache_ttl > 0 and not is_locked: + set_custom_attribute('contentserver.cacheable', True) + + response['Expires'] = StaticContentServer.get_expiration_value(datetime.datetime.utcnow(), cache_ttl) + response['Cache-Control'] = "public, max-age={ttl}, s-maxage={ttl}".format(ttl=cache_ttl) + elif is_locked: + set_custom_attribute('contentserver.cacheable', False) + + response['Cache-Control'] = "private, no-cache, no-store" - if not request.user.is_staff: - deprecated = getattr(location, 'deprecated', False) - if deprecated and not CourseEnrollment.is_enrolled_by_partial(request.user, location.course_key): - return False - if not deprecated and not CourseEnrollment.is_enrolled(request.user, location.course_key): - return False + response['Last-Modified'] = content.last_modified_at.strftime(HTTP_DATE_FORMAT) + # Force the Vary header to only vary responses on Origin, so that XHR and browser requests get cached + # separately and don't screw over one another. i.e. a browser request that doesn't send Origin, and + # caches a version of the response without CORS headers, in turn breaking XHR requests. + force_header_for_response(response, 'Vary', 'Origin') + +@staticmethod +def is_cdn_request(request): + """ + Attempts to determine whether or not the given request is coming from a CDN. + + Currently, this is a static check because edx.org only uses CloudFront, but may + be expanded in the future. + """ + cdn_user_agents = CdnUserAgentsConfig.get_cdn_user_agents() + user_agent = request.META.get('HTTP_USER_AGENT', '') + if user_agent in cdn_user_agents: + # This is a CDN request. return True - def load_asset_from_location(self, location): - """ - Loads an asset based on its location, either retrieving it from a cache - or loading it directly from the contentstore. - """ + return False - # See if we can load this item from cache. - content = get_cached_content(location) - if content is None: - # Not in cache, so just try and load it from the asset manager. - try: - content = AssetManager.find(location, as_stream=True) - except (ItemNotFoundError, NotFoundError): # lint-amnesty, pylint: disable=try-except-raise - raise - - # Now that we fetched it, let's go ahead and try to cache it. We cap this at 1MB - # because it's the default for memcached and also we don't want to do too much - # buffering in memory when we're serving an actual request. - if content.length is not None and content.length < 1048576: - content = content.copy_to_in_mem() - set_cached_content(content) - - return content +@staticmethod +def get_expiration_value(now, cache_ttl): + """Generates an RFC1123 datetime string based on a future offset.""" + expire_dt = now + datetime.timedelta(seconds=cache_ttl) + return expire_dt.strftime(HTTP_DATE_FORMAT) + +def is_content_locked(self, content): + """ + Determines whether or not the given content is locked. + """ + return bool(getattr(content, "locked", False)) + +def is_user_authorized(self, request, content, location): + """ + Determines whether or not the user for this request is authorized to view the given asset. + """ + if not self.is_content_locked(content): + return True + + if not hasattr(request, "user") or not request.user.is_authenticated: + return False + + if not request.user.is_staff: + deprecated = getattr(location, 'deprecated', False) + if deprecated and not CourseEnrollment.is_enrolled_by_partial(request.user, location.course_key): + return False + if not deprecated and not CourseEnrollment.is_enrolled(request.user, location.course_key): + return False + + return True + +def load_asset_from_location(self, location): + """ + Loads an asset based on its location, either retrieving it from a cache + or loading it directly from the contentstore. + """ + + # See if we can load this item from cache. + content = get_cached_content(location) + if content is None: + # Not in cache, so just try and load it from the asset manager. + try: + content = AssetManager.find(location, as_stream=True) + except (ItemNotFoundError, NotFoundError): # lint-amnesty, pylint: disable=try-except-raise + raise + + # Now that we fetched it, let's go ahead and try to cache it. We cap this at 1MB + # because it's the default for memcached and also we don't want to do too much + # buffering in memory when we're serving an actual request. + if content.length is not None and content.length < 1048576: + content = content.copy_to_in_mem() + set_cached_content(content) + + return content IMPL = StaticContentServer()