mbeckerle commented on a change in pull request #643: URL: https://github.com/apache/daffodil/pull/643#discussion_r716866298
########## File path: daffodil-test/src/test/resources/org/apache/daffodil/layers/IPv4.dfdl.xsd ########## @@ -0,0 +1,199 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +<!-- +Copyright (c) 2012-2021 Owl Cyber Defense. 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IN NO EVENT SHALL THE +CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE +SOFTWARE. +--> + +<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"; + xmlns:dfdl="http://www.ogf.org/dfdl/dfdl-1.0/"; + xmlns:dfdlx="http://www.ogf.org/dfdl/dfdl-1.0/extensions"; + xmlns:fn="http://www.w3.org/2005/xpath-functions"; + xmlns:daf="urn:ogf:dfdl:2013:imp:daffodil.apache.org:2018:ext" + xmlns:chksum="urn:org.apache.daffodil.layers.IPv4Checksum" + xmlns:eth="urn:ethernet" + xmlns:tns="urn:ethernet" + targetNamespace="urn:ethernet"> + + <xs:include schemaLocation="org/apache/daffodil/xsd/DFDLGeneralFormat.dfdl.xsd"/> + + <xs:import namespace="urn:org.apache.daffodil.layers.IPv4Checksum" + schemaLocation="org/apache/daffodil/layers/xsd/IPv4ChecksumLayer.dfdl.xsd"/> + + <xs:annotation> + <xs:appinfo source="http://www.ogf.org/dfdl/";> + <dfdl:defineFormat name="basicBigEndianBinary"> + <dfdl:format + ref="tns:GeneralFormat" + representation="binary" + binaryNumberRep="binary" + byteOrder="bigEndian" + bitOrder="mostSignificantBitFirst" + alignmentUnits="bits" + alignment="1" + occursCountKind="implicit"/> + </dfdl:defineFormat> + <dfdl:format ref="tns:basicBigEndianBinary"/> + </xs:appinfo> + </xs:annotation> + + <xs:element name="IPv4Header" type="tns:IPv4Header"/> + + <xs:complexType name="IPv4Header"> + <!-- + Modified with proposed checksum computation via layer transform + --> + <xs:sequence> + <xs:annotation> + <xs:appinfo source="http://www.ogf.org/dfdl/";> + <!-- + The checksum field in an IPv4 actually lives in the middle of the + data that it is a checksum of. + + That is, some of the 16-bit words going into the checksum are before + the checksum itself, others are after. + + At parse time we must check that this computed checksum value, and the + actual value of the element in the infoset are equal. + + We have an option to place the computed checksum in another element + and then have a schematron validation rule or just a DFDL assert (recoverable) + check that the checksum element and computed checksum are equal. + + Below, that element is called "ComputedChecksum". + + When unparsing, the infoset contains a checksum, which remains in the infoset, but + it is overwritten (in the layer transform) by the recomputed checksum available for comparison purposes in + the ComputedChecksum variable. + --> + <dfdl:newVariableInstance ref="chksum:IPv4Checksum"/> + </xs:appinfo> + </xs:annotation> + + <xs:sequence dfdl:ref="chksum:IPv4ChecksumLayer"> + <xs:sequence> + <xs:element name="Version" type="tns:bit" dfdl:length="4"/> + <xs:element name="IHL" type="tns:bit" dfdl:length="4"/> + <xs:element name="DSCP" type="tns:bit" dfdl:length="6"/> + <xs:element name="ECN" type="tns:bit" dfdl:length="2"/> + <xs:element name="Length" type="tns:bit" dfdl:length="16" + dfdl:outputValueCalc='{ ../RealLength }'/> + <xs:element name="Identification" type="tns:bit" dfdl:length="16"/> + <xs:element name="Flags" type="tns:bit" dfdl:length="3"/> + <xs:element name="FragmentOffset" type="tns:bit" dfdl:length="13"/> + <xs:element name="TTL" type="tns:bit" dfdl:length="8"/> + <xs:element name="Protocol" type="tns:bit" dfdl:length="8"/> + <xs:element name="Checksum" type="chksum:IPv4Checksum"/> + <xs:element name="IPSrc" type="tns:hexByte" dfdl:length="4"/> + <xs:element name="IPDest" type="tns:hexByte" dfdl:length="4"/> + </xs:sequence> + </xs:sequence> + <!-- + This exists purely to make unparsing of the header suspend when trying to unparse + the Length element. + + We just want the tests to rule out deadlock in this case. + --> + <xs:element name="RealLength" type="tns:bit" + dfdl:inputValueCalc='{ ../Length }'/> + <!-- + We want the schema author to have all options on what to do if the + checksum is incorrect when parsing. Hence, we just put the computed value + into this element. + --> + <xs:element name="ComputedChecksum" type="chksum:IPv4Checksum" + dfdl:inputValueCalc='{ $chksum:IPv4Checksum }'/> + <!-- + One recommendation is to treat incorrect checksum values as a validation + error. This preserves the ability to use the schema forensically to examine + data with incorrect checksums. + + This uses a DFDL recoverable error assertion to report that the + checksum is incorrect. A recoverable error assert is not technically + a validation error, but behaves similarly in that it does not prevent the + parse from completing. It is essentially a warning about the data. + + A schematron check would accomplish much the same thing, with the + advantage that the error would be reported as an "official" validation error. + --> + <xs:sequence> + <xs:annotation> + <xs:appinfo source="http://www.ogf.org/dfdl/";> + <dfdl:assert + failureType="recoverableError" + message="Incorrect checksum." + test='{ Checksum eq ComputedChecksum }' + /> + </xs:appinfo> + </xs:annotation> + </xs:sequence> + </xs:sequence> + </xs:complexType> + + <xs:simpleType name="bit" + dfdl:lengthKind="explicit" + dfdl:lengthUnits="bits"> + <xs:restriction base="xs:unsignedInt"/> + </xs:simpleType> + + <xs:simpleType name="hexByte" dfdl:lengthKind="explicit" dfdl:lengthUnits="bytes"> + <xs:restriction base="xs:hexBinary"/> + </xs:simpleType> + + <xs:simpleType name="uint16" dfdl:lengthKind="explicit" dfdl:length="16"> Review comment: I will specify lengthUnits bits, and remove the types the example isn't using. -- This is an automated message from the Apache Git Service. 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