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5106b01832
* Update JarFilter to remove certain annotations from primary constructors. * Enhance unit tests for deleting constructors. * Update the documentation to explain how to handle non-deterministic default constructor parameters. * Reduce the base logging level of SanitisingTransformer to DEBUG. * Simplify the execution of repeatable ClassVisitors. * Simplify Gradle usage slightly. * Add test for deterministic UniqueIdentifier. * Update README to cover handling default parameters.
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347 lines
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<style> .red {color:red} </style>
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.. role:: red
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Deterministic Corda Modules
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===========================
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A Corda contract's verify function should always produce the same results for the same input data. To that end,
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Corda provides the following modules:
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#. ``core-deterministic``
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#. ``serialization-deterministic``
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#. ``jdk8u-deterministic``
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These are reduced version of Corda's ``core`` and ``serialization`` modules and the OpenJDK 8 ``rt.jar``, where the
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non-deterministic functionality has been removed. The intention here is that all CorDapp classes required for
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contract verification should be compiled against these modules to prevent them containing non-deterministic behaviour.
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.. note:: These modules are only a development aid. They cannot guarantee determinism without also including
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deterministic versions of all their dependent libraries, e.g. ``kotlin-stdlib``.
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Generating the Deterministic Modules
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------------------------------------
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JDK 8
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``jdk8u-deterministic`` is a "pseudo JDK" image that we can point the Java and Kotlin compilers to. It downloads the
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``rt.jar`` containing a deterministic subset of the Java 8 APIs from the Artifactory.
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To build a new version of this JAR and upload it to the Artifactory, see the ``create-jdk8u`` module. This is a
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standalone Gradle project within the Corda repository that will clone the ``deterministic-jvm8`` branch of Corda's
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`OpenJDK repository <https://github.com/corda/openjdk>`_ and then build it. (This currently requires a C++ compiler,
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GNU Make and a UNIX-like development environment.)
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Corda Modules
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``core-deterministic`` and ``serialization-deterministic`` are generated from Corda's ``core`` and ``serialization``
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modules respectively using both `ProGuard <https://www.guardsquare.com/en/proguard>`_ and Corda's ``JarFilter`` Gradle
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plugin. Corda developers configure these tools by applying Corda's ``@KeepForDJVM`` and ``@DeleteForDJVM``
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annotations to elements of ``core`` and ``serialization`` as described :ref:`here <deterministic_annotations>`.
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The build generates each of Corda's deterministic JARs in six steps:
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#. Some *very few* classes in the original JAR must be replaced completely. This is typically because the original
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class uses something like ``ThreadLocal``, which is not available in the deterministic Java APIs, and yet the
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class is still required by the deterministic JAR. We must keep such classes to a minimum!
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#. The patched JAR is analysed by ProGuard for the first time using the following rule:
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.. sourcecode:: groovy
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keep '@interface net.corda.core.KeepForDJVM { *; }'
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..
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ProGuard works by calculating how much code is reachable from given "entry points", and in our case these entry
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points are the ``@KeepForDJVM`` classes. The unreachable classes are then discarded by ProGuard's ``shrink``
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option.
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#. The remaining classes may still contain non-deterministic code. However, there is no way of writing a ProGuard rule
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explicitly to discard anything. Consider the following class:
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.. sourcecode:: kotlin
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@CordaSerializable
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@KeepForDJVM
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data class UniqueIdentifier @JvmOverloads @DeleteForDJVM constructor(
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val externalId: String? = null,
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val id: UUID = UUID.randomUUID()
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) : Comparable<UniqueIdentifier> {
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...
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}
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..
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While CorDapps will definitely need to handle ``UniqueIdentifier`` objects, all of the secondary constructors
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generate a new random ``UUID`` and so are non-deterministic. Hence the next "determinising" step is to pass the
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classes to the ``JarFilter`` tool, which strips out all of the elements which have been annotated as
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``@DeleteForDJVM`` and stubs out any functions annotated with ``@StubOutForDJVM``. (Stub functions that
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return a value will throw ``UnsupportedOperationException``, whereas ``void`` or ``Unit`` stubs will do nothing.)
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#. After the ``@DeleteForDJVM`` elements have been filtered out, the classes are rescanned using ProGuard to remove
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any more code that has now become unreachable.
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#. The remaining classes define our deterministic subset. However, the ``@kotlin.Metadata`` annotations on the compiled
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Kotlin classes still contain references to all of the functions and properties that ProGuard has deleted. Therefore
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we now use the ``JarFilter`` to delete these references, as otherwise the Kotlin compiler will pretend that the
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deleted functions and properties are still present.
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#. Finally, we use ProGuard again to validate our JAR against the deterministic ``rt.jar``:
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.. literalinclude:: ../../core-deterministic/build.gradle
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:language: groovy
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:start-after: DOCSTART 01
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:end-before: DOCEND 01
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..
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This step will fail if ProGuard spots any Java API references that still cannot be satisfied by the deterministic
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``rt.jar``, and hence it will break the build.
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Configuring IntelliJ with a Deterministic SDK
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---------------------------------------------
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We would like to configure IntelliJ so that it will highlight uses of non-deterministic Java APIs as :red:`not found`.
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Or, more specifically, we would like IntelliJ to use the ``deterministic-rt.jar`` as a "Module SDK" for deterministic
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modules rather than the ``rt.jar`` from the default project SDK, to make IntelliJ consistent with Gradle.
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This is possible, but slightly tricky to configure because IntelliJ will not recognise an SDK containing only the
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``deterministic-rt.jar`` as being valid. It also requires that IntelliJ delegate all build tasks to Gradle, and that
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Gradle be configured to use the Project's SDK.
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Creating the Deterministic SDK
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Gradle creates a suitable JDK image in the project's ``jdk8u-deterministic/jdk`` directory, and you can
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configure IntelliJ to use this location for this SDK. However, you should also be aware that IntelliJ SDKs
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are available for *all* projects to use.
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To create this JDK image, execute the following:
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.. code-block:: bash
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$ gradlew jdk8u-deterministic:copyJdk
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..
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Now select ``File/Project Structure/Platform Settings/SDKs`` and add a new JDK SDK with the
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``jdk8u-deterministic/jdk`` directory as its home. Rename this SDK to something like "1.8 (Deterministic)".
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This *should* be sufficient for IntelliJ. However, if IntelliJ realises that this SDK does not contain a
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full JDK then you will need to configure the new SDK by hand:
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#. Create a JDK Home directory with the following contents:
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``jre/lib/rt.jar``
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where ``rt.jar`` here is this renamed artifact:
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.. code-block:: xml
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<dependency>
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<groupId>net.corda</groupId>
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<artifactId>deterministic-rt</artifactId>
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<classifier>api</classifier>
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</dependency>
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..
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#. While IntelliJ is *not* running, locate the ``config/options/jdk.table.xml`` file in IntelliJ's configuration
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directory. Add an empty ``<jdk>`` section to this file:
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.. code-block:: xml
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<jdk version="2">
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<name value="1.8 (Deterministic)"/>
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<type value="JavaSDK"/>
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<version value="java version "1.8.0""/>
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<homePath value=".. path to the deterministic JDK directory .."/>
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<roots>
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</roots>
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</jdk>
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..
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#. Open IntelliJ and select ``File/Project Structure/Platform Settings/SDKs``. The "1.8 (Deterministic)" SDK
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should now be present. Select it and then click on the ``Classpath`` tab. Press the "Add" / "Plus" button to
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add ``rt.jar`` to the SDK's classpath. Then select the ``Annotations`` tab and include the same JAR(s) as
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the other SDKs.
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Configuring the Corda Project
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#. Open the root ``build.gradle`` file and define this property:
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.. code-block:: gradle
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buildscript {
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ext {
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...
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deterministic_idea_sdk = '1.8 (Deterministic)'
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...
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}
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}
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..
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Configuring IntelliJ
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#. Go to ``File/Settings/Build, Execution, Deployment/Build Tools/Gradle``, and configure Gradle's JVM to be the
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project's JVM.
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#. Go to ``File/Settings/Build, Execution, Deployment/Build Tools/Gradle/Runner``, and select these options:
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- Delegate IDE build/run action to Gradle
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- Run tests using the Gradle Test Runner
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#. Delete all of the ``out`` directories that IntelliJ has previously generated for each module.
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#. Go to ``View/Tool Windows/Gradle`` and click the ``Refresh all Gradle projects`` button.
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These steps will enable IntelliJ's presentation compiler to use the deterministic ``rt.jar`` with the following modules:
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- ``core-deterministic``
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- ``serialization-deterministic``
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- ``core-deterministic:testing:common``
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but still build everything using Gradle with the full JDK.
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Testing the Deterministic Modules
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---------------------------------
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The ``core-deterministic:testing`` module executes some basic JUnit tests for the ``core-deterministic`` and
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``serialization-deterministic`` JARs. These tests are compiled against the deterministic ``rt.jar``, although
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they are still executed using the full JDK.
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The ``testing`` module also has two sub-modules:
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``core-deterministic:testing:data``
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This module generates test data such as serialised transactions and elliptic curve key pairs using the full
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non-deterministic ``core`` library and JDK. This data is all written into a single JAR which the ``testing``
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module adds to its classpath.
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``core-deterministic:testing:common``
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This module provides the test classes which the ``testing`` and ``data`` modules need to share. It is therefore
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compiled against the deterministic API subset.
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.. _deterministic_annotations:
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Applying @KeepForDJVM and @DeleteForDJVM annotations
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----------------------------------------------------
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Corda developers need to understand how to annotate classes in the ``core`` and ``serialization`` modules correctly
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in order to maintain the deterministic JARs.
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.. note:: Every Kotlin class still has its own ``.class`` file, even when all of those classes share the same
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source file. Also, annotating the file:
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.. sourcecode:: kotlin
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@file:KeepForDJVM
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package net.corda.core.internal
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..
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*does not* automatically annotate any class declared *within* this file. It merely annotates any
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accompanying Kotlin ``xxxKt`` class.
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For more information about how ``JarFilter`` is processing the byte-code inside ``core`` and ``serialization``,
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use Gradle's ``--info`` or ``--debug`` command-line options.
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Deterministic Classes
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Classes that *must* be included in the deterministic JAR should be annotated as ``@KeepForDJVM``.
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.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/KeepForDJVM.kt
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:language: kotlin
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:start-after: DOCSTART 01
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:end-before: DOCEND 01
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..
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To preserve any Kotlin functions, properties or type aliases that have been declared outside of a ``class``,
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you should annotate the source file's ``package`` declaration instead:
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.. sourcecode:: kotlin
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@file:JvmName("InternalUtils")
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@file:KeepForDJVM
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package net.corda.core.internal
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infix fun Temporal.until(endExclusive: Temporal): Duration = Duration.between(this, endExclusive)
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..
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Non-Deterministic Elements
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Elements that *must* be deleted from classes in the deterministic JAR should be annotated as ``@DeleteForDJVM``.
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.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/DeleteForDJVM.kt
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:language: kotlin
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:start-after: DOCSTART 01
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:end-before: DOCEND 01
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..
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You must also ensure that a deterministic class's primary constructor does not reference any classes that are
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not available in the deterministic ``rt.jar``. The biggest risk here would be that ``JarFilter`` would delete the
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primary constructor and that the class could no longer be instantiated, although ``JarFilter`` will print a warning
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in this case. However, it is also likely that the "determinised" class would have a different serialisation
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signature than its non-deterministic version and so become unserialisable on the deterministic JVM.
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Primary constructors that have non-deterministic default parameter values must still be annotated as
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``@DeleteForDJVM`` because they cannot be refactored without breaking Corda's binary interface. The Kotlin compiler
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will automatically apply this ``@DeleteForDJVM`` annotation - along with any others - to all of the class's
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secondary constructors too. The ``JarFilter`` plugin can then remove the ``@DeleteForDJVM`` annotation from the
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primary constructor so that it can subsequently delete only the secondary constructors.
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The annotations that ``JarFilter`` will "sanitise" from primary constructors in this way are listed in the plugin's
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configuration block, e.g.
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.. sourcecode:: groovy
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task jarFilter(type: JarFilterTask) {
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...
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annotations {
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...
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forSanitise = [
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"net.corda.core.DeleteForDJVM"
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]
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}
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}
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..
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Be aware that package-scoped Kotlin properties are all initialised within a common ``<clinit>`` block inside
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their host ``.class`` file. This means that when ``JarFilter`` deletes these properties, it cannot also remove
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their initialisation code. For example:
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.. sourcecode:: kotlin
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package net.corda.core
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@DeleteForDJVM
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val map: MutableMap<String, String> = ConcurrentHashMap()
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..
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In this case, ``JarFilter`` would delete the ``map`` property but the ``<clinit>`` block would still create
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an instance of ``ConcurrentHashMap``. The solution here is to refactor the property into its own file and then
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annotate the file itself as ``@DeleteForDJVM`` instead.
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Non-Deterministic Function Stubs
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Sometimes it is impossible to delete a function entirely. Or a function may have some non-deterministic code
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embedded inside it that cannot be removed. For these rare cases, there is the ``@StubOutForDJVM``
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annotation:
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.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/StubOutForDJVM.kt
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:language: kotlin
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:start-after: DOCSTART 01
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:end-before: DOCEND 01
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..
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This annotation instructs ``JarFilter`` to replace the function's body with either an empty body (for functions
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that return ``void`` or ``Unit``) or one that throws ``UnsupportedOperationException``. For example:
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.. sourcecode:: kotlin
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fun necessaryCode() {
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nonDeterministicOperations()
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otherOperations()
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}
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@StubOutForDJVM
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private fun nonDeterministicOperations() {
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// etc
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}
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..
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