io.hotmoka.whitelisting.HasDeterministicTerminatingEqualsAndHashCode Maven / Gradle / Ivy

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This module defines the implementation of white-listing in Hotmoka. It is used to define a subset of Java that can be used for Takamaka smart contracts.
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/*
Copyright 2021 Fausto Spoto

Licensed 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.
*/

package io.hotmoka.whitelisting;

import java.lang.annotation.Annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Optional;
import java.util.stream.Stream;

/**
 * States that an argument of a method or constructor of a white-listed
 * method has an {@code equals()} and a {@code hashCode} implementation
 * that is deterministic and terminating. It performs both checks of
 * {@link io.hotmoka.whitelisting.HasDeterministicTerminatingEquals} and
 * {@link io.hotmoka.whitelisting.HasDeterministicTerminatingHashCode}.
 * This annotation can also be applied
 * to a method, in which case it refers to the receiver of the method.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(value={ ElementType.PARAMETER, ElementType.METHOD })
@Inherited
@Documented
@WhiteListingProofObligation(check = HasDeterministicTerminatingEqualsAndHashCode.Check.class)
public @interface HasDeterministicTerminatingEqualsAndHashCode {

	class Check implements WhiteListingPredicate {

		@Override
		public boolean test(Object value, WhiteListingWizard wizard) {
			return testEquals(value, wizard) && testHashCode(value, wizard);
		}

		private static boolean testEquals(Object value, WhiteListingWizard wizard) {
			return value == null || equalsIsDeterministicAndTerminating(value.getClass(), wizard);
		}

		private static boolean equalsIsDeterministicAndTerminating(Class clazz, WhiteListingWizard wizard) {
			Optional equals = getEqualsFor(clazz);
			return equals.isPresent() &&
				// Object.equals() is deterministic and terminating, but its subclasses are not always so;
				// hence we cannot rely on the database for that special case, since proof-obligations are inherited
				(equals.get().getDeclaringClass() == Object.class || isInWhiteListingDatabaseWithoutProofObligations(equals.get(), wizard));
		}

		private static boolean isInWhiteListingDatabaseWithoutProofObligations(Method method, WhiteListingWizard wizard) {
            Optional model = wizard.whiteListingModelOf(method);
            return model.isPresent() && hasNoProofObligations(model.get());
        }

		private static boolean hasNoProofObligations(Method model) {
			return Stream.concat(Stream.of(model.getAnnotations()), Stream.of(model.getParameterAnnotations()).flatMap(Stream::of))
					.map(Annotation::annotationType)
					.map(Class::getAnnotations)
					.flatMap(Stream::of)
					.noneMatch(annotation -> annotation instanceof WhiteListingProofObligation);
		}

		private static boolean testHashCode(Object value, WhiteListingWizard wizard) {
			return value == null || hashCodelsIsDeterministicAndTerminating(value.getClass(), wizard);
		}

		private static boolean hashCodelsIsDeterministicAndTerminating(Class clazz, WhiteListingWizard wizard) {
			Optional hashCode = getHashCodeFor(clazz);
			return hashCode.isPresent() && isInWhiteListingDatabaseWithoutProofObligations(hashCode.get(), wizard);
		}

		private static Optional getHashCodeFor(Class clazz) {
			return Stream.of(clazz.getMethods())
				.filter(method -> !Modifier.isAbstract(method.getModifiers())
					&& Modifier.isPublic(method.getModifiers())
					&& !Modifier.isStatic(method.getModifiers())
					&& method.getParameters().length == 0
					&& "hashCode".equals(method.getName())
					&& method.getReturnType() == int.class)
				.findFirst();
		}

		private static Optional getEqualsFor(Class clazz) {
			return Stream.of(clazz.getMethods())
				.filter(method -> !Modifier.isAbstract(method.getModifiers())
					&& Modifier.isPublic(method.getModifiers())
					&& !Modifier.isStatic(method.getModifiers())
					&& method.getParameters().length == 1
					&& method.getParameterTypes()[0] == Object.class
					&& "equals".equals(method.getName())
					&& method.getReturnType() == boolean.class)
				.findFirst();
		}

		@Override
		public String messageIfFailed(String methodName) {
			return "cannot prove that equals() and hashCode() on this object are deterministic and terminating";
		}
	}
}