io.hotmoka.whitelisting.internal.checks.HasDeterministicTerminatingEqualsCheck Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of io-hotmoka-whitelisting Show documentation

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.

There is a newer version: 1.6.0

Show newest version

/*
Copyright 2023 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.internal.checks;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Optional;
import java.util.stream.Stream;

import io.hotmoka.whitelisting.api.WhiteListingPredicate;
import io.hotmoka.whitelisting.api.WhiteListingProofObligation;
import io.hotmoka.whitelisting.api.WhiteListingWizard;

/**
 * A check that a value has a deterministic and terminating implementation of {@code equals()}.
 */
public class HasDeterministicTerminatingEqualsCheck implements WhiteListingPredicate {

	@Override
	public boolean test(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 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() on this object is deterministic and terminating";
	}
}