io.hotmoka.whitelisting.HasDeterministicTerminatingEquals Maven / Gradle / Ivy
/*
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()} implementation that is deterministic and
* terminating. It checks that the value of the argument
* is a {@link java.lang.String} or a {@link java.math.BigInteger} or an enumeration
* or an object that redefines {@code equals()} in a Takamaka class in blockchain
* (hence not in the Java library) or an object that uses {@link java.lang.Object#equals(Object)}.
* 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 = HasDeterministicTerminatingEquals.Check.class)
public @interface HasDeterministicTerminatingEquals {
class Check 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";
}
}
}