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An unofficial backport of the JDK Classfile API to Java 17
/*
* Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package io.github.dmlloyd.classfile.impl;
import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UncheckedIOException;
import io.github.dmlloyd.classfile.ClassHierarchyResolver;
import java.lang.constant.ClassDesc;
import io.github.dmlloyd.classfile.extras.constant.ExtraClassDesc;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;
import static io.github.dmlloyd.classfile.ClassFile.ACC_INTERFACE;
import static io.github.dmlloyd.classfile.constantpool.PoolEntry.*;
import static java.lang.constant.ConstantDescs.CD_Object;
import static java.util.Objects.requireNonNull;
import static io.github.dmlloyd.classfile.extras.constant.ConstantUtils.referenceClassDesc;
/**
* Class hierarchy resolution framework is answering questions about classes assignability, common classes ancestor and whether the class represents an interface.
* All the requests are handled without class loading nor full verification, optionally with incomplete dependencies and with focus on maximum performance.
*
*/
public final class ClassHierarchyImpl {
public record ClassHierarchyInfoImpl(ClassDesc superClass, boolean isInterface) implements ClassHierarchyResolver.ClassHierarchyInfo {
static final ClassHierarchyResolver.ClassHierarchyInfo OBJECT_INFO = new ClassHierarchyInfoImpl(null, false);
}
public static final ClassHierarchyResolver DEFAULT_RESOLVER =
new ClassLoadingClassHierarchyResolver(ClassLoadingClassHierarchyResolver.SYSTEM_CLASS_PROVIDER);
private final ClassHierarchyResolver resolver;
/**
* Public constructor of ClassHierarchyImpl accepting instances of ClassHierarchyInfoResolver to resolve individual class streams.
* @param classHierarchyResolver ClassHierarchyInfoResolver instance
*/
public ClassHierarchyImpl(ClassHierarchyResolver classHierarchyResolver) {
requireNonNull(classHierarchyResolver);
this.resolver = classHierarchyResolver instanceof CachedClassHierarchyResolver
? classHierarchyResolver
: classHierarchyResolver.cached();
}
private ClassHierarchyInfoImpl resolve(ClassDesc classDesc) {
var res = resolver.getClassInfo(classDesc);
if (res != null) return (ClassHierarchyInfoImpl) res;
throw new IllegalArgumentException("Could not resolve class " + classDesc.displayName());
}
/**
* Method answering question whether given class is an interface,
* responding without the class stream resolution and parsing is preferred in case the interface status is known from previous activities.
* @param classDesc class path in form of <package>/<class_name>.class
* @return true if the given class name represents an interface
*/
public boolean isInterface(ClassDesc classDesc) {
return resolve(classDesc).isInterface();
}
/**
* Method resolving common ancestor of two classes
* @param symbol1 first class descriptor
* @param symbol2 second class descriptor
* @return common ancestor class name or null if it could not be identified
*/
public ClassDesc commonAncestor(ClassDesc symbol1, ClassDesc symbol2) {
//calculation of common ancestor is a robust (yet fast) way to decide about assignability in incompletely resolved class hierarchy
//exact order of symbol loops is critical for performance of the above isAssignableFrom method, so standard situations are resolved in linear time
//this method returns null if common ancestor could not be identified
if (isInterface(symbol1) || isInterface(symbol2)) return CD_Object;
for (var s1 = symbol1; s1 != null; s1 = resolve(s1).superClass()) {
for (var s2 = symbol2; s2 != null; s2 = resolve(s2).superClass()) {
if (s1.equals(s2)) return s1;
}
}
return null;
}
public boolean isAssignableFrom(ClassDesc thisClass, ClassDesc fromClass) {
//extra check if fromClass is an interface is necessary to handle situation when thisClass might not been fully resolved and so it is potentially an unidentified interface
//this special corner-case handling has been added based on better success rate of constructing stack maps with simulated broken resolution of classes and interfaces
if (isInterface(fromClass)) return resolve(thisClass).superClass() == null;
//regular calculation of assignability is based on common ancestor calculation
var anc = commonAncestor(thisClass, fromClass);
//if common ancestor does not exist (as the class hierarchy could not be fully resolved) we optimistically assume the classes might be accessible
//if common ancestor is equal to thisClass then the classes are clearly accessible
//if other common ancestor is calculated (which works even when their grandparents could not be resolved) then it is clear that thisClass could not be assigned from fromClass
return anc == null || thisClass.equals(anc);
}
public static final class CachedClassHierarchyResolver implements ClassHierarchyResolver {
// this instance should not leak out, appears only in cache in order to utilize Map.computeIfAbsent
// is already an invalid combination, so it can be compared with equals or as value class safely
private static final ClassHierarchyInfo NOPE =
new ClassHierarchyInfoImpl(null, true);
private final Map resolvedCache;
private final Function delegateFunction;
public CachedClassHierarchyResolver(ClassHierarchyResolver delegate, Map resolvedCache) {
this.resolvedCache = resolvedCache;
this.delegateFunction = new Function<>() {
@Override
public ClassHierarchyInfo apply(ClassDesc classDesc) {
var ret = delegate.getClassInfo(classDesc);
return ret == null ? NOPE : ret;
}
};
}
@Override
public ClassHierarchyInfo getClassInfo(ClassDesc classDesc) {
var ret = resolvedCache.computeIfAbsent(classDesc, delegateFunction);
return ret == NOPE ? null : ret;
}
}
public static final class ResourceParsingClassHierarchyResolver implements ClassHierarchyResolver {
public static final Function SYSTEM_STREAM_PROVIDER = new Function<>() {
@Override
public InputStream apply(ClassDesc cd) {
return ClassLoader.getSystemClassLoader().getResourceAsStream(Util.toInternalName(cd) + ".class");
}
};
private final Function streamProvider;
public ResourceParsingClassHierarchyResolver(Function classStreamProvider) {
this.streamProvider = classStreamProvider;
}
// resolve method looks for the class file using ClassStreamResolver instance and tries to briefly scan it just for minimal information necessary
// minimal information includes: identification of the class as interface, obtaining its superclass name and identification of all potential interfaces (to avoid unnecessary future resolutions of them)
// empty ClInfo is stored in case of an exception to avoid repeated scanning failures
@Override
public ClassHierarchyInfo getClassInfo(ClassDesc classDesc) {
var ci = streamProvider.apply(classDesc);
if (ci == null) return null;
try (var in = new DataInputStream(new BufferedInputStream(ci))) {
in.skipBytes(8);
int cpLength = in.readUnsignedShort();
String[] cpStrings = new String[cpLength];
int[] cpClasses = new int[cpLength];
for (int i = 1; i < cpLength; i++) {
int tag;
switch (tag = in.readUnsignedByte()) {
case TAG_UTF8 -> cpStrings[i] = in.readUTF();
case TAG_CLASS -> cpClasses[i] = in.readUnsignedShort();
case TAG_STRING, TAG_METHOD_TYPE, TAG_MODULE, TAG_PACKAGE -> in.skipBytes(2);
case TAG_METHOD_HANDLE -> in.skipBytes(3);
case TAG_INTEGER, TAG_FLOAT, TAG_FIELDREF, TAG_METHODREF, TAG_INTERFACE_METHODREF,
TAG_NAME_AND_TYPE, TAG_DYNAMIC, TAG_INVOKE_DYNAMIC -> in.skipBytes(4);
case TAG_LONG, TAG_DOUBLE -> {
in.skipBytes(8);
i++;
}
default -> throw new IllegalStateException("Bad tag (" + tag + ") at index (" + i + ")");
}
}
boolean isInterface = (in.readUnsignedShort() & ACC_INTERFACE) != 0;
in.skipBytes(2);
int superIndex = in.readUnsignedShort();
var superClass = superIndex > 0 ? ExtraClassDesc.ofInternalName(cpStrings[cpClasses[superIndex]]) : null;
return new ClassHierarchyInfoImpl(superClass, isInterface);
} catch (IOException ioe) {
throw new UncheckedIOException(ioe);
}
}
}
public static final class StaticClassHierarchyResolver implements ClassHierarchyResolver {
private final Map map;
public StaticClassHierarchyResolver(Collection interfaceNames, Map classToSuperClass) {
map = new HashMap<>(interfaceNames.size() + classToSuperClass.size() + 1);
map.put(CD_Object, ClassHierarchyInfoImpl.OBJECT_INFO);
for (var e : classToSuperClass.entrySet())
map.put(requireNonNull(e.getKey()), ClassHierarchyInfo.ofClass(e.getValue()));
for (var i : interfaceNames)
map.put(requireNonNull(i), ClassHierarchyInfo.ofInterface());
}
@Override
public ClassHierarchyInfo getClassInfo(ClassDesc classDesc) {
return map.get(classDesc);
}
}
public static final class ClassLoadingClassHierarchyResolver implements ClassHierarchyResolver {
public static final Function> SYSTEM_CLASS_PROVIDER = new Function<>() {
@Override
public Class apply(ClassDesc cd) {
try {
return Class.forName(Util.toBinaryName(cd), false, ClassLoader.getSystemClassLoader());
} catch (ClassNotFoundException ex) {
return null;
}
}
};
private final Function> classProvider;
public ClassLoadingClassHierarchyResolver(Function> classProvider) {
this.classProvider = classProvider;
}
@Override
public ClassHierarchyInfo getClassInfo(ClassDesc cd) {
if (!cd.isClassOrInterface())
return null;
if (cd.equals(CD_Object))
return ClassHierarchyInfo.ofClass(null);
var cl = classProvider.apply(cd);
if (cl == null) {
return null;
}
return cl.isInterface() ? ClassHierarchyInfo.ofInterface()
: ClassHierarchyInfo.ofClass(cl.getSuperclass().describeConstable().orElseThrow());
}
}
}
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