1 /*
  2  * Copyright (c) 2022, 2025, Oracle and/or its affiliates. All rights reserved.
  3  * Copyright (c) 2024, Alibaba Group Holding Limited. All Rights Reserved.
  4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  5  *
  6  * This code is free software; you can redistribute it and/or modify it
  7  * under the terms of the GNU General Public License version 2 only, as
  8  * published by the Free Software Foundation.  Oracle designates this
  9  * particular file as subject to the "Classpath" exception as provided
 10  * by Oracle in the LICENSE file that accompanied this code.
 11  *
 12  * This code is distributed in the hope that it will be useful, but WITHOUT
 13  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 14  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 15  * version 2 for more details (a copy is included in the LICENSE file that
 16  * accompanied this code).
 17  *
 18  * You should have received a copy of the GNU General Public License version
 19  * 2 along with this work; if not, write to the Free Software Foundation,
 20  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 21  *
 22  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 23  * or visit www.oracle.com if you need additional information or have any
 24  * questions.
 25  */
 26 
 27 package jdk.internal.classfile.impl;
 28 
 29 import java.lang.classfile.*;
 30 import java.lang.classfile.constantpool.ClassEntry;
 31 import java.lang.classfile.constantpool.Utf8Entry;
 32 import java.lang.constant.ConstantDescs;
 33 import java.util.Arrays;
 34 import java.util.Collections;
 35 import java.util.List;
 36 import java.util.function.Consumer;
 37 
 38 import static java.util.Objects.requireNonNull;
 39 
 40 public final class DirectClassBuilder
 41         extends AbstractDirectBuilder<ClassModel>
 42         implements ClassBuilder {
 43 
 44     /** The value of default class access flags */
 45     static final int DEFAULT_CLASS_FLAGS = ClassFile.ACC_PUBLIC;
 46     static final Util.Writable[] EMPTY_WRITABLE_ARRAY = {};
 47     static final WritableField[] EMPTY_WRITABLE_FIELD_ARRAY = {};
 48     static final ClassEntry[] EMPTY_CLASS_ENTRY_ARRAY = {};
 49     final ClassEntry thisClassEntry;
 50     private WritableField[] fields = EMPTY_WRITABLE_FIELD_ARRAY;
 51     private Util.Writable[] methods = EMPTY_WRITABLE_ARRAY;
 52     private int fieldsCount = 0;
 53     private int methodsCount = 0;
 54     private ClassEntry superclassEntry;
 55     private List<ClassEntry> interfaceEntries;
 56     private int majorVersion;
 57     private int minorVersion;
 58     private int flags;
 59     private int sizeHint;
 60 
 61     public DirectClassBuilder(SplitConstantPool constantPool,
 62                               ClassFileImpl context,
 63                               ClassEntry thisClass) {
 64         super(constantPool, context);
 65         this.thisClassEntry = AbstractPoolEntry.maybeClone(constantPool, thisClass);
 66         this.flags = DEFAULT_CLASS_FLAGS;
 67         this.superclassEntry = null;
 68         this.interfaceEntries = Collections.emptyList();
 69         this.majorVersion = ClassFile.latestMajorVersion();
 70         this.minorVersion = ClassFile.latestMinorVersion();
 71     }
 72 
 73     @Override
 74     public ClassBuilder with(ClassElement element) {
 75         if (element instanceof AbstractElement ae) {
 76             ae.writeTo(this);
 77         } else {
 78             writeAttribute((CustomAttribute<?>) requireNonNull(element));
 79         }
 80         return this;
 81     }
 82 
 83     @Override
 84     public ClassBuilder withFlags(int flags) {
 85         setFlags(flags);
 86         return this;
 87     }
 88 
 89     @Override
 90     public ClassBuilder withField(Utf8Entry name,
 91                                   Utf8Entry descriptor,
 92                                   int flags) {
 93         return withField(new DirectFieldBuilder(constantPool, context, name, descriptor, flags, null));
 94     }
 95 
 96     @Override
 97     public ClassBuilder withField(Utf8Entry name,
 98                                   Utf8Entry descriptor,
 99                                   Consumer<? super FieldBuilder> handler) {
100         return withField(new DirectFieldBuilder(constantPool, context, name, descriptor, 0, null)
101                                  .run(handler));
102     }
103 
104     @Override
105     public ClassBuilder transformField(FieldModel field, FieldTransform transform) {
106         DirectFieldBuilder builder = new DirectFieldBuilder(constantPool, context, field.fieldName(),
107                                                             field.fieldType(), 0, field);
108         builder.transform(field, transform);
109         return withField(builder);
110     }
111 
112     @Override
113     public ClassBuilder withMethod(Utf8Entry name,
114                                    Utf8Entry descriptor,
115                                    int flags,
116                                    Consumer<? super MethodBuilder> handler) {
117         return withMethod(new DirectMethodBuilder(constantPool, context, name, descriptor, flags, null)
118                                   .run(handler));
119     }
120 
121     @Override
122     public ClassBuilder transformMethod(MethodModel method, MethodTransform transform) {
123         DirectMethodBuilder builder = new DirectMethodBuilder(constantPool, context, method.methodName(),
124                                                               method.methodType(),
125                                                               method.flags().flagsMask(),
126                                                               method);
127         builder.transform(method, transform);
128         return withMethod(builder);
129     }
130 
131     // internal / for use by elements
132 
133     ClassBuilder withField(WritableField field) {
134         if (fieldsCount >= fields.length) {
135             int newCapacity = fieldsCount + 8;
136             this.fields = Arrays.copyOf(fields, newCapacity);
137         }
138         fields[fieldsCount++] = field;
139         return this;
140     }
141 
142     ClassBuilder withMethod(Util.Writable method) {
143         if (methodsCount >= methods.length) {
144             int newCapacity = methodsCount + 8;
145             this.methods = Arrays.copyOf(methods, newCapacity);
146         }
147         methods[methodsCount++] = method;
148         return this;
149     }
150 
151     void setSuperclass(ClassEntry superclassEntry) {
152         this.superclassEntry = superclassEntry;
153     }
154 
155     void setInterfaces(List<ClassEntry> interfaces) {
156         this.interfaceEntries = interfaces;
157     }
158 
159     void setVersion(int major, int minor) {
160         this.majorVersion = major;
161         this.minorVersion = minor;
162     }
163 
164     void setFlags(int flags) {
165         this.flags = flags;
166     }
167 
168     public void setSizeHint(int sizeHint) {
169         this.sizeHint = sizeHint;
170     }
171 
172     public byte[] build() {
173 
174         // The logic of this is very carefully ordered.  We want to avoid
175         // repeated buffer copyings, so we accumulate lists of writers which
176         // all get written later into the same buffer.  But, writing can often
177         // trigger CP / BSM insertions, so we cannot run the CP writer or
178         // BSM writers until everything else is written.
179 
180         // Do this early because it might trigger CP activity
181         var constantPool = this.constantPool;
182         ClassEntry superclass = superclassEntry;
183         if (superclass != null)
184             superclass = AbstractPoolEntry.maybeClone(constantPool, superclass);
185         else if ((flags & ClassFile.ACC_MODULE) == 0 && !"java/lang/Object".equals(thisClassEntry.asInternalName()))
186             superclass = constantPool.classEntry(ConstantDescs.CD_Object);
187         int interfaceEntriesSize = interfaceEntries.size();
188         ClassEntry[] ies = interfaceEntriesSize == 0 ? EMPTY_CLASS_ENTRY_ARRAY : buildInterfaceEnties(interfaceEntriesSize);
189 
190         // We maintain two writers, and then we join them at the end
191         int size = sizeHint == 0 ? 256 : sizeHint;
192         BufWriterImpl head = new BufWriterImpl(constantPool, context, size);
193         BufWriterImpl tail = new BufWriterImpl(constantPool, context, size, thisClassEntry, majorVersion);
194 
195         // The tail consists of fields and methods, and attributes
196         // This should trigger all the CP/BSM mutation
197         Util.writeList(tail, fields, fieldsCount);
198         var strictInstanceFields = WritableField.filterStrictInstanceFields(constantPool, fields, fieldsCount);
199         tail.setStrictInstanceFields(strictInstanceFields);
200         Util.writeList(tail, methods, methodsCount);
201         int attributesOffset = tail.size();
202         attributes.writeTo(tail);
203 
204         // Now we have to append the BSM, if there is one
205         if (constantPool.writeBootstrapMethods(tail)) {
206             // Update attributes count
207             tail.patchU2(attributesOffset, attributes.size() + 1);
208         }
209 
210         // Now we can make the head
211         head.writeInt(ClassFile.MAGIC_NUMBER);
212         head.writeU2U2(minorVersion, majorVersion);
213         constantPool.writeTo(head);
214         head.writeU2U2U2(flags, head.cpIndex(thisClassEntry), head.cpIndexOrZero(superclass));
215         head.writeU2(interfaceEntriesSize);
216         for (int i = 0; i < interfaceEntriesSize; i++) {
217             head.writeIndex(ies[i]);
218         }
219 
220         // Join head and tail into an exact-size buffer
221         return BufWriterImpl.join(head, tail);
222     }
223 
224     private ClassEntry[] buildInterfaceEnties(int interfaceEntriesSize) {
225         var ies = new ClassEntry[interfaceEntriesSize];
226         for (int i = 0; i < interfaceEntriesSize; i++)
227             ies[i] = AbstractPoolEntry.maybeClone(constantPool, interfaceEntries.get(i));
228         return ies;
229     }
230 }