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25 
26 package jdk.nashorn.internal.runtime;
27 
28 import static jdk.nashorn.internal.codegen.Compiler.SCRIPTS_PACKAGE;
29 import static jdk.nashorn.internal.codegen.Compiler.binaryName;
30 import static jdk.nashorn.internal.codegen.CompilerConstants.JS_OBJECT_DUAL_FIELD_PREFIX;
31 import static jdk.nashorn.internal.codegen.CompilerConstants.JS_OBJECT_SINGLE_FIELD_PREFIX;
32 
33 import java.lang.module.ModuleDescriptor;
34 import java.lang.module.ModuleDescriptor.Modifier;
35 import java.security.ProtectionDomain;
36 import java.util.Set;
37 import jdk.nashorn.internal.codegen.ObjectClassGenerator;
38 
39 /**
40  * Responsible for on the fly construction of structure classes.
41  */
42 final class StructureLoader extends NashornLoader {
43     private static final String SINGLE_FIELD_PREFIX = binaryName(SCRIPTS_PACKAGE) + '.' + JS_OBJECT_SINGLE_FIELD_PREFIX.symbolName();
44     private static final String DUAL_FIELD_PREFIX   = binaryName(SCRIPTS_PACKAGE) + '.' + JS_OBJECT_DUAL_FIELD_PREFIX.symbolName();
45 
46     private final Module structuresModule;
47 
48     /**
49      * Constructor.
50      */
StructureLoader(final ClassLoader parent)51     StructureLoader(final ClassLoader parent) {
52         super(parent);
53 
54         // new structures module, it's exports, read edges
55         structuresModule = createModule("jdk.scripting.nashorn.structures");
56 
57         // specific exports from nashorn to the structures module
58         NASHORN_MODULE.addExports(SCRIPTS_PKG, structuresModule);
59         NASHORN_MODULE.addExports(RUNTIME_PKG, structuresModule);
60 
61         // nashorn has to read fields from classes of the new module
62         NASHORN_MODULE.addReads(structuresModule);
63     }
64 
createModule(final String moduleName)65     private Module createModule(final String moduleName) {
66         final ModuleDescriptor descriptor =
67             ModuleDescriptor.newModule(moduleName, Set.of(Modifier.SYNTHETIC))
68                             .requires(NASHORN_MODULE.getName())
69                             .packages(Set.of(SCRIPTS_PKG))
70                             .build();
71 
72         final Module mod = Context.createModuleTrusted(descriptor, this);
73         loadModuleManipulator();
74         return mod;
75     }
76 
77     /**
78      * Returns true if the class name represents a structure object with dual primitive/object fields.
79      * @param name a class name
80      * @return true if a dual field structure class
81      */
isDualFieldStructure(final String name)82     private static boolean isDualFieldStructure(final String name) {
83         return name.startsWith(DUAL_FIELD_PREFIX);
84     }
85 
86     /**
87      * Returns true if the class name represents a structure object with single object-only fields.
88      * @param name a class name
89      * @return true if a single field structure class
90      */
isSingleFieldStructure(final String name)91     static boolean isSingleFieldStructure(final String name) {
92         return name.startsWith(SINGLE_FIELD_PREFIX);
93     }
94 
95     /**
96      * Returns true if the class name represents a Nashorn structure object.
97      * @param name a class name
98      * @return true if a structure class
99      */
isStructureClass(final String name)100     static boolean isStructureClass(final String name) {
101         return isDualFieldStructure(name) || isSingleFieldStructure(name);
102     }
103 
getModule()104     Module getModule() {
105         return structuresModule;
106     }
107 
108     @Override
findClass(final String name)109     protected Class<?> findClass(final String name) throws ClassNotFoundException {
110         if (isDualFieldStructure(name)) {
111             return generateClass(name, name.substring(DUAL_FIELD_PREFIX.length()), true);
112         } else if (isSingleFieldStructure(name)) {
113             return generateClass(name, name.substring(SINGLE_FIELD_PREFIX.length()), false);
114         }
115         return super.findClass(name);
116     }
117 
118     /**
119      * Generate a layout class.
120      * @param name       Name of class.
121      * @param descriptor Layout descriptor.
122      * @return Generated class.
123      */
generateClass(final String name, final String descriptor, final boolean dualFields)124     private Class<?> generateClass(final String name, final String descriptor, final boolean dualFields) {
125         final Context context = Context.getContextTrusted();
126 
127         final byte[] code = new ObjectClassGenerator(context, dualFields).generate(descriptor);
128         return defineClass(name, code, 0, code.length, new ProtectionDomain(null, getPermissions(null)));
129     }
130 }
131