/*!

* https://github.com/leonardosnt/java-class-tools

*

* Copyright (C) 2017 leonardosnt

* Licensed under the MIT License. See LICENSE file in the project root for full license information.

*/

import ByteBuffer from 'bytebuffer';

import ConstantType from './constant-type';

/**

* All objects (structure) follow Jvm8 specification.

*

* @see https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html

*/

class JavaClassFileReader {

/**

* Read and parse class file contents.

*

* @param {(Uint8Array|Buffer|ArrayBuffer)} source - Class file contents.

* @return {ClassFile}

* @see {@link https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.1}

*/

read(source) {

if (source == undefined) {

throw TypeError('source cannot be null or undefined');

}

if (typeof source === 'string') {

return this.readFromFile(source);

}

this.buf = ByteBuffer.wrap(source);

this.classFile = new (function ClassFile(){});

// Read magic

if (this.buf.readUint32() !== 0xCAFEBABE) {

throw Error('Invalid MAGIC value');

}

this.classFile.minor_version = this.buf.readUint16();

this.classFile.major_version = this.buf.readUint16();

this.classFile.constant_pool_count = this.buf.readUint16();

this.classFile.constant_pool = this._readConstantPool(this.classFile.constant_pool_count - 1);

this.classFile.access_flags = this.buf.readUint16();

this.classFile.this_class = this.buf.readUint16();

this.classFile.super_class = this.buf.readUint16();

this.classFile.interfaces_count = this.buf.readUint16();

this.classFile.interfaces = this._readInterfaces(this.classFile.interfaces_count);

this.classFile.fields_count = this.buf.readUint16();

this.classFile.fields = this._readMemberInfoArray(this.classFile.fields_count);

this.classFile.methods_count = this.buf.readUint16();

this.classFile.methods = this._readMemberInfoArray(this.classFile.methods_count);

this.classFile.attributes_count = this.buf.readUint16();

this.classFile.attributes = this._readAttributeInfoArray(this.classFile.attributes_count);

const classFile = this.classFile;

// Dispose

delete this.buf;

delete this.classFile;

return classFile;

}

readFromFile(path) {

if (typeof process !== undefined) {

const fs = require('fs');

return this.read(fs.readFileSync(path));

} else {

throw Error('readFromFile is not supported in the browser.');

}

}

/**

* Read an array of field_info or method_info structures.

*

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.6

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.5

*/

_readMemberInfoArray(count) {

const members = new Array(count);

for (let i = 0; i < count; i++) {

const memberInfo = {

access_flags: this.buf.readUint16(),

name_index: this.buf.readUint16(),

descriptor_index: this.buf.readUint16(),

attributes_count: this.buf.readUint16()

};

memberInfo.attributes = this._readAttributeInfoArray(memberInfo.attributes_count);

members[i] = memberInfo;

}

return members;

}

_readAttributeInfoArray(attributes_count) {

const attributes = new Array(attributes_count);

for (let i = 0; i < attributes_count; i++) {

attributes[i] = this._readAttributeInfo();

}

return attributes;

}

/**

* Reads the "verification_type_info" structure.

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.4

*/

_readVerificationTypeInfo() {

const type_info = {

tag: this.buf.readUint8()

};

if (type_info.tag === 7) {

type_info.cpool_index = this.buf.readUint16();

} else if (type_info.tag === 8) {

type_info.offset = this.buf.readUint16();

}

return type_info;

}

/**

* Reads the "type_annotation" structure

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.20

*/

_readTypeAnnotation() {

const type_annotation = {

target_type: this.buf.readUint8(),

target_info: {}

};

// Reads the "target_info" union.

// https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.20-400

switch (type_annotation.target_type) {

// type_parameter_target

case 0x00: case 0x01:

type_annotation.target_info.type_parameter_index = this.buf.readUint8();

break;

// supertype_target

case 0x10:

type_annotation.target_info.supertype_index = this.buf.readUint16();

break;

// type_parameter_bound_target

case 0x11: case 0x12:

type_annotation.target_info.type_parameter_index = this.buf.readUint8();

type_annotation.target_info.bound_index = this.buf.readUint8();

break;

// empty_target

case 0x13: case 0x14: case 0x15:

// empty

break;

// formal_parameter_target

case 0x16:

type_annotation.target_info.formal_parameter_index = this.buf.readUint8();

break;

// throws_target

case 0x17:

type_annotation.target_info.throws_type_index = this.buf.readUint16();

break;

// localvar_target

case 0x40: case 0x41: {

type_annotation.target_info.table_length = this.buf.readUint16();

type_annotation.target_info.table = new Array(type_annotation.target_info.table_length);

for (let i = 0; i < type_annotation.target_info.table_length; i++) {

const table_entry = {

start_pc: this.buf.readUint16(),

length: this.buf.readUint16(),

index: this.buf.readUint16()

};

type_annotation.target_info.table[i] = table_entry;

}

break;

}

// catch_target

case 0x42:

type_annotation.target_info.exception_table_index = this.buf.readUint16();

break;

// offset_target

case 0x43: case 0x44: case 0x45: case 0x46:

type_annotation.target_info.offset = this.buf.readUint16();

break;

// type_argument_target

case 0x47: case 0x48: case 0x49: case 0x4A: case 0x4B:

type_annotation.target_info.offset = this.buf.readUint16();

type_annotation.target_info.type_argument_index = this.buf.readUint8();

break;

default:

throw Error(`Unexpected target_type: ${type_annotation.target_type}`);

}

// Reads "type_path" structure

type_annotation.type_path = { path_length: this.buf.readUint8() };

type_annotation.type_path.path = new Array(type_annotation.type_path.path_length);

for (let i = 0; i < type_annotation.type_path.path_length; i++) {

type_annotation.type_path.path[i] = {

type_path_kind: this.buf.readUint8(),

type_argument_index: this.buf.readUint8()

};

}

type_annotation.type_index = this.buf.readUint16();

type_annotation.num_element_value_pairs = this.buf.readUint16();

type_annotation.element_value_pairs = new Array(type_annotation.num_element_value_pairs);

for (let i = 0; i < type_annotation.num_element_value_pairs; i++) {

type_annotation.element_value_pairs[i] = {

element_name_index: this.buf.readUint16(),

element_value: this._readElementValue()

};

}

return type_annotation;

}

/**

* Reads the "attribute_info" structure

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7

*/

_readAttributeInfo() {

const attribute = {

attribute_name_index: this.buf.readUint16(),

attribute_length: this.buf.readUint32()

};

const attributeNameBytes = this.classFile.constant_pool[attribute.attribute_name_index].bytes;

const attributeName = String.fromCharCode.apply(null, attributeNameBytes);

switch (attributeName) {

case 'Deprecated':

case 'Synthetic':

break;

case 'RuntimeInvisibleAnnotations':

case 'RuntimeVisibleAnnotations': {

attribute.num_annotations = this.buf.readUint16();

attribute.annotations = new Array(attribute.num_annotations);

for (let i = 0; i < attribute.num_annotations; i++) {

attribute.annotations[i] = this._readAttributeAnnotation();

}

break;

}

case 'InnerClasses': {

attribute.number_of_classes = this.buf.readUint16();

attribute.classes = new Array(attribute.number_of_classes);

for (let i = 0; i < attribute.number_of_classes; i++) {

attribute.classes[i] = {

inner_class_info_index: this.buf.readUint16(),

outer_class_info_index: this.buf.readUint16(),

inner_name_index: this.buf.readUint16(),

inner_class_access_flags: this.buf.readUint16()

};

}

break;

}

case 'LocalVariableTable': {

attribute.local_variable_table_length = this.buf.readUint16();

attribute.local_variable_table = new Array(attribute.local_variable_table_length);

for (let i = 0; i < attribute.local_variable_table_length; i++) {

attribute.local_variable_table[i] = {

start_pc: this.buf.readUint16(),

length: this.buf.readUint16(),

name_index: this.buf.readUint16(),

descriptor_index: this.buf.readUint16(),

index: this.buf.readUint16()

};

}

break;

}

case 'LocalVariableTypeTable': {

attribute.local_variable_type_table_length = this.buf.readUint16();

attribute.local_variable_type_table = new Array(attribute.local_variable_type_table_length);

for (let i = 0; i < attribute.local_variable_type_table_length; i++) {

attribute.local_variable_type_table[i] = {

start_pc: this.buf.readUint16(),

length: this.buf.readUint16(),

name_index: this.buf.readUint16(),

signature_index: this.buf.readUint16(),

index: this.buf.readUint16(),

};

}

break;

}

case 'RuntimeInvisibleParameterAnnotations':

case 'RuntimeVisibleParameterAnnotations': {

attribute.num_parameters = this.buf.readUint8();

attribute.parameter_annotations = new Array(attribute.num_parameters);

for (let parameterIndex = 0; parameterIndex < attribute.num_parameters; parameterIndex++) {

const parameter_annotation = { num_annotations: this.buf.readUint16()};

parameter_annotation.annotations = new Array(parameter_annotation.num_annotations);

for (let annotationIndex = 0; annotationIndex < parameter_annotation.num_annotations; annotationIndex++) {

parameter_annotation.annotations[annotationIndex] = this._readAttributeAnnotation();

}

attribute.parameter_annotations[parameterIndex] = parameter_annotation;

}

break;

}

case 'BootstrapMethods': {

attribute.num_bootstrap_methods = this.buf.readUint16();

attribute.bootstrap_methods = new Array(attribute.num_bootstrap_methods);

for (let bootstrapMethodIndex = 0; bootstrapMethodIndex < attribute.num_bootstrap_methods; bootstrapMethodIndex++) {

const bootstrap_method = {

bootstrap_method_ref: this.buf.readUint16(),

num_bootstrap_arguments: this.buf.readUint16()

};

bootstrap_method.bootstrap_arguments = new Array(bootstrap_method.num_bootstrap_arguments);

for (let bootstrapArgumentIndex = 0; bootstrapArgumentIndex < bootstrap_method.num_bootstrap_arguments; bootstrapArgumentIndex++) {

bootstrap_method.bootstrap_arguments[bootstrapArgumentIndex] = this.buf.readUint16();

}

attribute.bootstrap_methods[bootstrapMethodIndex] = bootstrap_method;

}

break;

}

case 'RuntimeInvisibleTypeAnnotations':

case 'RuntimeVisibleTypeAnnotations': {

attribute.num_annotations = this.buf.readUint16();

attribute.annotations = new Array(attribute.num_annotations);

for (let i = 0; i < attribute.num_annotations; i++) {

attribute.annotations[i] = this._readTypeAnnotation();

}

break;

}

case 'SourceDebugExtension': {

attribute.debug_extension = new Array(attribute.attribute_length);

for (let i = 0; i < attribute.attribute_length; i++) {

attribute.debug_extension[i] = this.buf.readUint8();

}

break;

}

case 'SourceFile':

attribute.sourcefile_index = this.buf.readUint16();

break;

case 'EnclosingMethod':

attribute.class_index = this.buf.readUint16();

attribute.method_index = this.buf.readUint16();

break;

case 'AnnotationDefault':

attribute.default_value = this._readElementValue();

break;

case 'MethodParameters': {

attribute.parameters_count = this.buf.readUint8();

attribute.parameters = new Array(attribute.parameters_count);

for (let i = 0; i < attribute.parameters_count; i++) {

attribute.parameters[i] = {

name_index: this.buf.readUint16(),

access_flags: this.buf.readUint16()

};

}

break;

}

case 'ConstantValue':

attribute.constantvalue_index = this.buf.readUint16();

break;

case 'Signature':

attribute.signature_index = this.buf.readUint16();

break;

case 'StackMap': return this._readStackMapAttribute(attribute);

case 'Exceptions': return this._readExceptionsAttribute(attribute);

case 'StackMapTable': return this._readStackMapTableAttribute(attribute);

case 'Code': return this._readCodeAttribute(attribute);

case 'LineNumberTable': return this._readLineNumberTableAttribute(attribute);

case 'Module': return this._readModuleAttribute(attribute);

case 'ModulePackages': return this._readModulePackagesAttribute(attribute);

case 'ModuleMainClass':

attribute.main_class_index = this.buf.readUint16();

break;

case 'NestHost':

attribute.host_class_index = this.buf.readUint16();

break;

case 'NestMembers':

attribute.number_of_classes = this.buf.readUint16();

attribute.classes = new Array(attribute.number_of_classes);

for (let i = 0; i < attribute.number_of_classes; i++) {

attribute.classes[i] = this.buf.readUint16();

}

break;

// Unknown attributes

// See: https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.1

default: {

attribute.info = new Array(attribute.attribute_length);

for (let i = 0; i < attribute.attribute_length; i++) {

attribute.info[i] = this.buf.readUint8();

}

}

}

return attribute;

}

_readCodeAttribute(attribute) {

attribute.max_stack = this.buf.readUint16();

attribute.max_locals = this.buf.readUint16();

attribute.code_length = this.buf.readUint32();

attribute.code = new Array(attribute.code_length);

// Reads "code" array

for (let i = 0; i < attribute.code_length; i++) {

attribute.code[i] = this.buf.readUint8();

}

attribute.exception_table_length = this.buf.readUint16();

attribute.exception_table = new Array(attribute.exception_table_length);

// Reads exception_table

for (let i = 0; i < attribute.exception_table_length; i++) {

attribute.exception_table[i] = {

start_pc: this.buf.readUint16(),

end_pc: this.buf.readUint16(),

handler_pc: this.buf.readUint16(),

catch_type: this.buf.readUint16()

};

}

attribute.attributes_count = this.buf.readUint16();

attribute.attributes = this._readAttributeInfoArray(attribute.attributes_count);

return attribute;

}

_readLineNumberTableAttribute(attribute) {

attribute.line_number_table_length = this.buf.readUint16();

attribute.line_number_table = new Array(attribute.line_number_table_length);

for (let i = 0; i < attribute.line_number_table_length; i++) {

attribute.line_number_table[i] = {

start_pc: this.buf.readUint16(),

line_number: this.buf.readUint16()

};

}

return attribute;

}

// TODO: this function is being deoptimized one time... Check why

_readStackMapTableAttribute(attribute) {

attribute.number_of_entries = this.buf.readUint16();

attribute.entries = new Array(attribute.number_of_entries);

for (let entryIndex = 0; entryIndex < attribute.number_of_entries; entryIndex++) {

const stack_map_frame = {

frame_type: this.buf.readUint8()

};

// Shorthand

const frame_type = stack_map_frame.frame_type;

/**

* offset_delta's that are "constant" are omitted.

* E.g:

* The offset_delta for the "same_frame" is the value of the tag item (frame_type).

* The offset_delta for the "same_locals_1_stack_item_frame " is given by the formula frame_type - 64.

*

* See https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.4

* for more information.

*/

// SAME

if (frame_type >= 0 && frame_type <= 63) {

attribute.entries[entryIndex] = stack_map_frame;

continue;

}

// SAME_LOCALS_1_STACK_ITEM

if (frame_type >= 64 && frame_type <= 127) {

stack_map_frame.stack = [this._readVerificationTypeInfo()];

}

// SAME_LOCALS_1_STACK_ITEM_EXTENDED

else if (stack_map_frame.frame_type === 247) {

stack_map_frame.offset_delta = this.buf.readUint16();

stack_map_frame.stack = [this._readVerificationTypeInfo()];

}

// CHOP = 248-250, SAME_FRAME_EXTENDED = 251

else if (frame_type >= 248 && frame_type <= 251) {

stack_map_frame.offset_delta = this.buf.readUint16();

}

// APPEND

else if (frame_type >= 252 && frame_type <= 254) {

const numberOfLocals = frame_type - 251;

stack_map_frame.offset_delta = this.buf.readUint16();

stack_map_frame.locals = new Array(numberOfLocals);

for (let i = 0; i < numberOfLocals; i++) {

stack_map_frame.locals[i] = this._readVerificationTypeInfo();

}

}

// FULL_FRAME

else if (frame_type === 255) {

stack_map_frame.offset_delta = this.buf.readUint16();

stack_map_frame.number_of_locals = this.buf.readUint16();

stack_map_frame.locals = new Array(stack_map_frame.number_of_locals);

for (let i = 0; i < stack_map_frame.number_of_locals; i++) {

stack_map_frame.locals[i] = this._readVerificationTypeInfo();

}

stack_map_frame.number_of_stack_items = this.buf.readUint16();

stack_map_frame.stack = new Array(stack_map_frame.number_of_stack_items);

for (let i = 0; i < stack_map_frame.number_of_stack_items; i++) {

stack_map_frame.stack[i] = this._readVerificationTypeInfo();

}

}

attribute.entries[entryIndex] = stack_map_frame;

}

return attribute;

}

_readExceptionsAttribute(attribute) {

attribute.number_of_exceptions = this.buf.readUint16();

attribute.exception_index_table = new Array(attribute.number_of_exceptions);

for (let i = 0; i < attribute.number_of_exceptions; i++) {

attribute.exception_index_table[i] = this.buf.readUint16();

}

return attribute;

}

/**

* http://download.oracle.com/otndocs/jcp/7247-j2me_cldc-1.1-fr-spec-oth-JSpec/

*

* Appendix1-verifier.pdf at "2.1 Stack map format"

*

* "According to the CLDC specification, the sizes of some fields are not 16bit

* but 32bit if the code size is more than 64K or the number of the local variables

* is more than 64K. However, for the J2ME CLDC technology, they are always 16bit.

* The implementation of the StackMap class assumes they are 16bit." - javaassist

*/

_readStackMapAttribute(attribute) {

attribute.number_of_entries = this.buf.readUint16();

attribute.entries = new Array(attribute.number_of_entries);

for (let entryIndex = 0; entryIndex < attribute.number_of_entries; entryIndex++) {

const stack_map_frame = { offset: this.buf.readUint16() };

// Read locals

stack_map_frame.number_of_locals = this.buf.readUint16();

stack_map_frame.locals = new Array(stack_map_frame.number_of_locals);

for (let i = 0; i < stack_map_frame.number_of_locals; i++) {

stack_map_frame.locals[i] = this._readVerificationTypeInfo();

}

// Read stack

stack_map_frame.number_of_stack_items = this.buf.readUint16();

stack_map_frame.stack = new Array(stack_map_frame.number_of_stack_items);

for (let i = 0; i < stack_map_frame.number_of_stack_items; i++) {

stack_map_frame.stack[i] = this._readVerificationTypeInfo();

}

attribute.entries[entryIndex] = stack_map_frame;

}

return attribute;

}

_readModuleAttribute(attribute) {

attribute.module_name_index = this.buf.readUint16();

attribute.module_flags = this.buf.readUint16();

attribute.module_version_index = this.buf.readUint16();

attribute.requires_count = this.buf.readUint16();

attribute.requires = new Array(attribute.requires_count);

for (let i = 0; i < attribute.requires_count; i++) {

attribute.requires[i] = {

requires_index: this.buf.readUint16(),

requires_flags: this.buf.readUint16(),

requires_version_index: this.buf.readUint16()

};

}

attribute.exports_count = this.buf.readUint16();

attribute.exports = new Array(attribute.exports_count);

for (let exportIndex = 0; exportIndex < attribute.exports_count; exportIndex++) {

const exportEntry = {

exports_index: this.buf.readUint16(),

exports_flags: this.buf.readUint16(),

exports_to_count: this.buf.readUint16()

};

exportEntry.exports_to_index = new Array(exportEntry.exports_to_count);

for (let exportsToIndex = 0; exportsToIndex < exportEntry.exports_to_count; exportsToIndex++) {

exportEntry.exports_to_index[exportsToIndex] = this.buf.readUint16();

}

attribute.exports[exportIndex] = exportEntry;

}

attribute.opens_count = this.buf.readUint16();

attribute.opens = new Array(attribute.opens_count);

for (let openIndex = 0; openIndex < attribute.opens_count; openIndex++) {

const openEntry = {

opens_index: this.buf.readUint16(),

opens_flags: this.buf.readUint16(),

opens_to_count: this.buf.readUint16()

};

openEntry.opens_to_index = new Array(openEntry.opens_to_count);

for (let opensToIndex = 0; opensToIndex < openEntry.opens_to_count; opensToIndex++) {

openEntry.opens_to_index[opensToIndex] = this.buf.readUint16();

}

attribute.opens[openIndex] = openEntry;

}

attribute.uses_count = this.buf.readUint16();

attribute.uses_index = new Array(attribute.uses_count);;

for (let i = 0; i < attribute.uses_count; i++) {

attribute.uses_index[i] = this.buf.readUint16();

}

attribute.provides_count = this.buf.readUint16();

attribute.provides = new Array(attribute.provides_count);

for (let providesIndex = 0; providesIndex < attribute.provides_count; providesIndex++) {

const provideEntry = {

provides_index: this.buf.readUint16(),

provides_with_count: this.buf.readUint16()

};

provideEntry.provides_with_index = new Array(provideEntry.provides_with_count);

for (let providesWithIndex = 0; providesWithIndex < provideEntry.provides_with_count; providesWithIndex++) {

provideEntry.provides_with_index[providesWithIndex] = this.buf.readUint16();

}

attribute.provides[providesIndex] = provideEntry;

}

return attribute;

}

_readModulePackagesAttribute(attribute) {

attribute.package_count = this.buf.readUint16();

attribute.package_index = new Array(attribute.package_count);

for (let i = 0; i < attribute.package_count; i++) {

attribute.package_index[i] = this.buf.readUint16();

}

return attribute;

}

/**

* Reads the "annotation" structure

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.16

*/

_readAttributeAnnotation() {

const annotation = {

type_index: this.buf.readUint16(),

num_element_value_pairs: this.buf.readUint16()

};

annotation.element_value_pairs = new Array(annotation.num_element_value_pairs);

for (let i = 0; i < annotation.num_element_value_pairs; i++) {

annotation.element_value_pairs[i] = {

element_name_index: this.buf.readUint16(),

element_value: this._readElementValue()

};

}

return annotation;

}

/**

* Reads the "element_value" structure

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.16.1

*/

_readElementValue() {

const element_value = {

tag: this.buf.readUint8(),

value: {}

};

/**

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.16.1-130

*/

switch (element_value.tag) {

case 101: // e

element_value.value.enum_const_value = {

type_name_index: this.buf.readUint16(),

const_name_index: this.buf.readUint16()

};

break;

case 99: // c

element_value.value.class_info_index = this.buf.readUint16();

break;

case 91: { // [

const num_values = this.buf.readUint16();

const values = new Array(num_values);

for (let i = 0; i < num_values; i++) {

values[i] = this._readElementValue();

}

element_value.value.array_value = {

num_values,

values

};

break;

}

case 64: // @

element_value.value.annotation = this._readAttributeAnnotation();

break;

case 66: // B

case 67: // C

case 68: // D

case 70: // F

case 73: // I

case 74: // J

case 83: // S

case 90: // Z

case 115:// s

element_value.value.const_value_index = this.buf.readUint16();

break;

default:

throw Error(`Unexpected tag: ${element_value.tag}`);

}

return element_value;

}

_readInterfaces(interfaceCount) {

const interfaces = new Array(interfaceCount);

for (let i = 0; i < interfaceCount; i++) {

interfaces[i] = this.buf.readUint16();

}

return interfaces;

}

/**

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4

*/

_readConstantPool(poolCount) {

/**

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.1

* The constant_pool table is indexed from 1 to constant_pool_count-1.

*/

const pool = new Array(poolCount);

for (let i = 1; i <= poolCount; i++) {

const entry = this._readConstantPoolEntry();

pool[i] = entry;

/**

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.5

*

* All 8-byte constants take up two entries in the constant_pool table of the class file.

* If a CONSTANT_Long_info or CONSTANT_Double_info structure is the item in the constant_pool table at index n,

* then the next usable item in the pool is located at index n+2.

* The constant_pool index n+1 must be valid but is considered unusable.

*/

if (entry.tag === ConstantType.LONG || entry.tag === ConstantType.DOUBLE) {

pool[++i] = undefined;

}

}

return pool;

}

_readUtf8PoolEntry(tag) {

const length = this.buf.readUint16();

const bytes = new Array(length);

for (let i = 0; i < length; i++) {

bytes[i] = this.buf.readUint8();

}

return { tag, length, bytes };

}

_readConstantPoolEntry() {

const tag = this.buf.readUint8();

switch (tag) {

case ConstantType.UTF8:

return this._readUtf8PoolEntry(tag);

case ConstantType.INTEGER:

case ConstantType.FLOAT:

return { tag, bytes: this.buf.readUint32() };

case ConstantType.LONG:

case ConstantType.DOUBLE:

return { tag, high_bytes: this.buf.readUint32(), low_bytes: this.buf.readUint32() };

case ConstantType.PACKAGE:

case ConstantType.MODULE:

case ConstantType.CLASS:

return { tag, name_index: this.buf.readUint16() };

case ConstantType.STRING:

return { tag, string_index: this.buf.readUint16() };

/**

* Fields, methods, and interface methods are represented by similar structures

* https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.2

*/

case ConstantType.FIELDREF:

case ConstantType.METHODREF:

case ConstantType.INTERFACE_METHODREF:

return { tag, class_index: this.buf.readUint16(), name_and_type_index: this.buf.readUint16() };

case ConstantType.NAME_AND_TYPE:

return { tag, name_index: this.buf.readUint16(), descriptor_index: this.buf.readUint16() };

case ConstantType.METHOD_HANDLE:

return { tag, reference_kind: this.buf.readUint8(), reference_index: this.buf.readUint16() };

case ConstantType.METHOD_TYPE:

return { tag, descriptor_index: this.buf.readUint16() };

case ConstantType.DYNAMIC:

case ConstantType.INVOKE_DYNAMIC:

return { tag, bootstrap_method_attr_index: this.buf.readUint16(), name_and_type_index: this.buf.readUint16() };

default:

throw Error(`Unexpected tag: ${tag}`);

}

}

}

export default JavaClassFileReader;