MultiMC5/java/constants.h

#pragma once
#include "errors.h"
#include <sstream>

namespace java
{
	class constant
	{
	public:
		enum type_t : uint8_t
		{
			j_hole = 0, // HACK: this is a hole in the array, because java is crazy
			j_string_data = 1,
			j_int = 3,
			j_float = 4,
			j_long = 5,
			j_double = 6,
			j_class = 7,
			j_string = 8,
			j_fieldref = 9,
			j_methodref = 10,
			j_interface_methodref = 11,
			j_nameandtype = 12
		} type;

		constant(util::membuffer & buf )
		{
			buf.read(type);
			// invalid constant type!
			if(type > j_nameandtype || type == (type_t)0 || type == (type_t)2)
				throw new classfile_exception();
			
			// load data depending on type
			switch(type)
			{
				case j_float:
				case j_int:
					buf.read_be(int_data); // same as float data really
					break;
				case j_double:
				case j_long:
					buf.read_be(long_data); // same as double
					break;
				case j_class:
					buf.read_be(ref_type.class_idx);
					break;
				case j_fieldref:
				case j_methodref:
				case j_interface_methodref:
					buf.read_be(ref_type.class_idx);
					buf.read_be(ref_type.name_and_type_idx);
					break;
				case j_string:
					buf.read_be(index);
					break;
				case j_string_data:
					// HACK HACK: for now, we call these UTF-8 and do no further processing.
					// Later, we should do some decoding. It's really modified UTF-8
					// * U+0000 is represented as 0xC0,0x80 invalid character
					// * any single zero byte ends the string
					// * characters above U+10000 are encoded like in CESU-8
					buf.read_jstr(str_data);
					break;
				case j_nameandtype:
					buf.read_be(name_and_type.name_index);
					buf.read_be(name_and_type.descriptor_index);
					break;
			}
		}

		constant(int fake)
		{
			type = j_hole;
		}

		std::string toString()
		{
			std::ostringstream ss;
			switch(type)
			{
				case j_hole:
					ss << "Fake legacy entry";
					break;
				case j_float:
					ss << "Float: " << float_data;
					break;
				case j_double:
					ss << "Double: " << double_data;
					break;
				case j_int:
					ss << "Int: " << int_data;
					break;
				case j_long:
					ss << "Long: " << long_data;
					break;
				case j_string_data:
					ss << "StrData: " << str_data;
					break;
				case j_string:
					ss << "Str: " << index;
					break;
				case j_fieldref:
					ss << "FieldRef: " << ref_type.class_idx << " " << ref_type.name_and_type_idx;
					break;
				case j_methodref:
					ss << "MethodRef: " << ref_type.class_idx << " " << ref_type.name_and_type_idx;
					break;
				case j_interface_methodref:
					ss << "IfMethodRef: " << ref_type.class_idx << " " << ref_type.name_and_type_idx;
					break;
				case j_class:
					ss << "Class: " << ref_type.class_idx;
					break;
				case j_nameandtype:
					ss << "NameAndType: " << name_and_type.name_index << " " << name_and_type.descriptor_index;
					break;
			}
			return ss.str();
		}

		std::string str_data; /** String data in 'modified utf-8'.*/
		// store everything here.
		union
		{
			int32_t int_data;
			int64_t long_data;
			float float_data;
			double double_data;
			uint16_t index;
			struct
			{
				/**
				 * Class reference:
				 *   an index within the constant pool to a UTF-8 string containing
				 *   the fully qualified class name (in internal format)
				 * Used for j_class, j_fieldref, j_methodref and j_interface_methodref
				 */
				uint16_t class_idx;
				// used for j_fieldref, j_methodref and j_interface_methodref
				uint16_t name_and_type_idx;
			} ref_type;
			struct
			{
				uint16_t name_index;
				uint16_t descriptor_index;
			} name_and_type;
		};
	};

	/**
	 * A helper class that represents the custom container used in Java class file for storage of constants
	 */
	class constant_pool
	{
	public:
		/**
		 * Create a pool of constants
		 */
		constant_pool(){}
		/**
		 * Load a java constant pool
		 */
		void load(util::membuffer & buf)
		{
			uint16_t length = 0;
			buf.read_be(length);
			length --;
			uint16_t index = 1;
			const constant * last_constant = nullptr;
			while(length)
			{
				const constant & cnst = constant(buf);
				constants.push_back(cnst);
				last_constant = &constants[constants.size() - 1];
				if(last_constant->type == constant::j_double || last_constant->type == constant::j_long)
				{
					// push in a fake constant to preserve indexing
					constants.push_back(constant(0));
					length-=2;
					index+=2;
				}
				else
				{
					length--;
					index++;
				}
			}
		}
		typedef std::vector<java::constant> container_type;
		/**
		 * Access constants based on jar file index numbers (index of the first element is 1)
		 */
		java::constant & operator[](std::size_t constant_index)
		{
			if(constant_index == 0 || constant_index > constants.size())
			{
				throw new classfile_exception();
			}
			return constants[constant_index - 1];
		};
		container_type::const_iterator begin() const
		{
			return constants.begin();
		};
		container_type::const_iterator end() const
		{
			return constants.end();
		}
	private:
		container_type constants;
	};
}