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/**
 * 对企业微信发送给企业后台的消息加解密示例代码.
 * 
 * @copyright Copyright (c) 1998-2014 Tencent Inc.
 */

// ------------------------------------------------------------------------

package com.qq.weixin.mp.aes;

import java.io.StringReader;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;

/**
 * XMLParse class
 *
 * 提供提取消息格式中的密文及生成回复消息格式的接口.
 */
class XMLParse {

	/**
	 * 提取出xml数据包中的加密消息
	 * @param xmltext 待提取的xml字符串
	 * @return 提取出的加密消息字符串
	 * @throws AesException 
	 */
	public static Object[] extract(String xmltext) throws AesException     {
		Object[] result = new Object[3];
		try {
			DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
			
			String FEATURE = null;
			// This is the PRIMARY defense. If DTDs (doctypes) are disallowed, almost all XML entity attacks are prevented
			// Xerces 2 only - http://xerces.apache.org/xerces2-j/features.html#disallow-doctype-decl
			FEATURE = "http://apache.org/xml/features/disallow-doctype-decl";
			dbf.setFeature(FEATURE, true);
			
			// If you can't completely disable DTDs, then at least do the following:
			// Xerces 1 - http://xerces.apache.org/xerces-j/features.html#external-general-entities
			// Xerces 2 - http://xerces.apache.org/xerces2-j/features.html#external-general-entities
			// JDK7+ - http://xml.org/sax/features/external-general-entities 
			FEATURE = "http://xml.org/sax/features/external-general-entities";
			dbf.setFeature(FEATURE, false);
			
			// Xerces 1 - http://xerces.apache.org/xerces-j/features.html#external-parameter-entities
			// Xerces 2 - http://xerces.apache.org/xerces2-j/features.html#external-parameter-entities
			// JDK7+ - http://xml.org/sax/features/external-parameter-entities 
			FEATURE = "http://xml.org/sax/features/external-parameter-entities";
			dbf.setFeature(FEATURE, false);
			
			// Disable external DTDs as well
			FEATURE = "http://apache.org/xml/features/nonvalidating/load-external-dtd";
			dbf.setFeature(FEATURE, false);
			
			// and these as well, per Timothy Morgan's 2014 paper: "XML Schema, DTD, and Entity Attacks"
			dbf.setXIncludeAware(false);
			dbf.setExpandEntityReferences(false);
			
			// And, per Timothy Morgan: "If for some reason support for inline DOCTYPEs are a requirement, then 
			// ensure the entity settings are disabled (as shown above) and beware that SSRF attacks
			// (http://cwe.mitre.org/data/definitions/918.html) and denial 
			// of service attacks (such as billion laughs or decompression bombs via "jar:") are a risk."
			
			// remaining parser logic
			DocumentBuilder db = dbf.newDocumentBuilder();
			StringReader sr = new StringReader(xmltext);
			InputSource is = new InputSource(sr);
			Document document = db.parse(is);

			Element root = document.getDocumentElement();
			NodeList nodelist1 = root.getElementsByTagName("Encrypt");
			result[0] = 0;
			result[1] = nodelist1.item(0).getTextContent();
			return result;
		} catch (Exception e) {
			e.printStackTrace();
			throw new AesException(AesException.ParseXmlError);
		}
	}

	/**
	 * 生成xml消息
	 * @param encrypt 加密后的消息密文
	 * @param signature 安全签名
	 * @param timestamp 时间戳
	 * @param nonce 随机字符串
	 * @return 生成的xml字符串
	 */
	public static String generate(String encrypt, String signature, String timestamp, String nonce) {

		String format = "\n" + "\n"
				+ "\n"
				+ "%3$s\n" + "\n" + "";
		return String.format(format, encrypt, signature, timestamp, nonce);

	}
}