配置Nutch模拟浏览器以绕过反爬虫限制

原文链接：http://yangshangchuan.iteye.com/blog/2030741

当我们配置Nutch抓取 http://yangshangchuan.iteye.com 的时候，抓取的所有页面内容均为：您的访问请求被拒绝 ...... 这是最简单的反爬虫策略（该策略简单地读取HTTP请求头User-Agent的值来判断是人（浏览器）还是机器爬虫），我们只需要简单地配置Nutch来模拟浏览器（simulate web browser）就可以绕过这种限制。

在nutch-default.xml中有项配置是和User-Agent相关的：

1. <property>
2. <name>http.agent.description</name>
3. <value></value>
4. <description>Further description of our bot- this text is used in
5. the User-Agent header.  It appears in parenthesis after the agent name.
6. </description>
7. </property>
8. <property>
9. <name>http.agent.url</name>
10. <value></value>
11. <description>A URL to advertise in the User-Agent header.  This will
12. appear in parenthesis after the agent name. Custom dictates that this
13. should be a URL of a page explaining the purpose and behavior of this
14. crawler.
15. </description>
16. </property>
17. <property>
18. <name>http.agent.email</name>
19. <value></value>
20. <description>An email address to advertise in the HTTP 'From' request
21. header and User-Agent header. A good practice is to mangle this
22. address (e.g. 'info at example dot com') to avoid spamming.
23. </description>
24. </property>
25. <property>
26. <name>http.agent.name</name>
27. <value></value>
28. <description>HTTP 'User-Agent' request header. MUST NOT be empty -
29. please set this to a single word uniquely related to your organization.
30. NOTE: You should also check other related properties:
31. http.robots.agents
32. http.agent.description
33. http.agent.url
34. http.agent.email
35. http.agent.version
36. and set their values appropriately.
37. </description>
38. </property>
39. <property>
40. <name>http.agent.version</name>
41. <value>Nutch-1.7</value>
42. <description>A version string to advertise in the User-Agent
43. header.</description>
44. </property>

<property>
  <name>http.agent.description</name>
  <value></value>
  <description>Further description of our bot- this text is used in
  the User-Agent header.  It appears in parenthesis after the agent name.
  </description>
</property>
<property>
  <name>http.agent.url</name>
  <value></value>
  <description>A URL to advertise in the User-Agent header.  This will
   appear in parenthesis after the agent name. Custom dictates that this
   should be a URL of a page explaining the purpose and behavior of this
   crawler.
  </description>
</property>
<property>
  <name>http.agent.email</name>
  <value></value>
  <description>An email address to advertise in the HTTP 'From' request
   header and User-Agent header. A good practice is to mangle this
   address (e.g. 'info at example dot com') to avoid spamming.
  </description>
</property>
<property>
  <name>http.agent.name</name>
  <value></value>
  <description>HTTP 'User-Agent' request header. MUST NOT be empty -
  please set this to a single word uniquely related to your organization.
  NOTE: You should also check other related properties:
	http.robots.agents
	http.agent.description
	http.agent.url
	http.agent.email
	http.agent.version
  and set their values appropriately.
  </description>
</property>
<property>
  <name>http.agent.version</name>
  <value>Nutch-1.7</value>
  <description>A version string to advertise in the User-Agent
   header.</description>
</property>

在类nutch1.7/src/plugin/lib-http/src/java/org/apache/nutch/protocol/http/api/HttpBase.java中可以看到这项配置是如何构成User-Agent的：

1. this.userAgent = getAgentString( conf.get("http.agent.name"),
2. conf.get("http.agent.version"),
3. conf.get("http.agent.description"),
4. conf.get("http.agent.url"),
5. conf.get("http.agent.email") );

this.userAgent = getAgentString( conf.get("http.agent.name"),
        conf.get("http.agent.version"),
        conf.get("http.agent.description"),
        conf.get("http.agent.url"),
        conf.get("http.agent.email") );

1. private static String getAgentString(String agentName,
2. String agentVersion,
3. String agentDesc,
4. String agentURL,
5. String agentEmail) {
6. if ( (agentName == null) || (agentName.trim().length() == 0) ) {
7. // TODO : NUTCH-258
8. if (LOGGER.isErrorEnabled()) {
9. LOGGER.error("No User-Agent string set (http.agent.name)!");
10. }
11. }
12. StringBuffer buf= new StringBuffer();
13. buf.append(agentName);
14. if (agentVersion != null) {
15. buf.append("/");
16. buf.append(agentVersion);
17. }
18. if ( ((agentDesc != null) && (agentDesc.length() != 0))
19. || ((agentEmail != null) && (agentEmail.length() != 0))
20. || ((agentURL != null) && (agentURL.length() != 0)) ) {
21. buf.append(" (");
22. if ((agentDesc != null) && (agentDesc.length() != 0)) {
23. buf.append(agentDesc);
24. if ( (agentURL != null) || (agentEmail != null) )
25. buf.append("; ");
26. }
27. if ((agentURL != null) && (agentURL.length() != 0)) {
28. buf.append(agentURL);
29. if (agentEmail != null)
30. buf.append("; ");
31. }
32. if ((agentEmail != null) && (agentEmail.length() != 0))
33. buf.append(agentEmail);
34. buf.append(")");
35. }
36. return buf.toString();
37. }

  private static String getAgentString(String agentName,
                                       String agentVersion,
                                       String agentDesc,
                                       String agentURL,
                                       String agentEmail) {

    if ( (agentName == null) || (agentName.trim().length() == 0) ) {
      // TODO : NUTCH-258
      if (LOGGER.isErrorEnabled()) {
        LOGGER.error("No User-Agent string set (http.agent.name)!");
      }
    }

    StringBuffer buf= new StringBuffer();

    buf.append(agentName);
    if (agentVersion != null) {
      buf.append("/");
      buf.append(agentVersion);
    }
    if ( ((agentDesc != null) && (agentDesc.length() != 0))
    || ((agentEmail != null) && (agentEmail.length() != 0))
    || ((agentURL != null) && (agentURL.length() != 0)) ) {
      buf.append(" (");

      if ((agentDesc != null) && (agentDesc.length() != 0)) {
        buf.append(agentDesc);
        if ( (agentURL != null) || (agentEmail != null) )
          buf.append("; ");
      }

      if ((agentURL != null) && (agentURL.length() != 0)) {
        buf.append(agentURL);
        if (agentEmail != null)
          buf.append("; ");
      }

      if ((agentEmail != null) && (agentEmail.length() != 0))
        buf.append(agentEmail);

      buf.append(")");
    }
    return buf.toString();
  }

在类nutch1.7/src/plugin/protocol-http/src/java/org/apache/nutch/protocol/http/HttpResponse.java中使用User-Agent请求头，这里的http.getUserAgent()返回的userAgent就是HttpBase.java中的userAgent：

1. String userAgent = http.getUserAgent();
2. if ((userAgent == null) || (userAgent.length() == 0)) {
3. if (Http.LOG.isErrorEnabled()) { Http.LOG.error("User-agent is not set!"); }
4. } else {
5. reqStr.append("User-Agent: ");
6. reqStr.append(userAgent);
7. reqStr.append("\r\n");
8. }

String userAgent = http.getUserAgent();
if ((userAgent == null) || (userAgent.length() == 0)) {
	if (Http.LOG.isErrorEnabled()) { Http.LOG.error("User-agent is not set!"); }
} else {
	reqStr.append("User-Agent: ");
	reqStr.append(userAgent);
	reqStr.append("\r\n");
}

通过上面的分析可知：在nutch-site.xml中只需要增加如下几种配置之一便可以模拟一个特定的浏览器（Imitating a specific browser）：

1、模拟Firefox浏览器：

1. <property>
2. <name>http.agent.name</name>
3. <value>Mozilla/5.0 (Windows NT 6.1; WOW64; rv:27.0) Gecko</value>
4. </property>
5. <property>
6. <name>http.agent.version</name>
7. <value>20100101 Firefox/27.0</value>
8. </property>

<property>
	<name>http.agent.name</name>
	<value>Mozilla/5.0 (Windows NT 6.1; WOW64; rv:27.0) Gecko</value>
</property>
<property>
	<name>http.agent.version</name>
	<value>20100101 Firefox/27.0</value>
</property>

2、模拟IE浏览器：

1. <property>
2. <name>http.agent.name</name>
3. <value>Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident</value>
4. </property>
5. <property>
6. <name>http.agent.version</name>
7. <value>6.0)</value>
8. </property>

<property>
	<name>http.agent.name</name>
	<value>Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident</value>
</property>
<property>
	<name>http.agent.version</name>
	<value>6.0)</value>
</property>

3、模拟Chrome浏览器：

1. <property>
2. <name>http.agent.name</name>
3. <value>Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.117 Safari</value>
4. </property>
5. <property>
6. <name>http.agent.version</name>
7. <value>537.36</value>
8. </property>

<property>
	<name>http.agent.name</name>
	<value>Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.117 Safari</value>
</property>
<property>
	<name>http.agent.version</name>
	<value>537.36</value>
</property>

4、模拟Safari浏览器：

1. <property>
2. <name>http.agent.name</name>
3. <value>Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.57.2 (KHTML, like Gecko) Version/5.1.7 Safari</value>
4. </property>
5. <property>
6. <name>http.agent.version</name>
7. <value>534.57.2</value>
8. </property>

<property>
	<name>http.agent.name</name>
	<value>Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.57.2 (KHTML, like Gecko) Version/5.1.7 Safari</value>
</property>
<property>
	<name>http.agent.version</name>
	<value>534.57.2</value>
</property>

5、模拟Opera浏览器：

1. <property>
2. <name>http.agent.name</name>
3. <value>Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1700.102 Safari/537.36 OPR</value>
4. </property>
5. <property>
6. <name>http.agent.version</name>
7. <value>19.0.1326.59</value>
8. </property>

<property>
	<name>http.agent.name</name>
	<value>Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1700.102 Safari/537.36 OPR</value>
</property>
<property>
	<name>http.agent.version</name>
	<value>19.0.1326.59</value>
</property>

后记：查看User-Agent的方法：

1、http://www.useragentstring.com

2、http://whatsmyuseragent.com

3、http://www.enhanceie.com/ua.aspx

NUTCH/HADOOP视频教程