wireshark抓包简单查看HTTP keep-alive原理
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HTTP keep-alive
要利用HTTP的keep-alive机制,需要服务器端和客户端同时支持,以下使用tomcat服务器(支持keep-alive),使用wireshark抓包测试几种客户端是否支持keep-alive
使用chrome浏览器作为客户端
- 往浏览器地址栏敲入
http://localhost:8080/user/object?name=ds&id=2&
,并刷新一次 - 抓包结果如下:
- 可以看到,浏览器和服务器先进行了三次握手,然后传数据,完成之后没有断开连接。接着刷新了页面之后,浏览器和服务器没重现进行三次握手连接,而是利用原来的连接传输数据。从下面的数据解析可以看到,浏览器传给服务器带
"Connection:keep-alive"
使用curl命令作为客户端
- 连续执行两次命令:
curl "http://localhost:8080/user/object?name=ds&id=2&"
- 抓包结果如下:
- 可以看到,curl客户端访问了两次服务器,但每次都是三次握手之后立即四次挥手。
- 加上keep-alive请求头,连续执行两次:
curl -H "Connection:keep-alive" "http://localhost:8080/user/object?name=ds&id=2&"
- 抓包结果一样:
- 加上浏览器一模一样的请求头,又执行两次:
curl -H "Host: localhost:8080" -H "Connection: keep-alive" -H "Upgrade-Insecure-Requests: 1" -H "User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36" -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8" -H "Accept-Encoding: gzip, deflate, sdch, br" -H "Accept-Language: zh-CN,zh;q=0.8,en;q=0.6" -H "AlexaToolbar-ALX_NS_PH: AlexaToolbar/alx-4.0" "http://localhost:8080/user/object?name=ds&id=2&"
,结果还是一样 - 总结:客户端利用keep-alive机制,不仅是加请求头keep-alive的问题,最重要的是客户端要支持。从抓包结果可以看到,每次请求完,curl客户端都是主动发送FIN包关闭连接。客户端想要支持keep-alive,客户端需要在完成请求之后,保持住连接的socket以便接下来的复用,而不是主动断开。
使用Java客户端HTTP client
Java代码如下:
package edu.kxw;import java.io.IOException;import org.apache.http.HttpEntity;import org.apache.http.HttpResponse;import org.apache.http.client.methods.HttpGet;import org.apache.http.impl.client.CloseableHttpClient;import org.apache.http.impl.client.HttpClientBuilder;import org.apache.http.util.EntityUtils;import org.junit.Test;/** * Created by kingsonwu on 17/5/18. */public class TestHttpKeepAliveClient { @Test public void testHeader() throws InterruptedException { String url = "http://localhost:8080/user/object?name=ds&id=2&"; //创建HttpClientBuilder HttpClientBuilder httpClientBuilder = HttpClientBuilder.create(); //HttpClient CloseableHttpClient closeableHttpClient = httpClientBuilder.build(); HttpGet httpGet = new HttpGet(url); httpGet.addHeader("Connection", "keep-alive"); try { //执行get请求 HttpResponse httpResponse = closeableHttpClient.execute(httpGet); //获取响应消息实体 HttpEntity entity = httpResponse.getEntity(); //响应状态 System.out.println("status:" + httpResponse.getStatusLine()); //判断响应实体是否为空 if (entity != null) { System.out.println("contentEncoding:" + entity.getContentEncoding()); String content = EntityUtils.toString(entity); System.out.println("response content:" + content); } Thread.sleep(5000); closeableHttpClient.execute(httpGet); } catch (IOException e) { e.printStackTrace(); } finally { try { //关闭流并释放资源 closeableHttpClient.close(); } catch (IOException e) { e.printStackTrace(); } } }}
抓包结果如下:
程序发请求时带上请求头keep-alive(不加也行), 并休眠5秒后重新发送请求,从抓包结果中看,复用了连接。
reference:
wireshark使用:http://blog.jobbole.com/70907/
,https://my.oschina.net/flashsword/blog/80037
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