wireshark抓包簡單檢視HTTP keep-alive原理
阿新 • • 發佈:2019-02-03
HTTP keep-alive
要利用HTTP的keep-alive機制,需要伺服器端和客戶端同時支援,以下使用tomcat伺服器(支援keep-alive),使用wireshark抓包測試幾種客戶端是否支援keep-alive
使用chrome瀏覽器作為客戶端
- 往瀏覽器位址列敲入
http://localhost:8080/user/object?name=ds&id=2&
,並重新整理一次 - 抓包結果如下:
- 可以看到,瀏覽器和伺服器先進行了三次握手,然後傳資料,完成之後沒有斷開連線。接著重新整理了頁面之後,瀏覽器和伺服器沒重現進行三次握手連線,而是利用原來的連線傳輸資料。從下面的資料解析可以看到,瀏覽器傳給伺服器帶
"Connection:keep-alive"
使用curl命令作為客戶端
- 連續執行兩次命令:
curl "http://localhost:8080/user/object?name=ds&id=2&"
- 抓包結果如下:
- 可以看到,curl客戶端訪問了兩次伺服器,但每次都是三次握手之後立即四次揮手。
- 加上keep-alive請求頭,連續執行兩次:
curl -H "Connection:keep-alive" "http://localhost:8080/user/object?name=ds&id=2&"
- 抓包結果一樣:
- 加上瀏覽器一模一樣的請求頭,又執行兩次:
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&"
- 總結:客戶端利用keep-alive機制,不僅是加請求頭keep-alive的問題,最重要的是客戶端要支援。從抓包結果可以看到,每次請求完,curl客戶端都是主動傳送FIN包關閉連線。客戶端想要支援keep-alive,客戶端需要在完成請求之後,保持住連線的socket以便接下來的複用,而不是主動斷開。
使用Java客戶端HTTP client
Java程式碼如下:
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&";
//建立HttpClientBuilder
HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
//HttpClient
CloseableHttpClient closeableHttpClient = httpClientBuilder.build();
HttpGet httpGet = new HttpGet(url);
httpGet.addHeader("Connection", "keep-alive");
try {
//執行get請求
HttpResponse httpResponse = closeableHttpClient.execute(httpGet);
//獲取響應訊息實體
HttpEntity entity = httpResponse.getEntity();
//響應狀態
System.out.println("status:" + httpResponse.getStatusLine());
//判斷響應實體是否為空
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 {
//關閉流並釋放資源
closeableHttpClient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
抓包結果如下:
程式發請求時帶上請求頭keep-alive(不加也行), 並休眠5秒後重新發送請求,從抓包結果中看,複用了連線。