使用curl获取网络请求中各个环节的响应时间

在处理网站打开慢 case 时，可以使用 curl 命令分别获取各个环节的用时，从而定位问题。

参数含义

下面以访问百度为例说明。

[root@host ~]# curl -so /dev/null http://www.baidu.com -w 'time_connect: %{time_connect}\ntime_starttransfer: %{time_starttransfer}\ntime_total: %{time_total}\ntime_namelookup: %{time_namelookup}\n' 
time_connect: 0.010
time_starttransfer: 0.186
time_total: 0.186
time_namelookup: 0.002

各个指标含义：

time_connect

建连时间，包括DNS解析时间

time_starttransfer

从建立TCP连接，到WEB服务器返回第一个字节数据所用的时间，包括建连、包括DNS解析时间。

time_total

请求所用总时间。从client发出请求，到WEB服务器发送所有响应数据的时间

time_namelookup

DNS解析时间，从请求开始到DNS解析完毕所用时间

其他参数含义：

-s

静默输出

-o

将输出保留在文件中，这里为保存到/dev/null，即空设备，不占用磁盘空间。

实例分析

近日，公司有同事反馈通过代理访问外网特别慢，遂在代理服务器上直接访问外网，查看各个响应时间，发现 DNS 解析耗时较长。

访问百度

下载大文件

root@test:~$curl -ksvo /dev/null https://ys.louxiaohui.com/mysql-bin.000015 -w 'time_connect: %{time_connect}\ntime_starttransfer: %{time_starttransfer}\ntime_total: %{time_total}\ntime_namelookup: %{time_namelookup}\n' 
* Hostname was NOT found in DNS cache 
*   Trying 95.169.20.135... 
* Connected to ys.louxiaohui.com (95.169.20.135) port 443 (#0) 
* successfully set certificate verify locations: 
*   CAfile: none 
  CApath: /etc/ssl/certs 
* SSLv3, TLS handshake, Client hello (1): 
} [data not shown] 
* SSLv3, TLS handshake, Server hello (2): 
{ [data not shown] 
* SSLv3, TLS handshake, CERT (11): 
{ [data not shown] 
* SSLv3, TLS handshake, Server key exchange (12): 
{ [data not shown] 
* SSLv3, TLS handshake, Server finished (14): 
{ [data not shown] 
* SSLv3, TLS handshake, Client key exchange (16): 
} [data not shown] 
* SSLv3, TLS change cipher, Client hello (1): 
} [data not shown] 
* SSLv3, TLS handshake, Finished (20): 
} [data not shown] 
* SSLv3, TLS change cipher, Client hello (1): 
{ [data not shown] 
* SSLv3, TLS handshake, Finished (20): 
{ [data not shown] 
* SSL connection using ECDHE-RSA-AES128-GCM-SHA256 
* Server certificate: 
*        subject: CN=ys.louxiaohui.com 
*        start date: 2018-11-28 15:34:14 GMT 
*        expire date: 2019-02-26 15:34:14 GMT 
*        issuer: C=US; O=Let's Encrypt; CN=Let's Encrypt Authority X3 
*        SSL certificate verify ok. 
> GET /mysql-bin.000015 HTTP/1.1 
> User-Agent: curl/7.35.0 
> Host: ys.louxiaohui.com 
> Accept: */* 
>  
< HTTP/1.1 200 OK 
* Server nginx is not blacklisted 
< Server: nginx 
< Date: Thu, 20 Dec 2018 16:51:00 GMT 
< Content-Type: application/octet-stream 
< Content-Length: 57663862 
< Last-Modified: Thu, 20 Dec 2018 16:42:12 GMT 
< Connection: keep-alive 
< ETag: "5c1bc664-36fe176" 
< Strict-Transport-Security: max-age=15768000 
< Accept-Ranges: bytes 
<  
{ [data not shown] 
* Connection #0 to host ys.louxiaohui.com left intact 
time_connect: 4.670 
time_starttransfer: 5.154 
time_total: 10.213 
time_namelookup: 4.513