#520 Susam Pal:Curl 计时


Here is a command I use often while measuring why an HTTP request is taking too long:

curl -L -w "time_namelookup: %{time_namelookup}
time_connect: %{time_connect}
time_appconnect: %{time_appconnect}
time_pretransfer: %{time_pretransfer}
time_redirect: %{time_redirect}
time_starttransfer: %{time_starttransfer}
time_total: %{time_total}
" https://example.com/

Here is the same command written as a one-liner, so that I can copy it easily from this page with a triple-click whenever I need it in future:

curl -L -w "time_namelookup: %{time_namelookup}\ntime_connect: %{time_connect}\ntime_appconnect: %{time_appconnect}\ntime_pretransfer: %{time_pretransfer}\ntime_redirect: %{time_redirect}\ntime_starttransfer: %{time_starttransfer}\ntime_total: %{time_total}\n" https://example.com/

Here is how the output of the above command typically looks:

$ curl -L -w "namelookup: %{time_namelookup}\nconnect: %{time_connect}\nappconnect: %{time_appconnect}\npretransfer: %{time_pretransfer}\nstarttransfer: %{time_starttransfer}\ntotal: %{time_total}\n" https://example.com/
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
time_namelookup: 0.001403
time_connect: 0.245464
time_appconnect: 0.757656
time_pretransfer: 0.757823
time_redirect: 0.000000
time_starttransfer: 0.982111
time_total: 0.982326

In the output above, I have omitted most of the HTML output and replaced the omitted part with ellipsis for the sake of brevity.

The list below provides a description of each number in the output above. This information is picked straight from the manual page of curl 7.20.0. Here are the details:

  • time_namelookup: The time, in seconds, it took from the start until the name resolving was completed.
  • time_connect: The time, in seconds, it took from the start until the TCP connect to the remote host (or proxy) was completed.
  • time_appconnect: The time, in seconds, it took from the start until the SSL/SSH/etc connect/handshake to the remote host was completed. (Added in 7.19.0)
  • time_pretransfer: The time, in seconds, it took from the start until the file transfer was just about to begin. This includes all pre-transfer commands and negotiations that are specific to the particular protocol(s) involved.
  • time_redirect: The time, in seconds, it took for all redirection steps include name lookup, connect, pretransfer and transfer before the final transaction was started. time_redirect shows the complete execution time for multiple redirections. (Added in 7.12.3)
  • time_starttransfer: The time, in seconds, it took from the start until the first byte was just about to be transferred. This includes time_pretransfer and also the time the server needed to calculate the result.
  • time_total: The total time, in seconds, that the full operation lasted. The time will be displayed with millisecond resolution.

An important thing worth noting here is that the difference in the numbers for time_appconnect and time_connect time tells us how much time is spent in SSL/TLS handshake. For a cleartext connection without SSL/TLS, this number is reported as zero. Here is an example output that demonstrates this:

$ curl -L -w "time_namelookup: %{time_namelookup}\ntime_connect: %{time_connect}\ntime_appconnect: %{time_appconnect}\ntime_pretransfer: %{time_pretransfer}\ntime_redirect: %{time_redirect}\ntime_starttransfer: %{time_starttransfer}\ntime_total: %{time_total}\n" http://example.com/
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
time_namelookup: 0.001507
time_connect: 0.247032
time_appconnect: 0.000000
time_pretransfer: 0.247122
time_redirect: 0.000000
time_starttransfer: 0.512645
time_total: 0.512853

Also note that time_redirect is zero in both outputs above. That is because no redirection occurs while visiting example.com. Here is another example that shows how the output looks when a redirection occurs:

$ curl -L -w "time_namelookup: %{time_namelookup}\ntime_connect: %{time_connect}\ntime_appconnect: %{time_appconnect}\ntime_pretransfer: %{time_pretransfer}\ntime_redirect: %{time_redirect}\ntime_starttransfer: %{time_starttransfer}\ntime_total: %{time_total}\n" https://susam.in/blog
time_namelookup: 0.001886
time_connect: 0.152445
time_appconnect: 0.465326
time_pretransfer: 0.465413
time_redirect: 0.614289
time_starttransfer: 0.763997
time_total: 0.765413

When faced with a potential latency issue in web services, this is often one of the first commands I run several times from multiple clients because the results form this command help to get a quick sense of the layer that might be responsible for the latency issue.

#519 转载:是谁拉黑了你的IP


邮件无法送达的原因有很多,例如 取消订阅、服务器不可达、地址格式错误或不存在、被判定为垃圾邮件、发信人/收信人被拒等等等等…今天,我们来聊一下 IP、域名被拒。

#518 UCloud UFile (US3) 文件分享


UFile 没有提供任何文件粒度的分享方式,只有一种方法: 使用公开存储空间。
PS: 七牛云也是一样。

存储空间(Bucket)类型为 public,相当于阿里云 OSS 的 public-read,整个 Bucket 中的所有文件都可以直接根据 URL 下载,不需要签名。

PS: 如果不希望文件被遍历下载,文件路径要加入随机字符串,或者 UUID,总之不能有规律。

#516 语言代码


作为开发,只要涉及多语言,都一定会接触到语言代码。在各种不通的技术、语言框架中,这些代码并没有非常统一,比如简体中文,我见过 zh, zh_CN, zh-Hans, chs, zh_chs 几种不同的表示。

#514 如何推送消息给手机



#509 元宇宙与人类的未来