使用 curl 命令分析请求的耗时情况

最近工作中遇到一个问题,某个请求的响应特别慢,因此我就希望有一种方法能够分析到底请求的哪一步耗时比较长,好进一步找到问题的原因。

在网络上搜索了一下,发现了一个非常好用的方法, curl 命令就能帮助分析请求的各个部分耗时情况。

curl 参数

curl 命令提供了 -w 参数,这个参数在 manpage 是这样解释的:

  -w, --write-out               Make curl display information on stdout after a completed transfer. The format is a string that may contain plain text mixed with any number of variables. The  format              can  be  specified  as  a literal "string", or you can have curl read the format from a file with "@filename" and to tell curl to read the format from stdin you write              "@-".              The variables present in the output format will be substituted by the value or text that curl thinks fit, as described below. All variables are specified  as  %{vari‐              able_name} and to output a normal % you just write them as %%. You can output a newline by using \n, a carriage return with \r and a tab space with \t.

它能够按照指定的格式打印某些信息,里面可以使用某些特定的变量,而且支持 \n、\t 和 \r 转义字符。提供的变量很多,比如 status_code、local_port、size_download 等等,这篇文章我们只关注和请求时间有关的变量(以 time_ 开头的变量)。

试用

  $ curl -o /dev/null -s -w "time_connect: %{time_connect}\ntime_starttransfer: %{time_starttransfer}\ntime_nslookup:%{time_namelookup}\ntime_total: %{time_total}\n" "https://www.baidu.com"time_connect: 0.009time_starttransfer: 0.065time_nslookup:0.007time_total: 0.065

步骤

先往文本文件 curl.txt 写入下面的内容:

     time_namelookup:  %{time_namelookup}\n      time_connect:  %{time_connect}\n   time_appconnect:  %{time_appconnect}\n     time_redirect:  %{time_redirect}\n  time_pretransfer:  %{time_pretransfer}\ntime_starttransfer:  %{time_starttransfer}\n                   ----------\n        time_total:  %{time_total}\n

每个变量的解释如下:

  time_namelookup:DNS 域名解析的时候,就是把 https://baidu.com 转换成 ip 地址的过程time_connect:TCP 连接建立的时间,就是三次握手的时间time_appconnect:SSL/SSH 等上层协议建立连接的时间,比如 connect/handshake 的时间time_redirect:从开始到最后一个请求事务的时间time_pretransfer:从请求开始到响应开始传输的时间time_starttransfer:从请求开始到第一个字节将要传输的时间time_total:这次请求花费的全部时间

示例

例子:

  $ curl -w "@curl.txt" -o /dev/null -s -L  'http://www.baidu.com'time_namelookup:  0.004       time_connect:  0.015    time_appconnect:  0.000      time_redirect:  0.000   time_pretransfer:  0.015 time_starttransfer:  0.027                    ----------         time_total:  0.027

可以看到这次请求各个步骤的时间都打印出来了,每个数字的单位都是秒(seconds),这样可以分析哪一步比较耗时,方便定位问题。这个命令各个参数的意义:

  -w:从文件中读取要打印信息的格式-o /dev/null:把响应的内容丢弃,因为我们这里并不关心它,只关心请求的耗时情况-s:不要打印进度条从这个输出,我们可以算出各个步骤的时间:DNS 查询:4msTCP 连接时间:pretransfter(15) - namelookup(4) = 11ms服务器处理时间:starttransfter(27) - pretransfer(15) = 12ms内容传输时间:total(27) - starttransfer(27) = 0ms

-w 参数详解

以下是 - w 参数对应的一些变量以及对应的解释:

  • url_effective 最终获取的 url 地址,尤其是当你指定给 curl 的地址存在 301 跳转,且通过 - L 继续追踪的情形。
  • http_code http 状态码,如 200 成功,301 转向,404 未找到,500 服务器错误等。(The numerical response code that was found in the last retrieved HTTP (S) or FTP (s) transfer. In 7.18.2 the alias response_code was added to show the same info.)
  • http_connect The numerical code that was found in the last response (from a proxy) to a curl CONNECT request. (Added in 7.12.4)
  • time_total 总时间,按秒计。精确到小数点后三位。 (The total time, in seconds, that the full operation lasted. The time will be displayed with millisecond resolution.)
  • time_namelookup DNS 解析时间,从请求开始到 DNS 解析完毕所用时间。(The time, in seconds, it took from the start until the name resolving was completed.)
  • time_connect 连接时间,从开始到建立 TCP 连接完成所用时间,包括前边 DNS 解析时间,如果需要单纯的得到连接时间,用这个 time_connect 时间减去前边 time_namelookup 时间。以下同理,不再赘述。(The time, in seconds, it took from the start until the TCP connect to the remote host (or proxy) was completed.)
  • time_appconnect 连接建立完成时间,如 SSL/SSH 等建立连接或者完成三次握手时间。(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 从开始到准备传输的时间。(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 重定向时间,包括到最后一次传输前的几次重定向的 DNS 解析,连接,预传输,传输时间。(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 开始传输时间。在发出请求之后,Web 服务器返回数据的第一个字节所用的时间 (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.)
  • size_download 下载大小。(The total amount of bytes that were downloaded.)
  • size_upload 上传大小。(The total amount of bytes that were uploaded.)
    size_header 下载的 header 的大小 (The total amount of bytes of the downloaded headers.)
  • size_request 请求的大小。(The total amount of bytes that were sent in the HTTP request.)
  • speed_download 下载速度,单位 - 字节每秒。(The average download speed that curl measured for the complete download. Bytes per second.)
  • speed_upload 上传速度,单位 - 字节每秒。(The average upload speed that curl measured for the complete upload. Bytes per second.)
  • content_type 就是 content-Type,不用多说了,这是一个访问我博客首页返回的结果示例 (text/html; charset=UTF-8);(The Content-Type of the requested document, if there was any.)
  • num_connects 最近的的一次传输中创建的连接数目。Number of new connects made in the recent transfer. (Added in 7.12.3)
  • num_redirects 在请求中跳转的次数。Number of redirects that were followed in the request. (Added in 7.12.3)
    redirect_url When a HTTP request was made without -L to follow redirects, this variable will show the actual URL a redirect would take you to. (Added in 7.18.2)
  • ftp_entry_path 当连接到远程的 ftp 服务器时的初始路径。The initial path libcurl ended up in when logging on to the remote FTP server. (Added in 7.15.4)
  • ssl_verify_result ssl 认证结果,返回 0 表示认证成功。(The result of the SSL peer certificate verification that was requested. 0 means the verification was successful. (Added in 7.19.0))

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