使用curl进行网站测速

原文地址:https://www.lujun9972.win/blog/2021/06/08/使用curl进行网站测速/index.html

网站访问可以分为下面几个阶段：

DNS 域名解析
通过SSL协议交换密钥（HTTPS)
与服务端创建 TCP 访问连接
客户端发起请求
服务端收到请求并准备回应内容
服务端回复回应内容

当我们优化网站速度时通常要现确定哪个阶段是耗时大头。而令我感到惊奇的是，原来 curl 的 -w 选项可以让 curl 完成访问网站的操作后将各阶段的耗时情况（以及其他一些访问信息）输出到标准输出。

man curl 中关于 -w 选项的说明如下：

-w, --write-out <format>Make curl display information on stdout after a completed trans‐fer. The format is a string that may contain  plain  text  mixedwith  any  number of variables. The format can be specified as aliteral "string", or you can have curl read the  format  from  afile  with  "@filename" and to tell curl to read the format fromstdin you write "@-".The variables present in the output format will  be  substitutedby  the  value or text that curl thinks fit, as described below.All variables are specified as %{variable_name} and to output  anormal  % you just write them as %%. You can output a newline byusing \n, a carriage return with \r and a tab space with \t.NOTE: The %-symbol is a special symbol in the win32-environment,where  all  occurrences  of  %  must  be doubled when using thisoption.The variables available are:content_type   The Content-Type of the  requested  document,  ifthere was any.filename_effectiveThe  ultimate  filename  that curl writes out to.This is only meaningful if curl is told to  writeto  a  file  with  the  -O,  --remote-name or -o,--output option. It's most useful in  combinationwith  the -J, --remote-header-name option. (Addedin 7.26.0)ftp_entry_path The initial path curl ended up in when logging onto the remote FTP server. (Added in 7.15.4)http_code      The numerical response code that was found in thelast retrieved HTTP(S)  or  FTP(s)  transfer.  In7.18.2  the alias response_code was added to showthe same info.http_connect   The numerical code that was  found  in  the  lastresponse   (from  a  proxy)  to  a  curl  CONNECTrequest. (Added in 7.12.4)http_version   The  http  version  that  was  effectively  used.(Added in 7.50.0)local_ip       The  IP  address  of  the  local  end of the mostrecently done connection - can be either IPv4  orIPv6 (Added in 7.29.0)local_port     The  local  port number of the most recently doneconnection (Added in 7.29.0)num_connects   Number of new connects made in the recent  trans‐fer. (Added in 7.12.3)num_redirects  Number  of  redirects  that  were followed in therequest. (Added in 7.12.3)proxy_ssl_verify_resultThe result of the HTTPS proxy's SSL peer certifi‐cate verification that was requested. 0 means theverification was successful. (Added in 7.52.0)redirect_url   When an HTTP request was made without -L, --loca‐tion  to follow redirects (or when --max-redir ismet), this variable will show the  actual  URL  aredirect would have gone to. (Added in 7.18.2)remote_ip      The  remote  IP address of the most recently doneconnection - can be either IPv4 or IPv6 (Added in7.29.0)remote_port    The  remote port number of the most recently doneconnection (Added in 7.29.0)scheme         The URL scheme (sometimes called  protocol)  thatwas effectively used (Added in 7.52.0)size_download  The total amount of bytes that were downloaded.size_header    The total amount of bytes of the downloaded head‐ers.size_request   The total amount of bytes that were sent  in  theHTTP request.size_upload    The total amount of bytes that were uploaded.speed_download The average download speed that curl measured forthe complete download. Bytes per second.speed_upload   The average upload speed that curl  measured  forthe complete upload. Bytes per second.ssl_verify_resultThe  result of the SSL peer certificate verifica‐tion that was requested. 0 means the verificationwas successful. (Added in 7.19.0)time_appconnectThe  time,  in  seconds,  it  took from the startuntil the SSL/SSH/etc  connect/handshake  to  theremote host was completed. (Added in 7.19.0)time_connect   The  time,  in  seconds,  it  took from the startuntil the TCP connect  to  the  remote  host  (orproxy) was completed.time_namelookupThe  time,  in  seconds,  it  took from the startuntil the name resolving was completed.time_pretransferThe time, in seconds,  it  took  from  the  startuntil  the file transfer was just about to begin.This includes all pre-transfer commands and nego‐tiations that are specific to the particular pro‐tocol(s) involved.time_redirect  The time, in seconds, it took for all redirectionsteps including name lookup, connect, pretransferand transfer before  the  final  transaction  wasstarted.  time_redirect shows the complete execu‐tion time for multiple  redirections.  (Added  in7.12.3)time_starttransferThe  time,  in  seconds,  it  took from the startuntil the first byte was just about to be  trans‐ferred.  This  includes time_pretransfer and alsothe time  the  server  needed  to  calculate  theresult.time_total     The  total time, in seconds, that the full opera‐tion lasted.url_effective  The URL that was fetched last. This is most mean‐ingful  if  you've  told curl to follow location:headers.If this option is used several times, the last one will be used.

其中与时间相关的变量包括：

time_namelookup: DNS 解析时间，可以与 --resolve 选项配合寻找最快的DNS
time_connect: 与服务端创建好 TCP 连接的时间，严格来说是客户端回复 ACK 的时间。我们可以通过 time_connect - time_namelookup 来大致推断网络延时。
time_appconnect: 完成 SSL/TLS 设置的时间，此时客户端与服务端完成密钥交换，客户端准备发起请求
time_pretransfer: 服务端收到请求的时间
time_starttransfer: 服务端准备好回应内容的时间。
time_total: 完成整个请求的所有时间
time_redirect: 若请求经过多次重定向，那么这个包含直到最后一次请求开始所耗的时间。

下面这张从 cloudflare 偷来的例子可以很直观的看出每个变量的对应关系

curl -so /dev/null -w "dnslookup: %{time_namelookup} | connect: %{time_connect} | appconnect: %{time_appconnect} | pretransfer: %{time_pretransfer} | starttransfer: %{time_starttransfer} | total: %{time_total} | size: %{size_download}\n" https://www.zasag.mn

其中 -s 表示进入 silent 模式， -o /dev/null 表示不显示获取到的文件内容

结果为：

dnslookup: 1.510 | connect: 1.757 | appconnect: 2.256 | pretransfer: 2.259 | starttransfer: 2.506 | total: 3.001 | size: 53107

图示如下：

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