使用curl来检测url耗时.md
curl是一个很强大的工具，可以分析URL在各个阶段的耗时。使用方法如下：
# curl -L --output /dev/null --silent --show-error --write-out '\n\nnamelookup: %{time_namelookup}\nconnect: %{time_connect}\nsslhandshake: %{time_appconnect}\npretransfer: %{time_pretransfer}\nredirect: %{time_redirect}\nfirstbyte: %{time_starttransfer}\ntotal: %{time_total}\n\n\n' http://www.qyer.com -x 106.2.6.210:80
namelookup: 0.000
connect: 0.190
sslhandshake: 0.000
pretransfer: 0.190
redirect: 0.000
firstbyte: 0.564
total: 0.564现在很多网站都是用的HTTP，上面的方法用不了，可以使用curl新功能resolve(curl 7.21.3+)
# curl -L --output /dev/null --silent --show-error --write-out '\n\nnamelookup: %{time_namelookup}\nconnect: %{time_connect}\nsslhandshake: %{time_appconnect}\npretransfer: %{time_pretransfer}\nredirect: %{time_redirect}\nfirstbyte: %{time_starttransfer}\ntotal: %{time_total}\n\n\n' https://www.baidu.com/ --resolve "www.baidu.com:443:180.97.33.108"
namelookup: 0.023074
connect: 0.056913
sslhandshake: 0.379040
pretransfer: 0.379117
redirect: 0.000000
firstbyte: 0.415180
total: 0.415550
各个阶段耗时解释
namelookup - The time, in seconds, it took from the start until the name resolving was completed.
connect - The time, in seconds, it took from the start until the TCP connect to the remote host(or proxy) was completed.#
sslhandshake - 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)
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.
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.
firstbyte - The time, in seconds, it took from the start until the first byte was just about to be transferred. This includes time_pre-transfer and also the time the server needed to calculate the result.
total - The total time, in seconds, that the full operation lasted. The time will be displayed with millisecond resolution.
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