经常使用HTTP状态码和CURL 000问题

　　最近在测试CDN服务质量问题，测试过程当中返回了一些不一样的状态码，固然有一些经常使用的，也有一些不经常使用的。最奇葩的是在使用curl命令的时候出现000状态码，问了不少同事，对这个000的反应跟新事物是的。

生产环境常见的HTTP CODE

生产环境常见的HTTP状态码列表（List of HTTP status codes）为：

2XX成功：

• 200 - OK，服务器成功返回网页
  　　- Standard response for successful HTTP requests.

3XX重定向：

• 301 - Moved Permanently（永久跳转），请求的网页已永久跳转到新位置。
  　　- This and all future requests should be directed to the given.
• 302 - Moved Temporarily（临时跳转），请求的网页已临时跳转到新位置。

4XX客户端错误：

• 403 - Forbidden（禁止访问）,服务器拒绝请求
  　　- forbidden request (matches a deny filter) => HTTP 403
  　　- The request was a legal request, but the server is refusing to respond to it.
• 404 - Not Found,服务器找不到请求的页面。
  　　- The requested resource could not be found but may be available again in the future.

5XX服务器错误：

• 500 - Internal Server Error（内部服务器错误）
  　　- internal error in haproxy => HTTP 500
  　　- A generic error message, given when no more specific message is suitable.
• 502 - Bad Gateway（坏的网关）,通常是网关服务器请求后端服务时，后端服务没有按照http协议正确返回结果。
  　　- the server returned an invalid or incomplete response => HTTP 502
  　　- The server was acting as a gateway or proxy and received an invalid response from the upstream server.
• 503 - Service Unavailable（服务当前不可用）,可能由于超载或停机维护。
  　　 - no server was available to handle the request => HTTP 503
  　　- The server is currently unavailable (because it is overloaded or down for maintenance).
• 504 - Gateway Timeout（网关超时）,通常是网关服务器请求后端服务时，后端服务没有在特定的时间内完成服务。
  　　- the server failed to reply in time => HTTP 504
  　　- The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.

curl奇怪的返回值000

通过测试发如今curl的时候出现000的状况有以下几种：

• 1.Failed DNS resolution (6)

  $ curl -w "%{http_code}\n" http://example.invalid/ ; echo "Exit code: $?"
  000
  curl: (6) Could not resolve host: example.invalid
  Exit code: 6

• 2.Connection refused (7)

  $ curl -w "%{http_code}\n" http://localhost:81/ ; echo "Exit code: $?"
  000
  curl: (7) Failed to connect to localhost port 81: Connection refused
  Exit code: 7

• Connection timed out (28)

  $ curl -w "%{http_code}\n" -m 5 http://10.255.255.1/ ; echo "Exit code: $?"
  000
  curl: (28) Connection timed out after 5001 milliseconds
  Exit code: 28

• Server actually returns 000 for some reason (0)
  开启一个监听端口：

nc -l -p 65535 & <<EOF

HTTP/1.1 000 Fake Status Code

Content-Length: 0

Connection: close

EOF

客户端请求：

$ curl -w "%{http_code}\n" http://localhost:65535/ ; echo "Exit code: $?"
000
Exit code: 0

*注释：通常状况下遇到000，默认考虑为200，正常。

在测试过程当中打印了000时的错误信息，错误为：Connection timed out。使用curl时，参数：-sS ,而后将curl的错误 2>> /tmp/err.log。

参考文章：
wikipedia：https://en.wikipedia.org/wiki/List_of_HTTP_status_codes

http://superuser.com/questions/501690/curl-http-code-of-000