最近在测试CDN服务质量问题，测试过程中返回了一些不同的状态码，当然有一些常用的，也有一些不常用的。最奇葩的是在使用curl命令的时候出现000状态码，问了很多同事，对这个000的反应跟新事物是的。

一、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（永久跳转），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）,一般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）,可能因为超载或停机维护。     　　- 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）,一般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.

二、curl奇怪的返回值000。

经过测试发现在curl的时候出现000的情况有如下几种：

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：一般情况下遇到000，默认考虑为200，正常。

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