tcpsock:connect方法，返回success但实际上连接故障，例如出现Connection Refused错误。
然而，后面尝试对cosocket对象的任何操作都将失败，并返回由失效连接操作所产生实际的错误状态消息。
这个问题是由于在Nginx的事件模型的局限性，似乎只影响Mac OS X系统。
English source:
The tcpsock:connect method may indicate success despite connection failures such as with Connection Refused errors.
However, later attempts to manipulate the cosocket object will fail and return the actual error status message generated by the failed connect operation.
This issue is due to limitations in the Nginx event model and only appears to affect Mac OS X.