根据http://golang.org/pkg/net/#Dialer：
type Dialer struct { // Timeout is the maximum amount of time a dial will wait for // a connect to complete. If Deadline is also set, it may fail // earlier. // // The default is no timeout. // // With or without a timeout, the operating system may impose // its own earlier timeout. For instance, TCP timeouts are // often around 3 minutes.因此，默认超时（不考虑操作系统施加的限制）为无。
可以使用设置超时
SetDeadline。
我认为默认的OSX超时可以通过进行检查
sysctl net.inet.tcp。
