What version of Go are you using (go version)?

1.7.1

What operating system and processor architecture are you using (go env)?

GOHOSTOS="darwin"
GOOS="darwin"
GOARCH="amd64"

What did you do?

https://play.golang.org/p/G_tVNv_Is7

What did you expect to see?

sample=val; Expires=Sat, 01 Jan 2000 10:04:02 GMT
sample=val; Expires=Sat, 01 Jan 1700 10:04:02 GMT

What did you see instead?

sample=val; Expires=Sat, 01 Jan 2000 10:04:02 GMT
sample=val

According to IETF RFC6265 section 5.2.1, the Expires attribute should be parsed as a cookie-date, as specified in section 5.1.1. The lower bound for the year field, as listed in section 5.1.1, should be 1601 inclusive ("Abort these steps and fail to parse the cookie-date if... the year-value is less than 1601"). However, go seems to use epoch as a lower bound, as can be found here: https://github.com/golang/go/blob/master/src/net/http/cookie.go#L171