net: UDPConn.ReadFromUDP returns non-nil Addr for generic errors #46238
Description
What version of Go are you using (go version)?
tip
Does this issue reproduce with the latest release?
Not 1.16
What operating system and processor architecture are you using (go env)?
linux/amd64
What did you do?
https://play.golang.org/p/IGSlLDraksK
What did you expect to see?
On 1.16, I see:
n = 0, addr = (*net.UDPAddr)(nil), err = read udp 127.0.0.1:1234: i/o timeout
What did you see instead?
On tip, I see:
n = 0, addr = &net.UDPAddr{IP:net.IP(nil), Port:0, Zone:""}, err = read udp 127.0.0.1:1234: i/o timeout
i.e., ReadFromUDP no longer returns a nil Addr for generic (non-address-specific) errors.
This breaks an internal test which retries if it receives a non-nil Addr and error from ReadFromUDP. (I'm actually unsure if it is possible to get a valid address along with an error? If not, perhaps this test is just broken.)
Either way, this change was caused by http://golang.org/cl/291509, where the difference in behavior appears to be unintentional, so I think it should be fixed.
cc @FiloSottile