net: return nil UDPAddr from ReadFromUDP

In cases where the socket operation has no underlying address,
golang.org/cl/291509 unintentionally changed ReadFromUDP from return a
nil *UDPAddr to a non-nil (but zero value) *UDPAddr.

This may break callers that assume "no address" is always addr == nil,
so change it back to remain nil.

Fixes #46238

Change-Id: I8531e8fa16b853ed7560088eabda0b9e3e53f5be
Reviewed-on: https://go-review.googlesource.com/c/go/+/320909
Trust: Michael Pratt <mpratt@google.com>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

diff --git a/src/net/udpsock_posix.go b/src/net/udpsock_posix.go
index fcfb9c004cd7dce406c99d17fef0cbd0239d913d..96fb373ce770ca91a8a8dc0eec2f1712ca381ed1 100644 (file)
--- a/src/net/udpsock_posix.go
+++ b/src/net/udpsock_posix.go
@@ -50,6 +50,9 @@ func (c *UDPConn) readFrom(b []byte, addr *UDPAddr) (int, *UDPAddr, error) {
                *addr = UDPAddr{IP: sa.Addr[0:], Port: sa.Port}
        case *syscall.SockaddrInet6:
                *addr = UDPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneCache.name(int(sa.ZoneId))}
+       default:
+               // No sockaddr, so don't return UDPAddr.
+               addr = nil
        }
        return n, addr, err
 }

diff --git a/src/net/udpsock_test.go b/src/net/udpsock_test.go
index b4000b5664d18271a4d1b9b9a089d2f900bafcab..0e8c3511c36e459258d617d7217b81d1b8ed6a3c 100644 (file)
--- a/src/net/udpsock_test.go
+++ b/src/net/udpsock_test.go
@@ -8,7 +8,9 @@
 package net
 
 import (
+       "errors"
        "internal/testenv"
+       "os"
        "reflect"
        "runtime"
        "testing"
@@ -446,6 +448,33 @@ func TestUDPReadSizeError(t *testing.T) {
        }
 }
 
+// TestUDPReadTimeout verifies that ReadFromUDP with timeout returns an error
+// without data or an address.
+func TestUDPReadTimeout(t *testing.T) {
+       la, err := ResolveUDPAddr("udp4", "127.0.0.1:0")
+       if err != nil {
+               t.Fatal(err)
+       }
+       c, err := ListenUDP("udp4", la)
+       if err != nil {
+               t.Fatal(err)
+       }
+       defer c.Close()
+
+       c.SetDeadline(time.Now())
+       b := make([]byte, 1)
+       n, addr, err := c.ReadFromUDP(b)
+       if !errors.Is(err, os.ErrDeadlineExceeded) {
+               t.Errorf("ReadFromUDP got err %v want os.ErrDeadlineExceeded", err)
+       }
+       if n != 0 {
+               t.Errorf("ReadFromUDP got n %d want 0", n)
+       }
+       if addr != nil {
+               t.Errorf("ReadFromUDP got addr %+#v want nil", addr)
+       }
+}
+
 func BenchmarkWriteToReadFromUDP(b *testing.B) {
        conn, err := ListenUDP("udp4", &UDPAddr{IP: IPv4(127, 0, 0, 1)})
        if err != nil {