net: add Source field to OpError

Not only by network, transport-layer intermediaries but by
virtualization stuff in a node, it is hard to identify the root cause of
weird faults without information of packet flows after disaster
happened.

This change adds Source field to OpError to be able to represent a
5-tuple of internet transport protocols for helping dealing with
complicated systems.

Also clarifies the usage of Source and Addr fields.

Updates #4856.

Change-Id: I96a523fe391ed14406bfb21604c461d4aac2fa19
Reviewed-on: https://go-review.googlesource.com/9231
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 7 insertions, 28 deletions

diff --git a/src/net/error_test.go b/src/net/error_test.go
index 03c646c7c9..75b125d435 100644
--- a/src/net/error_test.go
+++ b/src/net/error_test.go
@@ -32,34 +32,13 @@ func (e *OpError) isValid() error {
 	if e.Net == "" {
 		return fmt.Errorf("OpError.Net is empty: %v", e)
 	}
-	switch addr := e.Addr.(type) {
-	case *TCPAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *UDPAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *IPAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *IPNet:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *UnixAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case *pipeAddr:
-		if addr == nil {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
-		}
-	case fileAddr:
-		if addr == "" {
-			return fmt.Errorf("OpError.Addr is empty: %v", e)
+	for _, addr := range []Addr{e.Source, e.Addr} {
+		if addr != nil {
+			switch addr.(type) {
+			case *TCPAddr, *UDPAddr, *IPAddr, *IPNet, *UnixAddr, *pipeAddr, fileAddr:
+			default:
+				return fmt.Errorf("OpError.Source or Addr is unknown type: %T, %v", addr, e)
+			}
 		}
 	}
 	if e.Err == nil {