net: fix /proc/net/igmp,igmp6 reading bug on linux

Fixes #2130.

R=rsc, dave
CC=golang-dev
https://golang.org/cl/4846044

src/pkg/net/interface_linux.go

@@ -190,10 +190,8 @@ func newAddr(attrs []syscall.NetlinkRouteAttr, family int) []Addr {
 // addresses for a specific interface.
 func interfaceMulticastAddrTable(ifindex int) ([]Addr, os.Error) {
 	var (
-		ifi    *Interface
-		err    os.Error
-		ifmat4 []Addr
-		ifmat6 []Addr
+		ifi *Interface
+		err os.Error
 	)
 
 	if ifindex > 0 {
@@ -203,20 +201,13 @@ func interfaceMulticastAddrTable(ifindex int) ([]Addr, os.Error) {
 		}
 	}
 
-	ifmat4, err = parseProcNetIGMP(ifi)
-	if err != nil {
-		return nil, err
-	}
-
-	ifmat6, err = parseProcNetIGMP6(ifi)
-	if err != nil {
-		return nil, err
-	}
+	ifmat4 := parseProcNetIGMP(ifi)
+	ifmat6 := parseProcNetIGMP6(ifi)
 
 	return append(ifmat4, ifmat6...), nil
 }
 
-func parseProcNetIGMP(ifi *Interface) ([]Addr, os.Error) {
+func parseProcNetIGMP(ifi *Interface) []Addr {
 	var (
 		ifmat []Addr
 		name  string
@@ -224,7 +215,7 @@ func parseProcNetIGMP(ifi *Interface) ([]Addr, os.Error) {
 
 	fd, err := open("/proc/net/igmp")
 	if err != nil {
-		return nil, err
+		return nil
 	}
 	defer fd.close()
 
@@ -244,15 +235,15 @@ func parseProcNetIGMP(ifi *Interface) ([]Addr, os.Error) {
 		}
 	}
 
-	return ifmat, nil
+	return ifmat
 }
 
-func parseProcNetIGMP6(ifi *Interface) ([]Addr, os.Error) {
+func parseProcNetIGMP6(ifi *Interface) []Addr {
 	var ifmat []Addr
 
 	fd, err := open("/proc/net/igmp6")
 	if err != nil {
-		return nil, err
+		return nil
 	}
 	defer fd.close()
 
@@ -267,5 +258,5 @@ func parseProcNetIGMP6(ifi *Interface) ([]Addr, os.Error) {
 		}
 	}
 
-	return ifmat, nil
+	return ifmat
 }