libnetwork/portmapper: PortMapper.MapRange: rename err-return

Prevent accidentally shadowing the error, which is used in a defer.
Also re-format the code to make it more clear we're not acting on
a locally-scoped "allocatedHostPort" variable.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libnetwork/portmapper/mapper.go

@@ -52,7 +52,7 @@ func (pm *PortMapper) Map(container net.Addr, hostIP net.IP, hostPort int, usePr
 }
 
 // MapRange maps the specified container transport address to the host's network address and transport port range
-func (pm *PortMapper) MapRange(container net.Addr, hostIP net.IP, hostPortStart, hostPortEnd int, useProxy bool) (host net.Addr, err error) {
+func (pm *PortMapper) MapRange(container net.Addr, hostIP net.IP, hostPortStart, hostPortEnd int, useProxy bool) (host net.Addr, retErr error) {
 	pm.lock.Lock()
 	defer pm.lock.Unlock()
 
@@ -65,7 +65,10 @@ func (pm *PortMapper) MapRange(container net.Addr, hostIP net.IP, hostPortStart,
 	switch t := container.(type) {
 	case *net.TCPAddr:
 		proto = "tcp"
-		if allocatedHostPort, err = pm.allocator.RequestPortInRange(hostIP, proto, hostPortStart, hostPortEnd); err != nil {
+
+		var err error
+		allocatedHostPort, err = pm.allocator.RequestPortInRange(hostIP, proto, hostPortStart, hostPortEnd)
+		if err != nil {
 			return nil, err
 		}
 
@@ -88,7 +91,10 @@ func (pm *PortMapper) MapRange(container net.Addr, hostIP net.IP, hostPortStart,
 		}
 	case *net.UDPAddr:
 		proto = "udp"
-		if allocatedHostPort, err = pm.allocator.RequestPortInRange(hostIP, proto, hostPortStart, hostPortEnd); err != nil {
+
+		var err error
+		allocatedHostPort, err = pm.allocator.RequestPortInRange(hostIP, proto, hostPortStart, hostPortEnd)
+		if err != nil {
 			return nil, err
 		}
 
@@ -111,7 +117,10 @@ func (pm *PortMapper) MapRange(container net.Addr, hostIP net.IP, hostPortStart,
 		}
 	case *sctp.SCTPAddr:
 		proto = "sctp"
-		if allocatedHostPort, err = pm.allocator.RequestPortInRange(hostIP, proto, hostPortStart, hostPortEnd); err != nil {
+
+		var err error
+		allocatedHostPort, err = pm.allocator.RequestPortInRange(hostIP, proto, hostPortStart, hostPortEnd)
+		if err != nil {
 			return nil, err
 		}
 
@@ -142,7 +151,7 @@ func (pm *PortMapper) MapRange(container net.Addr, hostIP net.IP, hostPortStart,
 
 	// release the allocated port on any further error during return.
 	defer func() {
-		if err != nil {
+		if retErr != nil {
 			pm.allocator.ReleasePort(hostIP, proto, allocatedHostPort)
 		}
 	}()