Port Allocator as a libnetwork package

DESCRIPTION:
  As part of bringing libnetwork bridge driver features
  in parity with docker/daemon/network/driver/bridge
  features (Issue #46), this commit addresses the
  bridge.RequestPort() API.

  Currenlty docker/api/server.go needs an hold of port
  allocator in order to reserve a transport port which
  will be used by the http server on the host machine,
  so that portallocator does not give out that port when
  queried by portmapper as part of network driver operations.

ISSUE:
  Current implementation in docker is server.go directly
  access portmapper and then portallocator from bridge pkg
  calling bridge.RequestPort(). This also forces that function
  to trigger portmapper initialization (in case bridge init()
  was not executed yet), while portmapper life cycle should
  only be controlled by bridge network driver.
  We cannot mantain this behavior with libnetwrok as this
  violates the modularization of networking code which
  libnetwork is bringing in.

FIX:
  Make portallocator a singleton, now both docker core and
  portmapper code can initialize it and get the only one instance
  (Change in docker core code will happen when docker code
  will migrate to use libnetwork), given it is being used for
  host specific needs.

NOTE:
  Long term fix is having multiple portallocator instances (so
  no more singleton) each capable to be in sync with OS regarding
  current port allocation.
  When this change comes, no change whould be required on portallocator'
  clients side, changes will be confined to portallocator package.

Signed-off-by: Alessandro Boch <aboch@docker.com>

libnetwork/drivers/bridge/bridge.go

@@ -23,17 +23,10 @@ const (
 )
 
 var (
-	once        sync.Once
 	ipAllocator *ipallocator.IPAllocator
 	portMapper  *portmapper.PortMapper
 )
 
-func initPortMapper() {
-	once.Do(func() {
-		portMapper = portmapper.New()
-	})
-}
-
 // Configuration info for the "simplebridge" driver.
 type Configuration struct {
 	BridgeName            string
@@ -70,7 +63,7 @@ type driver struct {
 
 func init() {
 	ipAllocator = ipallocator.New()
-	initPortMapper()
+	portMapper = portmapper.New()
 }
 
 // New provides a new instance of bridge driver instance

libnetwork/pkg/portallocator/portallocator.go

@@ -26,6 +26,9 @@ var (
 	// ErrUnknownProtocol is returned when an unknown protocol was specified
 	ErrUnknownProtocol = errors.New("unknown protocol")
 	defaultIP          = net.ParseIP("0.0.0.0")
+	once               sync.Once
+	instance           *PortAllocator
+	createInstance     = func() { instance = newInstance() }
 )
 
 // ErrPortAlreadyAllocated is the returned error information when a requested port is already being used
@@ -79,6 +82,16 @@ type (
 
 // New returns a new instance of PortAllocator
 func New() *PortAllocator {
+	// Port Allocator is a singleton
+	// Note: Long term solution will be each PortAllocator will have access to
+	// the OS so that it can have up to date view of the OS port allocation.
+	// When this happens singleton behavior will be removed. Clients do not
+	// need to worry about this, they will not see a change in behavior.
+	once.Do(createInstance)
+	return instance
+}
+
+func newInstance() *PortAllocator {
 	start, end, err := getDynamicPortRange()
 	if err != nil {
 		logrus.Warn(err)

libnetwork/pkg/portallocator/portallocator_test.go

@@ -5,8 +5,13 @@ import (
 	"testing"
 )
 
+func resetPortAllocator() {
+	instance = newInstance()
+}
+
 func TestRequestNewPort(t *testing.T) {
 	p := New()
+	defer resetPortAllocator()
 
 	port, err := p.RequestPort(defaultIP, "tcp", 0)
 	if err != nil {
@@ -20,11 +25,13 @@ func TestRequestNewPort(t *testing.T) {
 
 func TestRequestSpecificPort(t *testing.T) {
 	p := New()
+	defer resetPortAllocator()
 
 	port, err := p.RequestPort(defaultIP, "tcp", 5000)
 	if err != nil {
 		t.Fatal(err)
 	}
+
 	if port != 5000 {
 		t.Fatalf("Expected port 5000 got %d", port)
 	}
@@ -48,6 +55,7 @@ func TestReleasePort(t *testing.T) {
 
 func TestReuseReleasedPort(t *testing.T) {
 	p := New()
+	defer resetPortAllocator()
 
 	port, err := p.RequestPort(defaultIP, "tcp", 5000)
 	if err != nil {
@@ -69,6 +77,7 @@ func TestReuseReleasedPort(t *testing.T) {
 
 func TestReleaseUnreadledPort(t *testing.T) {
 	p := New()
+	defer resetPortAllocator()
 
 	port, err := p.RequestPort(defaultIP, "tcp", 5000)
 	if err != nil {
@@ -95,6 +104,7 @@ func TestUnknowProtocol(t *testing.T) {
 
 func TestAllocateAllPorts(t *testing.T) {
 	p := New()
+	defer resetPortAllocator()
 
 	for i := 0; i <= p.End-p.Begin; i++ {
 		port, err := p.RequestPort(defaultIP, "tcp", 0)
@@ -145,6 +155,7 @@ func TestAllocateAllPorts(t *testing.T) {
 
 func BenchmarkAllocatePorts(b *testing.B) {
 	p := New()
+	defer resetPortAllocator()
 
 	for i := 0; i < b.N; i++ {
 		for i := 0; i <= p.End-p.Begin; i++ {
@@ -163,6 +174,7 @@ func BenchmarkAllocatePorts(b *testing.B) {
 
 func TestPortAllocation(t *testing.T) {
 	p := New()
+	defer resetPortAllocator()
 
 	ip := net.ParseIP("192.168.0.1")
 	ip2 := net.ParseIP("192.168.0.2")
@@ -224,6 +236,7 @@ func TestPortAllocation(t *testing.T) {
 
 func TestNoDuplicateBPR(t *testing.T) {
 	p := New()
+	defer resetPortAllocator()
 
 	if port, err := p.RequestPort(defaultIP, "tcp", p.Begin); err != nil {
 		t.Fatal(err)

libnetwork/portmapper/mapper.go

@@ -8,7 +8,7 @@ import (
 
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/docker/pkg/iptables"
-	"github.com/docker/libnetwork/portallocator"
+	"github.com/docker/libnetwork/pkg/portallocator"
 )
 
 type mapping struct {