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// Copyright 2016 The Netstack Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package ports provides PortManager that manages allocating, reserving and releasing ports.
package ports
import (
"math"
"math/rand"
"sync"
"gvisor.googlesource.com/gvisor/pkg/tcpip"
)
const (
// firstEphemeral is the first ephemeral port.
firstEphemeral uint16 = 16000
anyIPAddress = tcpip.Address("")
)
type portDescriptor struct {
network tcpip.NetworkProtocolNumber
transport tcpip.TransportProtocolNumber
port uint16
}
// PortManager manages allocating, reserving and releasing ports.
type PortManager struct {
mu sync.RWMutex
allocatedPorts map[portDescriptor]bindAddresses
}
// bindAddresses is a set of IP addresses.
type bindAddresses map[tcpip.Address]struct{}
// isAvailable checks whether an IP address is available to bind to.
func (b bindAddresses) isAvailable(addr tcpip.Address) bool {
if addr == anyIPAddress {
return len(b) == 0
}
// If all addresses for this portDescriptor are already bound, no
// address is available.
if _, ok := b[anyIPAddress]; ok {
return false
}
if _, ok := b[addr]; ok {
return false
}
return true
}
// NewPortManager creates new PortManager.
func NewPortManager() *PortManager {
return &PortManager{allocatedPorts: make(map[portDescriptor]bindAddresses)}
}
// PickEphemeralPort randomly chooses a starting point and iterates over all
// possible ephemeral ports, allowing the caller to decide whether a given port
// is suitable for its needs, and stopping when a port is found or an error
// occurs.
func (s *PortManager) PickEphemeralPort(testPort func(p uint16) (bool, *tcpip.Error)) (port uint16, err *tcpip.Error) {
count := uint16(math.MaxUint16 - firstEphemeral + 1)
offset := uint16(rand.Int31n(int32(count)))
for i := uint16(0); i < count; i++ {
port = firstEphemeral + (offset+i)%count
ok, err := testPort(port)
if err != nil {
return 0, err
}
if ok {
return port, nil
}
}
return 0, tcpip.ErrNoPortAvailable
}
// ReservePort marks a port/IP combination as reserved so that it cannot be
// reserved by another endpoint. If port is zero, ReservePort will search for
// an unreserved ephemeral port and reserve it, returning its value in the
// "port" return value.
func (s *PortManager) ReservePort(network []tcpip.NetworkProtocolNumber, transport tcpip.TransportProtocolNumber, addr tcpip.Address, port uint16) (reservedPort uint16, err *tcpip.Error) {
s.mu.Lock()
defer s.mu.Unlock()
// If a port is specified, just try to reserve it for all network
// protocols.
if port != 0 {
if !s.reserveSpecificPort(network, transport, addr, port) {
return 0, tcpip.ErrPortInUse
}
return port, nil
}
// A port wasn't specified, so try to find one.
return s.PickEphemeralPort(func(p uint16) (bool, *tcpip.Error) {
return s.reserveSpecificPort(network, transport, addr, p), nil
})
}
// reserveSpecificPort tries to reserve the given port on all given protocols.
func (s *PortManager) reserveSpecificPort(network []tcpip.NetworkProtocolNumber, transport tcpip.TransportProtocolNumber, addr tcpip.Address, port uint16) bool {
// Check that the port is available on all network protocols.
desc := portDescriptor{0, transport, port}
for _, n := range network {
desc.network = n
if addrs, ok := s.allocatedPorts[desc]; ok {
if !addrs.isAvailable(addr) {
return false
}
}
}
// Reserve port on all network protocols.
for _, n := range network {
desc.network = n
m, ok := s.allocatedPorts[desc]
if !ok {
m = make(bindAddresses)
s.allocatedPorts[desc] = m
}
m[addr] = struct{}{}
}
return true
}
// ReleasePort releases the reservation on a port/IP combination so that it can
// be reserved by other endpoints.
func (s *PortManager) ReleasePort(network []tcpip.NetworkProtocolNumber, transport tcpip.TransportProtocolNumber, addr tcpip.Address, port uint16) {
s.mu.Lock()
defer s.mu.Unlock()
for _, n := range network {
desc := portDescriptor{n, transport, port}
m := s.allocatedPorts[desc]
delete(m, addr)
if len(m) == 0 {
delete(s.allocatedPorts, desc)
}
}
}
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