syncthing/vendor/github.com/ccding/go-stun/stun/discover.go

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// Copyright 2013, Cong Ding. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Author: Cong Ding <dinggnu@gmail.com>
package stun
import (
"errors"
"net"
)
// Follow RFC 3489 and RFC 5389.
// Figure 2: Flow for type discovery process (from RFC 3489).
// +--------+
// | Test |
// | I |
// +--------+
// |
// |
// V
// /\ /\
// N / \ Y / \ Y +--------+
// UDP <-------/Resp\--------->/ IP \------------->| Test |
// Blocked \ ? / \Same/ | II |
// \ / \? / +--------+
// \/ \/ |
// | N |
// | V
// V /\
// +--------+ Sym. N / \
// | Test | UDP <---/Resp\
// | II | Firewall \ ? /
// +--------+ \ /
// | \/
// V |Y
// /\ /\ |
// Symmetric N / \ +--------+ N / \ V
// NAT <--- / IP \<-----| Test |<--- /Resp\ Open
// \Same/ | I | \ ? / Internet
// \? / +--------+ \ /
// \/ \/
// |Y |Y
// | |
// | V
// | Full
// | Cone
// V /\
// +--------+ / \ Y
// | Test |------>/Resp\---->Restricted
// | III | \ ? /
// +--------+ \ /
// \/
// |N
// | Port
// +------>Restricted
func (c *Client) discover(conn net.PacketConn, addr *net.UDPAddr) (NATType, *Host, error) {
// Perform test1 to check if it is under NAT.
c.logger.Debugln("Do Test1")
c.logger.Debugln("Send To:", addr)
resp, err := c.test1(conn, addr)
if err != nil {
return NATError, nil, err
}
c.logger.Debugln("Received:", resp)
if resp == nil {
return NATBlocked, nil, nil
}
// identical used to check if it is open Internet or not.
identical := resp.identical
// changedAddr is used to perform second time test1 and test3.
changedAddr := resp.changedAddr
// mappedAddr is used as the return value, its IP is used for tests
mappedAddr := resp.mappedAddr
// Make sure IP and port are not changed.
if resp.serverAddr.IP() != addr.IP.String() ||
resp.serverAddr.Port() != uint16(addr.Port) {
return NATError, mappedAddr, errors.New("Server error: response IP/port")
}
// changedAddr shall not be nil
if changedAddr == nil {
return NATError, mappedAddr, errors.New("Server error: no changed address.")
}
// Perform test2 to see if the client can receive packet sent from
// another IP and port.
c.logger.Debugln("Do Test2")
c.logger.Debugln("Send To:", addr)
resp, err = c.test2(conn, addr)
if err != nil {
return NATError, mappedAddr, err
}
c.logger.Debugln("Received:", resp)
// Make sure IP and port are changed.
if resp != nil &&
(resp.serverAddr.IP() == addr.IP.String() ||
resp.serverAddr.Port() == uint16(addr.Port)) {
return NATError, mappedAddr, errors.New("Server error: response IP/port")
}
if identical {
if resp == nil {
return NATSymetricUDPFirewall, mappedAddr, nil
}
return NATNone, mappedAddr, nil
}
if resp != nil {
return NATFull, mappedAddr, nil
}
// Perform test1 to another IP and port to see if the NAT use the same
// external IP.
c.logger.Debugln("Do Test1")
c.logger.Debugln("Send To:", changedAddr)
caddr, err := net.ResolveUDPAddr("udp", changedAddr.String())
resp, err = c.test1(conn, caddr)
if err != nil {
return NATError, mappedAddr, err
}
c.logger.Debugln("Received:", resp)
if resp == nil {
// It should be NAT_BLOCKED, but will be detected in the first
// step. So this will never happen.
return NATUnknown, mappedAddr, nil
}
// Make sure IP/port is not changed.
if resp.serverAddr.IP() != caddr.IP.String() ||
resp.serverAddr.Port() != uint16(caddr.Port) {
return NATError, mappedAddr, errors.New("Server error: response IP/port")
}
if mappedAddr.IP() == resp.mappedAddr.IP() && mappedAddr.Port() == resp.mappedAddr.Port() {
// Perform test3 to see if the client can receive packet sent
// from another port.
c.logger.Debugln("Do Test3")
c.logger.Debugln("Send To:", caddr)
resp, err = c.test3(conn, caddr)
if err != nil {
return NATError, mappedAddr, err
}
c.logger.Debugln("Received:", resp)
if resp == nil {
return NATPortRestricted, mappedAddr, nil
}
// Make sure IP is not changed, and port is changed.
if resp.serverAddr.IP() != caddr.IP.String() ||
resp.serverAddr.Port() == uint16(caddr.Port) {
return NATError, mappedAddr, errors.New("Server error: response IP/port")
}
return NATRestricted, mappedAddr, nil
}
return NATSymetric, mappedAddr, nil
}