lnd.xprv/brontide/listener.go

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package brontide
import (
"errors"
"fmt"
"io"
"net"
"time"
"github.com/btcsuite/btcd/btcec"
)
// defaultHandshakes is the maximum number of handshakes that can be done in
// parallel.
const defaultHandshakes = 1000
// Listener is an implementation of a net.Conn which executes an authenticated
// key exchange and message encryption protocol dubbed "Machine" after
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// initial connection acceptance. See the Machine struct for additional
// details w.r.t the handshake and encryption scheme used within the
// connection.
type Listener struct {
localStatic *btcec.PrivateKey
tcp *net.TCPListener
handshakeSema chan struct{}
conns chan maybeConn
quit chan struct{}
}
// A compile-time assertion to ensure that Conn meets the net.Listener interface.
var _ net.Listener = (*Listener)(nil)
// NewListener returns a new net.Listener which enforces the Brontide scheme
// during both initial connection establishment and data transfer.
func NewListener(localStatic *btcec.PrivateKey, listenAddr string) (*Listener,
error) {
addr, err := net.ResolveTCPAddr("tcp", listenAddr)
if err != nil {
return nil, err
}
l, err := net.ListenTCP("tcp", addr)
if err != nil {
return nil, err
}
brontideListener := &Listener{
localStatic: localStatic,
tcp: l,
handshakeSema: make(chan struct{}, defaultHandshakes),
conns: make(chan maybeConn),
quit: make(chan struct{}),
}
for i := 0; i < defaultHandshakes; i++ {
brontideListener.handshakeSema <- struct{}{}
}
go brontideListener.listen()
return brontideListener, nil
}
// listen accepts connection from the underlying tcp conn, then performs
// the brontinde handshake procedure asynchronously. A maximum of
// defaultHandshakes will be active at any given time.
//
// NOTE: This method must be run as a goroutine.
func (l *Listener) listen() {
for {
select {
case <-l.handshakeSema:
case <-l.quit:
return
}
conn, err := l.tcp.Accept()
if err != nil {
l.rejectConn(err)
l.handshakeSema <- struct{}{}
continue
}
go l.doHandshake(conn)
}
}
// rejectedConnErr is a helper function that prepends the remote address of the
// failed connection attempt to the original error message.
func rejectedConnErr(err error, remoteAddr string) error {
return fmt.Errorf("unable to accept connection from %v: %v", remoteAddr,
err)
}
// doHandshake asynchronously performs the brontide handshake, so that it does
// not block the main accept loop. This prevents peers that delay writing to the
// connection from block other connection attempts.
func (l *Listener) doHandshake(conn net.Conn) {
defer func() { l.handshakeSema <- struct{}{} }()
select {
case <-l.quit:
return
default:
}
remoteAddr := conn.RemoteAddr().String()
brontideConn := &Conn{
conn: conn,
noise: NewBrontideMachine(false, l.localStatic, nil),
}
// We'll ensure that we get ActOne from the remote peer in a timely
// manner. If they don't respond within 1s, then we'll kill the
// connection.
conn.SetReadDeadline(time.Now().Add(handshakeReadTimeout))
// Attempt to carry out the first act of the handshake protocol. If the
// connecting node doesn't know our long-term static public key, then
// this portion will fail with a non-nil error.
var actOne [ActOneSize]byte
if _, err := io.ReadFull(conn, actOne[:]); err != nil {
brontideConn.conn.Close()
l.rejectConn(rejectedConnErr(err, remoteAddr))
return
}
if err := brontideConn.noise.RecvActOne(actOne); err != nil {
brontideConn.conn.Close()
l.rejectConn(rejectedConnErr(err, remoteAddr))
return
}
// Next, progress the handshake processes by sending over our ephemeral
// key for the session along with an authenticating tag.
actTwo, err := brontideConn.noise.GenActTwo()
if err != nil {
brontideConn.conn.Close()
l.rejectConn(rejectedConnErr(err, remoteAddr))
return
}
if _, err := conn.Write(actTwo[:]); err != nil {
brontideConn.conn.Close()
l.rejectConn(rejectedConnErr(err, remoteAddr))
return
}
select {
case <-l.quit:
return
default:
}
// We'll ensure that we get ActTwo from the remote peer in a timely
// manner. If they don't respond within 1 second, then we'll kill the
// connection.
conn.SetReadDeadline(time.Now().Add(handshakeReadTimeout))
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// Finally, finish the handshake processes by reading and decrypting
// the connection peer's static public key. If this succeeds then both
// sides have mutually authenticated each other.
var actThree [ActThreeSize]byte
if _, err := io.ReadFull(conn, actThree[:]); err != nil {
brontideConn.conn.Close()
l.rejectConn(rejectedConnErr(err, remoteAddr))
return
}
if err := brontideConn.noise.RecvActThree(actThree); err != nil {
brontideConn.conn.Close()
l.rejectConn(rejectedConnErr(err, remoteAddr))
return
}
// We'll reset the deadline as it's no longer critical beyond the
// initial handshake.
conn.SetReadDeadline(time.Time{})
l.acceptConn(brontideConn)
}
// maybeConn holds either a brontide connection or an error returned from the
// handshake.
type maybeConn struct {
conn *Conn
err error
}
// acceptConn returns a connection that successfully performed a handshake.
func (l *Listener) acceptConn(conn *Conn) {
select {
case l.conns <- maybeConn{conn: conn}:
case <-l.quit:
}
}
// rejectConn returns any errors encountered during connection or handshake.
func (l *Listener) rejectConn(err error) {
select {
case l.conns <- maybeConn{err: err}:
case <-l.quit:
}
}
// Accept waits for and returns the next connection to the listener. All
// incoming connections are authenticated via the three act Brontide
// key-exchange scheme. This function will fail with a non-nil error in the
// case that either the handshake breaks down, or the remote peer doesn't know
// our static public key.
//
// Part of the net.Listener interface.
func (l *Listener) Accept() (net.Conn, error) {
select {
case result := <-l.conns:
return result.conn, result.err
case <-l.quit:
return nil, errors.New("brontide connection closed")
}
}
// Close closes the listener. Any blocked Accept operations will be unblocked
// and return errors.
//
// Part of the net.Listener interface.
func (l *Listener) Close() error {
select {
case <-l.quit:
default:
close(l.quit)
}
return l.tcp.Close()
}
// Addr returns the listener's network address.
//
// Part of the net.Listener interface.
func (l *Listener) Addr() net.Addr {
return l.tcp.Addr()
}