// Copyright (c) 2021 Tailscale Inc & 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 ipnlocal
import (
"context"
"errors"
"fmt"
"hash/crc32"
"html"
"io"
"net"
"net/http"
"strconv"
"inet.af/netaddr"
"tailscale.com/tailcfg"
)
var initListenConfig func(*net.ListenConfig, netaddr.IP) error
func peerAPIListen(ip netaddr.IP) (ln net.Listener, err error) {
var lc net.ListenConfig
if initListenConfig != nil {
// On iOS/macOS, this sets the lc.Control hook to
// setsockopt the interface index to bind to, to get
// out of the network sandbox.
if err := initListenConfig(&lc, ip); err != nil {
return nil, err
}
}
// Make a best effort to pick a deterministic port number for
// the ip The lower three bytes are the same for IPv4 and IPv6
// Tailscale addresses (at least currently), so we'll usually
// get the same port number on both address families for
// dev/debugging purposes, which is nice. But it's not so
// deterministic that people will bake this into clients.
// We try a few times just in case something's already
// listening on that port (on all interfaces, probably).
for try := uint8(0); try < 5; try++ {
a16 := ip.As16()
hashData := a16[len(a16)-3:]
hashData[0] += try
tryPort := (32 << 10) | uint16(crc32.ChecksumIEEE(hashData))
ln, err = lc.Listen(context.Background(), "tcp", net.JoinHostPort(ip.String(), strconv.Itoa(int(tryPort))))
if err == nil {
return ln, nil
}
}
// Fall back to random ephemeral port.
return lc.Listen(context.Background(), "tcp", net.JoinHostPort(ip.String(), "0"))
}
type peerAPIListener struct {
ln net.Listener
lb *LocalBackend
}
func (pln *peerAPIListener) serve() {
defer pln.ln.Close()
logf := pln.lb.logf
for {
c, err := pln.ln.Accept()
if errors.Is(err, net.ErrClosed) {
return
}
if err != nil {
logf("peerapi.Accept: %v", err)
return
}
ta, ok := c.RemoteAddr().(*net.TCPAddr)
if !ok {
c.Close()
logf("peerapi: unexpected RemoteAddr %#v", c.RemoteAddr())
continue
}
ipp, ok := netaddr.FromStdAddr(ta.IP, ta.Port, "")
if !ok {
logf("peerapi: bogus TCPAddr %#v", ta)
c.Close()
continue
}
peerNode, peerUser, ok := pln.lb.WhoIs(ipp)
if !ok {
logf("peerapi: unknown peer %v", ipp)
c.Close()
continue
}
pas := &peerAPIServer{
remoteAddr: ipp,
peerNode: peerNode,
peerUser: peerUser,
lb: pln.lb,
}
httpServer := &http.Server{
Handler: pas,
}
go httpServer.Serve(&oneConnListener{Listener: pln.ln, conn: c})
}
}
type oneConnListener struct {
net.Listener
conn net.Conn
}
func (l *oneConnListener) Accept() (c net.Conn, err error) {
c = l.conn
if c == nil {
err = io.EOF
return
}
err = nil
l.conn = nil
return
}
func (l *oneConnListener) Close() error { return nil }
type peerAPIServer struct {
remoteAddr netaddr.IPPort
peerNode *tailcfg.Node
peerUser tailcfg.UserProfile
lb *LocalBackend
}
func (s *peerAPIServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, `
Hello, %s (%v)
This is my Tailscale device. Your device is %v.
`, html.EscapeString(s.peerUser.DisplayName), s.remoteAddr.IP, html.EscapeString(s.peerNode.ComputedName))
}