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package snowflake_proxy
import (
"context"
"errors"
"fmt"
"io"
"log"
"net"
"regexp"
"sync"
"time"
"github.com/pion/ice/v2"
"github.com/pion/sdp/v3"
"github.com/pion/webrtc/v3"
)
const maxBufferedAmount uint64 = 512 * 1024 // 512 KB
var remoteIPPatterns = []*regexp.Regexp{
/* IPv4 */
regexp.MustCompile(`(?m)^c=IN IP4 ([\d.]+)(?:(?:\/\d+)?\/\d+)?(:? |\r?\n)`),
/* IPv6 */
regexp.MustCompile(`(?m)^c=IN IP6 ([0-9A-Fa-f:.]+)(?:\/\d+)?(:? |\r?\n)`),
}
type webRTCConn struct {
dc *webrtc.DataChannel
pc *webrtc.PeerConnection
pr *io.PipeReader
lock sync.Mutex // Synchronization for DataChannel destruction
once sync.Once // Synchronization for PeerConnection destruction
isClosing bool
inactivityTimeout time.Duration
activity chan struct{}
sendMoreCh chan struct{}
cancelTimeoutLoop context.CancelFunc
bytesLogger bytesLogger
}
func newWebRTCConn(pc *webrtc.PeerConnection, dc *webrtc.DataChannel, pr *io.PipeReader, bytesLogger bytesLogger) *webRTCConn {
conn := &webRTCConn{pc: pc, dc: dc, pr: pr, bytesLogger: bytesLogger}
conn.isClosing = false
conn.activity = make(chan struct{}, 100)
conn.sendMoreCh = make(chan struct{}, 1)
conn.inactivityTimeout = 30 * time.Second
ctx, cancel := context.WithCancel(context.Background())
conn.cancelTimeoutLoop = cancel
go conn.timeoutLoop(ctx)
return conn
}
func (c *webRTCConn) timeoutLoop(ctx context.Context) {
timer := time.NewTimer(c.inactivityTimeout)
for {
select {
case <-timer.C:
_ = c.Close()
log.Println("Closed connection due to inactivity")
return
case <-c.activity:
if !timer.Stop() {
<-timer.C
}
timer.Reset(c.inactivityTimeout)
continue
case <-ctx.Done():
return
}
}
}
func (c *webRTCConn) Read(b []byte) (int, error) {
return c.pr.Read(b)
}
func (c *webRTCConn) Write(b []byte) (int, error) {
c.bytesLogger.AddInbound(int64(len(b)))
select {
case c.activity <- struct{}{}:
default:
}
c.lock.Lock()
defer c.lock.Unlock()
if c.dc != nil {
_ = c.dc.Send(b)
if !c.isClosing && c.dc.BufferedAmount() >= maxBufferedAmount {
<-c.sendMoreCh
}
}
return len(b), nil
}
func (c *webRTCConn) Close() (err error) {
c.isClosing = true
select {
case c.sendMoreCh <- struct{}{}:
default:
}
c.once.Do(func() {
c.cancelTimeoutLoop()
err = errors.Join(c.pr.Close(), c.pc.Close())
})
return
}
func (c *webRTCConn) LocalAddr() net.Addr {
return nil
}
func (c *webRTCConn) RemoteAddr() net.Addr {
//Parse Remote SDP offer and extract client IP
clientIP := remoteIPFromSDP(c.pc.RemoteDescription().SDP)
if clientIP == nil {
return nil
}
return &net.IPAddr{IP: clientIP, Zone: ""}
}
func (c *webRTCConn) SetDeadline(t time.Time) error {
// nolint: golint
return fmt.Errorf("SetDeadline not implemented")
}
func (c *webRTCConn) SetReadDeadline(t time.Time) error {
// nolint: golint
return fmt.Errorf("SetReadDeadline not implemented")
}
func (c *webRTCConn) SetWriteDeadline(t time.Time) error {
// nolint: golint
return fmt.Errorf("SetWriteDeadline not implemented")
}
func remoteIPFromSDP(str string) net.IP {
// Look for remote IP in "a=candidate" attribute fields
// https://tools.ietf.org/html/rfc5245#section-15.1
var desc sdp.SessionDescription
err := desc.Unmarshal([]byte(str))
if err != nil {
log.Println("Error parsing SDP: ", err.Error())
return nil
}
for _, m := range desc.MediaDescriptions {
for _, a := range m.Attributes {
if a.IsICECandidate() {
c, err := ice.UnmarshalCandidate(a.Value)
if err == nil {
ip := net.ParseIP(c.Address())
if ip != nil && isRemoteAddress(ip) {
return ip
}
}
}
}
}
// Finally look for remote IP in "c=" Connection Data field
// https://tools.ietf.org/html/rfc4566#section-5.7
for _, pattern := range remoteIPPatterns {
m := pattern.FindStringSubmatch(str)
if m != nil {
// Ignore parsing errors, ParseIP returns nil.
ip := net.ParseIP(m[1])
if ip != nil && isRemoteAddress(ip) {
return ip
}
}
}
return nil
}
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