func newObfs4ClientConn(conn net.Conn, args *obfs4ClientArgs) (c *obfs4Conn, err error) {
// Generate the initial protocol polymorphism distribution(s).
var seed *drbg.Seed
if seed, err = drbg.NewSeed(); err != nil {
return
}
lenDist := probdist.New(seed, 0, framing.MaximumSegmentLength, biasedDist)
var iatDist *probdist.WeightedDist
if args.iatMode != iatNone {
var iatSeed *drbg.Seed
iatSeedSrc := sha256.Sum256(seed.Bytes()[:])
if iatSeed, err = drbg.SeedFromBytes(iatSeedSrc[:]); err != nil {
return
}
iatDist = probdist.New(iatSeed, 0, maxIATDelay, biasedDist)
}
// Allocate the client structure.
c = &obfs4Conn{conn, false, lenDist, iatDist, args.iatMode, bytes.NewBuffer(nil), bytes.NewBuffer(nil), nil, nil}
// Start the handshake timeout.
deadline := time.Now().Add(clientHandshakeTimeout)
if err = conn.SetDeadline(deadline); err != nil {
return nil, err
}
if err = c.clientHandshake(args.nodeID, args.publicKey, args.sessionKey); err != nil {
return nil, err
}
// Stop the handshake timeout.
if err = conn.SetDeadline(time.Time{}); err != nil {
return nil, err
}
return
}
func (conn *obfs4Conn) readPackets() (err error) {
// Attempt to read off the network.
var buf [consumeReadSize]byte
rdLen, rdErr := conn.Conn.Read(buf[:])
conn.receiveBuffer.Write(buf[:rdLen])
var decoded [framing.MaximumFramePayloadLength]byte
for conn.receiveBuffer.Len() > 0 {
// Decrypt an AEAD frame.
decLen := 0
decLen, err = conn.decoder.Decode(decoded[:], conn.receiveBuffer)
if err == framing.ErrAgain {
break
} else if err != nil {
break
} else if decLen < packetOverhead {
err = InvalidPacketLengthError(decLen)
break
}
// Decode the packet.
pkt := decoded[0:decLen]
pktType := pkt[0]
payloadLen := binary.BigEndian.Uint16(pkt[1:])
if int(payloadLen) > len(pkt)-packetOverhead {
err = InvalidPayloadLengthError(int(payloadLen))
break
}
payload := pkt[3 : 3+payloadLen]
switch pktType {
case packetTypePayload:
if payloadLen > 0 {
conn.receiveDecodedBuffer.Write(payload)
}
case packetTypePrngSeed:
// Only regenerate the distribution if we are the client.
if len(payload) == seedPacketPayloadLength && !conn.isServer {
var seed *drbg.Seed
seed, err = drbg.SeedFromBytes(payload)
if err != nil {
break
}
conn.lenDist.Reset(seed)
if conn.iatDist != nil {
iatSeedSrc := sha256.Sum256(seed.Bytes()[:])
iatSeed, err := drbg.SeedFromBytes(iatSeedSrc[:])
if err != nil {
break
}
conn.iatDist.Reset(iatSeed)
}
}
default:
// Ignore unknown packet types.
}
}
// Read errors (all fatal) take priority over various frame processing
// errors.
if rdErr != nil {
return rdErr
}
return
}