kcp

README

Introduction

kcp-go is a Production-Grade Reliable-UDP library for golang.

This library intents to provide a smooth, resilient, ordered, error-checked and anonymous delivery of streams over UDP packets, it has been battle-tested with opensource project kcptun. Millions of devices(from low-end MIPS routers to high-end servers) have deployed kcp-go powered program in a variety of forms like online games, live broadcasting, file synchronization and network acceleration.

Lastest Release

Features

1. Designed for Latency-sensitive scenarios.
2. Cache friendly and Memory optimized design, offers extremely High Performance core.
3. Handles >5K concurrent connections on a single commodity server.
4. Compatible with net.Conn and net.Listener, a drop-in replacement for net.TCPConn.
5. FEC(Forward Error Correction) Support with Reed-Solomon Codes
6. Packet level encryption support with AES, TEA, 3DES, Blowfish, Cast5, Salsa20, etc. in CFB mode, which generates completely anonymous packet.
7. Only A fixed number of goroutines will be created for the entire server application, costs in context switch between goroutines have been taken into consideration.
8. Compatible with skywind3000's C version with various improvements.
9. Platform-dependent optimizations: sendmmsg and recvmmsg were expoloited for linux.

Documentation

For complete documentation, see the associated Godoc.

Specification

NONCE:
  16bytes cryptographically secure random number, nonce changes for every packet.
  
CRC32:
  CRC-32 checksum of data using the IEEE polynomial
 
FEC TYPE:
  typeData = 0xF1
  typeParity = 0xF2
  
FEC SEQID:
  monotonically increasing in range: [0, (0xffffffff/shardSize) * shardSize - 1]
  
SIZE:
  The size of KCP frame plus 2

+-----------------+
| SESSION         |
+-----------------+
| KCP(ARQ)        |
+-----------------+
| FEC(OPTIONAL)   |
+-----------------+
| CRYPTO(OPTIONAL)|
+-----------------+
| UDP(PACKET)     |
+-----------------+
| IP              |
+-----------------+
| LINK            |
+-----------------+
| PHY             |
+-----------------+
(LAYER MODEL OF KCP-GO)

Examples

1. simple examples
2. kcptun client
3. kcptun server

Benchmark

  Model Name:	MacBook Pro
  Model Identifier:	MacBookPro14,1
  Processor Name:	Intel Core i5
  Processor Speed:	3.1 GHz
  Number of Processors:	1
  Total Number of Cores:	2
  L2 Cache (per Core):	256 KB
  L3 Cache:	4 MB
  Memory:	8 GB

$ go test -v -run=^$ -bench .
beginning tests, encryption:salsa20, fec:10/3
goos: darwin
goarch: amd64
pkg: github.com/xtaci/kcp-go
BenchmarkSM4-4                 	   50000	     32180 ns/op	  93.23 MB/s	       0 B/op	       0 allocs/op
BenchmarkAES128-4              	  500000	      3285 ns/op	 913.21 MB/s	       0 B/op	       0 allocs/op
BenchmarkAES192-4              	  300000	      3623 ns/op	 827.85 MB/s	       0 B/op	       0 allocs/op
BenchmarkAES256-4              	  300000	      3874 ns/op	 774.20 MB/s	       0 B/op	       0 allocs/op
BenchmarkTEA-4                 	  100000	     15384 ns/op	 195.00 MB/s	       0 B/op	       0 allocs/op
BenchmarkXOR-4                 	20000000	        89.9 ns/op	33372.00 MB/s	       0 B/op	       0 allocs/op
BenchmarkBlowfish-4            	   50000	     26927 ns/op	 111.41 MB/s	       0 B/op	       0 allocs/op
BenchmarkNone-4                	30000000	        45.7 ns/op	65597.94 MB/s	       0 B/op	       0 allocs/op
BenchmarkCast5-4               	   50000	     34258 ns/op	  87.57 MB/s	       0 B/op	       0 allocs/op
Benchmark3DES-4                	   10000	    117149 ns/op	  25.61 MB/s	       0 B/op	       0 allocs/op
BenchmarkTwofish-4             	   50000	     33538 ns/op	  89.45 MB/s	       0 B/op	       0 allocs/op
BenchmarkXTEA-4                	   30000	     45666 ns/op	  65.69 MB/s	       0 B/op	       0 allocs/op
BenchmarkSalsa20-4             	  500000	      3308 ns/op	 906.76 MB/s	       0 B/op	       0 allocs/op
BenchmarkCRC32-4               	20000000	        65.2 ns/op	15712.43 MB/s
BenchmarkCsprngSystem-4        	 1000000	      1150 ns/op	  13.91 MB/s
BenchmarkCsprngMD5-4           	10000000	       145 ns/op	 110.26 MB/s
BenchmarkCsprngSHA1-4          	10000000	       158 ns/op	 126.54 MB/s
BenchmarkCsprngNonceMD5-4      	10000000	       153 ns/op	 104.22 MB/s
BenchmarkCsprngNonceAES128-4   	100000000	        19.1 ns/op	 837.81 MB/s
BenchmarkFECDecode-4           	 1000000	      1119 ns/op	1339.61 MB/s	    1606 B/op	       2 allocs/op
BenchmarkFECEncode-4           	 2000000	       832 ns/op	1801.83 MB/s	      17 B/op	       0 allocs/op
BenchmarkFlush-4               	 5000000	       272 ns/op	       0 B/op	       0 allocs/op
BenchmarkEchoSpeed4K-4         	    5000	    259617 ns/op	  15.78 MB/s	    5451 B/op	     149 allocs/op
BenchmarkEchoSpeed64K-4        	    1000	   1706084 ns/op	  38.41 MB/s	   56002 B/op	    1604 allocs/op
BenchmarkEchoSpeed512K-4       	     100	  14345505 ns/op	  36.55 MB/s	  482597 B/op	   13045 allocs/op
BenchmarkEchoSpeed1M-4         	      30	  34859104 ns/op	  30.08 MB/s	 1143773 B/op	   27186 allocs/op
BenchmarkSinkSpeed4K-4         	   50000	     31369 ns/op	 130.57 MB/s	    1566 B/op	      30 allocs/op
BenchmarkSinkSpeed64K-4        	    5000	    329065 ns/op	 199.16 MB/s	   21529 B/op	     453 allocs/op
BenchmarkSinkSpeed256K-4       	     500	   2373354 ns/op	 220.91 MB/s	  166332 B/op	    3554 allocs/op
BenchmarkSinkSpeed1M-4         	     300	   5117927 ns/op	 204.88 MB/s	  310378 B/op	    6988 allocs/op
PASS
ok  	github.com/xtaci/kcp-go	50.349s

Typical Flame Graph

Key Design Considerations

1. slice vs. container/list

kcp.flush() loops through the send queue for retransmission checking for every 20ms(interval).

I've wrote a benchmark for comparing sequential loop through slice and container/list here:

https://github.com/xtaci/notes/blob/master/golang/benchmark2/cachemiss_test.go

BenchmarkLoopSlice-4   	2000000000	         0.39 ns/op
BenchmarkLoopList-4    	100000000	        54.6 ns/op

List structure introduces heavy cache misses compared to slice which owns better locality, 5000 connections with 32 window size and 20ms interval will cost 6us/0.03%(cpu) using slice, and 8.7ms/43.5%(cpu) for list for each kcp.flush().

1. Timing accuracy vs. syscall clock_gettime

Timing is critical to RTT estimator, inaccurate timing leads to false retransmissions in KCP, but calling time.Now() costs 42 cycles(10.5ns on 4GHz CPU, 15.6ns on my MacBook Pro 2.7GHz).

The benchmark for time.Now() lies here:

https://github.com/xtaci/notes/blob/master/golang/benchmark2/syscall_test.go

BenchmarkNow-4         	100000000	        15.6 ns/op

In kcp-go, after each kcp.output() function call, current clock time will be updated upon return, and for a single kcp.flush() operation, current time will be queried from system once. For most of the time, 5000 connections costs 5000 * 15.6ns = 78us(a fixed cost while no packet needs to be sent), as for 10MB/s data transfering with 1400 MTU, kcp.output() will be called around 7500 times and costs 117us for time.Now() in every second.

1. Memory management

Primary memory allocation are done from a global buffer pool xmit.Buf, in kcp-go, when we need to allocate some bytes, we can get from that pool, and a fixed-capacity 1500 bytes(mtuLimit) will be returned, the rx queue, tx queue and fec queue all receive bytes from there, and they will return the bytes to the pool after using to prevent unnecessary zer0ing of bytes. The pool mechanism maintained a high watermark for slice objects, these in-flight objects from the pool will survive from the perodical garbage collection, meanwhile the pool kept the ability to return the memory to runtime if in idle.

1. Information security

kcp-go is shipped with builtin packet encryption powered by various block encryption algorithms and works in Cipher Feedback Mode, for each packet to be sent, the encryption process will start from encrypting a nonce from the system entropy, so encryption to same plaintexts never leads to a same ciphertexts thereafter.

The contents of the packets are completely anonymous with encryption, including the headers(FEC,KCP), checksums and contents. Note that, no matter which encryption method you choose on you upper layer, if you disable encryption, the transmit will be insecure somehow, since the header is PLAINTEXT to everyone it would be susceptible to header tampering, such as jamming the sliding window size, round-trip time, FEC property and checksums. AES-128 is suggested for minimal encryption since modern CPUs are shipped with AES-NI instructions and performs even better than salsa20(check the table above).

Other possible attacks to kcp-go includes: a) traffic analysis, dataflow on specific websites may have pattern while interchanging data, but this type of eavesdropping has been mitigated by adapting smux to mix data streams so as to introduce noises, perfect solution to this has not appeared yet, theroretically by shuffling/mixing messages on larger scale network may mitigate this problem. b) replay attack, since the asymmetrical encryption has not been introduced into kcp-go for some reason, capturing the packets and replay them on a different machine is possible, (notice: hijacking the session and decrypting the contents is still impossible), so upper layers should contain a asymmetrical encryption system to guarantee the authenticity of each message(to process message exactly once), such as HTTPS/OpenSSL/LibreSSL, only by signing the requests with private keys can eliminate this type of attack.

Connection Termination

Control messages like SYN/FIN/RST in TCP are not defined in KCP, you need some keepalive/heartbeat mechanism in the application-level. A real world example is to use some multiplexing protocol over session, such as smux(with embedded keepalive mechanism), see kcptun for example.

FAQ

Q: I'm handling >5K connections on my server, the CPU utilization is so high.

A: A standalone agent or gate server for running kcp-go is suggested, not only for CPU utilization, but also important to the precision of RTT measurements(timing) which indirectly affects retransmission. By increasing update interval with SetNoDelay like conn.SetNoDelay(1, 40, 1, 1) will dramatically reduce system load, but lower the performance.

Q: When should I enable FEC?

A: Forward error correction is critical to long-distance transmission, because a packet loss will lead to a huge penalty in time. And for the complicated packet routing network in modern world, round-trip time based loss check will not always be efficient, the big deviation of RTT samples in the long way usually leads to a larger RTO value in typical rtt estimator, which in other words, slows down the transmission.

Q: Should I enable encryption?

A: Yes, for the safety of protocol, even if the upper layer has encrypted.

Who is using this?

1. https://github.com/xtaci/kcptun -- A Secure Tunnel Based On KCP over UDP.
2. https://github.com/getlantern/lantern -- Lantern delivers fast access to the open Internet.
3. https://github.com/smallnest/rpcx -- A RPC service framework based on net/rpc like alibaba Dubbo and weibo Motan.
4. https://github.com/gonet2/agent -- A gateway for games with stream multiplexing.
5. https://github.com/syncthing/syncthing -- Open Source Continuous File Synchronization.

Links

1. https://github.com/xtaci/libkcp -- FEC enhanced KCP session library for iOS/Android in C++
2. https://github.com/skywind3000/kcp -- A Fast and Reliable ARQ Protocol
3. https://github.com/klauspost/reedsolomon -- Reed-Solomon Erasure Coding in Go

Documentation

Overview

Package kcp-go is a Reliable-UDP library for golang.

This library intents to provide a smooth, resilient, ordered, error-checked and anonymous delivery of streams over UDP packets.

The interfaces of this package aims to be compatible with net.Conn in standard library, but offers powerful features for advanced users.

Index

• Constants
• func Dial(raddr string) (net.Conn, error)
• func Listen(laddr string) (net.Listener, error)
• type BlockCrypt
  • func NewAESBlockCrypt(key []byte) (BlockCrypt, error)
  • func NewBlowfishBlockCrypt(key []byte) (BlockCrypt, error)
  • func NewCast5BlockCrypt(key []byte) (BlockCrypt, error)
  • func NewNoneBlockCrypt(key []byte) (BlockCrypt, error)
  • func NewSM4BlockCrypt(key []byte) (BlockCrypt, error)
  • func NewSalsa20BlockCrypt(key []byte) (BlockCrypt, error)
  • func NewSimpleXORBlockCrypt(key []byte) (BlockCrypt, error)
  • func NewTEABlockCrypt(key []byte) (BlockCrypt, error)
  • func NewTripleDESBlockCrypt(key []byte) (BlockCrypt, error)
  • func NewTwofishBlockCrypt(key []byte) (BlockCrypt, error)
  • func NewXTEABlockCrypt(key []byte) (BlockCrypt, error)
• type Entropy
• type KCP
  • func NewKCP(conv uint32, output output_callback) *KCP
  • func (kcp *KCP) Check() uint32
  • func (kcp *KCP) Input(data []byte, regular, ackNoDelay bool) int
  • func (kcp *KCP) NoDelay(nodelay, interval, resend, nc int) int
  • func (kcp *KCP) PeekSize() (length int)
  • func (kcp *KCP) Recv(buffer []byte) (n int)
  • func (kcp *KCP) ReserveBytes(n int) bool
  • func (kcp *KCP) Send(buffer []byte) int
  • func (kcp *KCP) SetMtu(mtu int) int
  • func (kcp *KCP) Update()
  • func (kcp *KCP) WaitSnd() int
  • func (kcp *KCP) WndSize(sndwnd, rcvwnd int) int
• type Listener
  • func ListenWithOptions(laddr string, block BlockCrypt, dataShards, parityShards int) (*Listener, error)
  • func ServeConn(block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*Listener, error)
  • func (l *Listener) Accept() (net.Conn, error)
  • func (l *Listener) AcceptKCP() (*UDPSession, error)
  • func (l *Listener) Addr() net.Addr
  • func (l *Listener) Close() error
  • func (l *Listener) SetDSCP(dscp int) error
  • func (l *Listener) SetDeadline(t time.Time) error
  • func (l *Listener) SetReadBuffer(bytes int) error
  • func (l *Listener) SetReadDeadline(t time.Time) error
  • func (l *Listener) SetWriteBuffer(bytes int) error
  • func (l *Listener) SetWriteDeadline(t time.Time) error
• type Snmp
  • func (s *Snmp) Copy() *Snmp
  • func (s *Snmp) Header() []string
  • func (s *Snmp) Reset()
  • func (s *Snmp) ToSlice() []string
• type UDPSession
  • func DialWithOptions(raddr string, block BlockCrypt, dataShards, parityShards int) (*UDPSession, error)
  • func NewConn(raddr string, block BlockCrypt, dataShards, parityShards int, ...) (*UDPSession, error)
  • func NewConn2(raddr net.Addr, block BlockCrypt, dataShards, parityShards int, ...) (*UDPSession, error)
  • func NewConn3(convid uint32, raddr net.Addr, block BlockCrypt, dataShards, parityShards int, ...) (*UDPSession, error)
  • func (s *UDPSession) Close() error
  • func (s *UDPSession) GetConv() uint32
  • func (s *UDPSession) LocalAddr() net.Addr
  • func (s *UDPSession) Read(b []byte) (n int, err error)
  • func (s *UDPSession) RemoteAddr() net.Addr
  • func (s *UDPSession) SetACKNoDelay(nodelay bool)
  • func (s *UDPSession) SetDSCP(dscp int) error
  • func (s *UDPSession) SetDUP(dup int)
  • func (s *UDPSession) SetDeadline(t time.Time) error
  • func (s *UDPSession) SetMtu(mtu int) bool
  • func (s *UDPSession) SetNoDelay(nodelay, interval, resend, nc int)
  • func (s *UDPSession) SetReadBuffer(bytes int) error
  • func (s *UDPSession) SetReadDeadline(t time.Time) error
  • func (s *UDPSession) SetStreamMode(enable bool)
  • func (s *UDPSession) SetWindowSize(sndwnd, rcvwnd int)
  • func (s *UDPSession) SetWriteBuffer(bytes int) error
  • func (s *UDPSession) SetWriteDeadline(t time.Time) error
  • func (s *UDPSession) SetWriteDelay(delay bool)
  • func (s *UDPSession) Write(b []byte) (n int, err error)
  • func (s *UDPSession) WriteBuffers(v [][]byte) (n int, err error)

Constants

const (
	IKCP_RTO_NDL     = 30  // no delay min rto
	IKCP_RTO_MIN     = 100 // normal min rto
	IKCP_RTO_DEF     = 200
	IKCP_RTO_MAX     = 60000
	IKCP_CMD_PUSH    = 81 // cmd: push data
	IKCP_CMD_ACK     = 82 // cmd: ack
	IKCP_CMD_WASK    = 83 // cmd: window probe (ask)
	IKCP_CMD_WINS    = 84 // cmd: window size (tell)
	IKCP_ASK_SEND    = 1  // need to send IKCP_CMD_WASK
	IKCP_ASK_TELL    = 2  // need to send IKCP_CMD_WINS
	IKCP_WND_SND     = 32
	IKCP_WND_RCV     = 32
	IKCP_MTU_DEF     = 1400
	IKCP_ACK_FAST    = 3
	IKCP_INTERVAL    = 100
	IKCP_OVERHEAD    = 24
	IKCP_DEADLINK    = 20
	IKCP_THRESH_INIT = 2
	IKCP_THRESH_MIN  = 2
	IKCP_PROBE_INIT  = 7000   // 7 secs to probe window size
	IKCP_PROBE_LIMIT = 120000 // up to 120 secs to probe window
)

Functions

func Dial

func Dial(raddr string) (net.Conn, error)

Dial connects to the remote address "raddr" on the network "udp" without encryption and FEC

func Listen

func Listen(laddr string) (net.Listener, error)

Listen listens for incoming KCP packets addressed to the local address laddr on the network "udp",

Types

type BlockCrypt

type BlockCrypt interface {
	// Encrypt encrypts the whole block in src into dst.
	// Dst and src may point at the same memory.
	Encrypt(dst, src []byte)

	// Decrypt decrypts the whole block in src into dst.
	// Dst and src may point at the same memory.
	Decrypt(dst, src []byte)
}

BlockCrypt defines encryption/decryption methods for a given byte slice. Notes on implementing: the data to be encrypted contains a builtin nonce at the first 16 bytes

func NewAESBlockCrypt

func NewAESBlockCrypt(key []byte) (BlockCrypt, error)

NewAESBlockCrypt https://en.wikipedia.org/wiki/Advanced_Encryption_Standard

func NewBlowfishBlockCrypt

func NewBlowfishBlockCrypt(key []byte) (BlockCrypt, error)

NewBlowfishBlockCrypt https://en.wikipedia.org/wiki/Blowfish_(cipher)

func NewCast5BlockCrypt

func NewCast5BlockCrypt(key []byte) (BlockCrypt, error)

NewCast5BlockCrypt https://en.wikipedia.org/wiki/CAST-128

func NewNoneBlockCrypt

func NewNoneBlockCrypt(key []byte) (BlockCrypt, error)

NewNoneBlockCrypt does nothing but copying

func NewSM4BlockCrypt

func NewSM4BlockCrypt(key []byte) (BlockCrypt, error)

NewSM4BlockCrypt https://github.com/tjfoc/gmsm/tree/master/sm4

func NewSalsa20BlockCrypt

func NewSalsa20BlockCrypt(key []byte) (BlockCrypt, error)

NewSalsa20BlockCrypt https://en.wikipedia.org/wiki/Salsa20

func NewSimpleXORBlockCrypt

func NewSimpleXORBlockCrypt(key []byte) (BlockCrypt, error)

NewSimpleXORBlockCrypt simple xor with key expanding

func NewTEABlockCrypt

func NewTEABlockCrypt(key []byte) (BlockCrypt, error)

NewTEABlockCrypt https://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm

func NewTripleDESBlockCrypt

func NewTripleDESBlockCrypt(key []byte) (BlockCrypt, error)

NewTripleDESBlockCrypt https://en.wikipedia.org/wiki/Triple_DES

func NewTwofishBlockCrypt

func NewTwofishBlockCrypt(key []byte) (BlockCrypt, error)

NewTwofishBlockCrypt https://en.wikipedia.org/wiki/Twofish

func NewXTEABlockCrypt

func NewXTEABlockCrypt(key []byte) (BlockCrypt, error)

NewXTEABlockCrypt https://en.wikipedia.org/wiki/XTEA

type Entropy

type Entropy interface {
	Init()
	Fill(nonce []byte)
}

Entropy defines a entropy source

type KCP

type KCP struct {
	// contains filtered or unexported fields
}

KCP defines a single KCP connection

func NewKCP

func NewKCP(conv uint32, output output_callback) *KCP

NewKCP create a new kcp state machine

'conv' must be equal in the connection peers, or else data will be silently rejected.

'output' function will be called whenever these is data to be sent on wire.

func (*KCP) Check

func (kcp *KCP) Check() uint32

(deprecated)

Check determines when should you invoke ikcp_update: returns when you should invoke ikcp_update in millisec, if there is no ikcp_input/_send calling. you can call ikcp_update in that time, instead of call update repeatly. Important to reduce unnacessary ikcp_update invoking. use it to schedule ikcp_update (eg. implementing an epoll-like mechanism, or optimize ikcp_update when handling massive kcp connections)

func (*KCP) Input

func (kcp *KCP) Input(data []byte, regular, ackNoDelay bool) int

Input a packet into kcp state machine.

'regular' indicates it's a real data packet from remote, and it means it's not generated from ReedSolomon codecs.

'ackNoDelay' will trigger immediate ACK, but surely it will not be efficient in bandwidth

func (*KCP) NoDelay

func (kcp *KCP) NoDelay(nodelay, interval, resend, nc int) int

NoDelay options fastest: ikcp_nodelay(kcp, 1, 20, 2, 1) nodelay: 0:disable(default), 1:enable interval: internal update timer interval in millisec, default is 100ms resend: 0:disable fast resend(default), 1:enable fast resend nc: 0:normal congestion control(default), 1:disable congestion control

func (*KCP) PeekSize

func (kcp *KCP) PeekSize() (length int)

PeekSize checks the size of next message in the recv queue

func (*KCP) Recv

func (kcp *KCP) Recv(buffer []byte) (n int)

Receive data from kcp state machine

Return number of bytes read.

Return -1 when there is no readable data.

Return -2 if len(buffer) is smaller than kcp.PeekSize().

func (*KCP) ReserveBytes

func (kcp *KCP) ReserveBytes(n int) bool

ReserveBytes keeps n bytes untouched from the beginning of the buffer, the output_callback function should be aware of this.

Return false if n >= mss

func (*KCP) Send

func (kcp *KCP) Send(buffer []byte) int

Send is user/upper level send, returns below zero for error

func (*KCP) SetMtu

func (kcp *KCP) SetMtu(mtu int) int

SetMtu changes MTU size, default is 1400

func (*KCP) Update

func (kcp *KCP) Update()

(deprecated)

Update updates state (call it repeatedly, every 10ms-100ms), or you can ask ikcp_check when to call it again (without ikcp_input/_send calling). 'current' - current timestamp in millisec.

func (*KCP) WaitSnd

func (kcp *KCP) WaitSnd() int

WaitSnd gets how many packet is waiting to be sent

func (*KCP) WndSize

func (kcp *KCP) WndSize(sndwnd, rcvwnd int) int

WndSize sets maximum window size: sndwnd=32, rcvwnd=32 by default

type Listener

type Listener struct {
	// contains filtered or unexported fields
}

Listener defines a server which will be waiting to accept incoming connections

func ListenWithOptions

func ListenWithOptions(laddr string, block BlockCrypt, dataShards, parityShards int) (*Listener, error)

ListenWithOptions listens for incoming KCP packets addressed to the local address laddr on the network "udp" with packet encryption.

'block' is the block encryption algorithm to encrypt packets.

'dataShards', 'parityShards' specifiy how many parity packets will be generated following the data packets.

Check https://github.com/klauspost/reedsolomon for details

func ServeConn

func ServeConn(block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*Listener, error)

ServeConn serves KCP protocol for a single packet connection.

func (*Listener) Accept

func (l *Listener) Accept() (net.Conn, error)

Accept implements the Accept method in the Listener interface; it waits for the next call and returns a generic Conn.

func (*Listener) AcceptKCP

func (l *Listener) AcceptKCP() (*UDPSession, error)

AcceptKCP accepts a KCP connection

func (*Listener) Addr

func (l *Listener) Addr() net.Addr

Addr returns the listener's network address, The Addr returned is shared by all invocations of Addr, so do not modify it.

func (*Listener) Close

func (l *Listener) Close() error

Close stops listening on the UDP address, and closes the socket

func (*Listener) SetDSCP

func (l *Listener) SetDSCP(dscp int) error

SetDSCP sets the 6bit DSCP field in IPv4 header, or 8bit Traffic Class in IPv6 header.

if the underlying connection has implemented `func SetDSCP(int) error`, SetDSCP() will invoke this function instead.

func (*Listener) SetDeadline

func (l *Listener) SetDeadline(t time.Time) error

SetDeadline sets the deadline associated with the listener. A zero time value disables the deadline.

func (*Listener) SetReadBuffer

func (l *Listener) SetReadBuffer(bytes int) error

SetReadBuffer sets the socket read buffer for the Listener

func (*Listener) SetReadDeadline

func (l *Listener) SetReadDeadline(t time.Time) error

SetReadDeadline implements the Conn SetReadDeadline method.

func (*Listener) SetWriteBuffer

func (l *Listener) SetWriteBuffer(bytes int) error

SetWriteBuffer sets the socket write buffer for the Listener

func (*Listener) SetWriteDeadline

func (l *Listener) SetWriteDeadline(t time.Time) error

SetWriteDeadline implements the Conn SetWriteDeadline method.

type Snmp

type Snmp struct {
	BytesSent        uint64 // bytes sent from upper level
	BytesReceived    uint64 // bytes received to upper level
	MaxConn          uint64 // max number of connections ever reached
	ActiveOpens      uint64 // accumulated active open connections
	PassiveOpens     uint64 // accumulated passive open connections
	CurrEstab        uint64 // current number of established connections
	InErrs           uint64 // UDP read errors reported from net.PacketConn
	InCsumErrors     uint64 // checksum errors from CRC32
	KCPInErrors      uint64 // packet iput errors reported from KCP
	InPkts           uint64 // incoming packets count
	OutPkts          uint64 // outgoing packets count
	InSegs           uint64 // incoming KCP segments
	OutSegs          uint64 // outgoing KCP segments
	InBytes          uint64 // UDP bytes received
	OutBytes         uint64 // UDP bytes sent
	RetransSegs      uint64 // accmulated retransmited segments
	FastRetransSegs  uint64 // accmulated fast retransmitted segments
	EarlyRetransSegs uint64 // accmulated early retransmitted segments
	LostSegs         uint64 // number of segs infered as lost
	RepeatSegs       uint64 // number of segs duplicated
	FECRecovered     uint64 // correct packets recovered from FEC
	FECErrs          uint64 // incorrect packets recovered from FEC
	FECParityShards  uint64 // FEC segments received
	FECShortShards   uint64 // number of data shards that's not enough for recovery
}

Snmp defines network statistics indicator

var DefaultSnmp *Snmp

DefaultSnmp is the global KCP connection statistics collector

func (*Snmp) Copy

func (s *Snmp) Copy() *Snmp

Copy make a copy of current snmp snapshot

func (*Snmp) Header

func (s *Snmp) Header() []string

Header returns all field names

func (*Snmp) Reset

func (s *Snmp) Reset()

Reset values to zero

func (*Snmp) ToSlice

func (s *Snmp) ToSlice() []string

ToSlice returns current snmp info as slice

type UDPSession

type UDPSession struct {
	// contains filtered or unexported fields
}

UDPSession defines a KCP session implemented by UDP

func DialWithOptions

func DialWithOptions(raddr string, block BlockCrypt, dataShards, parityShards int) (*UDPSession, error)

DialWithOptions connects to the remote address "raddr" on the network "udp" with packet encryption

'block' is the block encryption algorithm to encrypt packets.

'dataShards', 'parityShards' specifiy how many parity packets will be generated following the data packets.

Check https://github.com/klauspost/reedsolomon for details

func NewConn

func NewConn(raddr string, block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*UDPSession, error)

NewConn establishes a session and talks KCP protocol over a packet connection.

func NewConn2

func NewConn2(raddr net.Addr, block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*UDPSession, error)

NewConn2 establishes a session and talks KCP protocol over a packet connection.

func NewConn3

func NewConn3(convid uint32, raddr net.Addr, block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*UDPSession, error)

NewConn3 establishes a session and talks KCP protocol over a packet connection.

func (*UDPSession) Close

func (s *UDPSession) Close() error

Close closes the connection.

func (*UDPSession) GetConv

func (s *UDPSession) GetConv() uint32

GetConv gets conversation id of a session

func (*UDPSession) LocalAddr

func (s *UDPSession) LocalAddr() net.Addr

LocalAddr returns the local network address. The Addr returned is shared by all invocations of LocalAddr, so do not modify it.

func (*UDPSession) Read

func (s *UDPSession) Read(b []byte) (n int, err error)

Read implements net.Conn

func (*UDPSession) RemoteAddr

func (s *UDPSession) RemoteAddr() net.Addr

RemoteAddr returns the remote network address. The Addr returned is shared by all invocations of RemoteAddr, so do not modify it.

func (*UDPSession) SetACKNoDelay

func (s *UDPSession) SetACKNoDelay(nodelay bool)

SetACKNoDelay changes ack flush option, set true to flush ack immediately,

func (*UDPSession) SetDSCP

func (s *UDPSession) SetDSCP(dscp int) error

SetDSCP sets the 6bit DSCP field in IPv4 header, or 8bit Traffic Class in IPv6 header.

if the underlying connection has implemented `func SetDSCP(int) error`, SetDSCP() will invoke this function instead.

It has no effect if it's accepted from Listener.

func (*UDPSession) SetDUP

func (s *UDPSession) SetDUP(dup int)

(deprecated)

SetDUP duplicates udp packets for kcp output.

func (*UDPSession) SetDeadline

func (s *UDPSession) SetDeadline(t time.Time) error

SetDeadline sets the deadline associated with the listener. A zero time value disables the deadline.

func (*UDPSession) SetMtu

func (s *UDPSession) SetMtu(mtu int) bool

SetMtu sets the maximum transmission unit(not including UDP header)

func (*UDPSession) SetNoDelay

func (s *UDPSession) SetNoDelay(nodelay, interval, resend, nc int)

SetNoDelay calls nodelay() of kcp https://github.com/skywind3000/kcp/blob/master/README.en.md#protocol-configuration

func (*UDPSession) SetReadBuffer

func (s *UDPSession) SetReadBuffer(bytes int) error

SetReadBuffer sets the socket read buffer, no effect if it's accepted from Listener

func (*UDPSession) SetReadDeadline

func (s *UDPSession) SetReadDeadline(t time.Time) error

SetReadDeadline implements the Conn SetReadDeadline method.

func (*UDPSession) SetStreamMode

func (s *UDPSession) SetStreamMode(enable bool)

SetStreamMode toggles the stream mode on/off

func (*UDPSession) SetWindowSize

func (s *UDPSession) SetWindowSize(sndwnd, rcvwnd int)

SetWindowSize set maximum window size

func (*UDPSession) SetWriteBuffer

func (s *UDPSession) SetWriteBuffer(bytes int) error

SetWriteBuffer sets the socket write buffer, no effect if it's accepted from Listener

func (*UDPSession) SetWriteDeadline

func (s *UDPSession) SetWriteDeadline(t time.Time) error

SetWriteDeadline implements the Conn SetWriteDeadline method.

func (*UDPSession) SetWriteDelay

func (s *UDPSession) SetWriteDelay(delay bool)

SetWriteDelay delays write for bulk transfer until the next update interval

func (*UDPSession) Write

func (s *UDPSession) Write(b []byte) (n int, err error)

Write implements net.Conn

func (*UDPSession) WriteBuffers

func (s *UDPSession) WriteBuffers(v [][]byte) (n int, err error)

WriteBuffers write a vector of byte slices to the underlying connection