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.
- Designed for Latency-sensitive scenarios.
- Cache friendly and Memory optimized design, offers extremely High Performance core.
- Handles >5K concurrent connections on a single commodity server.
- Compatible with net.Conn and net.Listener, a drop-in replacement for net.TCPConn.
- FEC(Forward Error Correction) Support with Reed-Solomon Codes
- Packet level encryption support with AES, TEA, 3DES, Blowfish, Cast5, Salsa20, etc. in CFB mode, which generates completely anonymous packet.
- 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.
- Compatible with skywind3000's C version with various improvements.
- Platform-dependent optimizations: sendmmsg and recvmmsg were expoloited for linux.
For complete documentation, see the associated Godoc.
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)
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
➜ kcp-go git:(master) cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 3 (v7l)
BogoMIPS : 108.00
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xd08
CPU revision : 3
➜ kcp-go git:(master) go test -run=^$ -bench .
2020/01/03 17:01:20 beginning tests, encryption:salsa20, fec:10/3
goos: linux
goarch: arm
pkg: github.com/xtaci/kcp-go/v5
BenchmarkSM4-4 10000 101301 ns/op 29.61 MB/s 0 B/op 0 allocs/op
BenchmarkAES128-4 20000 76029 ns/op 39.46 MB/s 0 B/op 0 allocs/op
BenchmarkAES192-4 20000 85112 ns/op 35.25 MB/s 0 B/op 0 allocs/op
BenchmarkAES256-4 20000 93801 ns/op 31.98 MB/s 0 B/op 0 allocs/op
BenchmarkTEA-4 50000 37356 ns/op 80.31 MB/s 0 B/op 0 allocs/op
BenchmarkXOR-4 50000 32239 ns/op 93.05 MB/s 0 B/op 0 allocs/op
BenchmarkBlowfish-4 20000 65694 ns/op 45.67 MB/s 0 B/op 0 allocs/op
BenchmarkNone-4 3000000 521 ns/op 5757.08 MB/s 0 B/op 0 allocs/op
BenchmarkCast5-4 20000 72051 ns/op 41.64 MB/s 0 B/op 0 allocs/op
Benchmark3DES-4 5000 398459 ns/op 7.53 MB/s 0 B/op 0 allocs/op
BenchmarkTwofish-4 5000 340181 ns/op 8.82 MB/s 0 B/op 0 allocs/op
BenchmarkXTEA-4 10000 120154 ns/op 24.97 MB/s 0 B/op 0 allocs/op
BenchmarkSalsa20-4 50000 37164 ns/op 80.72 MB/s 0 B/op 0 allocs/op
BenchmarkCRC32-4 1000000 1737 ns/op 589.43 MB/s
BenchmarkCsprngSystem-4 1000000 2196 ns/op 7.28 MB/s
BenchmarkCsprngMD5-4 2000000 818 ns/op 19.54 MB/s
BenchmarkCsprngSHA1-4 2000000 860 ns/op 23.25 MB/s
BenchmarkCsprngNonceMD5-4 2000000 891 ns/op 17.94 MB/s
BenchmarkCsprngNonceAES128-4 5000000 326 ns/op 49.05 MB/s
BenchmarkFECDecode-4 200000 9468 ns/op 158.41 MB/s 140 B/op 1 allocs/op
BenchmarkFECEncode-4 100000 12719 ns/op 117.93 MB/s 11 B/op 0 allocs/op
BenchmarkFlush-4 100000 22944 ns/op 0 B/op 0 allocs/op
BenchmarkEchoSpeed4K-4 2000 992565 ns/op 4.13 MB/s 12427 B/op 425 allocs/op
BenchmarkEchoSpeed64K-4 100 10391474 ns/op 6.31 MB/s 127564 B/op 3835 allocs/op
BenchmarkEchoSpeed512K-4 10 110521615 ns/op 4.74 MB/s 1492676 B/op 26791 allocs/op
BenchmarkEchoSpeed1M-4 5 298269651 ns/op 3.52 MB/s 3576904 B/op 60760 allocs/op
BenchmarkSinkSpeed4K-4 20000 94335 ns/op 43.42 MB/s 3971 B/op 99 allocs/op
BenchmarkSinkSpeed64K-4 2000 1164323 ns/op 56.29 MB/s 45752 B/op 1080 allocs/op
BenchmarkSinkSpeed256K-4 100 12246407 ns/op 42.81 MB/s 449397 B/op 9792 allocs/op
BenchmarkSinkSpeed1M-4 100 21781137 ns/op 48.14 MB/s 872098 B/op 17772 allocs/op
PASS
ok github.com/xtaci/kcp-go/v5 60.906s
- 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().
- 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.
- 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.
- 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.
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.
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.
- https://github.com/xtaci/kcptun -- A Secure Tunnel Based On KCP over UDP.
- https://github.com/getlantern/lantern -- Lantern delivers fast access to the open Internet.
- https://github.com/smallnest/rpcx -- A RPC service framework based on net/rpc like alibaba Dubbo and weibo Motan.
- https://github.com/gonet2/agent -- A gateway for games with stream multiplexing.
- https://github.com/syncthing/syncthing -- Open Source Continuous File Synchronization.
- https://github.com/xtaci/smux/ -- A Stream Multiplexing Library for golang with least memory
- https://github.com/xtaci/libkcp -- FEC enhanced KCP session library for iOS/Android in C++
- https://github.com/skywind3000/kcp -- A Fast and Reliable ARQ Protocol
- https://github.com/klauspost/reedsolomon -- Reed-Solomon Erasure Coding in Go
WeChat(付费技术咨询)
