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Improve handling of timestamps (#446) 

* Improve handling of timestamps
This commit is contained in:
KonradStaniec 2021-12-10 16:28:00 +01:00 committed by GitHub
parent 41d2d3c991
commit b56e19a590
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2 changed files with 45 additions and 41 deletions
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45
eth/utp/packets.nim
View File

@ -9,13 +9,16 @@
import
std/[monotimes],
faststreams,
chronos,
stew/[endians2, results, objects, arrayops], bearssl,
../p2p/discoveryv5/random2
export results
const minimalHeaderSize = 20
const protocolVersion = 1
const
minimalHeaderSize = 20
protocolVersion = 1
zeroMoment = Moment.init(0, Nanosecond)
type
PacketType* = enum
@ -47,22 +50,28 @@ type
header*: PacketHeaderV1
payload*: seq[uint8]
TimeStampInfo* = object
moment*: Moment
timestamp*: uint32
# Important timing assumptions for utp protocol here:
# 1. Microsecond precisions
# 2. Monotonicity
# Reference lib have a lot of checks to assume that this is monotonic on
# every system, and warnings when monotonic clock is not avaialable.
# For now we can use basic monotime, later it would be good to analyze:
# https://github.com/bittorrent/libutp/blob/master/utp_utils.cpp, to check all the
# timing assumptions on different platforms
proc getMonoTimeTimeStamp*(): uint32 =
# TODO
# this value is equivalent of:
# uint32((Moment.now() - Moment.init(0, Microseconds)).microseconds())
# on macOs
# so we we can use moment here and return (Moment, uint32) tuple from this function
let time = getMonoTime()
cast[uint32](time.ticks() div 1000)
proc getMonoTimestamp*(): TimeStampInfo =
let currentMoment = Moment.now()
# Casting this value from int64 to uin32, my lead to some sudden spikes in
# timestamp numeric values i.e it is possible that timestamp can suddenly change
# from 4294967296 to for example 10, this may lead to sudden spikes in
# calculated delays
# uTP implementation is resistant to those spikes are as it keeps history of
# few last delays on uses smallest one for calculating ledbat window.
# so any outlier huge value will be ignored
#
let timestamp = uint32((currentMoment - zeroMoment).microseconds())
TimeStampInfo(moment: currentMoment, timestamp: timestamp)
# Simple generator, not useful for cryptography
proc randUint16*(rng: var BrHmacDrbgContext): uint16 =
@ -157,7 +166,7 @@ proc synPacket*(seqNr: uint16, rcvConnectionId: uint16, bufferSize: uint32): Pac
# TODO for we do not handle extensions
extension: 0'u8,
connectionId: rcvConnectionId,
timestamp: getMonoTimeTimeStamp(),
timestamp: getMonoTimestamp().timestamp,
timestampDiff: 0'u32,
wndSize: bufferSize,
seqNr: seqNr,
@ -174,7 +183,7 @@ proc ackPacket*(seqNr: uint16, sndConnectionId: uint16, ackNr: uint16, bufferSiz
# TODO Handle selective acks
extension: 0'u8,
connectionId: sndConnectionId,
timestamp: getMonoTimeTimeStamp(),
timestamp: getMonoTimestamp().timestamp,
timestampDiff: timestampDiff,
wndSize: bufferSize,
seqNr: seqNr,
@ -197,7 +206,7 @@ proc dataPacket*(
# data packets always have extension field set to 0
extension: 0'u8,
connectionId: sndConnectionId,
timestamp: getMonoTimeTimeStamp(),
timestamp: getMonoTimestamp().timestamp,
timestampDiff: timestampDiff,
wndSize: bufferSize,
seqNr: seqNr,
@ -213,7 +222,7 @@ proc resetPacket*(seqNr: uint16, sndConnectionId: uint16, ackNr: uint16): Packet
# data packets always have extension field set to 0
extension: 0'u8,
connectionId: sndConnectionId,
timestamp: getMonoTimeTimeStamp(),
timestamp: getMonoTimestamp().timestamp,
# reset packet informs remote about lack of state for given connection, therefore
# we do not inform remote about its delay.
timestampDiff: 0,
@ -237,7 +246,7 @@ proc finPacket*(
# fin packets always have extension field set to 0
extension: 0'u8,
connectionId: sndConnectionId,
timestamp: getMonoTimeTimeStamp(),
timestamp: getMonoTimestamp().timestamp,
timestampDiff: timestampDiff,
wndSize: bufferSize,
seqNr: seqNr,

41
eth/utp/utp_socket.nim
View File

@ -297,7 +297,7 @@ proc init(
transmissions: uint16,
needResend: bool,
payloadLength: uint32,
timeSent: Moment = Moment.now()): T =
timeSent: Moment = getMonoTimestamp().moment): T =
OutgoingPacket(
packetBytes: packetBytes,
transmissions: transmissions,
@ -357,15 +357,14 @@ proc sendAck(socket: UtpSocket): Future[void] =
# Should be called before sending packet
proc setSend(s: UtpSocket, p: var OutgoingPacket): seq[byte] =
let currentMoment = Moment.now()
let currentTimeStamp = getMonoTimeTimeStamp()
let timestampInfo = getMonoTimestamp()
inc p.transmissions
p.needResend = false
p.timeSent = currentMoment
p.timeSent = timestampInfo.moment
# all bytearrays in outgoing buffer should be properly encoded utp packets
# so it is safe to directly modify fields
modifyTimeStampAndAckNr(p.packetBytes, currentTimeStamp, s.ackNr)
modifyTimeStampAndAckNr(p.packetBytes, timestampInfo.timestamp, s.ackNr)
return p.packetBytes
@ -410,7 +409,7 @@ proc shouldDisconnectFromFailedRemote(socket: UtpSocket): bool =
(socket.retransmitCount >= socket.socketConfig.dataResendsBeforeFailure)
proc checkTimeouts(socket: UtpSocket) {.async.} =
let currentTime = Moment.now()
let currentTime = getMonoTimestamp().moment
# flush all packets which needs to be re-send
if socket.state != Destroy:
await socket.flushPackets()
@ -508,7 +507,7 @@ proc getPacketSize*(socket: UtpSocket): int =
proc resetSendTimeout(socket: UtpSocket) =
socket.retransmitTimeout = socket.rto
socket.rtoTimeout = Moment.now() + socket.retransmitTimeout
socket.rtoTimeout = getMonoTimestamp().moment + socket.retransmitTimeout
proc handleDataWrite(socket: UtpSocket, data: seq[byte], writeFut: Future[WriteResult]): Future[void] {.async.} =
if writeFut.finished():
@ -620,7 +619,7 @@ proc new[A](
initialAckNr: uint16,
initialTimeout: Duration
): T =
let currentTime = Moment.now()
let currentTime = getMonoTimestamp().moment
T(
remoteAddress: to,
state: state,
@ -793,7 +792,7 @@ proc updateTimeouts(socket: UtpSocket, timeSent: Moment, currentTime: Moment) =
# but usually spec lags after implementation so milliseconds(1000) is used
socket.rto = max(socket.rtt + (socket.rttVar * 4), milliseconds(1000))
proc ackPacket(socket: UtpSocket, seqNr: uint16): AckResult =
proc ackPacket(socket: UtpSocket, seqNr: uint16, currentTime: Moment): AckResult =
let packetOpt = socket.outBuffer.get(seqNr)
if packetOpt.isSome():
let packet = packetOpt.get()
@ -805,8 +804,6 @@ proc ackPacket(socket: UtpSocket, seqNr: uint16): AckResult =
# TODO analyze if this case can happen with our impl
return PacketNotSentYet
let currentTime = Moment.now()
socket.outBuffer.delete(seqNr)
# from spec: The rtt and rtt_var is only updated for packets that were sent only once.
@ -830,11 +827,11 @@ proc ackPacket(socket: UtpSocket, seqNr: uint16): AckResult =
# the packet has already been acked (or not sent)
PacketAlreadyAcked
proc ackPackets(socket: UtpSocket, nrPacketsToAck: uint16) =
proc ackPackets(socket: UtpSocket, nrPacketsToAck: uint16, currentTime: Moment) =
## Ack packets in outgoing buffer based on ack number in the received packet
var i = 0
while i < int(nrPacketsToack):
let result = socket.ackPacket(socket.seqNr - socket.curWindowPackets)
let result = socket.ackPacket(socket.seqNr - socket.curWindowPackets, currentTime)
case result
of PacketAcked:
dec socket.curWindowPackets
@ -890,7 +887,7 @@ proc isAckNrInvalid(socket: UtpSocket, packet: Packet): bool =
# to scheduler which means there could be potentialy several processPacket procs
# running
proc processPacket*(socket: UtpSocket, p: Packet) {.async.} =
let receiptTime = Moment.now()
let timestampInfo = getMonoTimestamp()
if socket.isAckNrInvalid(p):
notice "Received packet with invalid ack nr"
@ -923,11 +920,9 @@ proc processPacket*(socket: UtpSocket, p: Packet) {.async.} =
notice "Received packet is totally of the mark"
return
var (ackedBytes, minRtt) = socket.calculateAckedbytes(acks, receiptTime)
var (ackedBytes, minRtt) = socket.calculateAckedbytes(acks, timestampInfo.moment)
# TODO caluclate bytes acked by selective acks here (if thats the case)
let receiptTimestamp = getMonoTimeTimeStamp()
let sentTimeRemote = p.header.timestamp
# we are using uint32 not a Duration, to wrap a round in case of
@ -939,14 +934,14 @@ proc processPacket*(socket: UtpSocket, p: Packet) {.async.} =
if (sentTimeRemote == 0):
0'u32
else:
receiptTimestamp - sentTimeRemote
timestampInfo.timestamp - sentTimeRemote
socket.replayMicro = remoteDelay
let prevRemoteDelayBase = socket.remoteHistogram.delayBase
if (remoteDelay != 0):
socket.remoteHistogram.addSample(remoteDelay, receiptTime)
socket.remoteHistogram.addSample(remoteDelay, timestampInfo.moment)
# remote new delay base is less than previous
# shift our delay base in other direction to take clock skew into account
@ -959,8 +954,8 @@ proc processPacket*(socket: UtpSocket, p: Packet) {.async.} =
let actualDelay = p.header.timestampDiff
if actualDelay != 0:
socket.ourHistogram.addSample(actualDelay, receiptTime)
socket.driftCalculator.addSample(actualDelay, receiptTime)
socket.ourHistogram.addSample(actualDelay, timestampInfo.moment)
socket.driftCalculator.addSample(actualDelay, timestampInfo.moment)
# adjust base delay if delay estimates exceeds rtt
if (socket.ourHistogram.getValue() > minRtt):
@ -989,7 +984,7 @@ proc processPacket*(socket: UtpSocket, p: Packet) {.async.} =
if (socket.sendBufferTracker.maxRemoteWindow == 0):
# when zeroWindowTimer will be hit and maxRemoteWindow still will be equal to 0
# then it will be reset to minimal value
socket.zeroWindowTimer = Moment.now() + socket.socketConfig.remoteWindowResetTimeout
socket.zeroWindowTimer = timestampInfo.moment + socket.socketConfig.remoteWindowResetTimeout
# socket.curWindowPackets == acks means that this packet acked all remaining packets
# including the sent fin packets
@ -1002,7 +997,7 @@ proc processPacket*(socket: UtpSocket, p: Packet) {.async.} =
# but in theory remote could stil write some data on this socket (or even its own fin)
socket.destroy()
socket.ackPackets(acks)
socket.ackPackets(acks, timestampInfo.moment)
case p.header.pType
of ST_DATA, ST_FIN: