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package flowcontrol
import (
"sync"
"time"
"github.com/quic-go/quic-go/internal/protocol"
"github.com/quic-go/quic-go/internal/utils"
)
type baseFlowController struct {
// for sending data
bytesSent protocol.ByteCount
sendWindow protocol.ByteCount
lastBlockedAt protocol.ByteCount
// for receiving data
//nolint:structcheck // The mutex is used both by the stream and the connection flow controller
mutex sync.Mutex
bytesRead protocol.ByteCount
highestReceived protocol.ByteCount
receiveWindow protocol.ByteCount
receiveWindowSize protocol.ByteCount
maxReceiveWindowSize protocol.ByteCount
allowWindowIncrease func(size protocol.ByteCount) bool
epochStartTime time.Time
epochStartOffset protocol.ByteCount
rttStats *utils.RTTStats
logger utils.Logger
}
// IsNewlyBlocked says if it is newly blocked by flow control.
// For every offset, it only returns true once.
// If it is blocked, the offset is returned.
func (c *baseFlowController) IsNewlyBlocked() (bool, protocol.ByteCount) {
if c.SendWindowSize() != 0 || c.sendWindow == c.lastBlockedAt {
return false, 0
}
c.lastBlockedAt = c.sendWindow
return true, c.sendWindow
}
func (c *baseFlowController) AddBytesSent(n protocol.ByteCount) {
c.bytesSent += n
}
// UpdateSendWindow is called after receiving a MAX_{STREAM_}DATA frame.
func (c *baseFlowController) UpdateSendWindow(offset protocol.ByteCount) (updated bool) {
if offset > c.sendWindow {
c.sendWindow = offset
return true
}
return false
}
func (c *baseFlowController) SendWindowSize() protocol.ByteCount {
// this only happens during connection establishment, when data is sent before we receive the peer's transport parameters
if c.bytesSent > c.sendWindow {
return 0
}
return c.sendWindow - c.bytesSent
}
// needs to be called with locked mutex
func (c *baseFlowController) addBytesRead(n protocol.ByteCount) {
c.bytesRead += n
}
func (c *baseFlowController) hasWindowUpdate() bool {
bytesRemaining := c.receiveWindow - c.bytesRead
// update the window when more than the threshold was consumed
return bytesRemaining <= protocol.ByteCount(float64(c.receiveWindowSize)*(1-protocol.WindowUpdateThreshold))
}
// getWindowUpdate updates the receive window, if necessary
// it returns the new offset
func (c *baseFlowController) getWindowUpdate(now time.Time) protocol.ByteCount {
if !c.hasWindowUpdate() {
return 0
}
c.maybeAdjustWindowSize(now)
c.receiveWindow = c.bytesRead + c.receiveWindowSize
return c.receiveWindow
}
// maybeAdjustWindowSize increases the receiveWindowSize if we're sending updates too often.
// For details about auto-tuning, see https://docs.google.com/document/d/1SExkMmGiz8VYzV3s9E35JQlJ73vhzCekKkDi85F1qCE/edit?usp=sharing.
func (c *baseFlowController) maybeAdjustWindowSize(now time.Time) {
bytesReadInEpoch := c.bytesRead - c.epochStartOffset
// don't do anything if less than half the window has been consumed
if bytesReadInEpoch <= c.receiveWindowSize/2 {
return
}
rtt := c.rttStats.SmoothedRTT()
if rtt == 0 {
return
}
fraction := float64(bytesReadInEpoch) / float64(c.receiveWindowSize)
if now.Sub(c.epochStartTime) < time.Duration(4*fraction*float64(rtt)) {
// window is consumed too fast, try to increase the window size
newSize := min(2*c.receiveWindowSize, c.maxReceiveWindowSize)
if newSize > c.receiveWindowSize && (c.allowWindowIncrease == nil || c.allowWindowIncrease(newSize-c.receiveWindowSize)) {
c.receiveWindowSize = newSize
}
}
c.startNewAutoTuningEpoch(now)
}
func (c *baseFlowController) startNewAutoTuningEpoch(now time.Time) {
c.epochStartTime = now
c.epochStartOffset = c.bytesRead
}
func (c *baseFlowController) checkFlowControlViolation() bool {
return c.highestReceived > c.receiveWindow
}
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