57 lines
2.0 KiB
Go
57 lines
2.0 KiB
Go
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package protocol
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// InferPacketNumber calculates the packet number based on the received packet number, its length and the last seen packet number
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func InferPacketNumber(packetNumberLength PacketNumberLen, lastPacketNumber PacketNumber, wirePacketNumber PacketNumber) PacketNumber {
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epochDelta := PacketNumber(1) << (uint8(packetNumberLength) * 8)
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epoch := lastPacketNumber & ^(epochDelta - 1)
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prevEpochBegin := epoch - epochDelta
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nextEpochBegin := epoch + epochDelta
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return closestTo(
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lastPacketNumber+1,
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epoch+wirePacketNumber,
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closestTo(lastPacketNumber+1, prevEpochBegin+wirePacketNumber, nextEpochBegin+wirePacketNumber),
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)
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}
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func closestTo(target, a, b PacketNumber) PacketNumber {
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if delta(target, a) < delta(target, b) {
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return a
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}
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return b
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}
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func delta(a, b PacketNumber) PacketNumber {
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if a < b {
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return b - a
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}
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return a - b
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}
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// GetPacketNumberLengthForPublicHeader gets the length of the packet number for the public header
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// it never chooses a PacketNumberLen of 1 byte, since this is too short under certain circumstances
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func GetPacketNumberLengthForPublicHeader(packetNumber PacketNumber, leastUnacked PacketNumber) PacketNumberLen {
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diff := uint64(packetNumber - leastUnacked)
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if diff < (2 << (uint8(PacketNumberLen2)*8 - 2)) {
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return PacketNumberLen2
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}
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if diff < (2 << (uint8(PacketNumberLen4)*8 - 2)) {
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return PacketNumberLen4
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}
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// we do not check if there are less than 2^46 packets in flight, since flow control and congestion control will limit this number *a lot* sooner
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return PacketNumberLen6
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}
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// GetPacketNumberLength gets the minimum length needed to fully represent the packet number
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func GetPacketNumberLength(packetNumber PacketNumber) PacketNumberLen {
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if packetNumber < (1 << (uint8(PacketNumberLen1) * 8)) {
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return PacketNumberLen1
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}
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if packetNumber < (1 << (uint8(PacketNumberLen2) * 8)) {
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return PacketNumberLen2
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}
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if packetNumber < (1 << (uint8(PacketNumberLen4) * 8)) {
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return PacketNumberLen4
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}
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return PacketNumberLen6
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}
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