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never use a 6 byte packet number

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According to the IETF draft, the only packet number lengths are 1, 2 and
4 bytes. With the given formula for the packet number derivation, we
would have only sent a 6 byte packet number if the difference between
the largest unacked and the current packet number exceeded 2^31, so this
would never have happened anyway.
This commit is contained in:
Marten Seemann
2017-10-22 00:15:09 +07:00
parent bbe9affa27
commit 6c394acde7
3 changed files with 13 additions and 19 deletions
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12
internal/protocol/packet_number.go
View File

@@ -27,18 +27,14 @@ func delta(a, b PacketNumber) PacketNumber {
return a - b
}
// GetPacketNumberLengthForPublicHeader gets the length of the packet number for the public header
// GetPacketNumberLengthForHeader gets the length of the packet number for the public header
// it never chooses a PacketNumberLen of 1 byte, since this is too short under certain circumstances
func GetPacketNumberLengthForPublicHeader(packetNumber PacketNumber, leastUnacked PacketNumber) PacketNumberLen {
func GetPacketNumberLengthForHeader(packetNumber PacketNumber, leastUnacked PacketNumber) PacketNumberLen {
diff := uint64(packetNumber - leastUnacked)
if diff < (2 << (uint8(PacketNumberLen2)*8 - 2)) {
if diff < (1 << (uint8(PacketNumberLen2)*8 - 1)) {
return PacketNumberLen2
}
if diff < (2 << (uint8(PacketNumberLen4)*8 - 2)) {
return PacketNumberLen4
}
// 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
return PacketNumberLen6
return PacketNumberLen4
}
// GetPacketNumberLength gets the minimum length needed to fully represent the packet number

18
internal/protocol/packet_number_test.go
View File

@@ -129,17 +129,17 @@ var _ = Describe("packet number calculation", func() {
Context("shortening a packet number for the publicHeader", func() {
Context("shortening", func() {
It("sends out low packet numbers as 2 byte", func() {
length := GetPacketNumberLengthForPublicHeader(4, 2)
length := GetPacketNumberLengthForHeader(4, 2)
Expect(length).To(Equal(PacketNumberLen2))
})
It("sends out high packet numbers as 2 byte, if all ACKs are received", func() {
length := GetPacketNumberLengthForPublicHeader(0xDEADBEEF, 0xDEADBEEF-1)
length := GetPacketNumberLengthForHeader(0xDEADBEEF, 0xDEADBEEF-1)
Expect(length).To(Equal(PacketNumberLen2))
})
It("sends out higher packet numbers as 4 bytes, if a lot of ACKs are missing", func() {
length := GetPacketNumberLengthForPublicHeader(40000, 2)
length := GetPacketNumberLengthForHeader(40000, 2)
Expect(length).To(Equal(PacketNumberLen4))
})
})
@@ -149,7 +149,7 @@ var _ = Describe("packet number calculation", func() {
for i := uint64(1); i < 10000; i++ {
packetNumber := PacketNumber(i)
leastUnacked := PacketNumber(1)
length := GetPacketNumberLengthForPublicHeader(packetNumber, leastUnacked)
length := GetPacketNumberLengthForHeader(packetNumber, leastUnacked)
wirePacketNumber := (uint64(packetNumber) << (64 - length*8)) >> (64 - length*8)
inferedPacketNumber := InferPacketNumber(length, leastUnacked, PacketNumber(wirePacketNumber))
@@ -161,7 +161,7 @@ var _ = Describe("packet number calculation", func() {
for i := uint64(1); i < 10000; i++ {
packetNumber := PacketNumber(i)
leastUnacked := PacketNumber(i / 2)
length := GetPacketNumberLengthForPublicHeader(packetNumber, leastUnacked)
length := GetPacketNumberLengthForHeader(packetNumber, leastUnacked)
wirePacketNumber := (uint64(packetNumber) << (64 - length*8)) >> (64 - length*8)
inferedPacketNumber := InferPacketNumber(length, leastUnacked, PacketNumber(wirePacketNumber))
@@ -171,10 +171,10 @@ var _ = Describe("packet number calculation", func() {
It("also works for larger packet numbers", func() {
increment := uint64(1 << (8 - 3))
for i := uint64(1); i < (2 << 46); i += increment {
for i := uint64(1); i < (2 << 31); i += increment {
packetNumber := PacketNumber(i)
leastUnacked := PacketNumber(1)
length := GetPacketNumberLengthForPublicHeader(packetNumber, leastUnacked)
length := GetPacketNumberLengthForHeader(packetNumber, leastUnacked)
wirePacketNumber := (uint64(packetNumber) << (64 - length*8)) >> (64 - length*8)
inferedPacketNumber := InferPacketNumber(length, leastUnacked, PacketNumber(wirePacketNumber))
@@ -185,8 +185,6 @@ var _ = Describe("packet number calculation", func() {
increment = 1 << (2*8 - 3)
case PacketNumberLen4:
increment = 1 << (4*8 - 3)
case PacketNumberLen6:
increment = 1 << (6*8 - 3)
}
}
})
@@ -195,7 +193,7 @@ var _ = Describe("packet number calculation", func() {
for i := (uint64(1) << 48); i < ((uint64(1) << 63) - 1); i += (uint64(1) << 48) {
packetNumber := PacketNumber(i)
leastUnacked := PacketNumber(i - 1000)
length := GetPacketNumberLengthForPublicHeader(packetNumber, leastUnacked)
length := GetPacketNumberLengthForHeader(packetNumber, leastUnacked)
wirePacketNumber := (uint64(packetNumber) << (64 - length*8)) >> (64 - length*8)
inferedPacketNumber := InferPacketNumber(length, leastUnacked, PacketNumber(wirePacketNumber))