package quic

import (
	"bytes"
	"math"

	"github.com/lucas-clemente/quic-go/ackhandler"
	"github.com/lucas-clemente/quic-go/internal/flowcontrol"
	"github.com/lucas-clemente/quic-go/internal/handshake"
	"github.com/lucas-clemente/quic-go/internal/protocol"
	"github.com/lucas-clemente/quic-go/internal/wire"
	. "github.com/onsi/ginkgo"
	. "github.com/onsi/gomega"
)

type mockSealer struct{}

func (s *mockSealer) Seal(dst, src []byte, packetNumber protocol.PacketNumber, associatedData []byte) []byte {
	return append(src, bytes.Repeat([]byte{0}, 12)...)
}

func (s *mockSealer) Overhead() int { return 12 }

var _ handshake.Sealer = &mockSealer{}

type mockCryptoSetup struct {
	handleErr          error
	divNonce           []byte
	encLevelSeal       protocol.EncryptionLevel
	encLevelSealCrypto protocol.EncryptionLevel
}

var _ handshake.CryptoSetup = &mockCryptoSetup{}

func (m *mockCryptoSetup) HandleCryptoStream() error {
	return m.handleErr
}
func (m *mockCryptoSetup) Open(dst, src []byte, packetNumber protocol.PacketNumber, associatedData []byte) ([]byte, protocol.EncryptionLevel, error) {
	return nil, protocol.EncryptionUnspecified, nil
}
func (m *mockCryptoSetup) GetSealer() (protocol.EncryptionLevel, handshake.Sealer) {
	return m.encLevelSeal, &mockSealer{}
}
func (m *mockCryptoSetup) GetSealerForCryptoStream() (protocol.EncryptionLevel, handshake.Sealer) {
	return m.encLevelSealCrypto, &mockSealer{}
}
func (m *mockCryptoSetup) GetSealerWithEncryptionLevel(protocol.EncryptionLevel) (handshake.Sealer, error) {
	return &mockSealer{}, nil
}
func (m *mockCryptoSetup) DiversificationNonce() []byte            { return m.divNonce }
func (m *mockCryptoSetup) SetDiversificationNonce(divNonce []byte) { m.divNonce = divNonce }

var _ = Describe("Packet packer", func() {
	var (
		packer          *packetPacker
		publicHeaderLen protocol.ByteCount
		maxFrameSize    protocol.ByteCount
		streamFramer    *streamFramer
		cryptoStream    *stream
	)

	BeforeEach(func() {
		version := versionGQUICFrames
		cryptoStream = &stream{streamID: version.CryptoStreamID(), flowController: flowcontrol.NewStreamFlowController(version.CryptoStreamID(), false, flowcontrol.NewConnectionFlowController(1000, 1000, nil), 1000, 1000, 1000, nil)}
		streamsMap := newStreamsMap(nil, protocol.PerspectiveServer, versionGQUICFrames)
		streamFramer = newStreamFramer(cryptoStream, streamsMap, nil, versionGQUICFrames)

		packer = &packetPacker{
			cryptoSetup:           &mockCryptoSetup{encLevelSeal: protocol.EncryptionForwardSecure},
			connectionID:          0x1337,
			packetNumberGenerator: newPacketNumberGenerator(1, protocol.SkipPacketAveragePeriodLength),
			streamFramer:          streamFramer,
			perspective:           protocol.PerspectiveServer,
		}
		publicHeaderLen = 1 + 8 + 2 // 1 flag byte, 8 connection ID, 2 packet number
		maxFrameSize = protocol.MaxPacketSize - protocol.ByteCount((&mockSealer{}).Overhead()) - publicHeaderLen
		packer.hasSentPacket = true
		packer.version = version
	})

	It("returns nil when no packet is queued", func() {
		p, err := packer.PackPacket()
		Expect(p).To(BeNil())
		Expect(err).ToNot(HaveOccurred())
	})

	It("packs single packets", func() {
		f := &wire.StreamFrame{
			StreamID: 5,
			Data:     []byte{0xDE, 0xCA, 0xFB, 0xAD},
		}
		streamFramer.AddFrameForRetransmission(f)
		p, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p).ToNot(BeNil())
		b := &bytes.Buffer{}
		f.Write(b, packer.version)
		Expect(p.frames).To(HaveLen(1))
		Expect(p.raw).To(ContainSubstring(string(b.Bytes())))
	})

	It("stores the encryption level a packet was sealed with", func() {
		packer.cryptoSetup.(*mockCryptoSetup).encLevelSeal = protocol.EncryptionForwardSecure
		f := &wire.StreamFrame{
			StreamID: 5,
			Data:     []byte("foobar"),
		}
		streamFramer.AddFrameForRetransmission(f)
		p, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p.encryptionLevel).To(Equal(protocol.EncryptionForwardSecure))
	})

	Context("generating a packet header", func() {
		const (
			versionPublicHeader = protocol.Version39  // a QUIC version that uses the Public Header format
			versionIETFHeader   = protocol.VersionTLS // a QUIC version taht uses the IETF Header format
		)

		Context("Public Header (for gQUIC)", func() {
			BeforeEach(func() {
				packer.version = versionPublicHeader
			})

			It("it omits the connection ID for forward-secure packets", func() {
				ph := packer.getHeader(protocol.EncryptionForwardSecure)
				Expect(ph.OmitConnectionID).To(BeFalse())
				packer.SetOmitConnectionID()
				ph = packer.getHeader(protocol.EncryptionForwardSecure)
				Expect(ph.OmitConnectionID).To(BeTrue())
			})

			It("doesn't omit the connection ID for non-forward-secure packets", func() {
				packer.SetOmitConnectionID()
				ph := packer.getHeader(protocol.EncryptionSecure)
				Expect(ph.OmitConnectionID).To(BeFalse())
			})

			It("adds the Version Flag to the Public Header before the crypto handshake is finished", func() {
				packer.perspective = protocol.PerspectiveClient
				ph := packer.getHeader(protocol.EncryptionSecure)
				Expect(ph.VersionFlag).To(BeTrue())
			})

			It("doesn't add the Version Flag to the Public Header for forward-secure packets", func() {
				packer.perspective = protocol.PerspectiveClient
				ph := packer.getHeader(protocol.EncryptionForwardSecure)
				Expect(ph.VersionFlag).To(BeFalse())
			})

			Context("diversificaton nonces", func() {
				var nonce []byte

				BeforeEach(func() {
					nonce = bytes.Repeat([]byte{'e'}, 32)
					packer.cryptoSetup.(*mockCryptoSetup).divNonce = nonce
				})

				It("doesn't include a div nonce, when sending a packet with initial encryption", func() {
					ph := packer.getHeader(protocol.EncryptionUnencrypted)
					Expect(ph.DiversificationNonce).To(BeEmpty())
				})

				It("includes a div nonce, when sending a packet with secure encryption", func() {
					ph := packer.getHeader(protocol.EncryptionSecure)
					Expect(ph.DiversificationNonce).To(Equal(nonce))
				})

				It("doesn't include a div nonce, when sending a packet with forward-secure encryption", func() {
					ph := packer.getHeader(protocol.EncryptionForwardSecure)
					Expect(ph.DiversificationNonce).To(BeEmpty())
				})

				It("doesn't send a div nonce as a client", func() {
					packer.perspective = protocol.PerspectiveClient
					ph := packer.getHeader(protocol.EncryptionSecure)
					Expect(ph.DiversificationNonce).To(BeEmpty())
				})
			})
		})

		Context("Header (for IETF draft QUIC)", func() {
			BeforeEach(func() {
				packer.version = versionIETFHeader
			})

			It("uses the Long Header format for non-forward-secure packets", func() {
				h := packer.getHeader(protocol.EncryptionSecure)
				Expect(h.IsLongHeader).To(BeTrue())
				Expect(h.PacketNumberLen).To(Equal(protocol.PacketNumberLen4))
				Expect(h.Version).To(Equal(versionIETFHeader))
			})

			It("uses the Short Header format for forward-secure packets", func() {
				h := packer.getHeader(protocol.EncryptionForwardSecure)
				Expect(h.IsLongHeader).To(BeFalse())
				Expect(h.PacketNumberLen).To(BeNumerically(">", 0))
			})

			It("it omits the connection ID for forward-secure packets", func() {
				h := packer.getHeader(protocol.EncryptionForwardSecure)
				Expect(h.OmitConnectionID).To(BeFalse())
				packer.SetOmitConnectionID()
				h = packer.getHeader(protocol.EncryptionForwardSecure)
				Expect(h.OmitConnectionID).To(BeTrue())
			})

			It("doesn't omit the connection ID for non-forward-secure packets", func() {
				packer.SetOmitConnectionID()
				h := packer.getHeader(protocol.EncryptionSecure)
				Expect(h.OmitConnectionID).To(BeFalse())
			})
		})
	})

	It("packs a ConnectionClose", func() {
		ccf := wire.ConnectionCloseFrame{
			ErrorCode:    0x1337,
			ReasonPhrase: "foobar",
		}
		p, err := packer.PackConnectionClose(&ccf)
		Expect(err).ToNot(HaveOccurred())
		Expect(p.frames).To(HaveLen(1))
		Expect(p.frames[0]).To(Equal(&ccf))
	})

	It("doesn't send any other frames when sending a ConnectionClose", func() {
		ccf := wire.ConnectionCloseFrame{
			ErrorCode:    0x1337,
			ReasonPhrase: "foobar",
		}
		packer.controlFrames = []wire.Frame{&wire.MaxStreamDataFrame{StreamID: 37}}
		streamFramer.AddFrameForRetransmission(&wire.StreamFrame{
			StreamID: 5,
			Data:     []byte("foobar"),
		})
		p, err := packer.PackConnectionClose(&ccf)
		Expect(err).ToNot(HaveOccurred())
		Expect(p.frames).To(HaveLen(1))
		Expect(p.frames[0]).To(Equal(&ccf))
	})

	It("packs only control frames", func() {
		packer.QueueControlFrame(&wire.RstStreamFrame{})
		packer.QueueControlFrame(&wire.MaxDataFrame{})
		p, err := packer.PackPacket()
		Expect(p).ToNot(BeNil())
		Expect(err).ToNot(HaveOccurred())
		Expect(p.frames).To(HaveLen(2))
		Expect(p.raw).NotTo(BeEmpty())
	})

	It("increases the packet number", func() {
		packer.QueueControlFrame(&wire.RstStreamFrame{})
		p1, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p1).ToNot(BeNil())
		packer.QueueControlFrame(&wire.RstStreamFrame{})
		p2, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p2).ToNot(BeNil())
		Expect(p2.header.PacketNumber).To(BeNumerically(">", p1.header.PacketNumber))
	})

	It("packs a STOP_WAITING frame first", func() {
		packer.packetNumberGenerator.next = 15
		swf := &wire.StopWaitingFrame{LeastUnacked: 10}
		packer.QueueControlFrame(&wire.RstStreamFrame{})
		packer.QueueControlFrame(swf)
		p, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p).ToNot(BeNil())
		Expect(p.frames).To(HaveLen(2))
		Expect(p.frames[0]).To(Equal(swf))
	})

	It("sets the LeastUnackedDelta length of a STOP_WAITING frame", func() {
		packetNumber := protocol.PacketNumber(0xDECAFB) // will result in a 4 byte packet number
		packer.packetNumberGenerator.next = packetNumber
		swf := &wire.StopWaitingFrame{LeastUnacked: packetNumber - 0x100}
		packer.QueueControlFrame(&wire.RstStreamFrame{})
		packer.QueueControlFrame(swf)
		p, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p.frames[0].(*wire.StopWaitingFrame).PacketNumberLen).To(Equal(protocol.PacketNumberLen4))
	})

	It("does not pack a packet containing only a STOP_WAITING frame", func() {
		swf := &wire.StopWaitingFrame{LeastUnacked: 10}
		packer.QueueControlFrame(swf)
		p, err := packer.PackPacket()
		Expect(p).To(BeNil())
		Expect(err).ToNot(HaveOccurred())
	})

	It("packs a packet if it has queued control frames, but no new control frames", func() {
		packer.controlFrames = []wire.Frame{&wire.BlockedFrame{}}
		p, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p).ToNot(BeNil())
	})

	It("refuses to send a packet that doesn't contain crypto stream data, if it has never sent a packet before", func() {
		packer.hasSentPacket = false
		packer.controlFrames = []wire.Frame{&wire.BlockedFrame{}}
		p, err := packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p).To(BeNil())
	})

	It("packs many control frames into 1 packets", func() {
		f := &wire.AckFrame{LargestAcked: 1}
		b := &bytes.Buffer{}
		err := f.Write(b, packer.version)
		Expect(err).ToNot(HaveOccurred())
		maxFramesPerPacket := int(maxFrameSize) / b.Len()
		var controlFrames []wire.Frame
		for i := 0; i < maxFramesPerPacket; i++ {
			controlFrames = append(controlFrames, f)
		}
		packer.controlFrames = controlFrames
		payloadFrames, err := packer.composeNextPacket(maxFrameSize, false)
		Expect(err).ToNot(HaveOccurred())
		Expect(payloadFrames).To(HaveLen(maxFramesPerPacket))
		payloadFrames, err = packer.composeNextPacket(maxFrameSize, false)
		Expect(err).ToNot(HaveOccurred())
		Expect(payloadFrames).To(BeEmpty())
	})

	It("packs a lot of control frames into 2 packets if they don't fit into one", func() {
		blockedFrame := &wire.BlockedFrame{}
		minLength, _ := blockedFrame.MinLength(packer.version)
		maxFramesPerPacket := int(maxFrameSize) / int(minLength)
		var controlFrames []wire.Frame
		for i := 0; i < maxFramesPerPacket+10; i++ {
			controlFrames = append(controlFrames, blockedFrame)
		}
		packer.controlFrames = controlFrames
		payloadFrames, err := packer.composeNextPacket(maxFrameSize, false)
		Expect(err).ToNot(HaveOccurred())
		Expect(payloadFrames).To(HaveLen(maxFramesPerPacket))
		payloadFrames, err = packer.composeNextPacket(maxFrameSize, false)
		Expect(err).ToNot(HaveOccurred())
		Expect(payloadFrames).To(HaveLen(10))
	})

	It("only increases the packet number when there is an actual packet to send", func() {
		packer.packetNumberGenerator.nextToSkip = 1000
		p, err := packer.PackPacket()
		Expect(p).To(BeNil())
		Expect(err).ToNot(HaveOccurred())
		Expect(packer.packetNumberGenerator.Peek()).To(Equal(protocol.PacketNumber(1)))
		f := &wire.StreamFrame{
			StreamID: 5,
			Data:     []byte{0xDE, 0xCA, 0xFB, 0xAD},
		}
		streamFramer.AddFrameForRetransmission(f)
		p, err = packer.PackPacket()
		Expect(err).ToNot(HaveOccurred())
		Expect(p).ToNot(BeNil())
		Expect(p.header.PacketNumber).To(Equal(protocol.PacketNumber(1)))
		Expect(packer.packetNumberGenerator.Peek()).To(Equal(protocol.PacketNumber(2)))
	})

	Context("STREAM Frame handling", func() {
		It("does not splits a STREAM frame with maximum size, for gQUIC frames", func() {
			f := &wire.StreamFrame{
				Offset:         1,
				StreamID:       5,
				DataLenPresent: false,
			}
			minLength, _ := f.MinLength(packer.version)
			maxStreamFrameDataLen := maxFrameSize - minLength
			f.Data = bytes.Repeat([]byte{'f'}, int(maxStreamFrameDataLen))
			streamFramer.AddFrameForRetransmission(f)
			payloadFrames, err := packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(HaveLen(1))
			Expect(payloadFrames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			payloadFrames, err = packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(BeEmpty())
		})

		It("does not splits a STREAM frame with maximum size, for IETF draft style frame", func() {
			packer.version = versionIETFFrames
			streamFramer.version = versionIETFFrames
			f := &wire.StreamFrame{
				Offset:         1,
				StreamID:       5,
				DataLenPresent: true,
			}
			minLength, _ := f.MinLength(packer.version)
			// for IETF draft style STREAM frames, we don't know the size of the DataLen, because it is a variable length integer
			// in the general case, we therefore use a STREAM frame that is 1 byte smaller than the maximum size
			maxStreamFrameDataLen := maxFrameSize - minLength - 1
			f.Data = bytes.Repeat([]byte{'f'}, int(maxStreamFrameDataLen))
			streamFramer.AddFrameForRetransmission(f)
			payloadFrames, err := packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(HaveLen(1))
			Expect(payloadFrames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			payloadFrames, err = packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(BeEmpty())
		})

		It("correctly handles a STREAM frame with one byte less than maximum size", func() {
			maxStreamFrameDataLen := maxFrameSize - (1 + 1 + 2) - 1
			f1 := &wire.StreamFrame{
				StreamID: 5,
				Offset:   1,
				Data:     bytes.Repeat([]byte{'f'}, int(maxStreamFrameDataLen)),
			}
			f2 := &wire.StreamFrame{
				StreamID: 5,
				Offset:   1,
				Data:     []byte("foobar"),
			}
			streamFramer.AddFrameForRetransmission(f1)
			streamFramer.AddFrameForRetransmission(f2)
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p.raw).To(HaveLen(int(protocol.MaxPacketSize - 1)))
			Expect(p.frames).To(HaveLen(1))
			Expect(p.frames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			p, err = packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p.frames).To(HaveLen(1))
			Expect(p.frames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
		})

		It("packs multiple small STREAM frames into single packet", func() {
			f1 := &wire.StreamFrame{
				StreamID: 5,
				Data:     []byte{0xDE, 0xCA, 0xFB, 0xAD},
			}
			f2 := &wire.StreamFrame{
				StreamID: 5,
				Data:     []byte{0xBE, 0xEF, 0x13, 0x37},
			}
			f3 := &wire.StreamFrame{
				StreamID: 3,
				Data:     []byte{0xCA, 0xFE},
			}
			streamFramer.AddFrameForRetransmission(f1)
			streamFramer.AddFrameForRetransmission(f2)
			streamFramer.AddFrameForRetransmission(f3)
			p, err := packer.PackPacket()
			Expect(p).ToNot(BeNil())
			Expect(err).ToNot(HaveOccurred())
			b := &bytes.Buffer{}
			f1.Write(b, 0)
			f2.Write(b, 0)
			f3.Write(b, 0)
			Expect(p.frames).To(HaveLen(3))
			Expect(p.frames[0].(*wire.StreamFrame).DataLenPresent).To(BeTrue())
			Expect(p.frames[1].(*wire.StreamFrame).DataLenPresent).To(BeTrue())
			Expect(p.frames[2].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			Expect(p.raw).To(ContainSubstring(string(f1.Data)))
			Expect(p.raw).To(ContainSubstring(string(f2.Data)))
			Expect(p.raw).To(ContainSubstring(string(f3.Data)))
		})

		It("splits one STREAM frame larger than maximum size", func() {
			f := &wire.StreamFrame{
				StreamID: 7,
				Offset:   1,
			}
			minLength, _ := f.MinLength(packer.version)
			maxStreamFrameDataLen := maxFrameSize - minLength
			f.Data = bytes.Repeat([]byte{'f'}, int(maxStreamFrameDataLen)+200)
			streamFramer.AddFrameForRetransmission(f)
			payloadFrames, err := packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(HaveLen(1))
			Expect(payloadFrames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			Expect(payloadFrames[0].(*wire.StreamFrame).Data).To(HaveLen(int(maxStreamFrameDataLen)))
			payloadFrames, err = packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(HaveLen(1))
			Expect(payloadFrames[0].(*wire.StreamFrame).Data).To(HaveLen(200))
			Expect(payloadFrames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			payloadFrames, err = packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(BeEmpty())
		})

		It("packs 2 STREAM frames that are too big for one packet correctly", func() {
			maxStreamFrameDataLen := maxFrameSize - (1 + 1 + 2)
			f1 := &wire.StreamFrame{
				StreamID: 5,
				Data:     bytes.Repeat([]byte{'f'}, int(maxStreamFrameDataLen)+100),
				Offset:   1,
			}
			f2 := &wire.StreamFrame{
				StreamID: 5,
				Data:     bytes.Repeat([]byte{'f'}, int(maxStreamFrameDataLen)+100),
				Offset:   1,
			}
			streamFramer.AddFrameForRetransmission(f1)
			streamFramer.AddFrameForRetransmission(f2)
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p.frames).To(HaveLen(1))
			Expect(p.frames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			Expect(p.raw).To(HaveLen(int(protocol.MaxPacketSize)))
			p, err = packer.PackPacket()
			Expect(p.frames).To(HaveLen(2))
			Expect(p.frames[0].(*wire.StreamFrame).DataLenPresent).To(BeTrue())
			Expect(p.frames[1].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			Expect(err).ToNot(HaveOccurred())
			Expect(p.raw).To(HaveLen(int(protocol.MaxPacketSize)))
			p, err = packer.PackPacket()
			Expect(p.frames).To(HaveLen(1))
			Expect(p.frames[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
			Expect(err).ToNot(HaveOccurred())
			Expect(p).ToNot(BeNil())
			p, err = packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p).To(BeNil())
		})

		It("packs a packet that has the maximum packet size when given a large enough STREAM frame", func() {
			f := &wire.StreamFrame{
				StreamID: 5,
				Offset:   1,
			}
			minLength, _ := f.MinLength(packer.version)
			f.Data = bytes.Repeat([]byte{'f'}, int(maxFrameSize-minLength+1)) // + 1 since MinceLength is 1 bigger than the actual StreamFrame header
			streamFramer.AddFrameForRetransmission(f)
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p).ToNot(BeNil())
			Expect(p.raw).To(HaveLen(int(protocol.MaxPacketSize)))
		})

		It("splits a STREAM frame larger than the maximum size", func() {
			f := &wire.StreamFrame{
				StreamID: 5,
				Offset:   1,
			}
			minLength, _ := f.MinLength(packer.version)
			f.Data = bytes.Repeat([]byte{'f'}, int(maxFrameSize-minLength+2)) // + 2 since MinceLength is 1 bigger than the actual StreamFrame header

			streamFramer.AddFrameForRetransmission(f)
			payloadFrames, err := packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(HaveLen(1))
			payloadFrames, err = packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(payloadFrames).To(HaveLen(1))
		})

		It("refuses to send unencrypted stream data on a data stream", func() {
			packer.cryptoSetup.(*mockCryptoSetup).encLevelSeal = protocol.EncryptionUnencrypted
			f := &wire.StreamFrame{
				StreamID: 3,
				Data:     []byte("foobar"),
			}
			streamFramer.AddFrameForRetransmission(f)
			p, err := packer.PackPacket()
			Expect(err).NotTo(HaveOccurred())
			Expect(p).To(BeNil())
		})

		It("sends non forward-secure data as the client", func() {
			packer.perspective = protocol.PerspectiveClient
			packer.cryptoSetup.(*mockCryptoSetup).encLevelSeal = protocol.EncryptionSecure
			f := &wire.StreamFrame{
				StreamID: 5,
				Data:     []byte("foobar"),
			}
			streamFramer.AddFrameForRetransmission(f)
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p.encryptionLevel).To(Equal(protocol.EncryptionSecure))
			Expect(p.frames[0]).To(Equal(f))
		})

		It("does not send non forward-secure data as the server", func() {
			packer.cryptoSetup.(*mockCryptoSetup).encLevelSeal = protocol.EncryptionSecure
			f := &wire.StreamFrame{
				StreamID: 5,
				Data:     []byte("foobar"),
			}
			streamFramer.AddFrameForRetransmission(f)
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p).To(BeNil())
		})

		It("sends unencrypted stream data on the crypto stream", func() {
			packer.cryptoSetup.(*mockCryptoSetup).encLevelSealCrypto = protocol.EncryptionUnencrypted
			cryptoStream.dataForWriting = []byte("foobar")
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p.encryptionLevel).To(Equal(protocol.EncryptionUnencrypted))
			Expect(p.frames).To(HaveLen(1))
			Expect(p.frames[0]).To(Equal(&wire.StreamFrame{
				StreamID: packer.version.CryptoStreamID(),
				Data:     []byte("foobar"),
			}))
		})

		It("sends encrypted stream data on the crypto stream", func() {
			packer.cryptoSetup.(*mockCryptoSetup).encLevelSealCrypto = protocol.EncryptionSecure
			cryptoStream.dataForWriting = []byte("foobar")
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p.encryptionLevel).To(Equal(protocol.EncryptionSecure))
			Expect(p.frames).To(HaveLen(1))
			Expect(p.frames[0]).To(Equal(&wire.StreamFrame{
				StreamID: packer.version.CryptoStreamID(),
				Data:     []byte("foobar"),
			}))
		})

		It("does not pack stream frames if not allowed", func() {
			packer.cryptoSetup.(*mockCryptoSetup).encLevelSeal = protocol.EncryptionUnencrypted
			packer.QueueControlFrame(&wire.AckFrame{})
			streamFramer.AddFrameForRetransmission(&wire.StreamFrame{StreamID: 3, Data: []byte("foobar")})
			p, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(p.frames).To(HaveLen(1))
			Expect(func() { _ = p.frames[0].(*wire.AckFrame) }).NotTo(Panic())
		})
	})

	Context("BLOCKED frames", func() {
		It("queues a BLOCKED frame", func() {
			length := 100
			streamFramer.blockedFrameQueue = []wire.Frame{&wire.StreamBlockedFrame{StreamID: 5}}
			f := &wire.StreamFrame{
				StreamID: 5,
				Data:     bytes.Repeat([]byte{'f'}, length),
			}
			streamFramer.AddFrameForRetransmission(f)
			_, err := packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(packer.controlFrames[0]).To(Equal(&wire.StreamBlockedFrame{StreamID: 5}))
		})

		It("removes the dataLen attribute from the last StreamFrame, even if it queued a BLOCKED frame", func() {
			length := 100
			streamFramer.blockedFrameQueue = []wire.Frame{&wire.StreamBlockedFrame{StreamID: 5}}
			f := &wire.StreamFrame{
				StreamID: 5,
				Data:     bytes.Repeat([]byte{'f'}, length),
			}
			streamFramer.AddFrameForRetransmission(f)
			p, err := packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(p).To(HaveLen(1))
			Expect(p[0].(*wire.StreamFrame).DataLenPresent).To(BeFalse())
		})

		It("packs a connection-level BlockedFrame", func() {
			streamFramer.blockedFrameQueue = []wire.Frame{&wire.BlockedFrame{}}
			f := &wire.StreamFrame{
				StreamID: 5,
				Data:     []byte("foobar"),
			}
			streamFramer.AddFrameForRetransmission(f)
			_, err := packer.composeNextPacket(maxFrameSize, true)
			Expect(err).ToNot(HaveOccurred())
			Expect(packer.controlFrames[0]).To(Equal(&wire.BlockedFrame{}))
		})
	})

	It("returns nil if we only have a single STOP_WAITING", func() {
		packer.QueueControlFrame(&wire.StopWaitingFrame{})
		p, err := packer.PackPacket()
		Expect(err).NotTo(HaveOccurred())
		Expect(p).To(BeNil())
	})

	It("packs a single ACK", func() {
		ack := &wire.AckFrame{LargestAcked: 42}
		packer.QueueControlFrame(ack)
		p, err := packer.PackPacket()
		Expect(err).NotTo(HaveOccurred())
		Expect(p).ToNot(BeNil())
		Expect(p.frames[0]).To(Equal(ack))
	})

	It("does not return nil if we only have a single ACK but request it to be sent", func() {
		ack := &wire.AckFrame{}
		packer.QueueControlFrame(ack)
		p, err := packer.PackPacket()
		Expect(err).NotTo(HaveOccurred())
		Expect(p).ToNot(BeNil())
	})

	It("queues a control frame to be sent in the next packet", func() {
		msd := &wire.MaxStreamDataFrame{StreamID: 5}
		packer.QueueControlFrame(msd)
		p, err := packer.PackPacket()
		Expect(err).NotTo(HaveOccurred())
		Expect(p.frames).To(HaveLen(1))
		Expect(p.frames[0]).To(Equal(msd))
	})

	Context("retransmitting of handshake packets", func() {
		swf := &wire.StopWaitingFrame{LeastUnacked: 1}
		sf := &wire.StreamFrame{
			StreamID: 1,
			Data:     []byte("foobar"),
		}

		BeforeEach(func() {
			packer.QueueControlFrame(swf)
		})

		It("packs a retransmission for a packet sent with no encryption", func() {
			packet := &ackhandler.Packet{
				EncryptionLevel: protocol.EncryptionUnencrypted,
				Frames:          []wire.Frame{sf},
			}
			p, err := packer.PackHandshakeRetransmission(packet)
			Expect(err).ToNot(HaveOccurred())
			Expect(p.frames).To(ContainElement(sf))
			Expect(p.frames).To(ContainElement(swf))
			Expect(p.encryptionLevel).To(Equal(protocol.EncryptionUnencrypted))
		})

		It("packs a retransmission for a packet sent with initial encryption", func() {
			nonce := bytes.Repeat([]byte{'e'}, 32)
			packer.cryptoSetup.(*mockCryptoSetup).divNonce = nonce
			packet := &ackhandler.Packet{
				EncryptionLevel: protocol.EncryptionSecure,
				Frames:          []wire.Frame{sf},
			}
			p, err := packer.PackHandshakeRetransmission(packet)
			Expect(err).ToNot(HaveOccurred())
			Expect(p.frames).To(ContainElement(sf))
			Expect(p.frames).To(ContainElement(swf))
			Expect(p.encryptionLevel).To(Equal(protocol.EncryptionSecure))
			// a packet sent by the server with initial encryption contains the SHLO
			// it needs to have a diversification nonce
			Expect(p.raw).To(ContainSubstring(string(nonce)))
		})

		It("includes the diversification nonce on packets sent with initial encryption", func() {
			packet := &ackhandler.Packet{
				EncryptionLevel: protocol.EncryptionSecure,
				Frames:          []wire.Frame{sf},
			}
			p, err := packer.PackHandshakeRetransmission(packet)
			Expect(err).ToNot(HaveOccurred())
			Expect(p.encryptionLevel).To(Equal(protocol.EncryptionSecure))
		})

		// this should never happen, since non forward-secure packets are limited to a size smaller than MaxPacketSize, such that it is always possible to retransmit them without splitting the StreamFrame
		// (note that the retransmitted packet needs to have enough space for the StopWaitingFrame)
		It("refuses to send a packet larger than MaxPacketSize", func() {
			packet := &ackhandler.Packet{
				EncryptionLevel: protocol.EncryptionSecure,
				Frames: []wire.Frame{
					&wire.StreamFrame{
						StreamID: 1,
						Data:     bytes.Repeat([]byte{'f'}, int(protocol.MaxPacketSize-5)),
					},
				},
			}
			_, err := packer.PackHandshakeRetransmission(packet)
			Expect(err).To(MatchError("PacketPacker BUG: packet too large"))
		})

		It("pads Initial packets to the required minimum packet size", func() {
			packer.version = protocol.VersionTLS
			packer.hasSentPacket = false
			packer.perspective = protocol.PerspectiveClient
			packer.cryptoSetup.(*mockCryptoSetup).encLevelSealCrypto = protocol.EncryptionUnencrypted
			cryptoStream.dataForWriting = []byte("foobar")
			packet, err := packer.PackPacket()
			Expect(err).ToNot(HaveOccurred())
			Expect(packet.raw).To(HaveLen(protocol.MinInitialPacketSize))
			Expect(packet.frames).To(HaveLen(1))
			sf := packet.frames[0].(*wire.StreamFrame)
			Expect(sf.Data).To(Equal([]byte("foobar")))
			Expect(sf.DataLenPresent).To(BeTrue())
		})

		It("refuses to retransmit packets that were sent with forward-secure encryption", func() {
			p := &ackhandler.Packet{
				EncryptionLevel: protocol.EncryptionForwardSecure,
			}
			_, err := packer.PackHandshakeRetransmission(p)
			Expect(err).To(MatchError("PacketPacker BUG: forward-secure encrypted handshake packets don't need special treatment"))
		})

		It("refuses to retransmit packets without a STOP_WAITING Frame", func() {
			packer.stopWaiting = nil
			_, err := packer.PackHandshakeRetransmission(&ackhandler.Packet{
				EncryptionLevel: protocol.EncryptionSecure,
			})
			Expect(err).To(MatchError("PacketPacker BUG: Handshake retransmissions must contain a StopWaitingFrame"))
		})
	})

	Context("packing ACK packets", func() {
		It("packs ACK packets", func() {
			packer.QueueControlFrame(&wire.AckFrame{})
			p, err := packer.PackAckPacket()
			Expect(err).NotTo(HaveOccurred())
			Expect(p.frames).To(Equal([]wire.Frame{&wire.AckFrame{DelayTime: math.MaxInt64}}))
		})

		It("packs ACK packets with SWFs", func() {
			packer.QueueControlFrame(&wire.AckFrame{})
			packer.QueueControlFrame(&wire.StopWaitingFrame{})
			p, err := packer.PackAckPacket()
			Expect(err).NotTo(HaveOccurred())
			Expect(p.frames).To(Equal([]wire.Frame{
				&wire.AckFrame{DelayTime: math.MaxInt64},
				&wire.StopWaitingFrame{PacketNumber: 1, PacketNumberLen: 2},
			}))
		})
	})
})