140 lines
3.1 KiB
Go
140 lines
3.1 KiB
Go
package quicvarint
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import (
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"fmt"
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"io"
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"github.com/lucas-clemente/quic-go/internal/protocol"
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)
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// taken from the QUIC draft
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const (
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// Min is the minimum value allowed for a QUIC varint.
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Min = 0
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// Max is the maximum allowed value for a QUIC varint (2^62-1).
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Max = maxVarInt8
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maxVarInt1 = 63
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maxVarInt2 = 16383
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maxVarInt4 = 1073741823
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maxVarInt8 = 4611686018427387903
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)
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// Read reads a number in the QUIC varint format from r.
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func Read(r io.ByteReader) (uint64, error) {
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firstByte, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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// the first two bits of the first byte encode the length
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len := 1 << ((firstByte & 0xc0) >> 6)
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b1 := firstByte & (0xff - 0xc0)
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if len == 1 {
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return uint64(b1), nil
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}
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b2, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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if len == 2 {
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return uint64(b2) + uint64(b1)<<8, nil
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}
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b3, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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b4, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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if len == 4 {
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return uint64(b4) + uint64(b3)<<8 + uint64(b2)<<16 + uint64(b1)<<24, nil
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}
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b5, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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b6, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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b7, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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b8, err := r.ReadByte()
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if err != nil {
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return 0, err
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}
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return uint64(b8) + uint64(b7)<<8 + uint64(b6)<<16 + uint64(b5)<<24 + uint64(b4)<<32 + uint64(b3)<<40 + uint64(b2)<<48 + uint64(b1)<<56, nil
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}
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// Write writes i in the QUIC varint format to w.
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func Write(w Writer, i uint64) {
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if i <= maxVarInt1 {
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w.WriteByte(uint8(i))
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} else if i <= maxVarInt2 {
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w.Write([]byte{uint8(i>>8) | 0x40, uint8(i)})
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} else if i <= maxVarInt4 {
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w.Write([]byte{uint8(i>>24) | 0x80, uint8(i >> 16), uint8(i >> 8), uint8(i)})
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} else if i <= maxVarInt8 {
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w.Write([]byte{
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uint8(i>>56) | 0xc0, uint8(i >> 48), uint8(i >> 40), uint8(i >> 32),
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uint8(i >> 24), uint8(i >> 16), uint8(i >> 8), uint8(i),
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})
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} else {
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panic(fmt.Sprintf("%#x doesn't fit into 62 bits", i))
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}
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}
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// WriteWithLen writes i in the QUIC varint format with the desired length to w.
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func WriteWithLen(w Writer, i uint64, length protocol.ByteCount) {
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if length != 1 && length != 2 && length != 4 && length != 8 {
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panic("invalid varint length")
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}
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l := Len(i)
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if l == length {
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Write(w, i)
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return
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}
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if l > length {
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panic(fmt.Sprintf("cannot encode %d in %d bytes", i, length))
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}
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if length == 2 {
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w.WriteByte(0b01000000)
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} else if length == 4 {
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w.WriteByte(0b10000000)
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} else if length == 8 {
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w.WriteByte(0b11000000)
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}
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for j := protocol.ByteCount(1); j < length-l; j++ {
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w.WriteByte(0)
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}
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for j := protocol.ByteCount(0); j < l; j++ {
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w.WriteByte(uint8(i >> (8 * (l - 1 - j))))
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}
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}
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// Len determines the number of bytes that will be needed to write the number i.
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func Len(i uint64) protocol.ByteCount {
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if i <= maxVarInt1 {
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return 1
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}
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if i <= maxVarInt2 {
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return 2
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}
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if i <= maxVarInt4 {
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return 4
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}
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if i <= maxVarInt8 {
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return 8
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}
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// Don't use a fmt.Sprintf here to format the error message.
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// The function would then exceed the inlining budget.
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panic(struct {
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message string
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num uint64
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}{"value doesn't fit into 62 bits: ", i})
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}
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