johnsonjh/gfsmux

package gfsmux

import (
    "encoding/binary"
    "fmt"
)

const (
    // Protocol version 1: old commands

    // CmdSyn ... stream open
    CmdSyn byte = iota
    // CmdFin ... stream close, EOF
    CmdFin
    // CmdPsh ... push data
    CmdPsh
    // CmdNop ... noop
    CmdNop

    // Protocol version 2: new commands

    // CmdUpd ... notify bytes consumed by remote peer-end
    CmdUpd
)

const (
    // data size of CmdUpd, format:
    // |4B data consumed(ACK)| 4B window size(WINDOW) |
    szCmdUPD = 8
)

const (
    // initial peer window guess, a slow-start
    initialPeerWindow = 262144
)

const (
    sizeOfVer    = 1
    sizeOfCmd    = 1
    sizeOfLength = 2
    sizeOfSid    = 4
    // HeaderSize ...
    HeaderSize = sizeOfVer + sizeOfCmd + sizeOfSid + sizeOfLength
)

// Frame defines a packet from or to be multiplexed into a single Connection
type Frame struct {
    Ver  byte
    Cmd  byte
    Sid  uint32
    Data []byte
}

// NewFrame ...
func NewFrame(
    Version,
    Cmd byte,
    Sid uint32,
) Frame {
    return Frame{Ver: Version, Cmd: Cmd, Sid: Sid}
}

type rawHeader [HeaderSize]byte

func (
    h rawHeader,
) Version() byte {
    return h[0]
}

func (
    h rawHeader,
) Cmd() byte {
    return h[1]
}

func (
    h rawHeader,
) Length() uint16 {
    return binary.LittleEndian.Uint16(
        h[2:],
    )
}

func (
    h rawHeader,
) StreamID() uint32 {
    return binary.LittleEndian.Uint32(
        h[4:],
    )
}

func (
    h rawHeader,
) String() string {
    return fmt.Sprintf(
        "Version:%d Cmd:%d StreamID:%d Length:%d",
        h.Version(),
        h.Cmd(),
        h.StreamID(),
        h.Length(),
    )
}

type updHeader [szCmdUPD]byte

func (
    h updHeader,
) Consumed() uint32 {
    return binary.LittleEndian.Uint32(
        h[:],
    )
}

func (
    h updHeader,
) Window() uint32 {
    return binary.LittleEndian.Uint32(
        h[4:],
    )
}