go-i2p/lib/tunnel/delivery.go

package tunnel

import (
	"encoding/binary"
)

const (
	DT_LOCAL = iota
	DT_TUNNEL
	DT_ROUTER
	DT_UNUSED
)

type DelayFactor byte

type DeliveryInstructions []byte

func (di DeliveryInstructions) DeliveryType() byte {
	return (di[0] & 0x30) >> 4
}

func (di DeliveryInstructions) IsFragmented() bool {
	return (di[0] & 0x08) == 0x08
}

// get the tunnel id in this devilevery instrcutions or 0 if not applicable
func (di DeliveryInstructions) TunnelID() (tid uint32) {
	if di.DeliveryType() == DT_TUNNEL {
		// TODO(psi):  what if this is 0?
		tid = binary.BigEndian.Uint32(di[1:5])
	}
	return
}

// do we have a delay factor?
func (di DeliveryInstructions) HasDelay() bool {
	return (di[0] & 0x10) == 0x10
}

// get the delay factor if it exists
func (di DeliveryInstructions) Delay() (d DelayFactor) {
	if di.HasDelay() {
		t := di.DeliveryType()
		if t == DT_TUNNEL {
			d = DelayFactor(di[37])
		} else if t == DT_ROUTER {
			d = DelayFactor(di[36])
		}
	}
	return
}

func (di DeliveryInstructions) HasExtendedOptions() bool {
	return (di[0] & 0x04) == 0x04
}

// get the to hash for these delivery instructions or nil if not applicable
func (di DeliveryInstructions) ToHash() (h []byte) {
	t := di.DeliveryType()
	if t == DT_TUNNEL {
		h = di[5:37]
	} else if t == DT_ROUTER || t == DT_LOCAL {
		h = di[4:36]
	}
	return
}

// get the i2np message id or 0 if not applicable
func (di DeliveryInstructions) MessageID() (msgid uint32) {
	if di.IsFragmented() {
		idx := 1
		t := di.DeliveryType()
		if t == DT_TUNNEL {
			idx += 36
		} else if t == DT_ROUTER {
			idx += 32
		}
		if di.HasDelay() {
			idx++
		}
		msgid = binary.BigEndian.Uint32(di[idx:])
	}
	return
}

// get the size of the associated i2np fragment
func (di DeliveryInstructions) GetFragmentSize() uint16 {
	idx := 5
	t := di.DeliveryType()
	if t == DT_TUNNEL {
		idx += 36
	} else if t == DT_ROUTER {
		idx += 32
	}
	if di.HasDelay() {
		idx++
	}
	if di.HasExtendedOptions() {
		// add extended options length to idx
	}
	return binary.BigEndian.Uint16(di[idx:])
}