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package otr3
import "bytes"
var (
fragmentSeparator = []byte{','}
fragmentItagsSeparator = []byte{'|'}
)
// fragmentationContext store the current fragmentation running. A fragmentationContext is zero-valid and can be immediately used without initialization.
// In order to follow the fragmentation rules, when the context needs to be reset, just create a new one - don't bother resetting variables
type fragmentationContext struct {
frag []byte
currentIndex, currentLen uint16
}
func min(l, r uint16) uint16 {
if l < r {
return l
}
return r
}
func fragmentStart(i, fraglen uint16) uint16 {
return uint16(i * fraglen)
}
func fragmentEnd(i, fraglen, l uint16) uint16 {
return uint16(min((i+1)*fraglen, l))
}
func fragmentData(data []byte, i int, fraglen, l uint16) []byte {
return data[fragmentStart(uint16(i), fraglen):fragmentEnd(uint16(i), fraglen, l)]
}
// SetFragmentSize sets the maximum size for a message fragment.
// If specified, all messages produced by Receive and Send
// will be fragmented into messages of, at most, this number of bytes.
func (c *Conversation) SetFragmentSize(size uint16) {
c.fragmentSize = size
}
func (c *Conversation) fragment(data encodedMessage, fraglen uint16) []ValidMessage {
l := len(data)
if l <= int(fraglen) || fraglen == 0 {
return []ValidMessage{ValidMessage(data)}
}
fakeHeader := c.version.fragmentPrefix(1, 1, c.ourInstanceTag, c.theirInstanceTag)
realFraglen := (fraglen - uint16(len(fakeHeader))) - 1
if realFraglen <= 0 {
return []ValidMessage{ValidMessage(data)}
}
numFragments := (l / int(realFraglen)) + 1
ret := make([]ValidMessage, numFragments)
for i := 0; i < numFragments; i++ {
prefix := c.version.fragmentPrefix(i, numFragments, c.ourInstanceTag, c.theirInstanceTag)
ret[i] = append(append(prefix, fragmentData(data, i, realFraglen, uint16(l))...), fragmentSeparator[0])
}
return ret
}
func fragmentsFinished(fctx fragmentationContext) bool {
return fctx.currentIndex > 0 && fctx.currentIndex == fctx.currentLen
}
func parseFragment(data []byte) (resultData []byte, ix uint16, length uint16, ok bool) {
parts := bytes.Split(data, fragmentSeparator)
if len(parts) != 4 {
return nil, 0, 0, false
}
var e1, e2 error
ix, e1 = bytesToUint16(parts[0])
length, e2 = bytesToUint16(parts[1])
resultData = parts[2]
ok = e1 == nil && e2 == nil
return
}
func fragmentIsInvalid(ix, l uint16) bool {
return ix == 0 || l == 0 || ix > l
}
func fragmentIsFirstMessage(ix, l uint16) bool {
return ix == 1
}
func fragmentIsNextMessage(beforeCtx fragmentationContext, ix, l uint16) bool {
return beforeCtx.currentIndex+1 == ix && beforeCtx.currentLen == l
}
func (ctx fragmentationContext) discardFragment() fragmentationContext {
return ctx
}
func (ctx fragmentationContext) appendFragment(data []byte, ix, l uint16) fragmentationContext {
return fragmentationContext{append(ctx.frag, data...), ix, l}
}
func restartFragment(data []byte, ix, l uint16) fragmentationContext {
return fragmentationContext{makeCopy(data), ix, l}
}
func forgetFragment() fragmentationContext {
return fragmentationContext{}
}
func (c *Conversation) receiveFragment(beforeCtx fragmentationContext, data ValidMessage) (fragmentationContext, error) {
fragBody, ignore, ok1 := c.parseFragmentPrefix(data)
resultData, ix, l, ok2 := parseFragment(fragBody)
if ignore {
c.messageEvent(MessageEventReceivedMessageForOtherInstance)
return beforeCtx, nil
}
if !ok1 || !ok2 {
return beforeCtx, newOtrError("invalid OTR fragment")
}
switch {
case fragmentIsInvalid(ix, l):
return beforeCtx.discardFragment(), nil
case fragmentIsFirstMessage(ix, l):
return restartFragment(resultData, ix, l), nil
case fragmentIsNextMessage(beforeCtx, ix, l):
return beforeCtx.appendFragment(resultData, ix, l), nil
default:
return forgetFragment(), nil
}
}
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