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package dtls
import (
"github.com/pion/dtls/v2/pkg/protocol"
"github.com/pion/dtls/v2/pkg/protocol/handshake"
"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
)
type fragment struct {
recordLayerHeader recordlayer.Header
handshakeHeader handshake.Header
data []byte
}
type fragmentBuffer struct {
// map of MessageSequenceNumbers that hold slices of fragments
cache map[uint16][]*fragment
currentMessageSequenceNumber uint16
}
func newFragmentBuffer() *fragmentBuffer {
return &fragmentBuffer{cache: map[uint16][]*fragment{}}
}
// Attempts to push a DTLS packet to the fragmentBuffer
// when it returns true it means the fragmentBuffer has inserted and the buffer shouldn't be handled
// when an error returns it is fatal, and the DTLS connection should be stopped
func (f *fragmentBuffer) push(buf []byte) (bool, error) {
frag := new(fragment)
if err := frag.recordLayerHeader.Unmarshal(buf); err != nil {
return false, err
}
// fragment isn't a handshake, we don't need to handle it
if frag.recordLayerHeader.ContentType != protocol.ContentTypeHandshake {
return false, nil
}
for buf = buf[recordlayer.HeaderSize:]; len(buf) != 0; frag = new(fragment) {
if err := frag.handshakeHeader.Unmarshal(buf); err != nil {
return false, err
}
if _, ok := f.cache[frag.handshakeHeader.MessageSequence]; !ok {
f.cache[frag.handshakeHeader.MessageSequence] = []*fragment{}
}
// end index should be the length of handshake header but if the handshake
// was fragmented, we should keep them all
end := int(handshake.HeaderLength + frag.handshakeHeader.Length)
if size := len(buf); end > size {
end = size
}
// Discard all headers, when rebuilding the packet we will re-build
frag.data = append([]byte{}, buf[handshake.HeaderLength:end]...)
f.cache[frag.handshakeHeader.MessageSequence] = append(f.cache[frag.handshakeHeader.MessageSequence], frag)
buf = buf[end:]
}
return true, nil
}
func (f *fragmentBuffer) pop() (content []byte, epoch uint16) {
frags, ok := f.cache[f.currentMessageSequenceNumber]
if !ok {
return nil, 0
}
// Go doesn't support recursive lambdas
var appendMessage func(targetOffset uint32) bool
rawMessage := []byte{}
appendMessage = func(targetOffset uint32) bool {
for _, f := range frags {
if f.handshakeHeader.FragmentOffset == targetOffset {
fragmentEnd := (f.handshakeHeader.FragmentOffset + f.handshakeHeader.FragmentLength)
if fragmentEnd != f.handshakeHeader.Length {
if !appendMessage(fragmentEnd) {
return false
}
}
rawMessage = append(f.data, rawMessage...)
return true
}
}
return false
}
// Recursively collect up
if !appendMessage(0) {
return nil, 0
}
firstHeader := frags[0].handshakeHeader
firstHeader.FragmentOffset = 0
firstHeader.FragmentLength = firstHeader.Length
rawHeader, err := firstHeader.Marshal()
if err != nil {
return nil, 0
}
messageEpoch := frags[0].recordLayerHeader.Epoch
delete(f.cache, f.currentMessageSequenceNumber)
f.currentMessageSequenceNumber++
return append(rawHeader, rawMessage...), messageEpoch
}
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