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