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// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT
package dtls
import (
"crypto/rand"
"github.com/pion/dtls/v3/pkg/protocol"
"github.com/pion/dtls/v3/pkg/protocol/extension"
"github.com/pion/dtls/v3/pkg/protocol/handshake"
"github.com/pion/dtls/v3/pkg/protocol/recordlayer"
)
// RandomCIDGenerator is a random Connection ID generator where CID is the
// specified size. Specifying a size of 0 will indicate to peers that sending a
// Connection ID is not necessary.
func RandomCIDGenerator(size int) func() []byte {
return func() []byte {
cid := make([]byte, size)
if _, err := rand.Read(cid); err != nil {
panic(err) //nolint -- nonrecoverable
}
return cid
}
}
// OnlySendCIDGenerator enables sending Connection IDs negotiated with a peer,
// but indicates to the peer that sending Connection IDs in return is not
// necessary.
func OnlySendCIDGenerator() func() []byte {
return func() []byte {
return nil
}
}
// cidDatagramRouter extracts connection IDs from incoming datagram payloads and
// uses them to route to the proper connection.
// NOTE: properly routing datagrams based on connection IDs requires using
// constant size connection IDs.
func cidDatagramRouter(size int) func([]byte) (string, bool) {
return func(packet []byte) (string, bool) {
pkts, err := recordlayer.ContentAwareUnpackDatagram(packet, size)
if err != nil || len(pkts) < 1 {
return "", false
}
for _, pkt := range pkts {
h := &recordlayer.Header{
ConnectionID: make([]byte, size),
}
if err := h.Unmarshal(pkt); err != nil {
continue
}
if h.ContentType != protocol.ContentTypeConnectionID {
continue
}
return string(h.ConnectionID), true
}
return "", false
}
}
// cidConnIdentifier extracts connection IDs from outgoing ServerHello records
// and associates them with the associated connection.
// NOTE: a ServerHello should always be the first record in a datagram if
// multiple are present, so we avoid iterating through all packets if the first
// is not a ServerHello.
func cidConnIdentifier() func([]byte) (string, bool) { //nolint:cyclop
return func(packet []byte) (string, bool) {
pkts, err := recordlayer.UnpackDatagram(packet)
if err != nil || len(pkts) < 1 {
return "", false
}
var h recordlayer.Header
if hErr := h.Unmarshal(pkts[0]); hErr != nil {
return "", false
}
if h.ContentType != protocol.ContentTypeHandshake {
return "", false
}
var hh handshake.Header
var sh handshake.MessageServerHello
for _, pkt := range pkts {
if hhErr := hh.Unmarshal(pkt[recordlayer.FixedHeaderSize:]); hhErr != nil {
continue
}
if err = sh.Unmarshal(pkt[recordlayer.FixedHeaderSize+handshake.HeaderLength:]); err == nil {
break
}
}
if err != nil {
return "", false
}
for _, ext := range sh.Extensions {
if e, ok := ext.(*extension.ConnectionID); ok {
return string(e.CID), true
}
}
return "", false
}
}
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