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server/vendor/github.com/pion/dtls/v2/flight.go

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+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package dtls
+
+/*
+  DTLS messages are grouped into a series of message flights, according
+  to the diagrams below.  Although each flight of messages may consist
+  of a number of messages, they should be viewed as monolithic for the
+  purpose of timeout and retransmission.
+  https://tools.ietf.org/html/rfc4347#section-4.2.4
+
+  Message flights for full handshake:
+
+  Client                                          Server
+  ------                                          ------
+                                      Waiting                 Flight 0
+
+  ClientHello             -------->                           Flight 1
+
+                          <-------    HelloVerifyRequest      Flight 2
+
+  ClientHello              -------->                           Flight 3
+
+                                             ServerHello    \
+                                            Certificate*     \
+                                      ServerKeyExchange*      Flight 4
+                                     CertificateRequest*     /
+                          <--------      ServerHelloDone    /
+
+  Certificate*                                              \
+  ClientKeyExchange                                          \
+  CertificateVerify*                                          Flight 5
+  [ChangeCipherSpec]                                         /
+  Finished                -------->                         /
+
+                                      [ChangeCipherSpec]    \ Flight 6
+                          <--------             Finished    /
+
+  Message flights for session-resuming handshake (no cookie exchange):
+
+  Client                                          Server
+  ------                                          ------
+                                      Waiting                 Flight 0
+
+  ClientHello             -------->                           Flight 1
+
+                                             ServerHello    \
+                                      [ChangeCipherSpec]      Flight 4b
+                          <--------             Finished    /
+
+  [ChangeCipherSpec]                                        \ Flight 5b
+  Finished                -------->                         /
+
+                                      [ChangeCipherSpec]    \ Flight 6
+                          <--------             Finished    /
+*/
+
+type flightVal uint8
+
+const (
+	flight0 flightVal = iota + 1
+	flight1
+	flight2
+	flight3
+	flight4
+	flight4b
+	flight5
+	flight5b
+	flight6
+)
+
+func (f flightVal) String() string {
+	switch f {
+	case flight0:
+		return "Flight 0"
+	case flight1:
+		return "Flight 1"
+	case flight2:
+		return "Flight 2"
+	case flight3:
+		return "Flight 3"
+	case flight4:
+		return "Flight 4"
+	case flight4b:
+		return "Flight 4b"
+	case flight5:
+		return "Flight 5"
+	case flight5b:
+		return "Flight 5b"
+	case flight6:
+		return "Flight 6"
+	default:
+		return "Invalid Flight"
+	}
+}
+
+func (f flightVal) isLastSendFlight() bool {
+	return f == flight6 || f == flight5b
+}
+
+func (f flightVal) isLastRecvFlight() bool {
+	return f == flight5 || f == flight4b
+}