You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: flight2handler.go
    path of file: ./repos/scan4all/vendor/github.com/pion/dtls/v2
    
    the code of the file until where you have to start completion: // SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT

package dtls

import (
	"bytes"
	"context"

	"github.com/pion/dtls/v2/pkg/protocol"
	"github.com/pion/dtls/v2/pkg/protocol/alert"
	"github.com/pion/dtls/v2/pkg/protocol/handshake"
	"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
)

func flight2Parse(ctx context.Context, c flightConn, state *State, cache *handshakeCache, cfg *handshakeConfig) (flightVal, *alert.Alert, error) {
	seq, msgs, ok := cache.fullPullMap(state.handshakeRecvSequence, state.cipherSuite,
		handshakeCachePullRule{handshake.TypeClientHello, cfg.initialEpoch, true, false},
	)
	if !ok {
		// Client may retransmit the first ClientHello when HelloVerifyRequest is dropped.
		// Parse as flight 0 in this case.
		return flight0Parse(ctx, c, state, cache, cfg)
	}

    
func flight2Parse(ctx context.Context, c flightConn, state *State, cache *handshakeCache, cfg *handshakeConfig) (flightVal, *alert.Alert, error) {
	seq, msgs, ok := cache.fullPullMap(state.handshakeRecvSequence, state.cipherSuite,
		handshakeCachePullRule{handshake.TypeClientHello, cfg.initialEpoch, true, false},
	)
	if !ok {
		// Client may retransmit the first ClientHello when HelloVerifyRequest is dropped.
		// Parse as flight 0 in this case.
		return flight0Parse(ctx, c, state, cache, cfg)
	}
	state.handshakeRecvSequence = seq

	var clientHello *handshake.MessageClientHello

	// Validate type
	if clientHello, ok = msgs[handshake.TypeClientHello].(*handshake.MessageClientHello); !ok {
		return 0, &alert.Alert{Level: alert.Fatal, Description: alert.InternalError}, nil
	}

	if !clientHello.Version.Equal(protocol.Version1_2) {
		return 0, &alert.Alert{Level: alert.Fatal, Description: alert.ProtocolVersion}, errUnsupportedProtocolVersion
	}

	if len(clientHello.Cookie) == 0 {
		return 0, nil, nil
	}
	if !bytes.Equal(state.cookie, clientHello.Cookie) {
		return 0, &alert.Alert{Level: alert.Fatal, Description: alert.AccessDenied}, errCookieMismatch
	}
	return flight4, nil, nil
}