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/*
 * Copyright 2020 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 * https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.pcap;

import io.netty.buffer.ByteBuf;

final class UDPPacket {

    private static final short UDP_HEADER_SIZE = 8;

    private UDPPacket() {
        // Prevent outside initialization
    }

    /**
     * Write UDP Packet
     *
     * @param byteBuf ByteBuf where Packet data will be set
     * @param payload Payload of this Packet
     * @param srcPort Source Port
     * @param dstPort Destination Port
     */
    static void writePacket(ByteBuf byteBuf, ByteBuf payload, int srcPort, int dstPort) {
        byteBuf.writeShort(srcPort); // Source Port
        byteBuf.writeShort(dstPort); // Destination Port
        byteBuf.writeShort(UDP_HEADER_SIZE + payload.readableBytes()); // UDP Header Length + Payload Length
        byteBuf.writeShort(0x0001);  // Checksum
        byteBuf.writeBytes(payload); //  Payload of Data
    }
}