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/*
 * Copyright @ 2015 - present 8x8, Inc
 *
 * Licensed 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
 *
 *     http://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 org.jitsi.srtp.utils;

import org.jitsi.utils.*;

import static org.jitsi.utils.ByteArrayUtils.*;

/**
 * SrtcpPacket is the low-level utilities to get the data fields needed by SRTCP.
 */
public class SrtcpPacketUtils
{
    /**
     * Get the sender SSRC of an SRTCP packet.
     *
     * This is the SSRC of the first packet of the compound packet.
     *
     * @param buf The buffer holding the SRTCP packet.
     */
    public static int getSenderSsrc(ByteArrayBuffer buf)
    {
        return readInt(buf, 4);
    }

    /**
     * Get the SRTCP index (sequence number) from an SRTCP packet
     *
     * @param buf The buffer holding the SRTCP packet.
     * @param authTagLen authentication tag length
     * @return SRTCP sequence num from source packet
     */
    public static int getIndex(ByteArrayBuffer buf, int authTagLen)
    {
        int authTagOffset = buf.getLength() - (4 + authTagLen);
        return readInt(buf, authTagOffset);
    }

    /**
     * Validate that the contents of a ByteArrayBuffer could contain a valid SRTCP packet.
     *
     * This validates that the packet is long enough to be a valid packet, i.e. attempts to read
     * fields of the packet will not fail.
     *
     * @param buf The buffer holding the SRTCP packet.
     * @param authTagLen The length of the packet's authentication tag.
     * @return true if the packet is syntactically valid (i.e., long enough); false if not.
     */
    public static boolean validatePacketLength(ByteArrayBuffer buf, int authTagLen)
    {
        int length = buf.getLength();
        int neededLength = 8 /* sender SSRC */ + 4 /* index */ + authTagLen;

        if (length < neededLength)
        {
            return false;
        }
        return true;
    }
}