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The AWS Java SDK for Amazon CloudFront module holds the client classes that are used for communicating with Amazon CloudFront Service
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/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 software.amazon.awssdk.services.cloudfront.internal.auth;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import software.amazon.awssdk.annotations.SdkInternalApi;

@SdkInternalApi
public class DerParser {
    // Classes
    public static final int UNIVERSAL = 0x00;
    public static final int APPLICATION = 0x40;
    public static final int CONTEXT = 0x80;
    public static final int PRIVATE = 0xC0;

    // Constructed Flag
    public static final int CONSTRUCTED = 0x20;

    // Tag and data types
    public static final int ANY = 0x00;
    public static final int BOOLEAN = 0x01;
    public static final int INTEGER = 0x02;
    public static final int BIT_STRING = 0x03;
    public static final int OCTET_STRING = 0x04;
    public static final int NULL = 0x05;
    public static final int OBJECT_IDENTIFIER = 0x06;
    public static final int REAL = 0x09;
    public static final int ENUMERATED = 0x0a;
    public static final int RELATIVE_OID = 0x0d;

    public static final int SEQUENCE = 0x10;
    public static final int SET = 0x11;

    public static final int NUMERIC_STRING = 0x12;
    public static final int PRINTABLE_STRING = 0x13;
    public static final int T61_STRING = 0x14;
    public static final int VIDEOTEX_STRING = 0x15;
    public static final int IA5_STRING = 0x16;
    public static final int GRAPHIC_STRING = 0x19;
    public static final int ISO646_STRING = 0x1A;
    public static final int GENERAL_STRING = 0x1B;

    public static final int UTF8_STRING = 0x0C;
    public static final int UNIVERSAL_STRING = 0x1C;
    public static final int BMP_STRING = 0x1E;

    public static final int UTC_TIME = 0x17;
    public static final int GENERALIZED_TIME = 0x18;

    protected final InputStream in;

    /**
     * Create a new DER decoder from an input stream.
     *
     * @param in
     *          The DER encoded stream
     */
    public DerParser(InputStream in) {
        this.in = in;
    }

    /**
     * Create a new DER decoder from a byte array.
     *
     * @param bytes
     *          the encoded bytes
     */
    public DerParser(byte[] bytes) {
        this(new ByteArrayInputStream(bytes));
    }

    /**
     * Read next object. If it's constructed, the value holds encoded content
     * and it should be parsed by a new parser from
     * {@code Asn1Object.getParser}.
     */
    public Asn1Object read() throws IOException {
        int tag = in.read();

        if (tag == -1) {
            throw new IOException("Invalid DER: stream too short, missing tag"); //$NON-NLS-1$
        }

        int length = getLength();

        byte[] value = new byte[length];
        int n = in.read(value);
        if (n < length) {
            throw new IOException(
                "Invalid DER: stream too short, missing value"); //$NON-NLS-1$
        }

        return new Asn1Object(tag, length, value);

    }

    /**
     * Decode the length of the field. Can only support length encoding up to 4
     * octets.
     *
     * In BER/DER encoding, length can be encoded in 2 forms,
     * 
     * Short form. One octet. Bit 8 has value "0" and bits 7-1 give the
     * length.
     * 
Long form. Two to 127 octets (only 4 is supported here). Bit 8 of
     * first octet has value "1" and bits 7-1 give the number of additional
     * length octets. Second and following octets give the length, base 256,
     * most significant digit first.
     * 
     *
     * @return The length as integer
     */
    private int getLength() throws IOException {

        int i = in.read();
        if (i == -1) {
            throw new IOException("Invalid DER: length missing"); //$NON-NLS-1$
        }

        // A single byte short length
        if ((i & ~0x7F) == 0) {
            return i;
        }

        int num = i & 0x7F;

        // We can't handle length longer than 4 bytes
        if (i >= 0xFF || num > 4) {
            throw new IOException("Invalid DER: length field too big (" //$NON-NLS-1$
                                  + i + ")"); //$NON-NLS-1$
        }

        byte[] bytes = new byte[num];
        int n = in.read(bytes);
        if (n < num) {
            throw new IOException("Invalid DER: length too short"); //$NON-NLS-1$
        }

        return new BigInteger(1, bytes).intValue();
    }
}