com.amazonaws.encryptionsdk.model.CiphertextFooters Maven / Gradle / Ivy

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/*
 * Copyright 2016 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 com.amazonaws.encryptionsdk.model;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.Arrays;

import com.amazonaws.encryptionsdk.exception.AwsCryptoException;
import com.amazonaws.encryptionsdk.exception.ParseException;
import com.amazonaws.encryptionsdk.internal.Constants;
import com.amazonaws.encryptionsdk.internal.PrimitivesParser;
import com.amazonaws.encryptionsdk.internal.Utils;

/**
 * This class encapsulates the optional footer information which follows the actual protected
 * content.
 * 
 * It contains the following fields in order:
 * 
 * AuthLength - 2 bytes
 * 
MAuth - {@code AuthLength} bytes
 * 
 */
public class CiphertextFooters {
    private int authLength_ = -1;
    private byte[] mAuth_ = null;
    private boolean isComplete_ = false;

    public CiphertextFooters() {
        // Do nothing
    }

    public CiphertextFooters(final byte[] mAuth) {
        final int length = Utils.assertNonNull(mAuth, "mAuth").length;
        if (length < 0 || length > Constants.UNSIGNED_SHORT_MAX_VAL) {
            throw new IllegalArgumentException("Invalid length for mAuth: " + length);
        }
        authLength_ = length;
        mAuth_ = mAuth.clone();
        isComplete_ = true;
    }

    /**
     * Parses the footers from the {@code b} starting at offset {@code off} and returns the number
     * of bytes parsed/consumed.
     */
    public int deserialize(final byte[] b, final int off) throws ParseException {
        if (b == null) {
            return 0;
        }
        int parsedBytes = 0;
        try {
            if (authLength_ < 0) {
                parsedBytes += parseLength(b, off + parsedBytes);
            }
            if (mAuth_ == null) {
                parsedBytes += parseMauth(b, off + parsedBytes);
            }
            isComplete_ = true;
        } catch (ParseException e) {
            // this results when we do partial parsing and there aren't enough
            // bytes to parse; ignore it and return the bytes parsed thus far.
        }
        return parsedBytes;
    }

    public int getAuthLength() {
        return authLength_;
    }

    public byte[] getMAuth() {
        return (mAuth_ != null) ? mAuth_.clone() : null;
    }

    /**
     * Check if this object has all the header fields populated and available for reading.
     * 
     * @return true if this object containing the single block header fields is complete; false
     *         otherwise.
     */
    public boolean isComplete() {
        return isComplete_;
    }

    public byte[] toByteArray() {
        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
                DataOutputStream dos = new DataOutputStream(baos)) {
            PrimitivesParser.writeUnsignedShort(dos, authLength_);
            dos.write(mAuth_);
            dos.close();
            baos.close();
            return baos.toByteArray();
        } catch (final IOException ex) {
            throw new AwsCryptoException(ex);
        }
    }

    private int parseLength(final byte[] b, final int off) throws ParseException {
        authLength_ = PrimitivesParser.parseUnsignedShort(b, off);
        return 2;
    }

    private int parseMauth(final byte[] b, final int off) throws ParseException {
        final int len = b.length - off;
        if (len >= authLength_) {
            mAuth_ = Arrays.copyOfRange(b, off, off + authLength_);
            return authLength_;
        } else {
            throw new ParseException("Not enough bytes to parse mAuth, "
                   + " needed at least " + authLength_ + " bytes, but only had "
                   + len + " bytes");
            
        }
    }
}