io.grpc.alts.internal.BufUnwrapper.java Source code

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Here is the source code for io.grpc.alts.internal.BufUnwrapper.java

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/*
 * Copyright 2018 The gRPC Authors
 *
 * 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 io.grpc.alts.internal;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.CompositeByteBuf;
import java.nio.ByteBuffer;

/** Unwraps {@link ByteBuf}s into {@link ByteBuffer}s. */
final class BufUnwrapper implements AutoCloseable {

    private final ByteBuffer[] singleReadBuffer = new ByteBuffer[1];
    private final ByteBuffer[] singleWriteBuffer = new ByteBuffer[1];

    /**
     * Called to get access to the underlying NIO buffers for a {@link ByteBuf} that will be used for
     * writing.
     */
    ByteBuffer[] writableNioBuffers(ByteBuf buf) {
        // Set the writer index to the capacity to guarantee that the returned NIO buffers will have
        // the capacity available.
        int readerIndex = buf.readerIndex();
        int writerIndex = buf.writerIndex();
        buf.readerIndex(writerIndex);
        buf.writerIndex(buf.capacity());

        try {
            return nioBuffers(buf, singleWriteBuffer);
        } finally {
            // Restore the writer index before returning.
            buf.readerIndex(readerIndex);
            buf.writerIndex(writerIndex);
        }
    }

    /**
     * Called to get access to the underlying NIO buffers for a {@link ByteBuf} that will be used for
     * reading.
     */
    ByteBuffer[] readableNioBuffers(ByteBuf buf) {
        return nioBuffers(buf, singleReadBuffer);
    }

    @Override
    public void close() {
        singleReadBuffer[0] = null;
        singleWriteBuffer[0] = null;
    }

    /**
     * Optimized accessor for obtaining the underlying NIO buffers for a Netty {@link ByteBuf}. Based
     * on code from Netty's {@code SslHandler}. This method returns NIO buffers that span the readable
     * region of the {@link ByteBuf}.
     */
    private static ByteBuffer[] nioBuffers(ByteBuf buf, ByteBuffer[] singleBuffer) {
        // As CompositeByteBuf.nioBufferCount() can be expensive (as it needs to check all composed
        // ByteBuf to calculate the count) we will just assume a CompositeByteBuf contains more than 1
        // ByteBuf. The worst that can happen is that we allocate an extra ByteBuffer[] in
        // CompositeByteBuf.nioBuffers() which is better than walking the composed ByteBuf in most
        // cases.
        if (!(buf instanceof CompositeByteBuf) && buf.nioBufferCount() == 1) {
            // We know its only backed by 1 ByteBuffer so use internalNioBuffer to keep object
            // allocation to a minimum.
            singleBuffer[0] = buf.internalNioBuffer(buf.readerIndex(), buf.readableBytes());
            return singleBuffer;
        }

        return buf.nioBuffers();
    }
}