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HttpComponents AsyncClient (base module)
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/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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
 *
 *   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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * .
 *
 */
package org.apache.http.nio.client.methods;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

import org.apache.http.HttpResponse;
import org.apache.http.entity.FileEntity;
import org.apache.http.nio.ContentDecoder;
import org.apache.http.nio.ContentDecoderChannel;
import org.apache.http.nio.FileContentDecoder;
import org.apache.http.nio.IOControl;
import org.apache.http.nio.protocol.AbstractAsyncResponseConsumer;
import org.apache.http.protocol.HTTP;
import org.apache.http.protocol.HttpContext;

public abstract class ZeroCopyConsumer extends AbstractAsyncResponseConsumer {

    private final File file;

    private HttpResponse response;
    private FileChannel fileChannel;
    private long idx = -1;

    public ZeroCopyConsumer(final File file) {
        super();
        if (file == null) {
            throw new IllegalArgumentException("File may nor be null");
        }
        this.file = file;
    }

    @Override
    protected void onResponseReceived(final HttpResponse response) {
        this.response = response;
    }

    @Override
    protected void onContentReceived(
            final ContentDecoder decoder, final IOControl ioctrl) throws IOException {
        if (this.fileChannel == null) {
            FileOutputStream out = new FileOutputStream(this.file);
            this.fileChannel = out.getChannel();
            this.idx = 0;
        }
        long transferred;
        if (decoder instanceof FileContentDecoder) {
            transferred = ((FileContentDecoder)decoder).transfer(
                    this.fileChannel, this.idx, Integer.MAX_VALUE);
        } else {
            transferred = this.fileChannel.transferFrom(
                    new ContentDecoderChannel(decoder), this.idx, Integer.MAX_VALUE);
        }
        if (transferred > 0) {
            this.idx += transferred;
        }
        if (decoder.isCompleted()) {
            this.fileChannel.close();
            this.fileChannel = null;
        }
    }

    protected abstract T process(final HttpResponse response, final File file) throws Exception;

    @Override
    protected T buildResult(final HttpContext context) throws Exception {
        FileEntity entity = new FileEntity(this.file);
        entity.setContentType(this.response.getFirstHeader(HTTP.CONTENT_TYPE));
        this.response.setEntity(entity);
        return process(this.response, this.file);
    }

    @Override
    protected void releaseResources() {
        if (this.fileChannel != null) {
            try {
                this.fileChannel.close();
            } catch (IOException ignore) {
            }
            this.fileChannel = null;
        }
    }

}