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Paint Upload is an asynchronous file upload library for servlets.

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/*
 * Copyright (C) 2015 Adam Forgacs
 *
 * 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 com.elopteryx.paint.upload;

import java.io.IOException;
import java.nio.ByteBuffer;
import javax.annotation.Nonnull;

/**
 * A functional interface. An implementation of it must be passed in the
 * {@link UploadParser#onPartBegin(OnPartBegin)} onPartBegin} method to call it at the start of parsing for each part.
 */
public interface OnPartBegin {

    /**
     * The function to implement. When it's called depends on the size threshold. If enough bytes
     * have been read or if the part is fully uploaded then this method is called
     * with a buffer containing the read bytes. Note that the buffer is only passed
     * for validation, it should not be written out. The buffered and the upcoming
     * bytes will be written out to the output object returned by this method. If the callback
     * is not set then the uploaded bytes are discarded.
     * @param context The upload context
     * @param buffer The byte buffer containing the first bytes of the part
     * @return A non-null output object (a channel or stream) to write out the part
     * @throws IOException If an error occurred with the channel
     */
    @Nonnull
    PartOutput onPartBegin(UploadContext context, ByteBuffer buffer) throws IOException;

}