PushPromiseGenerator.java

package com.firefly.codec.http2.encode;

import java.nio.ByteBuffer;
import java.util.LinkedList;
import java.util.List;

import com.firefly.codec.http2.frame.Flags;
import com.firefly.codec.http2.frame.Frame;
import com.firefly.codec.http2.frame.FrameType;
import com.firefly.codec.http2.frame.PushPromiseFrame;
import com.firefly.codec.http2.hpack.HpackEncoder;
import com.firefly.codec.http2.model.MetaData;
import com.firefly.utils.io.BufferUtils;

public class PushPromiseGenerator extends FrameGenerator {
	private final HpackEncoder encoder;

	public PushPromiseGenerator(HeaderGenerator headerGenerator, HpackEncoder encoder) {
		super(headerGenerator);
		this.encoder = encoder;
	}

	@Override
	public List<ByteBuffer> generate(Frame frame) {
		PushPromiseFrame pushPromiseFrame = (PushPromiseFrame) frame;
		return generatePushPromise(pushPromiseFrame.getStreamId(), pushPromiseFrame.getPromisedStreamId(),
				pushPromiseFrame.getMetaData());
	}

	public List<ByteBuffer> generatePushPromise(int streamId, int promisedStreamId, MetaData metaData) {
		if (streamId < 0)
			throw new IllegalArgumentException("Invalid stream id: " + streamId);
		if (promisedStreamId < 0)
			throw new IllegalArgumentException("Invalid promised stream id: " + promisedStreamId);

		List<ByteBuffer> list = new LinkedList<>();
		int maxFrameSize = getMaxFrameSize();
		// The promised streamId space.
		int extraSpace = 4;
		maxFrameSize -= extraSpace;

		ByteBuffer hpacked = ByteBuffer.allocate(maxFrameSize);
		BufferUtils.clearToFill(hpacked);
		encoder.encode(hpacked, metaData);
		int hpackedLength = hpacked.position();
		BufferUtils.flipToFlush(hpacked, 0);

		int length = hpackedLength + extraSpace;
		int flags = Flags.END_HEADERS;

		ByteBuffer header = generateHeader(FrameType.PUSH_PROMISE, length, flags, streamId);
		header.putInt(promisedStreamId);
		BufferUtils.flipToFlush(header, 0);

		list.add(header);
		list.add(hpacked);
		return list;
	}
}