我們知道，HTTP2.0使用header楨表達(dá)HTTP header+request line簿姨，data frame表達(dá)Body距误。header楨和data楨使用相同的stream id組成一個(gè)完整的HTTP請(qǐng)求/響應(yīng)包。這里的stream描述了一次請(qǐng)求和響應(yīng)扁位，相當(dāng)于完成了一次HTTP/1.x的短連接請(qǐng)求和響應(yīng)准潭。

Http1.x 的http request 在完成對(duì)請(qǐng)求頭編碼后，接下了就時(shí)對(duì)請(qǐng)求體編碼為Data Frame了域仇，如果時(shí)get請(qǐng)求刑然，沒(méi)有請(qǐng)求體，那就不需要發(fā)送data frame暇务，所以我們可以知道泼掠，只有post請(qǐng)求才會(huì)發(fā)data frame怔软。

在把請(qǐng)求體編碼成data frame時(shí)，一個(gè)重要的flag就時(shí)end_stream择镇，需要告訴服務(wù)端這是不是該stream上的最后一個(gè)frame爽雄，因?yàn)樵趆eader frame 發(fā)送時(shí)，介紹了沐鼠，
有data frame挚瘟，header frame 的end_stream 肯定為false，所以大部分在發(fā)送請(qǐng)求體即data frame時(shí)饲梭，end_stream為true乘盖，除非有trailers header，因?yàn)榘l(fā)完數(shù)據(jù)憔涉，還要發(fā)trailers header订框，那就時(shí)最后一個(gè)header frame，而且end_stream為true兜叨。

編碼pipeline

HttpToHttp2ConnectionHandler->DefaultHttp2ConnectionEncoder->DefaultHttp2FrameWriter

發(fā)送data frame時(shí)穿扳，需要判斷end stream 是否為true，如果分

    //endStream 如果為ture国旷，就不需要發(fā)data frame了矛物。
    if (!endStream && msg instanceof HttpContent) {
            boolean isLastContent = false;
            HttpHeaders trailers = EmptyHttpHeaders.INSTANCE;
            Http2Headers http2Trailers = EmptyHttp2Headers.INSTANCE;
            if (msg instanceof LastHttpContent) {
                isLastContent = true;

                // Convert any trailing headers.
                final LastHttpContent lastContent = (LastHttpContent) msg;
                trailers = lastContent.trailingHeaders();
                http2Trailers = HttpConversionUtil.toHttp2Headers(trailers, validateHeaders);
            }

            // Write the data
            final ByteBuf content = ((HttpContent) msg).content();
            endStream = isLastContent && trailers.isEmpty();
            release = false;
            encoder.writeData(ctx, currentStreamId, content, 0, endStream, promiseAggregator.newPromise());

            if (!trailers.isEmpty()) {
                // Write trailing headers.
                writeHeaders(ctx, encoder, currentStreamId, trailers, http2Trailers, true, promiseAggregator);
            }
        }

encoder data frame 時(shí)，直接添加到stream對(duì)應(yīng)的流控隊(duì)列跪但，代碼如下：

@Override
public ChannelFuture writeData(final ChannelHandlerContext ctx, final int streamId, ByteBuf data, int padding,
        final boolean endOfStream, ChannelPromise promise) {
    final Http2Stream stream;
    try {
        stream = requireStream(streamId);

        // Verify that the stream is in the appropriate state for sending DATA frames.
        switch (stream.state()) {
            case OPEN:
            case HALF_CLOSED_REMOTE:
                // Allowed sending DATA frames in these states.
                break;
            default:
                throw new IllegalStateException("Stream " + stream.id() + " in unexpected state " + stream.state());
        }
    } catch (Throwable e) {
        data.release();
        return promise.setFailure(e);
    }

    // Hand control of the frame to the flow controller.
    flowController().addFlowControlled(stream,
            new FlowControlledData(stream, data, padding, endOfStream, promise));
    return promise;
}

添加到隊(duì)列后履羞，代表write操作就結(jié)束咯，后面在flush時(shí)先把流控隊(duì)列里的數(shù)據(jù)寫到netty的循環(huán)隊(duì)列屡久，后面的 ctx.flush(); 會(huì)從循環(huán)隊(duì)列寫到os的寫緩沖區(qū)忆首。

@Override
public void flush(ChannelHandlerContext ctx) {
    try {
        // Trigger pending writes in the remote flow controller.
        //這里時(shí)流控機(jī)制，需要選擇哪些frame可以發(fā)送被环，通過(guò)后面的流控來(lái)具體分析
        encoder.flowController().writePendingBytes();
        ctx.flush();
    } catch (Http2Exception e) {
        onError(ctx, true, e);
    } catch (Throwable cause) {
        onError(ctx, true, connectionError(INTERNAL_ERROR, cause, "Error flushing"));
    }
}