Question

如何在基于Netty的HTTP客户端中重试HTTP请求？

考虑以下处理程序，如果收到HTTP响应代码503，则会在1秒后尝试重试HTTP请求：

public class RetryChannelHandler extends ChannelDuplexHandler {
    List<HttpObject> requestParts;

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        if (msg instanceof HttpRequest) {
            requestParts = new ArrayList<>();
            requestParts.add((HttpRequest)msg);
        } else if (msg instanceof HttpObject) {
            requestParts.add((HttpObject)msg);
        }

        super.write(ctx, msg, promise);
    }

    @Override
    public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
        if (msg instanceof HttpResponse) {
            HttpResponse res = (HttpResponse)msg;
            if (res.status().code() == 503) {
                ctx.executor().schedule(new Runnable() {
                    @Override
                    public void run() {
                        for (HttpObject obj : requestParts) {
                            ctx.channel().write(obj);
                        }
                    }
                }, 1000, TimeUnit.MILLISECONDS);
            } else {
                super.channelRead(ctx, msg);
            }
        } else {
            super.channelRead(ctx, msg);
        }
    }
}

当我在此示例中写入通道时，管道中的其他处理程序会看到HttpObjects，但HttpRequest实际上并未再次执行 - 只接收到一个HttpResponse。

我认为在这种情况下我只是误用了Channel，我需要创建一个新的Channel（表示与服务器的新连接）来执行重试。我不清楚的是如何从Handler的上下文创建新的Channel，以及我是否真的在Netty的正确层中做这种逻辑。

任何关于如何实现我所描述的行为的指导都将受到赞赏。

Answer 1

您还需要在致电flush()后致电write(...)，否则将无法刷新频道。此外，您需要确保您可能保留（）和复制（）HttpContent，否则您最终可能会尝试编写已发布的HttpContent对象。

像这样（未经测试）：

public class RetryChannelHandler extends ChannelDuplexHandler {
    Queue<HttpObject> requestParts;

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        if (msg instanceof HttpRequest) {
            requestParts = new ArrayDeque<>();
            requestParts.add((HttpRequest)msg);
        } else if (msg instanceof HttpContent) {
            requestParts.add(((HttpContent)msg).duplicate().retain());
        }

        super.write(ctx, msg, promise);
    }

    @Override
    public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
        if (msg instanceof HttpResponse) {
            HttpResponse res = (HttpResponse)msg;
            if (res.status().code() == 503) {
                ctx.executor().schedule(new Runnable() {
                    @Override
                    public void run() {
                        HttpObject obj;
                        while ((obj = requestParts.poll()) != null) {
                            ctx.write(obj);
                        }
                        ctx.flush();
                    }
                }, 1000, TimeUnit.MILLISECONDS);
            } else {
                HttpObject obj;
                while ((obj = requestParts.poll()) != null) {
                    ReferenceCountUtil.release(obj);
                }
                super.channelRead(ctx, msg);
            }
        } else {
            super.channelRead(ctx, msg);
        }
    }
}

使用Netty HTTP客户端

1 个答案: