How can I send multiple http requests asynchronous with Netty?

Question

I am trying to send asynchronously a large amount a http posts requests to one server. My goals is to compare each response to its orginal request.

To do so I am following the Netty Snoop example.

However, this example (and the other http examples) do not cover how to send multiple requests asynchrously, nor how to link them subsequently to the corresponding requests.

All similiar questions (such as this one, this one, or this one, implement the SimpleChannelUpstreamHandler class, which is from netty 3 and does not exists in 4.0 anymore (documentation netty 4.0)

Anyone has an idea how to solve this in netty 4.0?

Edit:

My problem is although I write lots of messages to the channel, I only receive very slowly the responses (1 response/sec, whereas a hope to receive few thousand / sec) . To clarify this, let me post what I got so far. I am sure that the server I send the requests too can handle lots of traffic.

What I got so far:

import java.net.URI
import java.nio.charset.StandardCharsets
import java.io.File

import io.netty.bootstrap.Bootstrap
import io.netty.buffer.{Unpooled, ByteBuf}
import io.netty.channel.{ChannelHandlerContext, SimpleChannelInboundHandler, ChannelInitializer}
import io.netty.channel.socket.SocketChannel
import io.netty.channel.socket.nio.NioSocketChannel
import io.netty.handler.codec.http._
import io.netty.handler.timeout.IdleStateHandler
import io.netty.util.{ReferenceCountUtil, CharsetUtil}
import io.netty.channel.nio.NioEventLoopGroup

import scala.io.Source

object ClientTest {

  val URL = System.getProperty("url", MY_URL)     
  val configuration = new Configuration

  def main(args: Array[String]) {
    println("Starting client")
    start()
  }

  def start(): Unit = {

    val group = new NioEventLoopGroup()

    try {

      val uri: URI = new URI(URL)
      val host: String= {val h = uri.getHost(); if (h != null) h else "127.0.0.1"}
      val port: Int = {val p = uri.getPort; if (p != -1) p else 80}

      val b = new Bootstrap()

      b.group(group)
      .channel(classOf[NioSocketChannel])
      .handler(new HttpClientInitializer())

      val ch = b.connect(host, port).sync().channel()

      val logFolder: File = new File(configuration.LOG_FOLDER)
      val fileToProcess: Array[File] = logFolder.listFiles()

      for (file <- fileToProcess){
        val name: String = file.getName()
        val source = Source.fromFile(configuration.LOG_FOLDER + "/" + name)

        val lineIterator: Iterator[String] = source.getLines()

        while (lineIterator.hasNext) {
            val line = lineIterator.next()
            val jsonString = parseLine(line)
            val request = createRequest(jsonString, uri, host)
            ch.writeAndFlush(request)
        }
        println("closing")
        ch.closeFuture().sync()
      }
    } finally {
      group.shutdownGracefully()
    }
  }

  private def parseLine(line: String) = {
    //do some parsing to get the json string I want
  }

  def createRequest(jsonString: String, uri: URI, host: String): FullHttpRequest = {
    val bytebuf: ByteBuf = Unpooled.copiedBuffer(jsonString, StandardCharsets.UTF_8)

    val request: FullHttpRequest = new DefaultFullHttpRequest(
      HttpVersion.HTTP_1_1, HttpMethod.POST, uri.getRawPath())
    request.headers().set(HttpHeaders.Names.HOST, host)
    request.headers().set(HttpHeaders.Names.CONNECTION, HttpHeaders.Values.KEEP_ALIVE)
    request.headers().set(HttpHeaders.Names.ACCEPT_ENCODING, HttpHeaders.Values.GZIP)
    request.headers().add(HttpHeaders.Names.CONTENT_TYPE, "application/json")

    request.headers().set(HttpHeaders.Names.CONTENT_LENGTH, bytebuf.readableBytes())
    request.content().clear().writeBytes(bytebuf)

    request
  }
}

class HttpClientInitializer() extends ChannelInitializer[SocketChannel] {

  override def initChannel(ch: SocketChannel) = {
  val pipeline = ch.pipeline()

  pipeline.addLast(new HttpClientCodec())

  //aggregates all http messages into one if content is chunked
  pipeline.addLast(new HttpObjectAggregator(1048576))

  pipeline.addLast(new IdleStateHandler(0, 0, 600))

  pipeline.addLast(new HttpClientHandler())
  }
}

class HttpClientHandler extends SimpleChannelInboundHandler[HttpObject] {

  override def channelRead0(ctx: ChannelHandlerContext, msg: HttpObject) {
    try {
      msg match {
        case res: FullHttpResponse =>
          println("response is: " + res.content().toString(CharsetUtil.US_ASCII))
          ReferenceCountUtil.retain(msg)
      }
    } finally {
      ReferenceCountUtil.release(msg)
    }
  }

  override def exceptionCaught(ctx: ChannelHandlerContext, e: Throwable) = {
    println("HttpHandler caught exception", e)
    ctx.close()
  }
}

Answer 1

ChannelFuture cf = channel.writeAndFlush(createRequest());

nor how to link them subsequently to the corresponding requests.

Can netty assign multiple IO threads to the same Channel?

The worker thread once assigned for a channel does not change for the lifetime of the channel. So we do not benefit from the threads. This is because you are keeping the connection alive and so is the channel kept alive.

To fix this problem, you might consider a pool of channels (say 30). Then use the channel pool to place your requests.

      int concurrent = 30;

  // Start the client.
  ChannelFuture[] channels = new ChannelFuture[concurrent];
  for (int i = 0; i < channels.length; i++) {
    channels[i] = b.connect(host, port).sync();
  }

  for (int i = 0; i < 1000; i++) {
      ChannelFuture requestHandle = process(channels[(i+1)%concurrent]); 
      // do something with the request handle       
  }

  for (int i = 0; i < channels.length; i++) {
    channels[i].channel().closeFuture().sync();
  }

HTH