为什么 ZeroMQ REQ / ROUTER 示例没有收到任何消息？

Question

ZeroMQ: Messaging for Many Applications 评论 REQ -> ROUTER 通讯：

If we rewrote our “Hello World” server using ROUTER, we’d be able to process any number of “Hello” requests in parallel.

所以我从 ZeroMQ 指南中输入 hwclient.hs and have slightly modified the hwserver.hs：

你好世界客户端

{-# LANGUAGE OverloadedStrings #-}

-- Hello World client

module Main where

import Control.Monad
import System.ZMQ4.Monadic

main :: IO ()
main = runZMQ $ do
    liftIO $ putStrLn "Connecting to hello world server…"

    requester <- socket Req
    connect requester "tcp://localhost:5555"

    forM_ [1..10] $ \i -> do
        liftIO . putStrLn $ "Sending Hello " ++ show i ++ "…"
        send requester [] "Hello"
        _ <- receive requester
        liftIO . putStrLn $ "Received World " ++ show i

路由器：

你好世界路由器

{-# LANGUAGE OverloadedStrings #-}

-- Hello World server

module Main where

import Control.Concurrent
import Control.Monad
import System.ZMQ4.Monadic

main :: IO ()
main = runZMQ $ do
    -- Socket to talk to clients
    responder <- socket Router
    bind responder "tcp://*:5555"

    forever $ do
        buffer <- receive responder
        liftIO $ do
            putStrLn "Received Hello"
            threadDelay 1000000 -- Do some 'work'
        send responder [] "World"

但是，当我运行它时，我看到客户端发送消息，但从未收到响应。

$stack exec -- client-exe
Connecting to hello world server…
Sending Hello 1…

在我的另一个 window 中，我看到服务器收到了 3 条消息，仅此而已：

$stack exec -- server-exe
Received Hello
Received Hello
Received Hello

Q1: 为什么客户端一直收不到回复？
Q2: 为什么服务器 (ROUTER) 收到 3 条消息而不是 1 条？

编辑

我更新了 hwserver.hs 以打印出它收到的消息，而不是简单地 "Hello"。

发布差异：

printf "received request: %s\n" . unpack $ buffer

已替换

putStrLn "Received Hello"

并且服务器（路由器）显示：

$stack exec -- server-exe
received request: A§
received request: 
received request: Hello

最后，这里是 send 的函数签名：

λ: :t send
send
  :: Sender t =>
     Socket z t
     -> [Flag] -> Data.ByteString.Internal.ByteString -> ZMQ z ()

Answer 1

反序回答...

你的3'messages'是收到消息的3帧。第一帧由 Router 套接字添加，用于标识消息的来源。第二个是 Requester 套接字添加的空分隔符帧，最后一个帧包含您发送的数据。

这就是为什么您没有收到响应的原因，当经销商套接字发送消息时，它会剥离第一个消息帧并将其用作地址来标识需要回复的客户端。由于您没有保存收到的第一帧并将其附加到传出消息，因此它会被丢弃。

遗憾的是，我对 haskell 或其 zeromq 绑定了解不够，无法为您提供代码解决方案，但如果您接收到地址缓冲区，直到读取空数据包，然后读取数据包入数据缓冲区。回复时发送地址缓冲区，空缓冲区然后回复。

Answer 2

根据 David's and user3666197's 的响应，我放弃了 identity 框架，我想出了：

{-# LANGUAGE OverloadedStrings #-}

-- Hello World server

module Main where

import Control.Concurrent
import Control.Monad
import System.ZMQ4.Monadic
import Text.Printf
import Data.ByteString.Char8 (unpack, pack)
import Data.List.NonEmpty

main :: IO ()
main = runZMQ $ do
    -- Socket to talk to clients
    responder <- socket Router
    bind responder "tcp://*:5555"

    forever $ do
        response @ (identity : _ : body : []) <- receiveMulti responder
        _ <- liftIO $ putStrLn . show . Prelude.length $ response
        _ <- liftIO $ forM_ response (printf "received request: %s\n" . unpack)
        liftIO $ putStrLn "sending world"
        sendMulti responder $ identity `cons` (pack "" `cons` (pack "world" :| []))

运行这

-- terminal 1
$stack exec -- client-exe
Connecting to hello world server…
Sending Hello 1…
received request: world
...

--terminal 2
$stack exec -- router-exe
3
received request: A§
received request: 
received request: Hello
sending world  
...

为什么 ZeroMQ REQ / ROUTER 示例没有收到任何消息？

Why a ZeroMQ REQ / ROUTER Example Does Not Receive Any Message?

haskell

zeromq

你好世界客户端

你好世界路由器