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HAProxy Stream Processing Offload Agent (SPOA) for .NET Core

The HAProxy Stream Processing Offload Protocol (SPOP) allows traffic data to be streamed to an external agent. This library allows you to write that agent using .NET Core.

For more information, read the blog post Extending HAProxy with the Stream Processing Offload Engine.

Supported SPOP Capabilities

Capability Supported
fragmentation yes
async no
pipelining no


Add a reference to the NuGet package using the .NET CLI:

$ dotnet add package HAProxy.StreamProcessingOffload.Agent --version 1.0.0 

Or use the NuGet Package Manager:

PS> Install-Package HAProxy.StreamProcessingOffload.Agent -Version 1.0.0 


  1. Download and install the .NET Core SDK.
  2. Create a new folder and cd into it.
  3. Create a new .NET Core project:
$ dotnet new console
  1. Add a reference to the package:
$ dotnet add package HAProxy.StreamProcessingOffload.Agent --version 1.0.0
  1. Edit Program.cs to start a service listening on an IP and port. Create an instance of FrameProcessor and call HandleStream to process SPOP messages received on new network connections. This method accepts a NetworkStream and a callback function that takes a NotifyFrame and returns List<SpoeAction>.



using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Threading.Tasks;
using HAProxy.StreamProcessingOffload.Agent;
using HAProxy.StreamProcessingOffload.Agent.Actions;
using HAProxy.StreamProcessingOffload.Agent.Payloads;

namespace spoa_dotnet_example
    class Program
        static void Main(string[] args)
            IPAddress address = IPAddress.Parse("");
            int port = 12345;
            var listener = new TcpListener(address, port);
            var frameProcessor = new FrameProcessor()
                EnableLogging = true,
                LogFunc = (msg) => Console.WriteLine(msg)

            Console.WriteLine("Listening on {0}:{1}", address, port);

            while (true)
                TcpClient client = listener.AcceptTcpClient();

                Task.Run(() =>
                    NetworkStream stream = client.GetStream();
                    frameProcessor.HandleStream(stream, (notifyFrame) =>
                        // NOTIFY frames contain HAProxy messages to the agent.
                        // The agent can send back "actions" to HAProxy via ACK frames.
                        var messages = ((ListOfMessagesPayload)notifyFrame.Payload).Messages;
                        var responseActions = new List<SpoeAction>();

                        if (messages.Any(msg => msg.Name == "my-message-name"))
                           var myMessage = messages.First(msg => msg.Name == "my-message-name");

                           // Each message may contain a collection of arguments, which hold the data.
                           TypedData myArg = myMessage.Args.First(arg => arg.Key == "ip").Value; 

                           int ip_score = 10;

                           if ((string)myArg.Value == "")
                               ip_score = 20;

                           // You can send actions back to HAProxy, such as setting a variable.
                           SpoeAction setVar = 
                              new SetVariableAction(
                                 new TypedData(DataType.Int32, ip_score));


                        return responseActions;

How it Works

All communication is handled by the FrameProcessor class. Its HandleStream method takes a NetworkStream object and a lambda function as parameters. The lambda function is called when a NOTIFY frame is received. From there, you can return a list of SpoeAction objects, which tell HAProxy to perform action(s).


  • SetVariableAction - set a variable in HAProxy
  • UnsetVariableAction - unset a variable

When setting a variable, you must pass in the variable scope (Process, Session, Transaction, Request, or Response). Then, set a name for the variable and its value as a TypedData instance.

SpoeAction setVar = 
   new SetVariableAction(
       VariableScope.Session, // scope
       "ip_score", // name
       new TypedData(DataType.Int32, ip_score)); // value

Both actions and arguments received in messages from HAProxy are represented as TypedData. This is simply a container for different types of data. DataType can be:

  • Null
  • Boolean
  • Int32
  • Uint32
  • Int64
  • Uint64
  • Ipv4
  • Ipv6
  • String
  • Binary

For message arguments, the type is set for you by HAProxy depending on the fetch method used. For example, the src fetch method is Ipv4 or Ipv6.

There can be multiple messages within a NOTIFY frame, so you should check for a message name to find the right one:

var messages = ((ListOfMessagesPayload)notifyFrame.Payload).Messages;
if (messages.Any(msg => msg.Name == "my-message-name"))
   // perform logic

Here is an example spoe.conf file that defines the messages and arguments HAProxy will send to the agent:

spoe-agent my-agent
   messages           my-message-name
   option var-prefix  myspoe
   log                global
   use-backend        be_agents
   timeout hello      10s
   timeout idle       10s
   timeout processing 10s

spoe-message my-message-name
   args ip=src anotherarg=str(abc)
   event on-frontend-http-request if { path / }

In your haproxy.cfg, the SPOE can be initialized by adding a filter spoe line:

frontend web
   bind :80
   filter spoe engine my-spoe config /etc/haproxy/spoe.conf
   http-request set-header "ip_score" %[var(sess.myspoe.ip_score)]
   default_backend servers

backend servers
   balance roundrobin
   server s1 check maxconn 30

backend be_agents
   mode tcp
   balance roundrobin
   option spop-check
   server agent1 check  inter 10s  maxconn 30

Building and Testing

To build and run the unit tests, use the following commands

$ dotnet clean
$ dotnet build
$ dotnet test
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