Tutorial4/5

4. Serialize, send, and run

Finish the send pipeline, create the host, and run two orders.

The Serializer

Keep the existing ExecuteAsync signature in src/Send/Serializer.cs. Replace only its body:

{
    var json = JsonSerializer.Serialize(input);
    return Task.FromResult<(TechnicalStepResult<string>, Context)>(
        (new TechnicalStepResult<string>.Success(json), context));
}

The Sender

The Sender writes through IFileAdapter. Keep the existing ExecuteAsync signature in src/Send/Sender.cs and add async to it. Replace only its body:

{
    var orderId = context.Metadata[Constants.ContextKeyOrderId];
    var fileName = $"{orderId}.json";
    await fileAdapter.WriteAsync(fileName, input, Encoding.UTF8);
    return (new BusinessStepResult<string>.Success(fileName), context);
}

The output file uses the order id from context.

Add a test to each step’s empty test class:

[Fact]
public async Task ExecuteAsync_WithOrder_RoundTripsThroughJson()
{
    var serializer = new Serializer();
    var output = new Out(
        OrderId: "ORD-1001",
        CustomerId: "CUST-42",
        ProcessedAt: new DateTimeOffset(2026, 1, 15, 9, 30, 0, TimeSpan.Zero),
        TotalAmount: 25.0m,
        Status: "Processed");

    var (result, _) = await serializer.ExecuteAsync(
        output, new Context(new Dictionary<string, string>()), CancellationToken.None);

    var success = Assert.IsType<TechnicalStepResult<string>.Success>(result);
    Assert.Equal(output, JsonSerializer.Deserialize<Out>(success.Value));
}

[Fact]
public async Task ExecuteAsync_WithOrderIdInContext_WritesPayloadToOrderNamedFile()
{
    var fileAdapter = Substitute.For<IFileAdapter>();
    var sender = new Sender(fileAdapter);
    var context = new Context(new Dictionary<string, string>
    {
        [Constants.ContextKeyOrderId] = "ORD-1001"
    });
    const string payload = """{"orderId":"ORD-1001"}""";

    var (result, _) = await sender.ExecuteAsync(payload, context, CancellationToken.None);

    // The text write is an extension over the adapter's binary WriteAsync: assert on the bytes.
    await fileAdapter.Received(1).WriteAsync("ORD-1001.json",
        Arg.Is<byte[]>(bytes => Encoding.UTF8.GetString(bytes) == payload),
        Arg.Any<string?>(), Arg.Any<CancellationToken>());
    var success = Assert.IsType<BusinessStepResult<string>.Success>(result);
    Assert.Equal("ORD-1001.json", success.Value);
}

Run the whole test suite:

dotnet test

Passed!  - Failed:     0, Passed:    10, Skipped:     0, Total:    10 - OrderSync.Test.Unit.dll (net10.0)
Passed!  - Failed:     0, Passed:     5, Skipped:     0, Total:     5 - OrderSync.Test.Integration.dll (net10.0)

The valid-message integration test now passes, and the build no longer warns about fileAdapter.

Create the system host

Create the host from the workspace directory, the parent of order-sync/:

cd ..
intropy sys create -n OrderSync -o order-sync-host

using cached integrio-intropy/intropy-templates@v2.0.0
created order-sync-host from integrio-intropy/intropy-templates@v2.0.0 (template system-host)
assembled system "order-sync": 1 component(s), 0 topic(s), 2 port(s), no contracts project

Use -o because the Component already owns the order-sync/ directory.

Open the generated system definition:

public sealed class OrderSyncSystem : ISystemDefinition
{
    public string SystemName => "order-sync";

    public void Define(SystemBuilder builder)
    {
        builder.AddTransactionalIntegration("order-sync")
            .From(Ports.OrderSyncSource)
            .To(Ports.OrderSyncDestination)
            .Calls(Services.Idempotency)
            .Calls(Services.BusinessIncidents);
    }
}

Validate the declaration and print the model:

cd order-sync-host
dotnet run -- check

ok: 'order-sync' is valid (1 components).

The build before it prints warning ASPIRE010 about AspireUseCliBundle=false. The host does not use the Aspire CLI bundle; ignore the warning.

dotnet run -- graph

The JSON follows the build output. It has two Ports and the Component-owned internal hop:

{
  "apiVersion": "topology.intropy.io/v1",
  "kind": "SystemTopology",
  "system": "order-sync",
  "components": [
    {
      "name": "order-sync",
      "kind": "transactional-integration",
      "ports": [
        { "port": "order-sync-source", "direction": "in" },
        { "port": "order-sync-destination", "direction": "out" }
      ],
      "uses": [
        "idempotency-service",
        "business-incident-service"
      ],
      "internalQueue": {
        "pubsub": "order-sync-pubsub",
        "topic": "internal-order-sync",
        "resource": "order-sync-subscription",
        "defaultPath": "/unhandled"
      },
      "channel": {
        "pubsub": "order-sync-pubsub",
        "topic": "internal-order-sync"
      }
    }
  ]
}

The internal queue is the topic internal-order-sync on the System’s pub/sub, order-sync-pubsub. channel is the pub/sub and topic the host passes to the Component as INTROPY_PUBSUB_NAME and INTROPY_TOPIC_NAME. The full output also aggregates the same declarations into top-level ports and services sections, one entry per name with its users, and lists a messagegroups entry for order-sync with no messages, because this Component declares no message contracts.

Check it

Seed the source folder with the two sample orders before starting the host:

mkdir -p test/order-sync-source
cp sample-data/sample-order-status-0.json sample-data/sample-order-status-1.json test/order-sync-source/

task seed PORT_DIR=./test/order-sync-source runs the same commands if you have Task installed. Then start the host:

dotnet run

Docker must be running, and dapr init must have completed — without the installed runtime, each sidecar starts and exits immediately. Open the dashboard URL if you want to inspect the run:

info: Aspire.Hosting.DistributedApplication[0]
      Login to the dashboard at http://localhost:15170/login?t=<token>
info: Aspire.Hosting.DistributedApplication[0]
      Distributed application started. Press Ctrl+C to shut down.

In a second terminal, from order-sync-host/, check the destination folder:

ls test/order-sync-destination
cat test/order-sync-destination/ORD-1001.json

ORD-1001.json
ORD-1002.json
{"OrderId":"ORD-1001","CustomerId":"CUST-42","ProcessedAt":"2026-10-08T14:33:26.432968+00:00","TotalAmount":88.90,"Status":"Processed"}

The source folder is empty again. Stop the host with Ctrl+C. To re-run, seed again and start it again.