Built-in services

The Worker provides services in addition to your [FlowService] classes. Request them in the node class constructor.

Service	Purpose
IMessageService	Exchange messages during one run; optionally allow external ingress.
IFlowWorkpiece	Save images, reports, and other node output files.
IFlowNativeLibraryLoader	Load native files bundled in the library ZIP. See Native DLLs.

Wait for a message

IMessageService.CreateMessageQueue() creates a queue view. A message on a topic is consumed by one receiver. This node allows the external API to publish JSON to device.inbox:

using SereinFlow.Core.Api;
using SereinFlow.Library;
using SereinFlow.Runtime.Abstractions;

[FlowLibrary("Device messages")]
public sealed class MessageNodes(IMessageService messages)
{
    [FlowNode(NodeType = NodeType.Flipflop, AnotherName = "Wait for device message")]
    public async Task<string> Wait(IFlowContext context)
    {
        var queue = messages.CreateMessageQueue(new MessageChannelOptions
        {
            ExternalIngress = true,
            ContractId = "device.message.v1"
        });
        return await queue.ReceiveAsync<string>("device.inbox", context.CancellationToken);
    }
}

Queues use JSON by default. External publishing requires ExternalIngress = true; internal topics are closed by default. Use CreateEventBus() to deliver an event to multiple subscribers and dispose subscriptions asynchronously. Messages exist only during this Worker run, so they are not persistent storage.

Save a generated file

IFlowWorkpiece.UploadNodeOutput stores a file with its producing node and execution from IFlowContext. It returns FlowWorkpieceInfo with ID, name, type, and size:

using SereinFlow.Core.Api;
using SereinFlow.Library;
using SereinFlow.Runtime.Abstractions;

[FlowLibrary("Report tools")]
public sealed class ReportNodes(IFlowWorkpiece workpieces)
{
    [FlowNode(AnotherName = "Save report")]
    public string Save(IFlowContext context)
    {
        var file = workpieces.UploadNodeOutput(
            context, "report.txt", "Inspection complete", "text/plain; charset=utf-8");
        return file.Id;
    }
}

It also accepts byte[] or Stream for binary content. List and download these files through the Runs and workpieces API.

Parameters versus constructor services

Put IFlowContext on each node method; put the three services above in the node class constructor.