Send Query

Overview

This tutorial builds the RPC half of KubeMQ's request/reply patterns: a query, where the caller awaits a handler's data payload instead of just a completion status. Reach for it whenever a caller needs an answer — fetching a record, running a lookup, or asking another service to compute a value on demand. This example runs the sender against a separately running handler to see the full round trip.

await client.SendQueryAsync(new QueryMessage { ... }) blocks until the handler returns a QueryResponse or the TimeoutInSeconds window elapses. The returned response.Body carries the handler's data payload, and response.Executed confirms the handler ran to completion — KubeMQ correlates the reply to this call automatically, so the caller never tracks request IDs itself.

Gotchas: the timeout must cover however long the handler takes to run — a slow handler throws KubeMQTimeoutException even though the handler eventually succeeds, so start the handler before the sender. response.Body is a raw byte span — decode or deserialize it yourself; KubeMQ doesn't interpret the payload. When Executed is false, check response.Error before assuming the call itself failed.

Prerequisites

• KubeMQ server running on localhost:50000
• C# SDK installed (dotnet add package KubeMQ.SDK.CSharp)

Code

// KubeMQ .NET SDK — Queries: Send Query
//
// This example demonstrates sending a query and receiving a data response.
// Queries are request/reply: the sender waits for the handler to return data.
//
// Prerequisites:
//   - KubeMQ server running on localhost:50000
//   - Run Queries.HandleQuery in a separate terminal first
//   - dotnet run

using KubeMQ.Sdk.Client;
using KubeMQ.Sdk.Queries;
using KubeMQ.Sdk.Exceptions;
using System.Text;

await using var client = new KubeMQClient(new KubeMQClientOptions
{
    ClientId = "csharp-queries-send-query-client",
});
await client.ConnectAsync();

Console.WriteLine("Connected to KubeMQ server");

try
{
    var response = await client.SendQueryAsync(new QueryMessage
    {
        Channel = "csharp-queries.send-query",
        Body = Encoding.UTF8.GetBytes("get-user:42"),
        TimeoutInSeconds = 10
    });

    Console.WriteLine($"Query executed: {response.Executed}");
    Console.WriteLine($"Response: {Encoding.UTF8.GetString(response.Body.Span)}");
}
catch (KubeMQTimeoutException)
{
    Console.WriteLine("Query timed out — no handler responded within 10 seconds");
}
catch (KubeMQOperationException ex) when (ex.Message.Contains("timeout", StringComparison.OrdinalIgnoreCase))
{
    Console.WriteLine($"Query timed out — server reported: {ex.Message}");
}

Console.WriteLine("Done.");

// Expected output:
// Connected to KubeMQ server
// Query executed: True
// Response: <handler-response-body>
// Done.

How It Works

• SendQueryAsync blocks until the handler returns a QueryResponse or the TimeoutInSeconds window elapses. The returned response.Body contains the handler's data payload.
• response.Executed confirms the handler ran to completion. Check response.Error for a handler-populated error message if Executed is false.
• KubeMQTimeoutException fires when no handler responds within the timeout — start the Handle Query example in a separate terminal before running this sender.
• Unlike commands, queries are expected to return data. Use Encoding.UTF8.GetString(response.Body.Span) or deserialise response.Body as JSON to consume the response.

Related

• Pattern overview
• C# SDK Reference
• Handle Query
• Cached Query