[.NET] Identify the SDK in the User-Agent header

dotnet/NEXT_CHANGELOG.md

@@ -8,6 +8,11 @@
 
 ### Bug Fixes
 
+- The SDK now identifies itself as `zerobus-sdk-dotnet/<version>` in the `User-Agent`
+  header. The identifier was only sent when the caller supplied one explicitly, so a
+  default-configured client sent the Rust core's own identifier and .NET traffic was
+  reported as Rust. An explicit `SdkIdentifier(...)` still takes precedence. No public
+  API change.
 - Fixed a use-after-free in which a custom `IHeadersProvider` could be freed
   while the Rust core was still inside a `GetHeaders()` call into it during
   connection recovery. Provider ownership is now handed to the FFI via the new

dotnet/src/Zerobus/ZerobusSdkBuilder.cs

@@ -1,3 +1,4 @@
+using System.Reflection;
 using Databricks.Zerobus.Native;
 
 namespace Databricks.Zerobus;
@@ -43,6 +44,22 @@ public sealed class ZerobusSdkBuilder : IDisposable
     private bool _disableTls;
     private int _consumed;  // 0 = live, 1 = consumed/disposed
 
+    // Sent when the caller doesn't set SdkIdentifier(); without it the Rust core's own
+    // identifier goes on the wire and .NET traffic is attributed to Rust.
+    private static readonly string DefaultSdkIdentifier = $"zerobus-sdk-dotnet/{SdkVersion()}";
+
+    // The informational version carries <Version> from the csproj, unlike AssemblyVersion,
+    // which callers may pin separately. SourceLink appends "+<commit>" to it.
+    private static string SdkVersion()
+    {
+        var informational = typeof(ZerobusSdkBuilder).Assembly
+            .GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion;
+
+        return string.IsNullOrEmpty(informational)
+            ? "0.0.0"
+            : informational.Split('+')[0];
+    }
+
     internal ZerobusSdkBuilder() { }
 
     /// <summary>
@@ -81,6 +98,10 @@ public ZerobusSdkBuilder UnityCatalogUrl(string unityCatalogUrl)
     /// Wrapper SDKs use this to identify themselves; end-user code should prefer
     /// <see cref="ApplicationName"/> instead.
     /// </summary>
+    /// <remarks>
+    /// Without this call the SDK sends <c>zerobus-sdk-dotnet/&lt;version&gt;</c>. A blank
+    /// or whitespace-only value falls back to that same default.
+    /// </remarks>
     /// <param name="sdkIdentifier">The SDK identifier string.</param>
     /// <returns>This builder, for chaining.</returns>
     /// <exception cref="ArgumentNullException">Thrown if <paramref name="sdkIdentifier"/> is null.</exception>
@@ -144,8 +165,11 @@ public ZerobusSdk Build()
                 NativeMethods.SdkBuilderEndpoint(builderPtr, _endpoint);
             if (_unityCatalogUrl is not null)
                 NativeMethods.SdkBuilderUnityCatalogUrl(builderPtr, _unityCatalogUrl);
-            if (_sdkIdentifier is not null)
-                NativeMethods.SdkBuilderSdkIdentifier(builderPtr, _sdkIdentifier);
+            // The core substitutes its own identifier only for a literal empty override, not
+            // for whitespace, so a blank value would otherwise reach the wire verbatim.
+            NativeMethods.SdkBuilderSdkIdentifier(
+                builderPtr,
+                string.IsNullOrWhiteSpace(_sdkIdentifier) ? DefaultSdkIdentifier : _sdkIdentifier);
             if (_applicationName is not null)
                 NativeMethods.SdkBuilderApplicationName(builderPtr, _applicationName);
             if (_disableTls)

dotnet/tests/Zerobus.IntegrationTests/SdkIdentifierIntegrationTests.cs

@@ -0,0 +1,122 @@
+using NUnit.Framework;
+
+namespace Databricks.Zerobus.IntegrationTests;
+
+[TestFixture]
+[Parallelizable(ParallelScope.Children)]
+public class SdkIdentifierIntegrationTests : IntegrationTestBase
+{
+    [Test]
+    public async Task DefaultSdkIdentifier_SentInUserAgent()
+    {
+        await using var fixture = await MockServerFixture.StartAsync();
+
+        fixture.MockServer.InjectResponses(TestTableName,
+        [
+            MockResponses.CreateStreamResponse("test_stream_sdk_identifier"),
+            MockResponses.RecordAckResponse(0),
+        ]);
+
+        using var sdk = CreateDefaultSdk(fixture);
+
+        using var stream = sdk.CreateStreamWithHeadersProvider(
+            CreateTableProperties(), new TestHeadersProvider(), CreateDefaultOptions());
+
+        stream.IngestRecord("test record data"u8.ToArray());
+        stream.Flush();
+
+        var observedHeaders = fixture.MockServer.GetLastRequestHeaders(TestTableName);
+        Assert.That(observedHeaders.TryGetValue("user-agent", out var userAgent), Is.True);
+        Assert.That(userAgent, Does.StartWith("zerobus-sdk-dotnet/"));
+    }
+
+    [Test]
+    public async Task ExplicitSdkIdentifier_TakesPrecedenceOverDefault()
+    {
+        await using var fixture = await MockServerFixture.StartAsync();
+
+        fixture.MockServer.InjectResponses(TestTableName,
+        [
+            MockResponses.CreateStreamResponse("test_stream_sdk_identifier_override"),
+            MockResponses.RecordAckResponse(0),
+        ]);
+
+        using var sdk = ZerobusSdk.CreateBuilder()
+            .Endpoint(fixture.ServerUrl)
+            .UnityCatalogUrl("https://mock-uc.com")
+            .SdkIdentifier("custom-wrapper/9.9.9")
+            .DisableTls()
+            .Build();
+
+        using var stream = sdk.CreateStreamWithHeadersProvider(
+            CreateTableProperties(), new TestHeadersProvider(), CreateDefaultOptions());
+
+        stream.IngestRecord("test record data"u8.ToArray());
+        stream.Flush();
+
+        var observedHeaders = fixture.MockServer.GetLastRequestHeaders(TestTableName);
+        Assert.That(observedHeaders.TryGetValue("user-agent", out var userAgent), Is.True);
+        Assert.That(userAgent, Does.StartWith("custom-wrapper/9.9.9"));
+    }
+
+    [Test]
+    public async Task BlankSdkIdentifier_FallsBackToDefault()
+    {
+        await using var fixture = await MockServerFixture.StartAsync();
+
+        fixture.MockServer.InjectResponses(TestTableName,
+        [
+            MockResponses.CreateStreamResponse("test_stream_sdk_identifier_blank"),
+            MockResponses.RecordAckResponse(0),
+        ]);
+
+        using var sdk = ZerobusSdk.CreateBuilder()
+            .Endpoint(fixture.ServerUrl)
+            .UnityCatalogUrl("https://mock-uc.com")
+            .SdkIdentifier("   ")
+            .DisableTls()
+            .Build();
+
+        using var stream = sdk.CreateStreamWithHeadersProvider(
+            CreateTableProperties(), new TestHeadersProvider(), CreateDefaultOptions());
+
+        stream.IngestRecord("test record data"u8.ToArray());
+        stream.Flush();
+
+        // The core only substitutes its default for a literal empty override, not whitespace.
+        var observedHeaders = fixture.MockServer.GetLastRequestHeaders(TestTableName);
+        Assert.That(observedHeaders.TryGetValue("user-agent", out var userAgent), Is.True);
+        Assert.That(userAgent, Does.StartWith("zerobus-sdk-dotnet/"));
+    }
+
+    [Test]
+    public async Task ApplicationName_AppendedToDefaultSdkIdentifier()
+    {
+        await using var fixture = await MockServerFixture.StartAsync();
+
+        fixture.MockServer.InjectResponses(TestTableName,
+        [
+            MockResponses.CreateStreamResponse("test_stream_sdk_identifier_app_name"),
+            MockResponses.RecordAckResponse(0),
+        ]);
+
+        using var sdk = ZerobusSdk.CreateBuilder()
+            .Endpoint(fixture.ServerUrl)
+            .UnityCatalogUrl("https://mock-uc.com")
+            .ApplicationName("integration-test")
+            .DisableTls()
+            .Build();
+
+        using var stream = sdk.CreateStreamWithHeadersProvider(
+            CreateTableProperties(), new TestHeadersProvider(), CreateDefaultOptions());
+
+        stream.IngestRecord("test record data"u8.ToArray());
+        stream.Flush();
+
+        // The core sends "<identifier> <application name>" and tonic appends its own token.
+        var observedHeaders = fixture.MockServer.GetLastRequestHeaders(TestTableName);
+        Assert.That(observedHeaders.TryGetValue("user-agent", out var userAgent), Is.True);
+        Assert.That(userAgent, Does.StartWith("zerobus-sdk-dotnet/"));
+        Assert.That(userAgent, Does.Contain(" integration-test"));
+    }
+}