Fix serialization

src/Elastic.Apm/Report/Serialization/PayloadItemSerializer.cs

@@ -83,8 +83,11 @@ internal PayloadItemSerializer() =>
 
 	public JsonTypeInfo GetTypeInfo(Type type) => Settings.TypeInfoResolver!.GetTypeInfo(type, Settings);
 
-	public void Serialize(object item, StreamWriter writer) =>
+	public void Serialize(object item, StreamWriter writer)
+	{
+		writer.Flush(); // ensure the base stream is "up-to-date" before we attempt to serialize into it
 		JsonSerializer.Serialize(writer.BaseStream, item, item.GetType(), Settings);
+	}
 
 	/// <summary>
 	/// Deserializes an instance of <typeparamref name="T"/> from JSON

test/Elastic.Apm.Tests/ActivityIntegrationTests.cs

@@ -168,9 +168,6 @@ public void MultipleTransactionInOneActivity()
 		}
 
 #if NET
-		/// <summary>
-		/// Makes sure that transactions on the same Activity are part of the same trace.
-		/// </summary>
 		[Fact]
 		public async Task ActivityRespectsSampling()
 		{
@@ -179,27 +176,28 @@ public async Task ActivityRespectsSampling()
 
 			Activity.Current = null;
 			Activity.DefaultIdFormat = ActivityIdFormat.W3C;
-			var source = new ActivitySource(GetType().FullName, "1.0.0");
+
+			using var source = new ActivitySource(GetType().FullName, "1.0.0");
 
 			var payloadSender = new MockPayloadSender();
 			var config = new MockConfiguration(
 				transactionSampleRate: rate.ToString("N2")
-
 			);
+
 			using var components = new TestAgentComponents(
 				apmServerInfo: MockApmServerInfo.Version716,
 				configuration: config,
 				payloadSender: payloadSender
-
 			);
+
 			using var agent = new ApmAgent(components);
 			for (var i = 0; i < count; i++)
 			{
 				using var transaction = source.StartActivity($"Trace {i}");
 				using var span = new Activity("UnitTestActivity").Start();
 				await Task.Delay(1);
 			}
-			//Activity.Current.Should().BeNull();
+
 			payloadSender.WaitForTransactions(count: count);
 
 			var sampled = payloadSender.Transactions.Where(t => t.IsSampled).ToArray();

test/startuphook/Elastic.Apm.StartupHook.Tests/StartupHookTests.cs

@@ -67,10 +67,18 @@ public async Task Auto_Instrument_With_StartupHook_Should_Capture_Transaction(st
 			apmServer.RunInBackground(port);
 			var waitHandle = new ManualResetEvent(false);
 
+			var error = string.Empty;
+
 			apmServer.OnReceive += o =>
 			{
 				if (o is TransactionDto)
 					waitHandle.Set();
+
+				else if (o is string s) // may occur if there is an error
+				{
+					waitHandle.Set();
+					error = s;
+				}
 			};
 
 			using (var sampleApp = new SampleApplication())
@@ -86,8 +94,9 @@ public async Task Auto_Instrument_With_StartupHook_Should_Capture_Transaction(st
 				var response = await client.GetAsync(uri);
 
 				response.IsSuccessStatusCode.Should().BeTrue();
+				waitHandle.WaitOne(TimeSpan.FromMinutes(1));
 
-				waitHandle.WaitOne(TimeSpan.FromMinutes(2));
+				error.Should().BeEmpty();
 				apmServer.ReceivedData.Transactions.Should().HaveCount(1);
 
 				var transaction = apmServer.ReceivedData.Transactions.First();
@@ -108,12 +117,22 @@ public async Task Auto_Instrument_With_StartupHook_Should_Capture_Error(string t
 			var transactionWaitHandle = new ManualResetEvent(false);
 			var errorWaitHandle = new ManualResetEvent(false);
 
+			var serverError = string.Empty;
+
 			apmServer.OnReceive += o =>
 			{
 				if (o is TransactionDto)
 					transactionWaitHandle.Set();
-				if (o is ErrorDto)
+
+				else if (o is ErrorDto)
 					errorWaitHandle.Set();
+
+				else if (o is string s) // may occur if there is an error
+				{
+					transactionWaitHandle.Set();
+					errorWaitHandle.Set();
+					serverError = s;
+				}
 			};
 
 			using (var sampleApp = new SampleApplication())
@@ -131,13 +150,15 @@ public async Task Auto_Instrument_With_StartupHook_Should_Capture_Error(string t
 
 				response.IsSuccessStatusCode.Should().BeFalse();
 
-				transactionWaitHandle.WaitOne(TimeSpan.FromMinutes(2));
+				transactionWaitHandle.WaitOne(TimeSpan.FromMinutes(1));
+				serverError.Should().BeEmpty();
 				apmServer.ReceivedData.Transactions.Should().HaveCount(1);
 
 				var transaction = apmServer.ReceivedData.Transactions.First();
 				transaction.Name.Should().Be("GET Home/Exception");
 
-				errorWaitHandle.WaitOne(TimeSpan.FromMinutes(2));
+				errorWaitHandle.WaitOne(TimeSpan.FromMinutes(1));
+				serverError.Should().BeEmpty();
 				apmServer.ReceivedData.Errors.Should().HaveCount(1);
 
 				var error = apmServer.ReceivedData.Errors.First();
@@ -159,11 +180,19 @@ public async Task Auto_Instrument_With_StartupHook_Should_Capture_Metadata(
 			var port = apmServer.FindAvailablePortToListen();
 			apmServer.RunInBackground(port);
 
+			var error = string.Empty;
 			var waitHandle = new ManualResetEvent(false);
+
 			apmServer.OnReceive += o =>
 			{
 				if (o is MetadataDto)
 					waitHandle.Set();
+
+				else if (o is string s) // may occur if there is an error
+				{
+					waitHandle.Set();
+					error = s;
+				}
 			};
 
 			using (var sampleApp = new SampleApplication())
@@ -180,7 +209,9 @@ public async Task Auto_Instrument_With_StartupHook_Should_Capture_Metadata(
 
 				response.IsSuccessStatusCode.Should().BeTrue();
 
-				waitHandle.WaitOne(TimeSpan.FromMinutes(2));
+				waitHandle.WaitOne(TimeSpan.FromMinutes(1));
+
+				error.Should().BeEmpty();
 				apmServer.ReceivedData.Metadata.Should().HaveCountGreaterOrEqualTo(1);
 
 				var metadata = apmServer.ReceivedData.Metadata.First();