Enforce that you can't update exporter settings to point to UDS on Windows (#7721)

## Summary of changes

Enforces that you can't _change_ the `AgentUri` to be a UDS Uri if
you're on Windows

## Reason for change

The trace exporter doesn't work with UDS on Windows, so we have a check
in `TracerSettings` that disables the pipeline if we find this scenario.
However, user's can still _change_ the agent URI at runtime in code (😭).

We currently assume that the data pipeline won't be toggled at runtime
(we _do_ allow for reconfiguring it in general, but not for completely
removing or reintroducing). Changing this to allow the scenario would be
a pain, so instead this PR blocks you from setting a UDS URI in code if
you're on Windows.

The good news is that as far as I can tell, noone does this today, so
while _technically_ it could be considered a breaking change, I think
it's ok.

## Implementation details

- Throw an `ArgumentException` in the Datadog.Trace.Manual library, if
you're on Windows (or .NET FX) and you try to set a UDS agent URI (using
the same "detection" we do in `ExporterSettings`.
- Add a check in the Instrumentation of `Tracer.Configure()` to make
sure it hasn't slipped through. This could happen if a customer was
using an old version of the Datadog.Trace NuGet package with a newer
version of auto instrumentation.

Note that this adds two additional framework references for .NET Core
3.1+, to check if we're on Windows.

## Test coverage

Added an extra step to the manual instrumentation integration test to
confirm we throw

## Other details

https://datadoghq.atlassian.net/browse/LANGPLAT-819

Part of a config stack

- #7522
- #7525
- #7530
- #7532
- #7543
- #7544
- #7721 👈
- #7722
- #7695
- #7723
- #7724

Author: andrewlock

tracer/src/Datadog.Trace.Manual/Configuration/TracerSettings.cs

@@ -397,7 +397,23 @@ public Uri AgentUri
         get => _agentUri.Value;
         [Browsable(false)]
         [EditorBrowsable(EditorBrowsableState.Never)]
-        set => _agentUri = _agentUri.Override(value);
+        set
+        {
+            if (
+#if !NETFRAMEWORK
+                System.Runtime.InteropServices.RuntimeInformation.IsOSPlatform(System.Runtime.InteropServices.OSPlatform.Windows) &&
+#endif
+                value.OriginalString.StartsWith("unix://", StringComparison.OrdinalIgnoreCase))
+            {
+                throw new ArgumentException(
+                    $"Error setting {nameof(AgentUri)} to '{value}'. " +
+                    $"{nameof(AgentUri)} can not be set to a UDS endpoint in code when running on Windows. " +
+                    "If you need to use UDS on Windows, set the environment variable DD_TRACE_AGENT_URL instead to " +
+                    "ensure the app starts with the correct configuration");
+            }
+
+            _agentUri = _agentUri.Override(value);
+        }
     }
 
     /// <summary>

tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/ManualInstrumentation/Tracer/ConfigureIntegration.cs

@@ -4,6 +4,7 @@
 // </copyright>
 
 #nullable enable
+using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using Datadog.Trace.ClrProfiler.CallTarget;
@@ -46,6 +47,23 @@ internal static void ConfigureSettingsWithManualOverrides(Dictionary<string, obj
     {
         TelemetryFactory.Metrics.Record(PublicApiUsage.Tracer_Configure);
 
+        // There's an edge case in our APIs where if a user changes the agent URI to UDS on Windows
+        // then we can no longer use the trace exporter, but this is something that we assume is
+        // immutable today. To work around this edge case, we block updating the exporter settings to
+        // point to UDS when you're running on Windows. Note that it's fine to set to UDS _initially_,
+        // it's only _updating_ it to UDS on Windows that we block
+        if (FrameworkDescription.Instance.IsWindows()
+         && values.TryGetValue(TracerSettingKeyConstants.AgentUriKey, out var raw)
+         && raw is Uri uri
+         && uri.OriginalString.StartsWith(ExporterSettings.UnixDomainSocketPrefix, StringComparison.OrdinalIgnoreCase))
+        {
+            InvalidConfigurationException.Throw(
+                $"Error changing AgentUri. " +
+                "AgentUri can not be set to a UDS endpoint in code when running on Windows. " +
+                "If you need to use UDS on Windows, set the environment variable DD_TRACE_AGENT_URL instead to " +
+                "ensure the app starts with the correct configuration");
+        }
+
         // Is this from calling new TracerSettings() or TracerSettings.Global?
         var isFromDefaults = values.TryGetValue(TracerSettingKeyConstants.IsFromDefaultSourcesKey, out var value) && value is true;
 

tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/ManualInstrumentation/Tracer/InvalidConfigurationException.cs

@@ -0,0 +1,20 @@
+// <copyright file="InvalidConfigurationException.cs" company="Datadog">
+// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
+// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2017 Datadog, Inc.
+// </copyright>
+
+#nullable enable
+
+using System.Diagnostics.CodeAnalysis;
+using Datadog.Trace.ClrProfiler.CallTarget;
+
+namespace Datadog.Trace.ClrProfiler.AutoInstrumentation.ManualInstrumentation.Tracer;
+
+/// <summary>
+/// An exception indicating that an invalid value was specified for a setting in the public API.
+/// </summary>
+internal class InvalidConfigurationException(string message) : CallTargetBubbleUpException(message)
+{
+    [DoesNotReturn]
+    public static void Throw(string message) => throw new InvalidConfigurationException(message);
+}

tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.Manual.AssemblyReferencesHaveNotChanged.net6.0.verified.txt

@@ -6,4 +6,5 @@ System.Linq, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Runtime, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Runtime.CompilerServices.Unsafe, Version=4.0.6.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Runtime.Extensions, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
+System.Runtime.InteropServices.RuntimeInformation, Version=4.0.4.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Threading, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a

tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.Manual.AssemblyReferencesHaveNotChanged.netcoreapp3.1.verified.txt

@@ -6,4 +6,5 @@ System.Linq, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Runtime, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Runtime.CompilerServices.Unsafe, Version=4.0.6.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Runtime.Extensions, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
+System.Runtime.InteropServices.RuntimeInformation, Version=4.0.4.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Threading, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a

tracer/test/test-applications/integrations/Samples.ManualInstrumentation/Program.cs

@@ -5,6 +5,7 @@
 using System.Net;
 using System.Net.Http;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -318,6 +319,23 @@ async Task OtherStuff()
             // Manually disable debug logs
             GlobalSettings.SetDebugEnabled(false);
 
+            // Try to reconfigure tracer to use UDS on Windows. This should throw an exception
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                try
+                {
+                    var invalidSettings = TracerSettings.FromDefaultSources();
+                    invalidSettings.ServiceName = "InvalidSettings";
+                    invalidSettings.AgentUri = new Uri("unix://apm.socket");
+                    Tracer.Configure(invalidSettings);
+                    ThrowIf(true, "We should not be able to configure the tracer with UDS on Windows");
+                }
+                catch
+                {
+                    LogAndAssertCurrentSettings(Tracer.Instance, "RejectedInvalidSettings", settings);
+                }
+            }
+
             // Force flush
             await Tracer.Instance.ForceFlushAsync();