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Loader.NetCore.cs
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Loader.NetCore.cs
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// <copyright file="Loader.NetCore.cs" company="OpenTelemetry Authors">
// Copyright The OpenTelemetry Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// </copyright>
#if NETCOREAPP
using System.Reflection;
namespace OpenTelemetry.AutoInstrumentation.Loader;
/// <summary>
/// A class that attempts to load the OpenTelemetry.AutoInstrumentation .NET assembly.
/// </summary>
internal partial class Loader
{
internal static System.Runtime.Loader.AssemblyLoadContext DependencyLoadContext { get; } = new ManagedProfilerAssemblyLoadContext();
private static string ResolveManagedProfilerDirectory()
{
string tracerFrameworkDirectory = "net";
string tracerHomeDirectory = ReadEnvironmentVariable("OTEL_DOTNET_AUTO_HOME") ?? string.Empty;
return Path.Combine(tracerHomeDirectory, tracerFrameworkDirectory);
}
private static Assembly? AssemblyResolve_ManagedProfilerDependencies(object? sender, ResolveEventArgs args)
{
var assemblyName = new AssemblyName(args.Name);
// On .NET Framework, having a non-US locale can cause mscorlib
// to enter the AssemblyResolve event when searching for resources
// in its satellite assemblies. This seems to have been fixed in
// .NET Core in the 2.0 servicing branch, so we should not see this
// occur, but guard against it anyways. If we do see it, exit early
// so we don't cause infinite recursion.
if (string.Equals(assemblyName.Name, "System.Private.CoreLib.resources", StringComparison.OrdinalIgnoreCase) ||
string.Equals(assemblyName.Name, "System.Net.Http", StringComparison.OrdinalIgnoreCase))
{
return null;
}
var path = Path.Combine(ManagedProfilerDirectory, $"{assemblyName.Name}.dll");
// Only load the main profiler into the default Assembly Load Context.
// If OpenTelemetry.AutoInstrumentation or other libraries are provided by the NuGet package their loads are handled in the following two ways.
// 1) The AssemblyVersion is greater than or equal to the version used by OpenTelemetry.AutoInstrumentation, the assembly
// will load successfully and will not invoke this resolve event.
// 2) The AssemblyVersion is lower than the version used by OpenTelemetry.AutoInstrumentation, the assembly will fail to load
// and invoke this resolve event. It must be loaded in a separate AssemblyLoadContext since the application will only
// load the originally referenced version
if (assemblyName.Name != null && assemblyName.Name.StartsWith("OpenTelemetry.AutoInstrumentation", StringComparison.OrdinalIgnoreCase) && File.Exists(path))
{
Logger.Debug("Loading {0} with Assembly.LoadFrom", path);
return Assembly.LoadFrom(path);
}
else if (File.Exists(path))
{
Logger.Debug("Loading {0} with DependencyLoadContext.LoadFromAssemblyPath", path);
return DependencyLoadContext.LoadFromAssemblyPath(path); // Load unresolved framework and third-party dependencies into a custom Assembly Load Context
}
return null;
}
}
#endif