ManagedProfilerAssemblyResolver.NetFramework.cs

// <copyright file="ManagedProfilerAssemblyResolver.NetFramework.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>

#if NETFRAMEWORK

#nullable enable

using System;
using System.IO;
using System.Reflection;

namespace Datadog.Trace.ClrProfiler.Managed.Loader;

// Owns the AppDomain.AssemblyResolve callback on .NET Framework. Kept on a
// separate class from Startup so the handler can be dispatched without
// forcing Startup's type-initializer to have finished. If the handler were
// a method on Startup, a configBuilder attached to <appSettings> that
// issues sync-over-async work during Startup..cctor could deadlock: the
// main thread would be blocked inside the .cctor waiting for a Task, whose
// continuation runs on a ThreadPool thread that probes Type.GetType and
// fires AssemblyResolve, whose handler would then wait on Startup..cctor.
internal static class ManagedProfilerAssemblyResolver
{
    // Seeded by Startup..cctor before the handler is subscribed.
    internal static string? ManagedProfilerDirectory { get; set; }

    internal static Assembly? OnAssemblyResolve(object sender, ResolveEventArgs args)
    {
        try
        {
            return ResolveAssembly(args.Name);
        }
        catch (Exception ex)
        {
            StartupLogger.Log(ex, "Error resolving assembly: {0}", args.Name);
        }

        return null;
    }

    internal static Assembly? ResolveAssembly(string name)
    {
        var assemblyName = new AssemblyName(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. Exit early so we don't cause
        // infinite recursion.
        if (string.Equals(assemblyName.Name, "mscorlib.resources", StringComparison.OrdinalIgnoreCase) ||
            string.Equals(assemblyName.Name, "System.Net.Http", StringComparison.OrdinalIgnoreCase) ||
            string.Equals(assemblyName.Name, "vstest.console.resources", StringComparison.OrdinalIgnoreCase))
        {
            return null;
        }

        // WARNING: Logs must not be added _before_ we check for the above bail-out conditions
        var path = string.IsNullOrEmpty(ManagedProfilerDirectory) ? $"{assemblyName.Name}.dll" : Path.Combine(ManagedProfilerDirectory, $"{assemblyName.Name}.dll");
        StartupLogger.Debug("Assembly Resolve event received for: {0}. Looking for: {1}", name, path);

        if (File.Exists(path))
        {
            if (name.StartsWith("Datadog.Trace, Version=", StringComparison.Ordinal) && name != Startup.AssemblyName)
            {
                StartupLogger.Debug("  Trying to load '{0}' which does not match the expected version ('{1}'). [Path={2}]", name, Startup.AssemblyName, path);
                return null;
            }

            StartupLogger.Debug("Calling Assembly.LoadFrom(\"{0}\")", path);
            var assembly = Assembly.LoadFrom(path);
            StartupLogger.Debug("Assembly loaded: {0}", assembly.FullName);
            return assembly;
        }

        StartupLogger.Debug("Assembly not found in path: {0}", path);
        return null;
    }
}

#endif