correct handling for shadowed assemblies when loading native extension

src/csharp/Grpc.Core/Internal/NativeExtension.cs

@@ -32,6 +32,7 @@
 #endregion
 
 using System;
+using System.Globalization;
 using System.IO;
 using System.Reflection;
 
@@ -99,14 +100,30 @@ namespace Grpc.Core.Internal
             // TODO: allow customizing path to native extension (possibly through exposing a GrpcEnvironment property).
 
             var libraryFlavor = string.Format("{0}_{1}", GetPlatformString(), GetArchitectureString());
-            var fullPath = Path.Combine(GetExecutingAssemblyDirectory(),
+            var fullPath = Path.Combine(Path.GetDirectoryName(GetAssemblyPath()),
                 NativeLibrariesDir, libraryFlavor, GetNativeLibraryFilename());
             return new UnmanagedLibrary(fullPath);
         }
 
-        private static string GetExecutingAssemblyDirectory()
+        private static string GetAssemblyPath()
         {
-            return Path.GetDirectoryName(typeof(NativeExtension).GetTypeInfo().Assembly.Location);
+            var assembly = typeof(NativeExtension).GetTypeInfo().Assembly;
+
+            // If assembly is shadowed (e.g. in a webapp), EscapedCodeBase is pointing
+            // to the original location of the assembly, and Location is pointing
+            // to the shadow copy. We care about the original location because
+            // the native dlls don't get shadowed.
+            var escapedCodeBase = assembly.EscapedCodeBase;
+            if (IsFileUri(escapedCodeBase))
+            {
+                return new Uri(escapedCodeBase).LocalPath;
+            }
+            return assembly.Location;
+        }
+
+        private static bool IsFileUri(string uri)
+        {
+            return uri.ToLowerInvariant().StartsWith(Uri.UriSchemeFile);
         }
 
         private static string GetPlatformString()