Handle exceptional cases when looking up unmanaged delegates

src/mono/browser/runtime/runtime.c

@@ -209,14 +209,26 @@ get_native_to_interp (MonoMethod *method, void *extra_arg)
 	const char *name = mono_assembly_name_get_name (aname);
 	const char *class_name = mono_class_get_name (klass);
 	const char *method_name = mono_method_get_name (method);
-	char key [128];
+	char buf [128];
+	char *key = &buf[0];
 	int len;
+	name = name ? name : "";
+
+	len = snprintf (key, sizeof(buf), "%s_%s_%s", name, class_name, method_name);
+
+	if (len >= sizeof (buf)) {
+		// The key is too long, try again with a larger buffer
+		key = g_new (char, len + 1);
+	    snprintf (key, len + 1, "%s_%s_%s", name, class_name, method_name);
+	}
 
-	assert (strlen (name) < 100);
-	snprintf (key, sizeof(key), "%s_%s_%s", name, class_name, method_name);
 	char *fixedName = mono_fixup_symbol_name ("", key, "");
 	addr = wasm_dl_get_native_to_interp (fixedName, extra_arg);
 	free (fixedName);
+
+	if (len >= sizeof (buf))
+		free (key);
+
 	MONO_EXIT_GC_UNSAFE;
 	return addr;
 }

src/mono/wasm/Wasm.Build.Tests/PInvokeTableGeneratorTests.cs

@@ -952,6 +952,7 @@ public void UCOWithSpecialCharacters(BuildArgs buildArgs, RunHost host, string i
 
             var runOutput = RunAndTestWasmApp(buildArgs, buildDir: _projectDir, expectedExitCode: 42, host: host, id: id);
             Assert.Contains("ManagedFunc returned 42", runOutput);
+            Assert.Contains("caught PlatformNotSupportedException", runOutput);
         }
     }
 }

src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/UnmanagedCallback.cs

@@ -9,6 +9,13 @@ public unsafe static int Main(string[] args)
 
         Console.WriteLine($"main: {args.Length}");
         Interop.UnmanagedFunc();
+
+        try {
+            nint fptr = Marshal.GetFunctionPointerForDelegate(new Action(() => Console.WriteLine("Managed method callee")));
+            ((delegate* unmanaged<void>)fptr)();
+        } catch (PlatformNotSupportedException) {
+            Console.WriteLine("caught PlatformNotSupportedException");
+        }
         return 42;
     }
 }