Remove the use of toJavaScriptString (#20260)

* Allow readString to optionally read boolean values as string

Fixes https://github.com/dotnet/aspnetcore/issues/19784

src/Components/Web.JS/src/Platform/Mono/MonoPlatform.ts

@@ -41,17 +41,6 @@ export const monoPlatform: Platform = {
     invokeEntrypoint(assemblyName, null);
   },
 
-  toJavaScriptString: function toJavaScriptString(managedString: System_String) {
-    // Comments from original Mono sample:
-    // FIXME this is wastefull, we could remove the temp malloc by going the UTF16 route
-    // FIXME this is unsafe, cuz raw objects could be GC'd.
-
-    const utf8 = mono_string_get_utf8(managedString);
-    const res = (<any>window['Module']).UTF8ToString(utf8);
-    Module._free(utf8 as any);
-    return res;
-  },
-
   toUint8Array: function toUint8Array(array: System_Array<any>): Uint8Array {
     const dataPtr = getArrayDataPointer(array);
     const length = Module.getValue(dataPtr, 'i32');
@@ -102,9 +91,23 @@ export const monoPlatform: Platform = {
     return Module.getValue((baseAddress as any as number) + (fieldOffset || 0), 'i32') as any as T;
   },
 
-  readStringField: function readHeapObject(baseAddress: Pointer, fieldOffset?: number): string | null {
+  readStringField: function readHeapObject(baseAddress: Pointer, fieldOffset?: number, readBoolValueAsString?: boolean): string | null {
     const fieldValue = Module.getValue((baseAddress as any as number) + (fieldOffset || 0), 'i32');
-    return fieldValue === 0 ? null : monoPlatform.toJavaScriptString(fieldValue as any as System_String);
+    if (fieldValue === 0) {
+      return null;
+    }
+
+    if (readBoolValueAsString) {
+      // Some fields are stored as a union of bool | string | null values, but need to read as a string.
+      // If the stored value is a bool, the behavior we want is empty string ('') for true, or null for false.
+      const unboxedValue = BINDING.unbox_mono_obj(fieldValue as any as System_Object);
+      if (typeof (unboxedValue) === 'boolean') {
+        return unboxedValue ? '' : null;
+      }
+      return unboxedValue;
+    }
+
+    return BINDING.conv_string(fieldValue as any as System_String);
   },
 
   readStructField: function readStructField<T extends Pointer>(baseAddress: Pointer, fieldOffset?: number): T {

src/Components/Web.JS/src/Platform/Mono/MonoTypes.ts

@@ -18,9 +18,11 @@ declare interface BINDING {
   mono_array_to_js_array<TInput, TOutput>(array: System_Array<TInput>) : Array<TOutput>;
   conv_string(dotnetString: System_String | null): string | null;
   bind_static_method(fqn: string, signature?: string): Function;
+  unbox_mono_obj(object: System_Object): any;
 }
 
 declare global {
   var MONO: MONO;
   var BINDING: BINDING;
-}
+}
+

src/Components/Web.JS/src/Platform/Platform.ts

@@ -5,7 +5,6 @@ export interface Platform {
 
   callEntryPoint(assemblyName: string): void;
 
-  toJavaScriptString(dotNetString: System_String): string;
   toUint8Array(array: System_Array<any>): Uint8Array;
 
   getArrayLength(array: System_Array<any>): number;
@@ -17,7 +16,7 @@ export interface Platform {
   readUint64Field(baseAddress: Pointer, fieldOffset?: number): number;
   readFloatField(baseAddress: Pointer, fieldOffset?: number): number;
   readObjectField<T extends System_Object>(baseAddress: Pointer, fieldOffset?: number): T;
-  readStringField(baseAddress: Pointer, fieldOffset?: number): string | null;
+  readStringField(baseAddress: Pointer, fieldOffset?: number, readBoolValueAsString?: boolean): string | null;
   readStructField<T extends Pointer>(baseAddress: Pointer, fieldOffset?: number): T;
 }
 

src/Components/Web.JS/src/Rendering/RenderBatch/SharedMemoryRenderBatch.ts

@@ -107,7 +107,7 @@ const frameReader = {
   textContent: (frame: RenderTreeFrame) => platform.readStringField(frame as any, 16),
   markupContent: (frame: RenderTreeFrame) => platform.readStringField(frame as any, 16)!,
   attributeName: (frame: RenderTreeFrame) => platform.readStringField(frame as any, 16),
-  attributeValue: (frame: RenderTreeFrame) => platform.readStringField(frame as any, 24),
+  attributeValue: (frame: RenderTreeFrame) => platform.readStringField(frame as any, 24, true),
   attributeEventHandlerId: (frame: RenderTreeFrame) => platform.readUint64Field(frame as any, 8),
 };