Fix js string marshaling (#100997)

Author: lewing

src/mono/browser/browser.proj

@@ -185,6 +185,7 @@
       <EmccExportedRuntimeMethod Include="getValue" />
       <EmccExportedRuntimeMethod Include="UTF8ToString" />
       <EmccExportedRuntimeMethod Include="UTF8ArrayToString" />
+      <EmccExportedRuntimeMethod Include="lengthBytesUTF8" />
       <EmccExportedRuntimeMethod Include="stringToUTF8Array" />
       <EmccExportedRuntimeMethod Include="FS_createPath" />
       <EmccExportedRuntimeMethod Include="FS_createDataFile" />

src/mono/browser/runtime/strings.ts

@@ -39,19 +39,20 @@ export function strings_init (): void {
 
 export function stringToUTF8 (str: string): Uint8Array {
     if (_text_encoder_utf8 === undefined) {
-        const buffer = new Uint8Array(str.length * 2);
-        Module.stringToUTF8Array(str, buffer, 0, str.length * 2);
+        const len = Module.lengthBytesUTF8(str);
+        const buffer = new Uint8Array(len);
+        Module.stringToUTF8Array(str, buffer, 0, len);
         return buffer;
     }
     return _text_encoder_utf8.encode(str);
 }
 
 export function stringToUTF8Ptr (str: string): CharPtr {
-    const bytes = (str.length + 1) * 2;
-    const ptr = Module._malloc(bytes) as any;
-    _zero_region(ptr, str.length * 2);
-    const buffer = localHeapViewU8().subarray(ptr, ptr + bytes);
-    buffer.set(stringToUTF8(str));
+    const size = Module.lengthBytesUTF8(str) + 1;
+    const ptr = Module._malloc(size) as any;
+    const buffer = localHeapViewU8().subarray(ptr, ptr + size);
+    Module.stringToUTF8Array(str, buffer, 0, size);
+    buffer[size - 1] = 0;
     return ptr;
 }
 

src/mono/browser/runtime/types/emscripten.ts

@@ -40,6 +40,7 @@ export declare interface EmscriptenModule {
     UTF8ToString(ptr: CharPtr, maxBytesToRead?: number): string;
     UTF8ArrayToString(u8Array: Uint8Array, idx?: number, maxBytesToRead?: number): string;
     stringToUTF8Array(str: string, heap: Uint8Array, outIdx: number, maxBytesToWrite: number): void;
+    lengthBytesUTF8(str: string): number;
     FS_createPath(parent: string, path: string, canRead?: boolean, canWrite?: boolean): string;
     FS_createDataFile(parent: string, name: string, data: TypedArray, canRead: boolean, canWrite: boolean, canOwn?: boolean): string;
     addFunction(fn: Function, signature: string): number;