Add __newArrayBuffer() to the loader.

This will facilitate passing binary strings more easily to AssemblyScript
from the host environment.

Co-authored-by: Max Graey <maxgraey@gmail.com>

Author: FGasper

NOTICE

@@ -41,6 +41,7 @@ under the licensing terms detailed in LICENSE:
 * Ryan Pivovar <ryanpivovar@gmail.com>
 * Roman F. <70765447+romdotdog@users.noreply.github.com>
 * Joe Pea <trusktr@gmail.com>
+* Felipe Gasper <fgasper@users.noreply.github.com>
 
 Portions of this software are derived from third-party works licensed under
 the following terms:

lib/loader/index.d.ts

@@ -86,6 +86,8 @@ export interface ASUtil {
   __instanceof(ptr: number, baseId: number): boolean;
   /** Allocates a new string in the module's memory and returns a reference (pointer) to it. */
   __newString(str: string): number;
+  /** Allocates a new ArrayBuffer in the module's memory and returns a reference (pointer) to it. */
+  __newArrayBuffer(buf: ArrayBuffer): number;
   /** Allocates a new array in the module's memory and returns a reference (pointer) to it. */
   __newArray(id: number, values: ArrayLike<number>): number;
 

lib/loader/index.js

@@ -150,6 +150,18 @@ function postInstantiate(extendedExports, instance) {
 
   extendedExports.__newString = __newString;
 
+  /** Allocates a new ArrayBuffer in the module's memory and returns its pointer. */
+  function __newArrayBuffer(buf) {
+    if (buf == null) return 0;
+    const bufview = new Uint8Array(buf);
+    const ptr = __new(bufview.length, ARRAYBUFFER_ID);
+    const U8 = new Uint8Array(memory.buffer);
+    U8.set(bufview, ptr);
+    return ptr;
+  }
+
+  extendedExports.__newArrayBuffer = __newArrayBuffer;
+
   /** Reads a string from the module's memory by its pointer. */
   function __getString(ptr) {
     if (!ptr) return null;

lib/loader/tests/index.js

@@ -36,6 +36,17 @@ function test(file) {
     assert.strictEqual(exports.strlen(ref), str.length);
   }
 
+  // should be able to allocate and work with a new small ArrayBuffer
+  {
+    let u8arr = new Uint8Array([1, 2, 3, 4]);
+    let buf = u8arr.buffer;
+    let ref = exports.__newArrayBuffer(buf);
+    let got = exports.__getArrayBuffer(ref);
+    let gotu8arr = new Uint8Array(got);
+
+    assert.deepStrictEqual(gotu8arr, u8arr);
+  }
+
   // should be able to allocate and work with a new big string
   {
     let str = `