Use async/await for internal readAsync function. NFC

Followup to emscripten-core#23104.

Author: sbc100

src/closure-externs/node-externs.js

@@ -86,6 +86,12 @@ Buffer.from = function(arrayBufferOrString, byteOffsetOrEncoding, length) {};
  */
 Buffer.alloc = function(size, fill, encoding) {};
 
+/**
+ * @return {boolean}
+ * @nosideeffects
+ */
+Buffer.isBuffer = function(obj) {};
+
 /**
  * @param {number=} start
  * @param {number=} end

src/node_shell_read.js

@@ -9,18 +9,17 @@ readBinary = (filename) => {
   filename = isFileURI(filename) ? new URL(filename) : filename;
   var ret = fs.readFileSync(filename);
 #if ASSERTIONS
-  assert(ret.buffer);
+  assert(Buffer.isBuffer(ret));
 #endif
   return ret;
 };
 
-readAsync = (filename, binary = true) => {
+readAsync = async (filename, binary = true) => {
   // See the comment in the `readBinary` function.
   filename = isFileURI(filename) ? new URL(filename) : filename;
-  return new Promise((resolve, reject) => {
-    fs.readFile(filename, binary ? undefined : 'utf8', (err, data) => {
-      if (err) reject(err);
-      else resolve(binary ? data.buffer : data);
-    });
-  });
+  var ret = fs.readFileSync(filename, binary ? undefined : 'utf8');
+#if ASSERTIONS
+  assert(binary ? Buffer.isBuffer(ret) : typeof ret == 'string');
+#endif
+  return ret;
 };

src/shell.js

@@ -300,11 +300,7 @@ if (ENVIRONMENT_IS_SHELL) {
     return data;
   };
 
-  readAsync = (f) => {
-    return new Promise((resolve, reject) => {
-      setTimeout(() => resolve(readBinary(f)));
-    });
-  };
+  readAsync = async (f) => readBinary(f);
 
   globalThis.clearTimeout ??= (id) => {};
 

src/web_or_worker_shell_read.js

@@ -16,7 +16,7 @@
   }
 #endif
 
-  readAsync = (url) => {
+  readAsync = async (url) => {
 #if ENVIRONMENT_MAY_BE_WEBVIEW
     // Fetch has some additional restrictions over XHR, like it can't be used on a file:// url.
     // See https://github.com/github/fetch/pull/92#issuecomment-140665932
@@ -41,11 +41,9 @@
 #elif ASSERTIONS
     assert(!isFileURI(url), "readAsync does not work with file:// URLs");
 #endif
-    return fetch(url, {{{ makeModuleReceiveExpr('fetchSettings', "{ credentials: 'same-origin' }") }}})
-      .then((response) => {
-        if (response.ok) {
-          return response.arrayBuffer();
-        }
-        return Promise.reject(new Error(response.status + ' : ' + response.url));
-      })
+    var response = await fetch(url, {{{ makeModuleReceiveExpr('fetchSettings', "{ credentials: 'same-origin' }") }}});
+    if (response.ok) {
+      return response.arrayBuffer();
+    }
+    throw new Error(response.status + ' : ' + response.url);
   };

test/other/codesize/test_codesize_cxx_ctors1.gzsize

@@ -1 +1 @@
-8576
+8545

test/other/codesize/test_codesize_cxx_ctors1.jssize

@@ -1 +1 @@
-20969
+20951

test/other/codesize/test_codesize_cxx_ctors2.gzsize

@@ -1 +1 @@
-8560
+8530

test/other/codesize/test_codesize_cxx_ctors2.jssize

@@ -1 +1 @@
-20937
+20919

test/other/codesize/test_codesize_cxx_except.gzsize

@@ -1 +1 @@
-9614
+9579

test/other/codesize/test_codesize_cxx_except.jssize

@@ -1 +1 @@
-24814
+24796