Fix loading wasm in electron by falling back to XHR (#12921)

fixes mono/mono#20592

should fix #11671

Author: 0x53A

AUTHORS

@@ -525,6 +525,7 @@ a license to everyone to use it as detailed in LICENSE.)
 * Jean-Sébastien Nadeau <[email protected]> (copyright owned by Foundry Interactive Inc.)
 * Wouter van Oortmerssen <[email protected]> (copyright owned by Google, LLC)
 * Alexey Sokolov <[email protected]> (copyright owned by Google, LLC)
+* Lukas Rieger <[email protected]>
 * Ivan Romanovski <[email protected]>
 * Max Brunsfeld <[email protected]>
 * Basil Fierz <[email protected]>

src/preamble.js

@@ -767,23 +767,38 @@ function getBinary(file) {
 }
 
 function getBinaryPromise() {
-  // If we don't have the binary yet, and have the Fetch api, use that;
-  // in some environments, like Electron's render process, Fetch api may be present, but have a different context than expected, let's only use it on the Web
-  if (!wasmBinary && (ENVIRONMENT_IS_WEB || ENVIRONMENT_IS_WORKER) && typeof fetch === 'function'
+  // If we don't have the binary yet, try to to load it asynchronously.
+  // 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
+  // Cordova or Electron apps are typically loaded from a file:// url.
+  // So use fetch if it is available and the url is not a file, otherwise fall back to XHR.
+  if (!wasmBinary && (ENVIRONMENT_IS_WEB || ENVIRONMENT_IS_WORKER)) {
+    if (typeof fetch === 'function'
 #if ENVIRONMENT_MAY_BE_WEBVIEW
-      // Let's not use fetch to get objects over file:// as it's most likely Cordova which doesn't support fetch for file://
       && !isFileURI(wasmBinaryFile)
 #endif
-      ) {
-    return fetch(wasmBinaryFile, { credentials: 'same-origin' }).then(function(response) {
-      if (!response['ok']) {
-        throw "failed to load wasm binary file at '" + wasmBinaryFile + "'";
+    ) {
+      return fetch(wasmBinaryFile, { credentials: 'same-origin' }).then(function(response) {
+        if (!response['ok']) {
+          throw "failed to load wasm binary file at '" + wasmBinaryFile + "'";
+        }
+        return response['arrayBuffer']();
+      }).catch(function () {
+          return getBinary(wasmBinaryFile);
+      });
+    }
+#if ENVIRONMENT_MAY_BE_WEBVIEW
+    else {
+      if (readAsync) {
+        // fetch is not available or url is file => try XHR (readAsync uses XHR internally)
+        return new Promise(function(resolve, reject) {
+          readAsync(wasmBinaryFile, function(response) { resolve(new Uint8Array(/** @type{!ArrayBuffer} */(response))) }, reject)
+        });
       }
-      return response['arrayBuffer']();
-    }).catch(function () {
-      return getBinary(wasmBinaryFile);
-    });
+    }
+#endif
   }
+    
   // Otherwise, getBinary should be able to get it synchronously
   return Promise.resolve().then(function() { return getBinary(wasmBinaryFile); });
 }

src/web_or_worker_shell_read.js

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: MIT
  */
 
-  read_ = function shell_read(url) {
+  read_ = function(url) {
 #if SUPPORT_BASE64_EMBEDDING
     try {
 #endif
@@ -24,7 +24,7 @@
   };
 
   if (ENVIRONMENT_IS_WORKER) {
-    readBinary = function readBinary(url) {
+    readBinary = function(url) {
 #if SUPPORT_BASE64_EMBEDDING
       try {
 #endif
@@ -45,11 +45,11 @@
     };
   }
 
-  readAsync = function readAsync(url, onload, onerror) {
+  readAsync = function(url, onload, onerror) {
     var xhr = new XMLHttpRequest();
     xhr.open('GET', url, true);
     xhr.responseType = 'arraybuffer';
-    xhr.onload = function xhr_onload() {
+    xhr.onload = function() {
       if (xhr.status == 200 || (xhr.status == 0 && xhr.response)) { // file URLs can return 0
         onload(xhr.response);
         return;

tests/test_other.py

@@ -8781,7 +8781,7 @@ def test(args):
     # Changing this option to [] should decrease code size.
     self.assertLess(changed, normal)
     # Check an absolute code size as well, with some slack.
-    self.assertLess(abs(changed - 5627), 150)
+    self.assertLess(abs(changed - 5872), 150)
 
   def test_llvm_includes(self):
     create_test_file('atomics.c', '#include <stdatomic.h>')