Re-enable XHR as fallback for fetch on webview (#22026)

In #22015 we switched `readAsync` to be based on fetch rather than
XHR.  However that broke the assumption in `getBinaryenPromise` that was
assuming `readAsync` was XHR-based.

This change reinstates the XHR fallback in the case of webviews where
loading from `file://` URLs is not only possible but (apparently)
common.

Sadly we don't have any webview tests so I have no way to actually test
this within our current frameworks.

Author: sbc100

src/preamble.js

@@ -642,36 +642,21 @@ function getBinarySync(file) {
 
 function getBinaryPromise(binaryFile) {
 #if !SINGLE_FILE
-  // If we don't have the binary yet, try 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 we don't have the binary yet, load it asynchronously using readAsync.
   if (!wasmBinary
 #if SUPPORT_BASE64_EMBEDDING
-      && !isDataURI(binaryFile)
-#endif
-      && (ENVIRONMENT_IS_WEB || ENVIRONMENT_IS_WORKER)) {
-    if (typeof fetch == 'function'
-#if ENVIRONMENT_MAY_BE_WEBVIEW
-      && !isFileURI(binaryFile)
-#endif
-    ) {
-      return fetch(binaryFile, {{{ makeModuleReceiveExpr('fetchSettings', "{ credentials: 'same-origin' }") }}}).then((response) => {
-        if (!response['ok']) {
-          throw `failed to load wasm binary file at '${binaryFile}'`;
-        }
-        return response['arrayBuffer']();
-      }).catch(() => getBinarySync(binaryFile));
-    }
-#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((resolve, reject) => {
-        readAsync(binaryFile, (response) => resolve(new Uint8Array(/** @type{!ArrayBuffer} */(response))), reject)
-      });
-    }
+      || isDataURI(binaryFile)
 #endif
+      ) {
+    // Fetch the binary use readAsync
+    return new Promise((resolve, reject) => {
+      readAsync(binaryFile,
+        (response) => resolve(new Uint8Array(/** @type{!ArrayBuffer} */(response))),
+        (error) => {
+          try { resolve(getBinarySync(binaryFile)); }
+          catch (e) { reject(e); }
+        });
+    });
   }
 #endif
 

src/web_or_worker_shell_read.js

@@ -22,12 +22,35 @@
   }
 
   readAsync = (url, onload, onerror) => {
-    fetch(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
+    // Cordova or Electron apps are typically loaded from a file:// url.
+    // So use XHR on webview if URL is a file URL.
+    if (isFileURI(url)) {
+      var xhr = new XMLHttpRequest();
+      xhr.open('GET', url, true);
+      xhr.responseType = 'arraybuffer';
+      xhr.onload = () => {
+        if (xhr.status == 200 || (xhr.status == 0 && xhr.response)) { // file URLs can return 0
+          onload(xhr.response);
+          return;
+        }
+        onerror();
+      };
+      xhr.onerror = onerror;
+      xhr.send(null);
+      return;
+    }
+#elif ASSERTIONS
+    assert(!isFileURI(url), "readAsync does not work with file:// URLs");
+#endif
+    fetch(url, {{{ makeModuleReceiveExpr('fetchSettings', "{ credentials: 'same-origin' }") }}})
     .then((response) => {
       if (response.ok) {
         return response.arrayBuffer();
       }
-      return Promise.reject(new Error(response.statusText + ' : ' + response.url));
+      return Promise.reject(new Error(response.status + ' : ' + response.url));
     })
     .then(onload, onerror)
   };

test/other/metadce/test_metadce_cxx_ctors1.gzsize

@@ -1 +1 @@
-9813
+9817

test/other/metadce/test_metadce_cxx_ctors1.jssize

@@ -1 +1 @@
-24096
+24102

test/other/metadce/test_metadce_cxx_ctors2.gzsize

@@ -1 +1 @@
-9797
+9801

test/other/metadce/test_metadce_cxx_ctors2.jssize

@@ -1 +1 @@
-24064
+24070

test/other/metadce/test_metadce_cxx_except.gzsize

@@ -1 +1 @@
-10897
+10895

test/other/metadce/test_metadce_cxx_except.jssize

@@ -1 +1 @@
-28002
+28008

test/other/metadce/test_metadce_cxx_except_wasm.gzsize

@@ -1 +1 @@
-9777
+9774

test/other/metadce/test_metadce_cxx_except_wasm.jssize

@@ -1 +1 @@
-23989
+23995