WasmFS: Get emscripten_run_preload_plugins working (#19634)

Add a minimal version of FS.analyzePath.

Fix FS.findObject, which was not tested before.

Remove a hack from FS_createPreloadedFile that prevented things from working (it
canonicalized paths in a way that didn't match other expectations).

Author: kripken

src/library_browser.js

@@ -711,6 +711,8 @@ var LibraryBrowser = {
     FS.createPreloadedFile(
       PATH.dirname(_file),
       PATH.basename(_file),
+      // TODO: This copy is not needed if the contents are already a Uint8Array,
+      //       which they often are (and always are in WasmFS).
       new Uint8Array(data.object.contents), true, true,
       () => {
         {{{ runtimeKeepalivePop() }}}

src/library_fs_shared.js

@@ -42,20 +42,17 @@ mergeInto(LibraryManager.library, {
   // You can also call this with a typed array instead of a url. It will then
   // do preloading for the Image/Audio part, as if the typed array were the
   // result of an XHR that you did manually.
-  $FS_createPreloadedFile__deps: ['$asyncLoad',
+  $FS_createPreloadedFile__deps: [
+    '$asyncLoad',
+    '$PATH_FS',
 #if !MINIMAL_RUNTIME
     '$FS_handledByPreloadPlugin',
 #endif
   ],
   $FS_createPreloadedFile: function(parent, name, url, canRead, canWrite, onload, onerror, dontCreateFile, canOwn, preFinish) {
-#if WASMFS
-    // TODO: use WasmFS code to resolve and join the path here?
-    var fullname = name ? parent + '/' + name : parent;
-#else
     // TODO we should allow people to just pass in a complete filename instead
     // of parent and name being that we just join them anyways
     var fullname = name ? PATH_FS.resolve(PATH.join2(parent, name)) : parent;
-#endif
     var dep = getUniqueRunDependency(`cp ${fullname}`); // might have several active requests for the same fullname
     function processData(byteArray) {
       function finish(byteArray) {

src/library_wasmfs.js

@@ -129,6 +129,19 @@ FS.createPreloadedFile = FS_createPreloadedFile;
 #if FORCE_FILESYSTEM
     // Full JS API support
 
+    analyzePath: (path) => {
+      // TODO: Consider simplifying this API, which for now matches the JS FS.
+      var exists = !!FS.findObject(path);
+      return {
+        exists: exists,
+        object: {
+          contents: exists ? FS.readFile(path) : null
+        }
+      };
+    },
+
+    // libc methods
+
     mkdir: (path, mode) => FS.handleError(withStackSave(() => {
       mode = mode !== undefined ? mode : 511 /* 0777 */;
       var buffer = stringToUTF8OnStack(path);
@@ -312,7 +325,7 @@ FS.createPreloadedFile = FS_createPreloadedFile;
       return FS.handleError(__wasmfs_ftruncate(fd, {{{ splitI64('len') }}}));
     },
     findObject: (path) => {
-      var result = __wasmfs_identify(path);
+      var result = withStackSave(() => __wasmfs_identify(stringToUTF8OnStack(path)));
       if (result == {{{ cDefs.ENOENT }}}) {
         return null;
       }

test/test_browser.py

@@ -794,6 +794,7 @@ def test_sdl_image_jpeg(self):
       '-lSDL', '-lGL',
     ])
 
+  @also_with_wasmfs
   def test_sdl_image_prepare(self):
     # load an image file, get pixel data.
     shutil.copyfile(test_file('screenshot.jpg'), 'screenshot.not')