Fix --use-preload-plugins with -s LZ4 (#13235)

src/library_lz4.js

@@ -20,7 +20,7 @@ mergeInto(LibraryManager.library, {
       })();
       LZ4.CHUNK_SIZE = LZ4.codec.CHUNK_SIZE;
     },
-    loadPackage: function (pack) {
+    loadPackage: function (pack, preloadPlugin) {
       LZ4.init();
       var compressedData = pack['compressedData'];
       if (!compressedData) compressedData = LZ4.codec.compressPackage(pack['data']);
@@ -42,6 +42,31 @@ mergeInto(LibraryManager.library, {
           end: file.end,
         });
       });
+      // Preload files if necessary. This code is largely similar to
+      // createPreloadedFile in library_fs.js. However, a main difference here
+      // is that we only decompress the file if it can be preloaded.
+      // Abstracting out the common parts seems to be more effort than it is
+      // worth.
+      if (preloadPlugin) {
+        Browser.init();
+        pack['metadata'].files.forEach(function(file) {
+          var handled = false;
+          var fullname = file.filename;
+          Module['preloadPlugins'].forEach(function(plugin) {
+            if (handled) return;
+            if (plugin['canHandle'](fullname)) {
+              var dep = getUniqueRunDependency('fp ' + fullname);
+              addRunDependency(dep);
+              var finish = function() {
+                removeRunDependency(dep);
+              }
+              var byteArray = FS.readFile(fullname);
+              plugin['handle'](byteArray, fullname, finish, finish);
+              handled = true;
+            }
+          });
+        });
+      }
     },
     createNode: function (parent, name, mode, dev, contents, mtime) {
       var node = FS.createNode(parent, name, mode);

tests/test_browser.py

@@ -2415,7 +2415,11 @@ void *getBindBuffer() {
     self.compile_btest([path_from_root('tests', 'browser_module.cpp'), '-o', 'lib.wasm', '-O2', '-s', 'SIDE_MODULE', '-s', 'EXPORTED_FUNCTIONS=[_one,_two]'])
     self.btest('browser_main.cpp', args=['-O2', '-s', 'MAIN_MODULE'], expected='8')
 
-  def test_preload_module(self):
+  @parameterized({
+    'non-lz4': ([],),
+    'lz4': (['-s', 'LZ4'],)
+  })
+  def test_preload_module(self, args):
     create_test_file('library.c', r'''
       #include <stdio.h>
       int library_func() {
@@ -2449,7 +2453,7 @@ void *getBindBuffer() {
     ''')
     self.btest_exit(
       'main.c',
-      args=['-s', 'MAIN_MODULE', '--preload-file', '.@/', '-O2', '--use-preload-plugins', '-s', 'EXPORT_ALL'],
+      args=['-s', 'MAIN_MODULE', '--preload-file', '.@/', '-O2', '--use-preload-plugins', '-s', 'EXPORT_ALL'] + args,
       expected='0')
 
   def test_mmap_file(self):

tools/file_packager.py

@@ -516,9 +516,9 @@ def main():
             var compressedData = %s;
             compressedData['data'] = byteArray;
             assert(typeof Module.LZ4 === 'object', 'LZ4 not present - was your app build with  -s LZ4=1  ?');
-            Module.LZ4.loadPackage({ 'metadata': metadata, 'compressedData': compressedData });
+            Module.LZ4.loadPackage({ 'metadata': metadata, 'compressedData': compressedData }, %s);
             Module['removeRunDependency']('datafile_%s');
-      ''' % (meta, shared.JS.escape_for_js_string(data_target))
+      ''' % (meta, "true" if use_preload_plugins else "false", shared.JS.escape_for_js_string(data_target))
 
     package_uuid = uuid.uuid4()
     package_name = data_target