Implement open() in library_wasmfs.js (#18919)

Implemented FS.open() in library_wasmfs.js
Added tests to test FS.open() with different flags.

Author: jameshu15869

emcc.py

@@ -2329,6 +2329,7 @@ def phase_linker_setup(options, state, newargs):
       # JS API directly.
       settings.REQUIRED_EXPORTS += [
         '_wasmfs_write_file',
+        '_wasmfs_open',
         '_wasmfs_mkdir',
         '_wasmfs_unlink',
         '_wasmfs_chdir',

src/library_wasmfs.js

@@ -61,6 +61,25 @@ mergeInto(LibraryManager.library, {
       if (canWrite) mode |= {{{ cDefine('S_IWUGO') }}};
       return mode;
     },
+    modeStringToFlags: (str) => {
+      var flags = FS.flagModes[str];
+      if (typeof flags == 'undefined') {
+        throw new Error('Unknown file open mode: ' + str);
+      }
+      return flags;
+    },
+    flagModes: {
+      // copied directly from library_fs.js
+      // Extra quotes used here on the keys to this object otherwise jsifier will
+      // erase them in the process of reading and then writing the JS library
+      // code.
+      '"r"': {{{ cDefine('O_RDONLY') }}},
+      '"r+"': {{{ cDefine('O_RDWR') }}},
+      '"w"': {{{ cDefine('O_TRUNC') }}} | {{{ cDefine('O_CREAT') }}} | {{{ cDefine('O_WRONLY') }}},
+      '"w+"': {{{ cDefine('O_TRUNC') }}} | {{{ cDefine('O_CREAT') }}} | {{{ cDefine('O_RDWR') }}},
+      '"a"': {{{ cDefine('O_APPEND') }}} | {{{ cDefine('O_CREAT') }}} | {{{ cDefine('O_WRONLY') }}},
+      '"a+"': {{{ cDefine('O_APPEND') }}} | {{{ cDefine('O_CREAT') }}} | {{{ cDefine('O_RDWR') }}},
+    },
     createDataFile: (parent, name, data, canRead, canWrite, canOwn) => {
       // Data files must be cached until the file system itself has been initialized.
       var mode = FS.getMode(canRead, canWrite);
@@ -122,6 +141,14 @@ mergeInto(LibraryManager.library, {
     // TODO: mkdirTree
     // TDOO: rmdir
     // TODO: open
+    open: (path, flags, mode) => {
+      flags = typeof flags == 'string' ? FS.modeStringToFlags(flags) : flags;
+      mode = typeof mode == 'undefined' ? 438 /* 0666 */ : mode;
+      return withStackSave(() => {
+        var buffer = allocateUTF8OnStack(path);
+        return __wasmfs_open({{{ to64('buffer') }}}, flags, mode);
+      })
+    },
     // TODO: create
     // TODO: close
     unlink: (path) => {

system/lib/wasmfs/js_api.cpp

@@ -100,6 +100,10 @@ int _wasmfs_mkdir(char* path, int mode) {
   return __syscall_mkdirat(AT_FDCWD, (intptr_t)path, mode);
 }
 
+int _wasmfs_open(char* path, int flags, mode_t mode) {
+  return __syscall_openat(AT_FDCWD, (intptr_t)path, flags, mode);
+}
+
 int _wasmfs_unlink(char* path) {
   return __syscall_unlinkat(AT_FDCWD, (intptr_t)path, 0);
 }

test/fs/test_open_wasmfs.c

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2023 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <assert.h>
+#include <emscripten/emscripten.h>
+#include <stdio.h>
+
+
+int main() {
+  EM_ASM(
+    FS.writeFile('testfile', 'a=1\nb=2\n');
+    var readStream = FS.open('testfile', 'r');
+    assert(readStream >= 0);
+
+    var writeStream = FS.open('testfile', 'w');
+    assert(writeStream >= 0);
+
+    var writePlusStream = FS.open('testfile', 'w+');
+    assert(writePlusStream >= 0);
+
+    var appendStream = FS.open('testfile', 'a');
+    assert(appendStream >= 0);
+
+    var notFound = FS.open('filenothere', 'r');
+    assert(notFound < 0);
+
+    var createFileNotHere = FS.open('filenothere', 'w+');
+    assert(createFileNotHere >= 0);
+  );
+  puts("success");
+  
+
+  return 0;
+}

test/test_core.py

@@ -6037,13 +6037,14 @@ def test_fs_trackingdelegate(self):
     self.do_run_in_out_file_test('fs/test_trackingdelegate.c')
 
   @also_with_noderawfs
+  @also_with_wasmfs_js
   def test_fs_writeFile(self):
     self.do_run_in_out_file_test('fs/test_writeFile.cpp')
 
-  def test_fs_writeFile_wasmfs(self):
+  def test_fs_open_wasmfs(self):
     self.emcc_args += ['-sWASMFS']
     self.emcc_args += ['-sFORCE_FILESYSTEM']
-    self.do_run_in_out_file_test('fs/test_writeFile.cpp')
+    self.do_runf(test_file('fs/test_open_wasmfs.c'), 'success')
 
   def test_fs_write(self):
     self.do_run_in_out_file_test('fs/test_write.cpp')