WasmFS JS API: Implement write (#19508)

Author: jameshu15869

.circleci/config.yml

@@ -516,6 +516,7 @@ jobs:
             wasmfs.test_unistd_truncate
             wasmfs.test_readdir
             wasmfs.test_unistd_pipe
+            wasmfs.test_fs_write
             wasmfs.test_webidl
             wasmfs.test_dlfcn_self
             wasmfs.test_dlfcn_unique_sig

emcc.py

@@ -2318,6 +2318,8 @@ def phase_linker_setup(options, state, newargs):
         '_wasmfs_write_file',
         '_wasmfs_open',
         '_wasmfs_close',
+        '_wasmfs_write',
+        '_wasmfs_pwrite',
         '_wasmfs_rename',
         '_wasmfs_mkdir',
         '_wasmfs_unlink',

src/library_wasmfs.js

@@ -162,7 +162,26 @@ FS.createPreloadedFile = FS_createPreloadedFile;
       _free(dataBuffer);
       return bytesRead;
     },
-    // TODO: write
+    // Note that canOwn is an optimization that we ignore for now in WasmFS.
+    write: (fd, buffer, offset, length, position, canOwn) => {
+      var seeking = typeof position != 'undefined';
+
+      var dataBuffer = _malloc(length);
+      for (var i = 0; i < length; i++) {
+        {{{ makeSetValue('dataBuffer', 'i', 'buffer[offset + i]', 'i8') }}};
+      }
+
+      var bytesRead;
+      if (seeking) {
+        bytesRead = __wasmfs_pwrite(fd, dataBuffer, length, position);
+      } else {
+        bytesRead = __wasmfs_write(fd, dataBuffer, length);
+      }
+      bytesRead = FS.handleError(bytesRead);
+      _free(dataBuffer);
+
+      return bytesRead;
+    },
     // TODO: allocate
     // TODO: mmap
     // TODO: msync

system/lib/wasmfs/js_api.cpp

@@ -143,6 +143,32 @@ int _wasmfs_symlink(char* old_path, char* new_path) {
   return __syscall_symlink((intptr_t)old_path, (intptr_t)new_path);
 }
 
+int _wasmfs_write(int fd, void *buf, size_t count) {
+  __wasi_ciovec_t iovs[1];
+  iovs[0].buf = (uint8_t*)buf;
+  iovs[0].buf_len = count;
+
+  __wasi_size_t numBytes;
+  __wasi_errno_t err = __wasi_fd_write(fd, iovs, 1, &numBytes);
+  if (err) {
+    return -err;
+  }
+  return numBytes;
+}
+
+int _wasmfs_pwrite(int fd, void *buf, size_t count, off_t offset) {
+  __wasi_ciovec_t iovs[1];
+  iovs[0].buf = (uint8_t*)buf;
+  iovs[0].buf_len = count;
+
+  __wasi_size_t numBytes;
+  __wasi_errno_t err = __wasi_fd_pwrite(fd, iovs, 1, offset, &numBytes);
+  if (err) {
+    return -err;
+  }
+  return numBytes;
+}
+
 int _wasmfs_chmod(char* path, mode_t mode) {
   return __syscall_chmod((intptr_t)path, mode);
 }

test/fs/test_write.cpp

@@ -29,6 +29,14 @@ int main()
         FS.write(stream, data, 0, lengthBytesUTF8(str)+1, pos, /*canOwn=*/false);
 
         FS.close(stream);
+
+        var ex;
+        try {
+            FS.write(stream, data, 0, lengthBytesUTF8(str)+1, pos, /*canOwn=*/false);
+        } catch (err) {
+            ex = err;
+        }
+        assert(ex.name === 'ErrnoError' && ex.errno === 8 /* EBADF */)
     );
 
     std::ifstream file("testfile");

test/test_core.py

@@ -6022,6 +6022,8 @@ def test_fs_js_api(self):
     self.do_runf(test_file('fs/test_fs_js_api.c'), 'success')
 
   def test_fs_write(self):
+    if self.get_setting('WASMFS'):
+      self.set_setting("FORCE_FILESYSTEM")
     self.do_run_in_out_file_test('fs/test_write.cpp')
 
   @also_with_noderawfs