File and Directory Entries API

1. Goals

This specification documents the types and operations made available by web browsers to script when a hierarchy of files and directories are dragged and dropped onto a page or selected using form elements, or equivalent user actions.

This is heavily based upon earlier drafts of [file-system-api] which defines similar types in the context of a sandboxed file system, including operations for creating and modifying files and directories, but which has not been broadly adopted by web browsers.

note: The APIs described by this document was initially implemented in Google Chrome. Other browsers (at this time: Edge, Firefox and Safari) are starting to support subsets of Chrome’s APIs and behavior. The intent of this document is to specify the common subset to ensure that the implementations are interoperable.

2. Concepts

2.1. Names and Paths

A name is a string which:

• does not contain '/' (U+002F SOLIDUS)

• does not contain NUL (U+0000)

• does not contain '\' (U+005C REVERSE SOLIDUS)

• is not '.' (U+002E FULL STOP)

• is not '..' (U+002E FULL STOP, U+002E FULL STOP)

A path segment is a name, '.' (U+002E FULL STOP) or '..' (U+002E FULL STOP, U+002E FULL STOP).

A relative path is a string consisting of one or more path segments joined by '/' (U+002F SOLIDUS) that does not start with '/' (U+002F SOLIDUS).

An absolute path is a string consisting of '/' (U+002F SOLIDUS) followed by zero or more path segments joined by '/' (U+002F SOLIDUS).

A path is either a relative path or an absolute path.

A valid path is a USVString which is a path.

2.2. Files and Directories

A file consists of binary data and a name (a non-empty name).

A directory consists of a name (a name) and an ordered list of members. Each member is either a file or a directory. Each member of a directory must have a distinct non-empty name.

A root directory is a directory that is not a member of a directory. A root directory's name is empty.

The parent of a file or directory is the directory it is a member of. A root directory has no parent.

note: In most cases, the files and directories selected by the user will be presented by the API as if contained by a virtual root that does not exist as an entity in the actual native file system backing the interaction with the API.

A file system consists of a name and a root which is an associated root directory. The name of a file system is a USVString which is implementation defined but is unique to the file system. A root directory is associated with exactly one file system.

note: Implementations could produce a name by generating a UUID for each file system instance with some fixed prefix and suffix strings applied. Authors using the API are adviised not to make assumptions about the structure or content of the names.

2.3. Entries

An entry is either a file entry or a directory entry.

An entry has an name (a name) and a full path (an absolute path).

An entry also has a root, which is an associated root directory.

note: Entries are defined in terms of paths relative to a root directory to account for the fact that a native file system backing the interaction with the API could be modified asynchronously during operations such as enumerating the contents of a directory. Operations exposed on entries will produce errors in such cases where the paths no longer reference the same entity.

The file system of an entry is the file system associated with the entry's root.

3. Algorithms

4. The File Interface

partial interface File {
    readonly attribute USVString webkitRelativePath;
};

The webkitRelativePath getter steps are to return this's relative path, or the empty string if not specified.

5. HTML: Forms

partial interface HTMLInputElement {
    attribute boolean webkitdirectory;
    readonly attribute FrozenArray<FileSystemEntry> webkitEntries;
};

When an input element’s type attribute is in the File Upload state, the rules in this section apply.

The webkitdirectory attribute is a boolean attribute that indicates whether the user is to be allowed to select a directory rather than a file or files. When specified, the behavior on the selection of a directory is as if all files with that directory as an ancestor were selected. In addition, the webkitRelativePath property of each File is set to a relative path starting from (and including) the selected directory to the file.

documents/
  to_upload/
    a/
      b/
        1.txt
        2.txt
      3.txt
  not_uploaded.txt

note: A user agent could represent any hierarchical data as directories during a selection operation. For example, on a device that does not expose a native file system directly to the user, photo albums could be presented as directories if "image/*" is specified for the accept attribute.

<input id=b type=file webkitdirectory>

document.querySelector('#b').addEventListener('change', e => {
  for (file entry of e.target.files) {
    console.log(file.name, file.webkitRelativePath);
  }
});

The webkitEntries IDL attribute allows scripts to access the element’s selected entries. On getting, if the IDL attribute applies, it must return an array of FileSystemEntry objects that represent the current selected files (including directories, if permitted). If the IDL attribute does not apply, then it must instead return null.

<input id=a type=file multiple>

document.querySelector('#a').addEventListener('change', e => {
  for (const entry of e.target.webkitEntries) {
    handleEntry(entry);
  }
});

6. HTML: Drag and drop

During a drag-and-drop operation, file and directory items are associated with entries. Each entry is a member of a root directory unique to the drag data store.

Additionally, each directory item is represented in the drag data store item list as an item whose kind is File. If it is accessed via getAsFile() a zero-length File is returned.

note: A user agent could represent any hierarchical data as files and directories during a drag-and-drop operation. For example, audio data stored in a relational database with separate tables for albums metadata and blobs for tracks could be exposed to script as directories and files when dragged from a media player application.

partial interface DataTransferItem {
    FileSystemEntry? webkitGetAsEntry();
};

elem.addEventListener('dragover', e => {
  // Prevent navigation.
  e.preventDefault();
});
elem.addEventListener('drop', e => {
  // Prevent navigation.
  e.preventDefault();

  // Process all of the items.
  for (const item of e.dataTransfer.items) {
    // kind will be 'file' for file/directory entries.
    if (item.kind === 'file') {
      const entry = item.webkitGetAsEntry();
      handleEntry(entry);
    }
  }
});

7. Files and Directories

callback ErrorCallback = undefined (DOMException err);

An ErrorCallback function is used for operations that may return an error asynchronously.

7.1. The FileSystemEntry Interface

[Exposed=Window]
interface FileSystemEntry {
    readonly attribute boolean isFile;
    readonly attribute boolean isDirectory;
    readonly attribute USVString name;
    readonly attribute USVString fullPath;
    readonly attribute FileSystem filesystem;

    undefined getParent(optional FileSystemEntryCallback successCallback,
                   optional ErrorCallback errorCallback);
};

An FileSystemEntry has an associated entry.

The isFile getter steps are to return true if this is a file entry and false otherwise.

The isDirectory getter steps are to return true if this is a directory entry and false otherwise.

The name getter steps are to return this's name.

The fullPath getter steps are to return this's full path.

The filesystem getter steps are to return this's file system.

note: An error is possible if files have been modified on disk since the FileSystemEntry was created.

function handleEntry(entry) {
  console.log('name: ' + entry.name);
  console.log('path: ' + entry.fullPath);
  if (entry.isFile) {
    console.log('... is a file');
  } else if (entry.isDirectory) {
    console.log('... is a directory');
  }
}

function getParentAsPromise(entry) {
  return new Promise((resolve, reject) => {
    entry.getParent(resolve, reject);
  });
}

7.2. The FileSystemDirectoryEntry Interface

[Exposed=Window]
interface FileSystemDirectoryEntry : FileSystemEntry {
    FileSystemDirectoryReader createReader();
    undefined getFile(optional USVString? path,
                 optional FileSystemFlags options = {},
                 optional FileSystemEntryCallback successCallback,
                 optional ErrorCallback errorCallback);
    undefined getDirectory(optional USVString? path,
                      optional FileSystemFlags options = {},
                      optional FileSystemEntryCallback successCallback,
                      optional ErrorCallback errorCallback);
};

dictionary FileSystemFlags {
    boolean create = false;
    boolean exclusive = false;
};

callback FileSystemEntryCallback = undefined (FileSystemEntry entry);

note: The create member of FileSystemFlags and the associated behavior are included for compatibility with existing implementations, even though there is no useful behavior when the flag is specified. Similarly, the exclusive member is not explicitly referenced, but the binding behavior is observable from script if an object with a getter is passed.

A FileSystemDirectoryEntry's associated entry is a directory entry.

function getFileAsPromise(entry, path) {
  return new Promise((resolve, reject) => {
    entry.getFile(path, {}, resolve, reject);
  });
}
function getDirectoryAsPromise(entry, path) {
  return new Promise((resolve, reject) => {
    entry.getDirectory(path, {}, resolve, reject);
  });
}

7.3. The FileSystemDirectoryReader Interface

[Exposed=Window]
interface FileSystemDirectoryReader {
    undefined readEntries(FileSystemEntriesCallback successCallback,
                     optional ErrorCallback errorCallback);
};
callback FileSystemEntriesCallback = undefined (sequence<FileSystemEntry> entries);

const reader = dirEntry.createReader();
const doBatch = () => {

  // Read a batch.
  reader.readEntries(entries => {

    // Complete?
    if (entries.length === 0) {
      return;
    }

    // Process the batch.
    entries.forEach(handleEntry);

    // Read the next batch.
    doBatch();

  }, error => console.warn(error));
};

// Start reading
doBatch();

function getEntriesAsPromise(dirEntry) {
  return new Promise((resolve, reject) => {
    const result = [];
    const reader = dirEntry.createReader();
    const doBatch = () => {
      reader.readEntries(entries => {
        if (entries.length > 0) {
          entries.forEach(e => result.push(e));
          doBatch();
        } else {
          resolve(result);
        }
      }, reject);
    };
    doBatch();
  });
}

async function* getEntriesAsAsyncIterator(dirEntry) {
  const reader = dirEntry.createReader();
  const getNextBatch = () => new Promise((resolve, reject) => {
    reader.readEntries(resolve, reject);
  });

  let entries;
  do {
    entries = await getNextBatch();
    for (const entry of entries) {
      yield entry;
    }
  } while (entries.length > 0);
}

async function show(entry) {
  console.log(entry.fullPath);
  if (entry.isDirectory) {
    for await (const e of getEntriesAsAsyncIterator(entry)) {
      await show(e);
    }
  }
}

7.4. The FileSystemFileEntry Interface

[Exposed=Window]
interface FileSystemFileEntry : FileSystemEntry {
    undefined file(FileCallback successCallback,
              optional ErrorCallback errorCallback);
};
callback FileCallback = undefined (File file);

A FileSystemFileEntry's associated entry is a file entry.

function readFileEntry(entry) {
  entry.file(file => {
    const reader = new FileReader();
    reader.readAsText(file);
    reader.onerror = error => console.warn(error);
    reader.onload = () => {
      console.log(reader.result);
    };
  }, error => console.warn(error));
}

function fileAsPromise(entry) {
  return new Promise((resolve, reject) => {
    entry.file(resolve, reject);
  });
}

7.5. The FileSystem Interface

[Exposed=Window]
interface FileSystem {
    readonly attribute USVString name;
    readonly attribute FileSystemDirectoryEntry root;
};

A FileSystem has an associated file system.

The name getter steps are to return this's name.

The root getter steps are to return a FileSystemDirectoryEntry associated with this's root.

8. Acknowledgements

This specification is based heavily on the work of Eric Uhrhane in [file-system-api], which introduced the FileSystemEntry types.

Thanks to Tab Atkins, Jr. for creating and maintaining Bikeshed, the specification authoring tool used to create this document.

And thanks to Ali Alabbas, Philip Jägenstedt, Marijn Kruisselbrink, Olli Pettay, and Kent Tamura for suggestions, reviews, and other feedback.