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.

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.

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.

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.

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

2.4. Directory Reader

A directory reader consists of an associated directory entry, an associated directory (initially null), a reading flag (initially unset), a done flag (initially unset), and a reader error (initially null).

3. Algorithms

To resolve a relative path with abspath (an absolute path) and path (an absolute path, a relative path, or the empty string), run the following steps which return an absolute path:

If path is an absolute path, return path.
Let abspath segments be the result of strictly splitting abspath on '/' (U+002F SOLIDUS).

The first string will be empty.
Let path segments be the result of strictly splitting path on '/' (U+002F SOLIDUS).
For each segment in path segments, switch on segment:

empty string
Continue.
'.' (U+002E FULL STOP)
Continue.
'..' (U+002E FULL STOP, U+002E FULL STOP)
Remove the last member of abspath segments unless it is the only member.
Otherwise
Append segment to abspath segments.

Return abspath segments joined by '/' (U+002F SOLIDUS).

To evaluate a path with directory (an root directory) and path (an absolute path), run the following steps which return a file, directory, or failure.

Let segments be the result of strictly splitting path on '/' (U+002F SOLIDUS).
Remove the first entry from segments.

Since path was an absolute path, this first entry will always be empty.
For each segment in segments, switch on segment:
empty string
Continue.
'.' (U+002E FULL STOP)
Continue.
'..' (U+002E FULL STOP, U+002E FULL STOP)
Let directory be directory’s parent, or directory if none.
Otherwise
Run these substeps:
1. Let item be the member of directory with name equal to segment, or return failure if none.
2. If segment is the last item in segments, return item.
3. If item is a file, return failure.
4. Let directory be item.

4. The `File` Interface

partial interface File {
    readonly attribute USVString webkitRelativePath;
};

The webkitRelativePath attribute of the File interface must return the relative path of the file, or the empty string if not specified.

5. HTML: Forms

EDITORIAL: This section should be merged into [HTML] once it is complete. Sections such as the steps to construct the form data set need to be extended to include the webkitRelativePath property.

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.

Given the following directory structure:

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

If the to_upload directory was selected, then files would include:

An entry with name == "1.txt" and webkitRelativePath == "to_upload/a/b/1.txt"
An entry with name == "2.txt" and webkitRelativePath == "to_upload/a/b/2.txt"
An entry with name == "3.txt" and webkitRelativePath == "to_upload/a/3.txt"

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.

Inspecting the webkitRelativePath properties after a directory is selected with an input element:

  <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.

Enumerating entries using webkitEntries:

  <input id=a type=file multiple>

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

INTEROP: In Chrome, webkitEntries is only populated as the result of a drag-and-drop operation, not when the element is clicked. Should we fix this so it is always populated?

INTEROP: In Chrome, if webkitdirectory is specified on a HTMLInputElement, webkitEntries is not populated; the files collection and webkitRelativePath properties must be used instead to reconstruct the directory structure. Should we fix this so it is always populated?

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 a File. If it is accessed via getAsFile() a zero-length File is returned.

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

The webkitGetAsEntry() method must run the following steps when invoked:

If the DataTransferItem object is not in the read/write mode or the read-only mode, return null and abort these steps.
If the drag data item kind is not File, then return null and abort these steps.
Return a new FileSystemEntry object representing the entry.

Handling drag and drop of files and directories:

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

WEB COMPAT: The legacy TypeMismatchError has been replaced in most specifications by TypeError, but the name differs. Is it compatible to switch here as well?

callback ErrorCallback = void (DOMException err);

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

7.1. The `FileSystemEntry` Interface

interface FileSystemEntry {
    readonly attribute boolean isFile;
    readonly attribute boolean isDirectory;
    readonly attribute USVString name;
    readonly attribute USVString fullPath;
    readonly attribute FileSystem filesystem;

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

An FileSystemEntry has an associated entry.

The isFile attribute of the FileSystemEntry interface must return true if the entry is a file entry and false otherwise.

The isDirectory attribute of the FileSystemEntry interface must return true if the entry is a directory entry and false otherwise.

The name attribute of the FileSystemEntry interface must return the name of the entry.

The fullPath attribute of the FileSystemEntry interface must return the full path of the entry.

The filesystem attribute of the FileSystemEntry interface must return the file system of the entry.

The getParent(successCallback, errorCallback) method, when invoked, must run the following steps:

Queue a task to perform the following substeps:
1. Let path be the result of running the steps to resolve a relative path with the entry's full path and '..'.
2. Let item be the result of running the steps to evaluate a path with the entry's root and path.
3. If item is failure, invoke errorCallback (if given) with a newly created "NotFoundError" DOMException, and terminate these steps.
4. Let entry be a new directory entry with item’s name as name and path as full path.
5. Invoke successCallback with a new FileSystemDirectoryEntry object associated with entry.

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

Handling an entry:

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');
  }
}

Helper function to adapt getParent() for use with Promises [ECMA-262]:

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

7.2. The `FileSystemDirectoryEntry` Interface

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

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

callback FileSystemEntryCallback = void (FileSystemEntry entry);

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.

The createReader() method, when invoked, must run the following steps:

Let reader be a new directory reader associated with the directory entry's directory.
Return a newly created FileSystemDirectoryReader object associated with reader.

The getFile(path, options, successCallback, errorCallback) method, when invoked, must run the following steps:

Queue a task to run the following substeps:
1. If path is undefined or null let path be the empty string.
2. If path is not a valid path, invoke errorCallback (if given) with a newly created "TypeMismatchError" DOMException, and terminate these steps.
3. If options’s create member is true, invoke errorCallback (if given) with a newly created "SecurityError" DOMException, and terminate these steps.
4. Let path be the result of running the steps to resolve a relative path with the directory entry's full path and path.
5. Let item be the result of running the steps to evaluate a path with the directory entry's root and path.
6. If item is failure, invoke errorCallback (if given) with a newly created "NotFoundError" DOMException, and terminate these steps.
7. If item is not a file, invoke errorCallback (if given) with a newly created "TypeMismatchError" DOMException, and terminate these steps.
8. Let entry be a new file entry with item’s name as name and path as full path.
9. Invoke successCallback (if given) with a new FileSystemFileEntry object associated with entry.

The getDirectory(path, options, successCallback, errorCallback) method, when invoked, must run the following steps:

Queue a task to run the following substeps:
1. If path is undefined or null let path be the empty string.
2. If path is not a valid path, invoke errorCallback (if given) with a newly created "TypeMismatchError" DOMException, and terminate these steps.
3. If options’s create member is true, invoke errorCallback (if given) with a newly created "SecurityError" DOMException, and terminate these steps.
4. Let path be the result of running the steps to resolve a relative path with the directory entry's full path and path.
5. Let item be the result of running the steps to evaluate a path with the directory entry's root and path.
6. If item is failure, invoke errorCallback (if given) with a newly created "NotFoundError" DOMException, and terminate these steps.
7. If item is not a directory, invoke errorCallback (if given) with a newly created "TypeMismatchError" DOMException, and terminate these steps.
8. Let entry be a new directory entry with item’s name as name and path as full path.
9. invoke successCallback (if given) with a new FileSystemDirectoryEntry associated with entry.

Helper functions to adapt getFile() and getDirectory() for use with Promises [ECMA-262]:

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

interface FileSystemDirectoryReader {
    void readEntries(FileSystemEntriesCallback successCallback,
                     optional ErrorCallback errorCallback);
};
callback FileSystemEntriesCallback = void (sequence<FileSystemEntry> entries);

A FileSystemDirectoryReader has an associated directory reader.

The readEntries(successCallback, errorCallback) method, when invoked, must run the following steps:

If the directory reader's reading flag is set, queue a task to invoke errorCallback with a newly created "InvalidStateError" DOMException, and terminate these steps.
If the directory reader's reader error is not null, queue a task to invoke errorCallback (if given) with reader error, and terminate these steps.
If the directory reader's done flag is set, queue a task to invoke successCallback with an empty sequence and terminate these steps.
Set the directory reader's reading flag.
Queue a task to perform the following substeps:
1. Clear the directory reader's reading flag.
2. Let dir be the directory reader's directory.
3. If dir is null, run these substeps:
  1. Let dir be the result of running the steps to evaluate a path with the entry's root and full path.
  2. If dir is failure, set the directory reader's reader error to a newly created "NotFoundError" DOMException, invoke errorCallback (if given) with reader error, and terminate these steps.
  3. Set the directory reader's directory to dir.
4. Let entries be a non-zero number of entries from the dir that have not yet been produced by this directory reader, if any.
5. If the previous step failed (for example, the directory was deleted or permission is denied), then set the directory reader's reader error to an appropriate DOMException, invoke errorCallback (if given) with reader error, and terminate these steps.
6. If entries is empty, set the directory reader's done flag.
7. invoke successCallback with entries.

Enumerating a directory:

let reader = dirEntry.createReader();
let doBatch = function() {

    // 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();

Helper function to adapt FileSystemDirectoryReader for use with Promises [ECMA-262]:

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();
  });
}

Helper function to adapt FileSystemDirectoryReader for use with AsyncIterators [ECMA-262]:

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

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

This allows for ordered asynchronous traversal of a directory tree using for-await-of:

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

interface FileSystemFileEntry : FileSystemEntry {
    void file(FileCallback successCallback,
              optional ErrorCallback errorCallback);
};
callback FileCallback = void (File file);

A FileSystemFileEntry's associated entry is a file entry.

The file(successCallback, errorCallback) method, when invoked, must run the following steps:

Queue a task to perform the following substeps:
1. Let item be the result of running the steps to evaluate a path with the file entry's root and full path.
2. If item is failure, invoke errorCallback (if given) with a newly created "NotFoundError" DOMException, and terminate these steps.
3. If item is a directory, invoke errorCallback (if given) with a newly created "TypeMismatchError" DOMException, and terminate these steps.
4. invoke successCallback with a new File object representing item.

Read the contents of a dropped file using FileReader:

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));
}

Helper function to adapt file() for use with Promises [ECMA-262]:

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

7.5. The `FileSystem` Interface

interface FileSystem {
    readonly attribute USVString name;
    readonly attribute FileSystemDirectoryEntry root;
};

A FileSystem has an associated file system.

The name attribute of the FileSystem interface must return the name of the file system.

The root attribute of the FileSystem interface must return a FileSystemDirectoryEntry associated with the root of the file system.

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.

File and Directory Entries API

Draft Community Group Report, 4 September 2019

Abstract

Status of this document

1. Goals

2. Concepts

2.1. Names and Paths

2.2. Files and Directories

2.3. Entries

2.4. Directory Reader

3. Algorithms

4. The `File` Interface

5. HTML: Forms

6. HTML: Drag and drop

7. Files and Directories

7.1. The `FileSystemEntry` Interface

7.2. The `FileSystemDirectoryEntry` Interface

7.3. The `FileSystemDirectoryReader` Interface

7.4. The `FileSystemFileEntry` Interface

7.5. The `FileSystem` Interface

8. Acknowledgements

Conformance

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

Informative References

IDL Index

Issues Index

File and Directory Entries API

Draft Community Group Report, 4 September 2019

Abstract

Status of this document

1. Goals

2. Concepts

2.1. Names and Paths

2.2. Files and Directories

2.3. Entries

2.4. Directory Reader

3. Algorithms

4. The File Interface

5. HTML: Forms

6. HTML: Drag and drop

7. Files and Directories

7.1. The FileSystemEntry Interface

7.2. The FileSystemDirectoryEntry Interface

7.3. The FileSystemDirectoryReader Interface

7.4. The FileSystemFileEntry Interface

7.5. The FileSystem Interface

8. Acknowledgements

Conformance

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

Informative References

IDL Index

Issues Index

4. The `File` Interface

7.1. The `FileSystemEntry` Interface

7.2. The `FileSystemDirectoryEntry` Interface

7.3. The `FileSystemDirectoryReader` Interface

7.4. The `FileSystemFileEntry` Interface

7.5. The `FileSystem` Interface