Add VFS capabilities method

__tests__/vfs.js

@@ -43,6 +43,12 @@ const call = (method, ...args) => VFS[method](testAdapter, testMount)(...args);
 const callOther = (method, ...args) => VFS[method](testAdapter, otherMount)(...args);
 
 describe('VFS', () => {
+  test('#capabilities', () => {
+    return expect(call('capabilities', 'null:/'))
+      .resolves
+      .toMatchObject({});
+  });
+
   test('#readdir', () => {
     return expect(call('readdir', 'null:/'))
       .resolves
@@ -79,7 +85,7 @@ describe('VFS', () => {
       .toBeInstanceOf(ArrayBuffer);
   });
 
-  test('writefile - blob', () => {
+  test('#writefile - blob', () => {
     return expect(call('writefile', 'null:/filename', new Blob()))
       .resolves
       .toBe(-1);

src/adapters/vfs/null.js

@@ -34,6 +34,7 @@
  * @param {object} [options] Adapter options
  */
 const nullAdapter = ({
+  capabilities: (path, options) => Promise.resolve({}),
   readdir: (path, options) => Promise.resolve([]),
   readfile: (path, type, options) => Promise.resolve({body: new ArrayBuffer(), mime: 'application/octet-stream'}),
   writefile: (path, data, options) => Promise.resolve(-1),

src/adapters/vfs/system.js

@@ -28,7 +28,7 @@
  * @license Simplified BSD License
  */
 
-const getters = ['exists', 'stat', 'readdir', 'readfile'];
+const getters = ['capabilities', 'exists', 'stat', 'readdir', 'readfile'];
 
 const requester = core => (fn, body, type, options = {}) =>
   core.request(`/vfs/${fn}`, {
@@ -57,6 +57,8 @@ const methods = (core, request) => {
       .then(({body}) => body);
 
   return {
+    capabilities: passthrough('capabilities'),
+
     readdir: ({path}, options) => request('readdir', {
       path,
       options,

src/filesystem.js

@@ -63,6 +63,7 @@ import merge from 'deepmerge';
  * Filesystem Adapter Methods
  * TODO: typedef
  * @typedef {Object} FilesystemAdapterMethods
+ * @property {Function} capabilities
  * @property {Function} readdir
  * @property {Function} readfile
  * @property {Function} writefile

src/vfs.js

@@ -74,6 +74,17 @@ const handleDirectoryList = (path, options) => result =>
       filter: options.filter
     }));
 
+/**
+ * Get vfs capabilities
+ *
+ * @param {string|VFSFile} path The path of a file
+ * @param {VFSMethodOptions} [options] Options
+ * @return {Promise<object[]>} An object of capabilities
+ */
+export const capabilities = (adapter, mount) => (path, options = {}) =>
+  adapter.capabilities(pathToObject(path), options, mount);
+
+
 /**
  * Read a directory
  *