Add manifest

README.md

@@ -82,6 +82,7 @@ db.put('name', 'levelup', function (err) {
 ## API
 
 - <a href="#ctor"><code><b>levelup()</b></code></a>
+- <a href="#supports"><code>db.<b>supports</b></code></a>
 - <a href="#open"><code>db.<b>open()</b></code></a>
 - <a href="#close"><code>db.<b>close()</b></code></a>
 - <a href="#put"><code>db.<b>put()</b></code></a>
@@ -137,6 +138,22 @@ db.get('foo', function (err, value) {
 })
 ```
 
+<a name="supports"></a>
+
+### `db.supports`
+
+A read-only [manifest](https://github.com/Level/supports). Not [widely supported yet](https://github.com/Level/community/issues/83). Might be used like so:
+
+```js
+if (!db.supports.permanence) {
+  throw new Error('Persistent storage is required')
+}
+
+if (db.supports.bufferKeys && db.supports.promises) {
+  await db.put(Buffer.from('key'), 'value')
+}
+```
+
 <a name="open"></a>
 
 ### `db.open([options][, callback])`

lib/levelup.js

@@ -5,6 +5,7 @@ var DeferredLevelDOWN = require('deferred-leveldown')
 var IteratorStream = require('level-iterator-stream')
 var Batch = require('./batch')
 var errors = require('level-errors')
+var supports = require('level-supports')
 var assert = require('assert')
 var promisify = require('./promisify')
 var getCallback = require('./common').getCallback
@@ -55,6 +56,25 @@ function LevelUP (db, options, callback) {
   this._db = db
   this.db = new DeferredLevelDOWN(db)
   this.open(callback)
+
+  // Create manifest based on deferred-leveldown's
+  this.supports = supports(this.db.supports, {
+    status: false,
+    deferredOpen: true,
+    openCallback: true,
+    promises: true,
+    streams: true
+  })
+
+  // Experimental: enrich levelup interface
+  Object.keys(this.supports.additionalMethods).forEach(function (method) {
+    if (this[method] != null) return
+
+    // Don't do this.db[method].bind() because this.db is dynamic.
+    this[method] = function () {
+      return this.db[method].apply(this.db, arguments)
+    }
+  }, this)
 }
 
 LevelUP.prototype.emit = EventEmitter.prototype.emit
@@ -324,6 +344,8 @@ LevelUP.prototype.toString = function () {
   return 'LevelUP'
 }
 
+LevelUP.prototype.type = 'levelup'
+
 function maybeError (db, callback) {
   if (!db._isOpening() && !db.isOpen()) {
     process.nextTick(callback, new ReadError('Database is not open'))

package.json

@@ -17,6 +17,7 @@
     "deferred-leveldown": "~5.2.1",
     "level-errors": "~2.0.0",
     "level-iterator-stream": "~4.0.0",
+    "level-supports": "~1.0.0",
     "xtend": "~4.0.0"
   },
   "devDependencies": {

test/index.js

@@ -7,6 +7,7 @@ function suite (options) {
   var test = testCommon.test
 
   require('./argument-checking-test')(test, testCommon)
+  require('./manifest-test')(test, testCommon)
   require('./batch-test')(test, testCommon)
   if (testCommon.encodings) require('./binary-test')(test, testCommon)
   if (testCommon.clear) require('./clear-test')(test)

test/manifest-test.js

@@ -0,0 +1,18 @@
+var suite = require('level-supports/test')
+
+module.exports = function (test, testCommon) {
+  suite(test, testCommon)
+
+  // TODO (once manifest lands in other modules): add integration tests.
+  test('manifest has expected properties', function (t) {
+    var db = testCommon.factory()
+
+    t.is(db.supports.status, false)
+    t.is(db.supports.deferredOpen, true)
+    t.is(db.supports.openCallback, true)
+    t.is(db.supports.promises, true)
+    t.is(db.supports.streams, true)
+
+    db.close(t.end.bind(t))
+  })
+}