From 10ee4d9652c906626f49d4e91b813911c4a34203 Mon Sep 17 00:00:00 2001
From: Vincent Weevers <mail@vincentweevers.nl>
Date: Tue, 17 Sep 2019 22:14:17 +0300
Subject: [PATCH] Use reachdown package (Level/community#82) (#75)

---
 leveldown.js  | 21 ++++----------
 matchdown.js  |  8 ++++++
 package.json  |  4 ++-
 test/index.js | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 92 insertions(+), 17 deletions(-)
 create mode 100644 matchdown.js

diff --git a/leveldown.js b/leveldown.js
index a07988e..cffa5c2 100644
--- a/leveldown.js
+++ b/leveldown.js
@@ -1,6 +1,8 @@
 var inherits = require('inherits')
 var abstract = require('abstract-leveldown')
 var wrap = require('level-option-wrap')
+var reachdown = require('reachdown')
+var matchdown = require('./matchdown')
 
 var rangeOptions = 'start end gt gte lt lte'.split(' ')
 var defaultClear = abstract.AbstractLevelDOWN.prototype._clear
@@ -83,13 +85,13 @@ SubDown.prototype._open = function (opts, cb) {
   this.db.open(function (err) {
     if (err) return cb(err)
 
-    var subdb = down(self.db, 'subleveldown')
+    var subdb = reachdown(self.db, 'subleveldown')
 
     if (subdb && subdb.prefix) {
       self.prefix = subdb.prefix + self.prefix
-      self.leveldown = down(subdb.db)
+      self.leveldown = reachdown(subdb.db, matchdown, false)
     } else {
-      self.leveldown = down(self.db)
+      self.leveldown = reachdown(self.db, matchdown, false)
     }
 
     if (self._beforeOpen) self._beforeOpen(cb)
@@ -179,16 +181,3 @@ SubDown.prototype._iterator = function (opts) {
 }
 
 module.exports = SubDown
-
-function down (db, type) {
-  if (typeof db.down === 'function') return db.down(type)
-  if (type && db.type === type) return db
-  if (isLooseAbstract(db.db)) return down(db.db, type)
-  if (isLooseAbstract(db._db)) return down(db._db, type)
-  return type ? null : db
-}
-
-function isLooseAbstract (db) {
-  if (!db || typeof db !== 'object') { return false }
-  return typeof db._batch === 'function' && typeof db._iterator === 'function'
-}
diff --git a/matchdown.js b/matchdown.js
new file mode 100644
index 0000000..089ce39
--- /dev/null
+++ b/matchdown.js
@@ -0,0 +1,8 @@
+module.exports = function matchdown (db, type) {
+  // Skip layers that we handle ourselves
+  if (type === 'levelup') return false
+  if (type === 'encoding-down') return false
+  if (type === 'deferred-leveldown') return false
+
+  return true
+}
diff --git a/package.json b/package.json
index 4f18f5d..a00a235 100644
--- a/package.json
+++ b/package.json
@@ -20,7 +20,8 @@
     "encoding-down": "^6.2.0",
     "inherits": "^2.0.3",
     "level-option-wrap": "^1.1.0",
-    "levelup": "^4.2.0"
+    "levelup": "^4.2.0",
+    "reachdown": "^1.0.0"
   },
   "devDependencies": {
     "after": "^0.8.2",
@@ -30,6 +31,7 @@
     "hallmark": "^2.0.0",
     "level-community": "^3.0.0",
     "level-concat-iterator": "^2.0.1",
+    "memdb": "^1.3.1",
     "memdown": "^5.0.0",
     "nyc": "^14.0.0",
     "standard": "^14.0.0",
diff --git a/test/index.js b/test/index.js
index a59feb1..e3503e9 100644
--- a/test/index.js
+++ b/test/index.js
@@ -7,6 +7,10 @@ var after = require('after')
 var subdown = require('../leveldown')
 var subdb = require('..')
 var levelup = require('levelup')
+var reachdown = require('reachdown')
+var memdb = require('memdb')
+var abstract = require('abstract-leveldown')
+var inherits = require('util').inherits
 
 // Test abstract-leveldown compliance
 suite({
@@ -359,6 +363,78 @@ test('SubDb main function', function (t) {
   }
 })
 
+// Test that we peel off the levelup, deferred-leveldown and encoding-down
+// layers from db, but stop at any other intermediate layer like encrypt-down,
+// cachedown, etc.
+test('subleveldown on intermediate layer', function (t) {
+  t.plan(7)
+
+  function Intermediate (db) {
+    abstract.AbstractLevelDOWN.call(this)
+    this.db = db
+  }
+
+  inherits(Intermediate, abstract.AbstractLevelDOWN)
+
+  Intermediate.prototype._put = function (key, value, options, callback) {
+    t.pass('got _put call')
+    this.db._put('mitm' + key, value, options, callback)
+  }
+
+  Intermediate.prototype._get = function (key, options, callback) {
+    t.pass('got _get call')
+    this.db._get('mitm' + key, options, callback)
+  }
+
+  var db = levelup(encoding(new Intermediate(memdown())))
+  var sub = subdb(db, 'test')
+
+  sub.put('key', 'value', function (err) {
+    t.error(err, 'no err')
+
+    db.get('!test!key', function (err, value) {
+      t.ifError(err, 'no levelup get error')
+      t.is(value, 'value')
+    })
+
+    reachdown(db).get('mitm!test!key', { asBuffer: false }, function (err, value) {
+      t.ifError(err, 'no memdown get error')
+      t.is(value, 'value')
+    })
+  })
+})
+
+test('legacy memdb (old levelup)', function (t) {
+  t.plan(7)
+
+  // Should not result in double json encoding
+  var db = memdb({ valueEncoding: 'json' })
+  var sub = subdb(db, 'test', { valueEncoding: 'json' })
+
+  // Integration with memdb still works because subleveldown waits to reachdown
+  // until the (old levelup) db is open. Reaching down then correctly lands on
+  // the memdown db. If subleveldown were to reachdown immediately it'd land on
+  // the old deferred-leveldown (which when unopened doesn't have a reference to
+  // the memdown db yet) so we'd be unable to persist anything.
+  t.is(Object.getPrototypeOf(reachdown(db)).constructor.name, 'DeferredLevelDOWN')
+
+  sub.put('key', { a: 1 }, function (err) {
+    t.ifError(err, 'no put error')
+
+    sub.get('key', function (err, value) {
+      t.ifError(err, 'no get error')
+      t.same(value, { a: 1 })
+    })
+
+    t.is(Object.getPrototypeOf(reachdown(db)).constructor.name, 'MemDOWN')
+
+    reachdown(db).get('!test!key', { asBuffer: false }, function (err, value) {
+      t.ifError(err, 'no get error')
+      t.is(value, '{"a":1}')
+    })
+  })
+})
+
 function getKey (entry) {
   return entry.key
 }