fix watch when first one is destroyed (#44)

Author: mafintosh

Diff for: index.js

@@ -9,6 +9,7 @@ const isOptions = require('is-options')
 const hypercore = require('hypercore')
 const inherits = require('inherits')
 const alru = require('array-lru')
+const set = require('unordered-set')
 
 const Extension = require('./lib/extension')
 const Node = require('./lib/node')
@@ -74,6 +75,22 @@ Object.defineProperty(HyperTrie.prototype, 'version', {
   }
 })
 
+HyperTrie.prototype._removeWatch = function (w) {
+  set.remove(this._watchers, w)
+}
+
+HyperTrie.prototype._addWatch = function (w) {
+  const self = this
+
+  set.add(this._watchers, w)
+  if (this._watchers.length > 1 || !this.feed.sparse) return
+
+  this.feed.update({ ifAvailable: false }, function loop () {
+    if (self._watchers.length === 0) return
+    self.feed.update({ ifAvailable: false }, loop)
+  })
+}
+
 HyperTrie.prototype.reconnect = function (from, opts) {
   opts = opts ? Object.assign({}, opts, { reconnect: true }) : { reconnect: true }
   return this.diff(from, opts)

Diff for: lib/watch.js

@@ -1,4 +1,3 @@
-const set = require('unordered-set')
 const inherits = require('inherits')
 const events = require('events')
 
@@ -15,29 +14,15 @@ function Watch (db, prefix, onchange) {
   this._kicking = false
   this._index = 0
 
-  const self = this
-  const feed = this._db.feed
-  const watchers = this._db._watchers
-
   if (onchange) this.on('change', onchange)
-  set.add(watchers, this)
+  this._db._addWatch(this)
   this.update()
-
-  if (watchers.length === 1 && feed.sparse) {
-    feedUpdateLoop()
-  }
-
-  function feedUpdateLoop () {
-    if (self._destroyed) return
-    // TODO: Expose a way to cancel this update when the watcher is destroyed, since it is not ifAvailable.
-    feed.update({ ifAvailable: false }, feedUpdateLoop)
-  }
 }
 
 inherits(Watch, events.EventEmitter)
 
 Watch.prototype.destroy = function () {
-  set.remove(this._db._watchers, this)
+  this._db._removeWatch(this)
   this._destroyed = true
 }
 

Diff for: test/watch.js

@@ -61,6 +61,39 @@ tape('watch and stop watching', function (t) {
   db.put('foo/bar', 'baz')
 })
 
+tape('watch, watch and stop watch first one', function (t) {
+  t.plan(5 + 1)
+
+  const db = create()
+  var bs = 5
+
+  db.ready(function () {
+    const clone = create(db.key, { sparse: true })
+
+    const a = clone.watch('foo', function () {
+      t.pass('got a update')
+      a.destroy()
+    })
+
+    const b = clone.watch('foo', function () {
+      t.pass('got b update')
+
+      if (!--bs) {
+        b.destroy()
+        t.end()
+        return
+      }
+
+      db.put('foo/bar', 'baz')
+    })
+
+    db.put('foo/bar', 'baz')
+
+    const stream = db.replicate(true, { live: true })
+    stream.pipe(clone.replicate(false, { live: true })).pipe(stream)
+  })
+})
+
 tape('remote watch', function (t) {
   const db = create()