Implement cache serialization

Implement dump method

implement load

README.md

@@ -107,3 +107,13 @@ away.
     Return total quantity of objects currently in cache. Note, that
     `stale` (see options) items are returned as part of this item
     count.
+
+* `dump()`
+
+    Return an array of the cache entries ready for serialization and usage
+    with 'destinationCache.load(arr)`.
+
+* `load(cacheEntriesArray)`
+
+    Loads another cache entries array, obtained with `sourceCache.dump()`,
+    into the cache. The destination cache is reset before loading new entries

lib/lru-cache.js

@@ -137,10 +137,24 @@ LRUCache.prototype.reset = function () {
   this._itemCount = 0
 }
 
-// Provided for debugging/dev purposes only. No promises whatsoever that
-// this API stays stable.
 LRUCache.prototype.dump = function () {
-  return this._cache
+  var arr = []
+  var i = 0
+
+  for (var k = this._mru - 1; k >= 0 && i < this._itemCount; k--) if (this._lruList[k]) {
+    var hit = this._lruList[k]
+    if (!isStale(this, hit)) {
+      //Do not store staled hits
+      ++i
+      arr.push({
+        k: hit.key,
+        v: hit.value,
+        e: hit.now + (hit.maxAge || 0)
+      });
+    }
+  }
+  //arr has the most read first
+  return arr
 }
 
 LRUCache.prototype.dumpLru = function () {
@@ -209,6 +223,26 @@ LRUCache.prototype.del = function (key) {
   del(this, this._cache[key])
 }
 
+LRUCache.prototype.load = function (arr) {
+  //reset the cache
+  this.reset();
+
+  var now = Date.now()
+  //A previous serialized cache has the most recent items first
+  for (var l = arr.length - 1; l >= 0; l-- ) {
+    var hit = arr[l]
+    var expiresAt = hit.e || 0
+    if (expiresAt === 0) {
+      //the item was created without expiration in a non aged cache
+      this.set(hit.k, hit.v)
+    } else {
+      var maxAge = expiresAt - now
+      //dont add already expired items
+      if (maxAge > 0) this.set(hit.k, hit.v, maxAge)
+    }
+  }
+}
+
 function get (self, key, doUse) {
   var hit = self._cache[key]
   if (hit) {

test/basic.js

@@ -93,31 +93,6 @@ test("reset", function (t) {
 })
 
 
-// Note: `<cache>.dump()` is a debugging tool only. No guarantees are made
-// about the format/layout of the response.
-test("dump", function (t) {
-  var cache = new LRU(10)
-  var d = cache.dump();
-  t.equal(Object.keys(d).length, 0, "nothing in dump for empty cache")
-  cache.set("a", "A")
-  var d = cache.dump()  // { a: { key: "a", value: "A", lu: 0 } }
-  t.ok(d.a)
-  t.equal(d.a.key, "a")
-  t.equal(d.a.value, "A")
-  t.equal(d.a.lu, 0)
-
-  cache.set("b", "B")
-  cache.get("b")
-  d = cache.dump()
-  t.ok(d.b)
-  t.equal(d.b.key, "b")
-  t.equal(d.b.value, "B")
-  t.equal(d.b.lu, 2)
-
-  t.end()
-})
-
-
 test("basic with weighed length", function (t) {
   var cache = new LRU({
     max: 100,

test/serialize.js

@@ -0,0 +1,216 @@
+var test = require('tap').test
+var LRU = require('../')
+
+test('dump', function (t) {
+  var cache = new LRU()
+
+  t.equal(cache.dump().length, 0, "nothing in dump for empty cache")
+
+  cache.set("a", "A")
+  cache.set("b", "B")
+  t.deepEqual(cache.dump(), [
+    { k: "b", v: "B", e: 0 },
+    { k: "a", v: "A", e: 0 }
+  ])
+
+  cache.set("a", "A");
+  t.deepEqual(cache.dump(), [
+    { k: "a", v: "A", e: 0 },
+    { k: "b", v: "B", e: 0 }
+  ])
+
+  cache.get("b");
+  t.deepEqual(cache.dump(), [
+    { k: "b", v: "B", e: 0 },
+    { k: "a", v: "A", e: 0 }
+  ])
+
+  cache.del("a");
+  t.deepEqual(cache.dump(), [
+    { k: "b", v: "B",  e: 0 }
+  ])
+
+  t.end()
+})
+
+test("do not dump stale items", function(t) {
+  var cache = new LRU({
+    max: 5,
+    maxAge: 50
+  })
+
+  //expires at 50
+  cache.set("a", "A")
+
+  setTimeout(function () {
+    //expires at 75
+    cache.set("b", "B")
+    var s = cache.dump()
+    t.equal(s.length, 2)
+    t.equal(s[0].k, "b")
+    t.equal(s[1].k, "a")
+  }, 25)
+
+  setTimeout(function () {
+    //expires at 110
+    cache.set("c", "C")
+    var s = cache.dump()
+    t.equal(s.length, 2)
+    t.equal(s[0].k, "c")
+    t.equal(s[1].k, "b")
+  }, 60)
+
+  setTimeout(function () {
+    //expires at 130
+    cache.set("d", "D", 40)
+    var s = cache.dump()
+    t.equal(s.length, 2)
+    t.equal(s[0].k, "d")
+    t.equal(s[1].k, "c")
+  }, 90)
+
+  setTimeout(function () {
+    var s = cache.dump()
+    t.equal(s.length, 1)
+    t.equal(s[0].k, "d")
+  }, 120)
+
+  setTimeout(function () {
+    var s = cache.dump()
+    t.deepEqual(s, [])
+    t.end()
+  }, 155)
+})
+
+test("load basic cache", function(t) {
+  var cache = new LRU(),
+      copy = new LRU()
+
+  cache.set("a", "A")
+  cache.set("b", "B")
+
+  copy.load(cache.dump())
+  t.deepEquals(cache.dump(), copy.dump())
+
+  t.end()
+})
+
+
+test("load staled cache", function(t) {
+  var cache = new LRU({maxAge: 50}),
+      copy = new LRU({maxAge: 50}),
+      arr
+
+  //expires at 50
+  cache.set("a", "A")
+  setTimeout(function () {
+    //expires at 80
+    cache.set("b", "B")
+    arr = cache.dump()
+    t.equal(arr.length, 2)
+  }, 30)
+
+  setTimeout(function () {
+    copy.load(arr)
+    t.equal(copy.get("a"), undefined)
+    t.equal(copy.get("b"), "B")
+  }, 60)
+
+  setTimeout(function () {
+    t.equal(copy.get("b"), undefined)
+    t.end()
+  }, 90)
+})
+
+test("load to other size cache", function(t) {
+  var cache = new LRU({max: 2}),
+      copy = new LRU({max: 1})
+
+  cache.set("a", "A")
+  cache.set("b", "B")
+
+  copy.load(cache.dump())
+  t.equal(copy.get("a"), undefined)
+  t.equal(copy.get("b"), "B")
+
+  //update the last read from original cache
+  cache.get("a")
+  copy.load(cache.dump())
+  t.equal(copy.get("a"), "A")
+  t.equal(copy.get("b"), undefined)
+
+  t.end()
+})
+
+
+test("load to other age cache", function(t) {
+  var cache = new LRU({maxAge: 50}),
+      aged = new LRU({maxAge: 100}),
+      simple = new LRU(),
+      arr,
+      expired
+
+  //created at 0
+  //a would be valid till 0 + 50
+  cache.set("a", "A")
+  setTimeout(function () {
+    //created at 20
+    //b would be valid till 20 + 50
+    cache.set("b", "B")
+    //b would be valid till 20 + 70
+    cache.set("c", "C", 70)
+    arr = cache.dump()
+    t.equal(arr.length, 3)
+  }, 20)
+
+  setTimeout(function () {
+    t.equal(cache.get("a"), undefined)
+    t.equal(cache.get("b"), "B")
+    t.equal(cache.get("c"), "C")
+
+    aged.load(arr)
+    t.equal(aged.get("a"), undefined)
+    t.equal(aged.get("b"), "B")
+    t.equal(aged.get("c"), "C")
+
+    simple.load(arr)
+    t.equal(simple.get("a"), undefined)
+    t.equal(simple.get("b"), "B")
+    t.equal(simple.get("c"), "C")
+  }, 60)
+
+  setTimeout(function () {
+    t.equal(cache.get("a"), undefined)
+    t.equal(cache.get("b"), undefined)
+    t.equal(cache.get("c"), "C")
+
+    aged.load(arr)
+    t.equal(aged.get("a"), undefined)
+    t.equal(aged.get("b"), undefined)
+    t.equal(aged.get("c"), "C")
+
+    simple.load(arr)
+    t.equal(simple.get("a"), undefined)
+    t.equal(simple.get("b"), undefined)
+    t.equal(simple.get("c"), "C")
+  }, 80)
+
+  setTimeout(function () {
+    t.equal(cache.get("a"), undefined)
+    t.equal(cache.get("b"), undefined)
+    t.equal(cache.get("c"), undefined)
+
+    aged.load(arr)
+    t.equal(aged.get("a"), undefined)
+    t.equal(aged.get("b"), undefined)
+    t.equal(aged.get("c"), undefined)
+
+    simple.load(arr)
+    t.equal(simple.get("a"), undefined)
+    t.equal(simple.get("b"), undefined)
+    t.equal(simple.get("c"), undefined)
+    t.end()
+  }, 100)
+
+})
+