allow a discrete refilling rate

lib/db.js

@@ -24,7 +24,8 @@ function normalizeType(params) {
     'per_interval',
     'interval',
     'size',
-    'unlimited'
+    'unlimited',
+    'discrete'
   ]);
 
   INTERVAL_SHORTCUTS.forEach(ish => {
@@ -100,7 +101,11 @@ class LimitDB {
     const now = Date.now();
     const deltaMS = Math.max(now - bucket.lastDrip, 0);
     const dripAmount = deltaMS * (type.per_interval / type.interval);
-    const content = Math.min(bucket.content + dripAmount, type.size);
+    var content = bucket.content;
+
+    if (!type.discrete || dripAmount >= type.per_interval) {
+      content = Math.floor(Math.min(bucket.content + dripAmount, type.size));
+    }
 
     return {
       content:    content,
@@ -204,7 +209,7 @@ class LimitDB {
       if (err) { return callback(err); }
       callback(null, {
         conformant: bucket.lastConformant,
-        remaining:  Math.floor(bucket.content),
+        remaining:  bucket.content,
         reset:      bucket.reset,
         limit:      typeParams.size
       });

test/discrete_example.tests.js

@@ -0,0 +1,46 @@
+const LimitDB  = require('../lib/db');
+const MockDate = require('mockdate');
+const assert   = require('chai').assert;
+
+const types = {
+  ip: {
+    size:         5,
+    per_interval: 5,
+    interval:     500,
+    discrete:     true
+  }
+};
+
+describe('when the fill rate is discrete', () => {
+  afterEach(function () {
+    MockDate.reset();
+  });
+
+  const db = new LimitDB({
+    inMemory: true,
+    types
+  });
+
+  beforeEach(function(done) {
+    MockDate.set(Date.now());
+    db.take({ type: 'ip', key: '21.17.65.41', count: 5 }, done);
+  });
+
+  it('should not add less than the per_interval amount', function(done) {
+    MockDate.set(Date.now() + 150);
+    db.status({ type: 'ip', prefix: '21.17.65.41' }, (err, result) => {
+      if (err) { return done(err); }
+      assert.equal(result.items[0].remaining, 0);
+      done();
+    });
+  });
+
+  it('should add the per_interval amount after the elapsed interval', function(done) {
+    MockDate.set(Date.now() + 500);
+    db.status({ type: 'ip', prefix: '21.17.65.41' }, (err, result) => {
+      if (err) { return done(err); }
+      assert.equal(result.items[0].remaining, 5);
+      done();
+    });
+  });
+});