Add bucket reclamation.

After RWTransaction.DeleteBucket() is called, all pages related to the
bucket are moved to the freelist for that transaction.

rwtransaction.go

@@ -63,14 +63,18 @@ func (t *RWTransaction) CreateBucketIfNotExists(name string) error {
 // DeleteBucket deletes a bucket.
 // Returns an error if the bucket cannot be found.
 func (t *RWTransaction) DeleteBucket(name string) error {
-	if b := t.Bucket(name); b == nil {
+	b := t.Bucket(name)
+	if b == nil {
 		return ErrBucketNotFound
 	}
 
 	// Remove from buckets page.
 	t.buckets.del(name)
 
-	// TODO(benbjohnson): Free all pages.
+	// Free all pages.
+	t.forEachPage(b.root, 0, func(p *page, depth int) {
+		t.db.freelist.free(t.id(), p)
+	})
 
 	return nil
 }

rwtransaction_test.go

@@ -66,6 +66,7 @@ func TestRWTransactionCreateBucketIfNotExists(t *testing.T) {
 	withOpenDB(func(db *DB, path string) {
 		assert.NoError(t, db.CreateBucketIfNotExists("widgets"))
 		assert.NoError(t, db.CreateBucketIfNotExists("widgets"))
+		assert.Equal(t, db.CreateBucketIfNotExists(""), ErrBucketNameRequired)
 
 		// Read the bucket through a separate transaction.
 		b, err := db.Bucket("widgets")
@@ -113,12 +114,17 @@ func TestRWTransactionDeleteBucket(t *testing.T) {
 		db.CreateBucket("widgets")
 		db.Put("widgets", []byte("foo"), []byte("bar"))
 
+		b, _ := db.Bucket("widgets")
+
 		// Delete the bucket and make sure we can't get the value.
 		assert.NoError(t, db.DeleteBucket("widgets"))
 		value, err := db.Get("widgets", []byte("foo"))
 		assert.Equal(t, err, ErrBucketNotFound)
 		assert.Nil(t, value)
 
+		// Verify that the bucket's page is free.
+		assert.Equal(t, db.freelist.all(), []pgid{b.root})
+
 		// Create the bucket again and make sure there's not a phantom value.
 		assert.NoError(t, db.CreateBucket("widgets"))
 		value, err = db.Get("widgets", []byte("foo"))