From f448639ce4a632980eef6394f75aca12b89b6d1c Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Fri, 13 Jun 2014 07:56:10 -0600
Subject: [PATCH] Check for freelist overflow.

---
 freelist.go | 19 ++++++++++++++++++-
 tx.go       |  4 +++-
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/freelist.go b/freelist.go
index a236079..407dc79 100644
--- a/freelist.go
+++ b/freelist.go
@@ -1,11 +1,18 @@
 package bolt
 
 import (
+	"errors"
 	"fmt"
 	"sort"
 	"unsafe"
 )
 
+var (
+	// ErrFreelistOverflow is returned when the total number of free pages
+	// exceeds 65,536 and the freelist cannot hold any more.
+	ErrFreelistOverflow = errors.New("freelist overflow")
+)
+
 // freelist represents a list of all pages that are available for allocation.
 // It also tracks pages that have been freed but are still in use by open transactions.
 type freelist struct {
@@ -134,9 +141,19 @@ func (f *freelist) read(p *page) {
 // write writes the page ids onto a freelist page. All free and pending ids are
 // saved to disk since in the event of a program crash, all pending ids will
 // become free.
-func (f *freelist) write(p *page) {
+func (f *freelist) write(p *page) error {
+	// Combine the old free pgids and pgids waiting on an open transaction.
 	ids := f.all()
+
+	// Make sure that the sum of all free pages is less than the max uint16 size.
+	if len(ids) > (1 << 16) {
+		return ErrFreelistOverflow
+	}
+
+	// Update the header and write the ids to the page.
 	p.flags |= freelistPageFlag
 	p.count = uint16(len(ids))
 	copy(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[:], ids)
+
+	return nil
 }
diff --git a/tx.go b/tx.go
index a9781f2..211085a 100644
--- a/tx.go
+++ b/tx.go
@@ -173,7 +173,9 @@ func (tx *Tx) Commit() error {
 		tx.close()
 		return err
 	}
-	tx.db.freelist.write(p)
+	if err := tx.db.freelist.write(p); err != nil {
+		return err
+	}
 	tx.meta.freelist = p.id
 
 	// Write dirty pages to disk.