From aa13f7f94f882fa0964b801c062217c0b9a45436 Mon Sep 17 00:00:00 2001
From: sasha-s <sasha@scaledinference.com>
Date: Mon, 18 May 2015 12:00:40 -0700
Subject: [PATCH] make ignoring Truncate() explicit

https://github.com/boltdb/bolt/pull/371#issuecomment-103176330
---
 bolt_unix.go    | 4 ++--
 bolt_windows.go | 8 +++++---
 db.go           | 7 -------
 3 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/bolt_unix.go b/bolt_unix.go
index 8107f4a..266222a 100644
--- a/bolt_unix.go
+++ b/bolt_unix.go
@@ -48,8 +48,8 @@ func funlock(f *os.File) error {
 func mmap(db *DB, sz int) error {
 	// Truncate and fsync to ensure file size metadata is flushed.
 	// https://github.com/boltdb/bolt/issues/284
-	if !db.NoGrowSync {
-		if err := db.ops.Truncate(int64(sz)); err != nil {
+	if !db.NoGrowSync && !db.readOnly {
+		if err := db.file.Truncate(int64(sz)); err != nil {
 			return fmt.Errorf("file resize error: %s", err)
 		}
 		if err := db.file.Sync(); err != nil {
diff --git a/bolt_windows.go b/bolt_windows.go
index 783b633..8b782be 100644
--- a/bolt_windows.go
+++ b/bolt_windows.go
@@ -28,9 +28,11 @@ func funlock(f *os.File) error {
 // mmap memory maps a DB's data file.
 // Based on: https://github.com/edsrzf/mmap-go
 func mmap(db *DB, sz int) error {
-	// Truncate the database to the size of the mmap.
-	if err := db.ops.Truncate(int64(sz)); err != nil {
-		return fmt.Errorf("truncate: %s", err)
+	if !db.readOnly {
+		// Truncate the database to the size of the mmap.
+		if err := db.file.Truncate(int64(sz)); err != nil {
+			return fmt.Errorf("truncate: %s", err)
+		}
 	}
 
 	// Open a file mapping handle.
diff --git a/db.go b/db.go
index 5ae35cc..d1b722a 100644
--- a/db.go
+++ b/db.go
@@ -103,7 +103,6 @@ type DB struct {
 
 	ops struct {
 		writeAt  func(b []byte, off int64) (n int, err error)
-		Truncate func(size int64) error
 	}
 
 	readOnly bool // Read only mode. Update()/Begin(true) would return ErrDatabaseReadOnly immediately.
@@ -144,8 +143,6 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 	if options.ReadOnly {
 		flag = os.O_RDONLY
 		db.readOnly = true
-		// Ignore truncations.
-		db.ops.Truncate = func(int64) error { return nil }
 	}
 
 	// Open data file and separate sync handler for metadata writes.
@@ -156,10 +153,6 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 		return nil, err
 	}
 
-	if !db.readOnly {
-		db.ops.Truncate = db.file.Truncate
-	}
-
 	// Lock file so that other processes using Bolt in read-write mode cannot
 	// use the database  at the same time. This would cause corruption since
 	// the two processes would write meta pages and free pages separately.