From faf497feb87228535c394d7e93f3be1a6a818796 Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Thu, 29 May 2014 19:19:03 -0700
Subject: [PATCH] Important Fix: Avoid overwriting the index file!!!

---
 go/storage/needle_map.go | 22 ++++++++++------------
 go/tools/read_index.go   | 27 +++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 12 deletions(-)
 create mode 100644 go/tools/read_index.go

diff --git a/go/storage/needle_map.go b/go/storage/needle_map.go
index 33d3d1747..6d94ee1ca 100644
--- a/go/storage/needle_map.go
+++ b/go/storage/needle_map.go
@@ -51,7 +51,7 @@ const (
 
 func LoadNeedleMap(file *os.File) (*NeedleMap, error) {
 	nm := NewNeedleMap(file)
-	e := walkIndexFile(file, func(key uint64, offset, size uint32) error {
+	e := WalkIndexFile(file, func(key uint64, offset, size uint32) error {
 		if key > nm.MaximumFileKey {
 			nm.MaximumFileKey = key
 		}
@@ -78,7 +78,7 @@ func LoadNeedleMap(file *os.File) (*NeedleMap, error) {
 
 // walks through the index file, calls fn function with each key, offset, size
 // stops with the error returned by the fn function
-func walkIndexFile(r *os.File, fn func(key uint64, offset, size uint32) error) error {
+func WalkIndexFile(r *os.File, fn func(key uint64, offset, size uint32) error) error {
 	var readerOffset int64
 	bytes := make([]byte, 16*RowsToRead)
 	count, e := r.ReadAt(bytes, readerOffset)
@@ -124,6 +124,9 @@ func (nm *NeedleMap) Put(key uint64, offset uint32, size uint32) (int, error) {
 		nm.DeletionCounter++
 		nm.DeletionByteCounter = nm.DeletionByteCounter + uint64(oldSize)
 	}
+	if _, err := nm.indexFile.Seek(0, 2); err != nil {
+		return 0, fmt.Errorf("cannot go to the end of indexfile %s: %s", nm.indexFile.Name(), err.Error())
+	}
 	return nm.indexFile.Write(bytes)
 }
 func (nm *NeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
@@ -132,20 +135,15 @@ func (nm *NeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
 }
 func (nm *NeedleMap) Delete(key uint64) error {
 	nm.DeletionByteCounter = nm.DeletionByteCounter + uint64(nm.m.Delete(Key(key)))
-	offset, err := nm.indexFile.Seek(0, 1)
-	if err != nil {
-		return fmt.Errorf("cannot get position of indexfile: %s", err)
-	}
 	bytes := make([]byte, 16)
 	util.Uint64toBytes(bytes[0:8], key)
 	util.Uint32toBytes(bytes[8:12], 0)
 	util.Uint32toBytes(bytes[12:16], 0)
-	if _, err = nm.indexFile.Write(bytes); err != nil {
-		plus := ""
-		if e := nm.indexFile.Truncate(offset); e != nil {
-			plus = "\ncouldn't truncate index file: " + e.Error()
-		}
-		return fmt.Errorf("error writing to indexfile %s: %s%s", nm.indexFile.Name(), err, plus)
+	if _, err := nm.indexFile.Seek(0, 2); err != nil {
+		return fmt.Errorf("cannot go to the end of indexfile %s: %s", nm.indexFile.Name(), err.Error())
+	}
+	if _, err := nm.indexFile.Write(bytes); err != nil {
+		return fmt.Errorf("error writing to indexfile %s: %s", nm.indexFile.Name(), err.Error())
 	}
 	nm.DeletionCounter++
 	return nil
diff --git a/go/tools/read_index.go b/go/tools/read_index.go
new file mode 100644
index 000000000..a958de410
--- /dev/null
+++ b/go/tools/read_index.go
@@ -0,0 +1,27 @@
+package main
+
+import (
+	"code.google.com/p/weed-fs/go/storage"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+)
+
+var (
+	indexFileName = flag.String("file", "", ".idx file to analyze")
+)
+
+func main() {
+	flag.Parse()
+	indexFile, err := os.OpenFile(*indexFileName, os.O_RDONLY, 0644)
+	if err != nil {
+		log.Fatalf("Create Volume Index [ERROR] %s\n", err)
+	}
+	defer indexFile.Close()
+
+	storage.WalkIndexFile(indexFile, func(key uint64, offset, size uint32) error {
+		fmt.Printf("key %d, offset %d, size %d, nextOffset %d\n", key, offset*8, size, offset*8+size)
+		return nil
+	})
+}