From d5a6ba3b8bc849dce85bec694e6cbabe0aef41f9 Mon Sep 17 00:00:00 2001
From: Masahiro Nagano <m-nagano@sakura.ad.jp>
Date: Wed, 15 Jul 2026 23:51:48 +0900
Subject: [PATCH] safeer posfile

---
 .github/workflows/tagpr.yml |  1 -
 README.md                   |  2 +-
 fpos.go                     | 20 ++++++++++++++------
 go.mod                      |  4 ++--
 4 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/.github/workflows/tagpr.yml b/.github/workflows/tagpr.yml
index f67df12..9644ce8 100644
--- a/.github/workflows/tagpr.yml
+++ b/.github/workflows/tagpr.yml
@@ -17,4 +17,3 @@ jobs:
         id: tagpr
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
diff --git a/README.md b/README.md
index f824125..c053981 100644
--- a/README.md
+++ b/README.md
@@ -32,7 +32,7 @@ As a library, implement the `Callback` interface and call `Parse` on a `Parser`.
 ```go
 cb := &MyParserImpl{}
 parser := &followparser.Parser{
-    WorkDir:  "/var/tmp", // where pos files are stored
+    WorkDir:  "/path/to/workdir", // where pos files are stored
     Callback: cb,
     // optional:
     // ArchiveDir: "/var/log/archive",
diff --git a/fpos.go b/fpos.go
index 963cbb2..e925412 100644
--- a/fpos.go
+++ b/fpos.go
@@ -77,21 +77,29 @@ func (pf *posFile) write(pos int64, fstat *fStat) error {
 		Inode: fstat.Inode,
 		Dev:   fstat.Dev,
 	}
-	file, err := os.Create(pf.filename)
+	jb, err := json.Marshal(fp)
 	if err != nil {
 		return err
 	}
-	defer file.Close()
-	jb, err := json.Marshal(fp)
+	// To avoid race condition, we create a temporary file and then rename it to the target filename.
+	f, err := os.CreateTemp(filepath.Dir(pf.filename), filepath.Base(pf.filename))
 	if err != nil {
 		return err
 	}
-	_, err = file.Write(jb)
+	defer f.Close()
+	_, err = f.Write(jb)
 	if err != nil {
 		return err
 	}
-	return file.Sync()
-
+	err = f.Sync()
+	if err != nil {
+		return err
+	}
+	err = f.Close()
+	if err != nil {
+		return err
+	}
+	return os.Rename(f.Name(), pf.filename)
 }
 
 func fileStat(filename string) (*fStat, error) {
diff --git a/go.mod b/go.mod
index d829959..86aedbf 100644
--- a/go.mod
+++ b/go.mod
@@ -1,5 +1,5 @@
-module github.com/kazeburo/followparser
+module github.com/monitoring-forge/followparser
 
-go 1.23.4
+go 1.25
 
 require github.com/avast/retry-go/v4 v4.7.0