init

config/atomic.go

@@ -0,0 +1,55 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// AtomicWrite writes data to the target path atomically by writing to a temp file
+// in the same directory, fsyncing, then renaming over the target.
+func AtomicWrite(path string, data []byte, perm os.FileMode) error {
+	dir := filepath.Dir(path)
+
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("create directory: %w", err)
+	}
+
+	tmp, err := os.CreateTemp(dir, ".tmp-*")
+	if err != nil {
+		return fmt.Errorf("create temp file: %w", err)
+	}
+	tmpName := tmp.Name()
+
+	cleanup := func() {
+		tmp.Close()
+		os.Remove(tmpName)
+	}
+
+	if _, err := tmp.Write(data); err != nil {
+		cleanup()
+		return fmt.Errorf("write temp file: %w", err)
+	}
+
+	if err := tmp.Sync(); err != nil {
+		cleanup()
+		return fmt.Errorf("fsync temp file: %w", err)
+	}
+
+	if err := tmp.Close(); err != nil {
+		os.Remove(tmpName)
+		return fmt.Errorf("close temp file: %w", err)
+	}
+
+	if err := os.Chmod(tmpName, perm); err != nil {
+		os.Remove(tmpName)
+		return fmt.Errorf("chmod temp file: %w", err)
+	}
+
+	if err := os.Rename(tmpName, path); err != nil {
+		os.Remove(tmpName)
+		return fmt.Errorf("rename temp to target: %w", err)
+	}
+
+	return nil
+}