feat: harden jsonl runtime reliability

pkg/jsonlog/store.go

@@ -0,0 +1,96 @@
+package jsonlog
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// AppendLine appends a single JSON-encoded line and returns the resulting file size.
+func AppendLine(path string, value interface{}) (int64, error) {
+	data, err := json.Marshal(value)
+	if err != nil {
+		return 0, err
+	}
+	return AppendRawLine(path, data)
+}
+
+// AppendRawLine appends a raw JSON line and returns the resulting file size.
+func AppendRawLine(path string, line []byte) (int64, error) {
+	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
+		return 0, err
+	}
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+	if _, err := f.Write(append(line, '\n')); err != nil {
+		return 0, err
+	}
+	st, err := f.Stat()
+	if err != nil {
+		return 0, err
+	}
+	return st.Size(), nil
+}
+
+// Scan walks each non-empty JSONL line in order.
+func Scan(path string, fn func(line []byte) error) error {
+	f, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	scanner.Buffer(make([]byte, 0, 64*1024), 8*1024*1024)
+	for scanner.Scan() {
+		line := append([]byte(nil), scanner.Bytes()...)
+		if len(line) == 0 {
+			continue
+		}
+		if err := fn(line); err != nil {
+			return err
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return fmt.Errorf("scan %s: %w", path, err)
+	}
+	return nil
+}
+
+// FileSize returns 0 when the file does not exist.
+func FileSize(path string) (int64, error) {
+	st, err := os.Stat(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return 0, nil
+		}
+		return 0, err
+	}
+	return st.Size(), nil
+}
+
+// ReadJSON reads a JSON sidecar file into dst.
+func ReadJSON(path string, dst interface{}) error {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(data, dst)
+}
+
+// WriteJSON writes a JSON sidecar file atomically enough for local runtime use.
+func WriteJSON(path string, value interface{}) error {
+	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
+		return err
+	}
+	data, err := json.MarshalIndent(value, "", "  ")
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(path, data, 0644)
+}