feat: load packet logs from configured source

internal/isphere/file_source.go

@@ -0,0 +1,36 @@
+package isphere
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+func LoadEncryptedPacketLogSourceFromFile(path string) (EncryptedPacketLogSource, error) {
+	trimmedPath := strings.TrimSpace(path)
+	if trimmedPath == "" {
+		return EncryptedPacketLogSource{}, fmt.Errorf("packet log file path is empty")
+	}
+
+	file, err := os.Open(trimmedPath)
+	if err != nil {
+		return EncryptedPacketLogSource{}, fmt.Errorf("open packet log file %q: %w", trimmedPath, err)
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	scanner.Buffer(make([]byte, 64*1024), 16*1024*1024)
+	lines := []string{}
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" {
+			continue
+		}
+		lines = append(lines, line)
+	}
+	if err := scanner.Err(); err != nil {
+		return EncryptedPacketLogSource{}, fmt.Errorf("read packet log file %q: %w", trimmedPath, err)
+	}
+	return EncryptedPacketLogSource{Lines: lines}, nil
+}