Added access log to server and modified mock-fts to use it

internal/logging/accesslog.go

@@ -5,6 +5,8 @@ import (
 	"log"
 	"net"
 	"net/http"
+	"os"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
@@ -26,12 +28,20 @@ func (s *statusRecorder) WriteHeader(code int) {
 	s.ResponseWriter.WriteHeader(code)
 }
 
+// Unwrap returns the wrapped ResponseWriter, so that http.ResponseController
+// can reach its Hijack and Flush: a WebSocket upgrade hijacks the connection.
+func (s *statusRecorder) Unwrap() http.ResponseWriter {
+	return s.ResponseWriter
+}
+
 func (s *statusRecorder) Write(data []byte) (int, error) {
 	if s.status == 0 {
 		s.status = http.StatusOK
 	}
+
 	written, err := s.ResponseWriter.Write(data)
 	s.bytes += written
+
 	return written, err
 }
 
@@ -108,3 +118,23 @@ func AccessLog(
 		logger.Println(line)
 	})
 }
+
+// OpenAccessLog opens the access log at path for appending, creating it if
+// needed, or stdout for "-", for AccessLog. It returns a logger writing to it
+// and a function that closes it (doing nothing for stdout).
+func OpenAccessLog(path string) (*log.Logger, func() error, error) {
+	if path == "-" {
+		return log.New(os.Stdout, "", 0), func() error {
+			return nil
+		}, nil
+	}
+
+	file, err := os.OpenFile(
+		filepath.Clean(path), os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600,
+	)
+	if err != nil {
+		return nil, nil, fmt.Errorf("opening access log: %w", err)
+	}
+
+	return log.New(file, "", 0), file.Close, nil
+}