Guard against panics from unchecked type assertions

Replace two unchecked type assertions that could crash the server:

- server.go: the file-transfer logger built remoteAddr via a bare
  ctx.Value(contextKeyReq).(requestCtx) assertion, which panics if the
  context value is absent or the wrong type. Use the comma-ok form and
  degrade to an empty string.

- access.go: the legacy (< v0.17.0) AccessBitmap YAML array path used
  byte(v.(int)) with no element-type or bounds check, panicking on a
  non-int element or an array longer than the [8]byte bitmap. Iterate the
  slice from the type switch, bounds-check the index, and comma-ok each
  element, returning a wrapped error so a malformed user file fails to
  load loudly instead of crashing the server.

Add regression tests for the non-int and oversized legacy array cases.

1 files changed, 5 insertions, 1 deletions

diff --git a/hotline/server.go b/hotline/server.go
index d757062..7bc6a4a 100644
--- a/hotline/server.go
+++ b/hotline/server.go
@@ -690,8 +690,12 @@ func (s *Server) handleFileTransfer(ctx context.Context, rwc io.ReadWriter) erro
 		time.Sleep(3 * time.Second)
 	}()
 
+	var remoteAddr string
+	if rc, ok := ctx.Value(contextKeyReq).(requestCtx); ok {
+		remoteAddr = rc.remoteAddr
+	}
 	rLogger := s.Logger.With(
-		"remoteAddr", ctx.Value(contextKeyReq).(requestCtx).remoteAddr,
+		"remoteAddr", remoteAddr,
 		"login", fileTransfer.ClientConn.Account.Login,
 		"Name", string(fileTransfer.ClientConn.UserName),
 	)