30. (1) No president or member of a court-martial, no judge advocate, no party to any proceeding before a court-martial, or his legal practitioner or agent, and no witness acting in obedience to a summons to attend a court-martial, shall, while proceeding to, attending, or returning from a court-martial, be liable to arrest by civil or revenue process. (2) If any such person is arrested under any such process, he may be discharged by order of the court-martial.