René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Background node process corrupts terminal state with tcsetattr() on exit","articleBody":"* **Version**: v14.9.0\r\n* **Platform**: NixOS 21.03, Linux 5.8.11 x86_64\r\n* **Subsystem**: `ResetStdio` in `src/node.cc`\r\n\r\nIn Bash, run the following:\r\n\r\n```bash\r\nnode -e 'setTimeout(() =\u003e {}, 2000)' \u0026 sleep 1\r\n```\r\n\r\nThis launches `node -e 'setTimeout(() =\u003e {}, 2000)'` in the background and `sleep 1` in the foreground. After 1 second, control returns to Bash. After 2 seconds, Node exits and corrupts Bash’s terminal state:\r\n\r\n* the ↑, ↓, →, ← arrow keys start printing `^[[A`, `^[[B`, `^[[C`, `^[[D` instead of scrolling through the Bash history or moving the insert point,\r\n* the Tab key starts moving the cursor 8 spaces forward instead of Tab-completing the command,\r\n* Ctrl+A and Ctrl+E print `^A` and `^E` instead of jumping to the beginning and end of the command, etc.\r\n\r\nThis happens when the `ResetStdio` handler uses `tcsetattr` to “restore” the terminal to the state it was in when Node started (#24260). This interferes with Bash, which uses and expects a different terminal state than `sleep 1`.\r\n\r\n(The bug is sometimes reproducible without the `sleep 1` depending on whether Node records the initial terminal state before Bash updates it, but the `sleep 1` makes it reliable.)\r\n\r\nNormally, the terminal state would be protected from such undesired modifications by a background process: the kernel generates `SIGTTOU` to suspend the process until it’s brought to the foreground. But `ResetStdio` now deliberately overrides this protection by blocking `SIGTTOU` (#28535).\r\n\r\nIMO, both #24260 and #28535 should be reverted. Node is a programming language; it should never make changes to the terminal state that programs did not request.","author":{"url":"https://github.com/andersk","@type":"Person","name":"andersk"},"datePublished":"2020-10-07T05:28:25.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":9},"url":"https://github.com/35536/node/issues/35536"}