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The docker_exec console resized its exec PTY to 80x24 until a client sent NAWS. CLIs that page on the PTY window size instead of the terminal length (the IOS-XR pager) therefore parked long output at --More-- for clients that never negotiate NAWS — netmiko, bare telnet — making copilot device commands time out on XRd. Default the exec to 511x10000 instead (511 matches netmiko's own 'terminal width 511' convention): no paging and no hard wrapping for non-NAWS clients, while real NAWS clients keep resizing to their actual geometry as before. Also updates the project memory record with the confirmed root cause and the fix.
73 lines
5.2 KiB
Markdown
73 lines
5.2 KiB
Markdown
# XRd Console --More-- Pager Bug (PTY window size paging vs terminal length 0)
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## Background
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Copilot commands with long output consistently failed against XRd (IOS XRv 9000 container) nodes: `device_show_run` running `show ipv4 interface brief` always reported `netmiko_multiline (failed)` (even as a single command); short-output commands like `show ipv4 interface <iface>` worked fine.
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Failure sequence (from the 2026-08-18 logs):
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1. First failure: `ReadTimeout: Pattern not detected: 'RP/0/RP0/CPU0:ios\#'` — the command echo matched, but the prompt never appeared within 60s
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2. The copilot's single-retry reused the same netmiko session (nornir caches it on the host object) with half-consumed output in the buffer → the second failure died earlier in `command_echo_read` — a follow-on effect of the dirty session, not an independent fault
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## Root Cause (fully traced)
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The XRd node uses the `docker_exec` console type (`gns3server/compute/docker/vendor_docker_vm.py`, `_LazyExecTelnetServer`): a telnet TCP server whose backend is a `docker exec` PTY. Three facts combine:
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1. The XR pager (at least for table-engine/TABLAST-style commands) pages on the **PTY window size (TIOCGWINSZ)**, not the CLI-level `terminal length` — `show terminal` happily reports `Length: 0 lines` while output still pages
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2. `_LazyExecTelnetServer.client_connected_hook` explicitly resized the exec PTY to **80×24** "before NAWS" (`await self._on_naws(80, 24)`) — the 24 rows were **our own initial geometry, not a Docker default**. Live test: `show ipv4 interface brief` paged after exactly 24 lines
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3. netmiko's telnetlib never negotiates **NAWS**, so the initial geometry is never corrected for copilot/bare-telnet clients. Real NAWS clients resize to their own geometry via the existing `_on_naws` → `POST /exec/{id}/resize` wiring
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### Dead ends (do not retry)
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- `show ipv4 interface brief | no-more` → `% Invalid input detected`. `| no-more` is a **Junos** pipe modifier; IOS-XR does not have it
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- `terminal length 0`: takes effect at the CLI layer, but this pager ignores it
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- The XR CLI has no command to change PTY rows
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### Related fact: paramiko vs docker_exec
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paramiko (SSH) cannot connect to a `docker_exec` console — the client-side endpoint is a plain telnet server (`AsyncioTelnetServer`); only `console_type: ssh` (standard attach path, `AsyncioSSHServer`) speaks SSH. The copilot correctly uses netmiko `*_telnet` drivers (netmiko's vendored `_telnetlib`, stdlib-free on Python 3.13).
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## Decision/Implementation
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### Fix (implemented 2026-08-18, branch `feat/docker-exec-default-pty-geometry`)
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Change the initial exec geometry in `vendor_docker_vm.py` `client_connected_hook` from 80×24 to **511×10000** (`await self._on_naws(511, 10000)`):
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- Tall/wide default so CLIs that page on PTY rows never hit `--More--` for clients that never send NAWS (netmiko, bare telnet)
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- Width 511 matches netmiko's `terminal width 511` convention
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- Real NAWS clients still resize to their actual geometry right after connecting (existing `_on_naws` path unchanged)
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- Test: `test_first_connect_sets_tall_default_pty_geometry` in `tests/compute/docker/test_vendor_docker_vm.py`
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### Fallback design (NOT implemented — keep if the pager ever resurfaces on another console type)
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Channel-level loop answering `--More--` in the copilot display tool for `cisco_xr*`: prompt regex breaks; **tail-anchored** `re.search(r"--More--\s*$", buf)` with a ~150ms quiet double-confirmation before `write_channel(" ")`. Never put `--More--` into netmiko's `expect_string` — expect `re.search`es accumulated output, so content containing "More" would false-trigger.
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### Still-open copilot improvements (agreed, not yet implemented)
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1. Reconnect before retry: `_run_all_device_configs_with_single_retry` (display tool) and the config tool's retry should `task.host.close_connection("netmiko")` first — retrying on a dirty session is doomed
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2. `session_log_file` in hosts_data netmiko extras — the copilot has no session_log anywhere, which made this bug a guessing game
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## Rationale
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Resizing the PTY at exec creation attacks the root (geometry is fixed before the CLI outputs anything); it covers every consumer of the docker_exec console (copilot, MCP, bare telnet) with a one-line change, while the `--More--` auto-answer design remains as a generic fallback for consoles without a resize path.
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## Related Files
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- `gns3server/compute/docker/vendor_docker_vm.py` — `_LazyExecTelnetServer`: `_on_naws` (exec resize), `_create_exec` (Tty=True, TERM=xterm), `client_connected_hook` (initial geometry — the fix)
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- `gns3server/compute/docker/docker_vm.py:1074-1087` — standard console path: NAWS → `containers/{cid}/resize`
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- `gns3server/agent/gns3_copilot/tools_v2/display_tools_nornir.py:284-341` — dirty-session retry (open item)
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- `gns3server/agent/gns3_copilot/utils/get_gns3_device_port.py` — hosts_data (session_log extras insertion point)
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## Examples
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Live console transcript (2026-08-17):
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```
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RP/0/RP0/CPU0:ios#show terminal
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Length: 0 lines, Width: 511 columns <- CLI-layer setting in effect
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RP/0/RP0/CPU0:ios#show ipv4 interface brief
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(exactly 24 lines: timestamp + blank + header + 21 interface rows)
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--More-- <- the 80x24 initial exec geometry was paging
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```
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