fix(core): lose every packet at 100% loss with a run length set - #214
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burst_loss_params returned (1.0, r, 1.0) for total loss: a two-state chain meant to stay in the bad state, which still leaves it with probability r and lets that packet through. 100% loss in runs of 2, 4, 6 and 8 delivered 66.6, 79.9, 85.6 and 88.9%, while "achievable" said 100%, so neither the apply log nor the summary strip noticed. The shipped mobile-lte-to-3g scenario hits it at 60 s, where "loss": 100 inherits a run length of 8. Total loss now takes the independent draw: every packet is dropped with the same single draw per packet, so a seed replays the same way, and nothing below 100% changes. The log and the strip ask the same function, so they stop describing runs that do not exist. The run counter stays at 0 at 100%, and its tooltip and the README now say so. With asymmetry on, the upload walks its own chain from its own loss, but only the download was described: an upload loss the runs could not carry was clamped in silence, and the strip showed the upload loss without its run length. Both directions are now described, the upload only while the switch is on. The test that asserted the old tuple is rewritten on purpose. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Navigate logical layers of code changes, visualize relationships, and explore their blast radius. 📝 WalkthroughWalkthroughTotal loss now drops every packet without modeling burst runs. Burst-loss diagnostics and summary descriptions also cover upload settings when asymmetry is enabled. ChangesBurst loss behavior and reporting
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix · Severity of issue fixed: Low Sequence Diagram(s)sequenceDiagram
participant ApplySettings as apply_settings
participant Diagnostics as _say_burst_loss_for
participant BurstParams as burst_loss_params
participant Messages as Direction-specific message keys
ApplySettings->>Diagnostics: Pass settings getter
Diagnostics->>BurstParams: Get parameters for each active direction
BurstParams-->>Diagnostics: Return parameters or None
Diagnostics->>Messages: Select clamp and gap messages
Suggested labels: Merge Risk: 🔵 Low · up to The packet-loss behavior has no established remaining defect, but the zero-run tooltip can mislead users and the new test path should follow the project’s Python convention. Both are bounded corrections. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The change makes configured 100% packet loss behave as a full outage and makes the displayed behavior more accurate. Review found no new route to configure traffic or bypass of an existing control. Residual uncertainty concerns live reconfiguration and the limited security coverage, not an identified new vulnerability. Retained concerns Security review detailsSecurity Blast Radius
Trust Boundaries and Controls
Resilience and Maintainability Implications
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Review comments at @lang/en.json:
- Line 595: Update the stat_loss_runs tooltip so zero runs can mean either the
session was too short or every packet was lost; preserve the separate
clarification that 100% loss produces no runs to count. Apply the equivalent
wording in lang/en.json lines 595-595, lang/pl.json lines 595-595, and
lang/zh.json lines 595-595.
Review comments at @tests/test_burst_loss.py:
- Around line 507-508: Update the scenario path passed to load_scenario_file to
use pathlib by composing Path(ROOT) with the scenarios directory and filename;
keep the os import only if it is used elsewhere in the module.
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🪛 ast-grep (0.45.3)
tests/test_burst_loss.py
[info] 482-482: use secrets package over random package
Context: random.Random(9)
Note: [CWE-330] Use of Insufficiently Random Values.
(avoid-random-python)
[info] 486-486: use secrets package over random package
Context: random.Random(9)
Note: [CWE-330] Use of Insufficiently Random Values.
(avoid-random-python)
| "tips.stat_local": "Packets to/from the local network dropped by \"Internet only\".", | ||
| "tips.stat_loss": "Packets dropped because of the configured Loss. Link outages are counted separately, under Link outage.", | ||
| "tips.stat_loss_runs": "How many runs of lost packets this session produced. Zero with \"Losses in a row\" set means the session was too short to see one, not that nothing was configured.", | ||
| "tips.stat_loss_runs": "How many runs of lost packets this session produced. Zero with \"Losses in a row\" set means the session was too short to see one, not that nothing was configured. At 100% loss every packet is lost, so there are no separate runs to count.", |
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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win
Make the zero-run tooltip consistent with total loss. Each tooltip first says zero runs mean the session was too short. At 100% loss, the counter stays at zero regardless of session length.
lang/en.json#L595-L595: say zero can mean a short session or 100% loss.lang/pl.json#L595-L595: make the same distinction in Polish.lang/zh.json#L595-L595: make the same distinction in Chinese.
As per path instructions, "Text must agree with the state it describes."
📍 Affects 3 files
lang/en.json#L595-L595(this comment)lang/pl.json#L595-L595lang/zh.json#L595-L595
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Review comment at @lang/en.json at line 595:
Update the stat_loss_runs tooltip so zero runs can mean either the session was
too short or every packet was lost; preserve the separate clarification that
100% loss produces no runs to count. Apply the equivalent wording in
lang/en.json lines 595-595, lang/pl.json lines 595-595, and lang/zh.json lines
595-595.
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| scenario = load_scenario_file(os.path.join(ROOT, "scenarios", | ||
| "mobile-lte-to-3g.json")) |
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sed -n '175,205p' beantester/scenario.py
rg -n '^(ROOT|def load_scenario_file)|Path\\(ROOT\\)' beantester tests | head -50Repository: donislawdev/BeanNetworkTester
Length of output: 2706
Build the scenario file path with pathlib.
The test path uses os.path.join for a file read. The loader accepts the resulting path, so os.path.join is not required by its contract. Use Path(ROOT) / "scenarios" / "mobile-lte-to-3g.json" and retain os only if the module uses it elsewhere.
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Review comment at @tests/test_burst_loss.py around lines 507 - 508:
Update the scenario path passed to load_scenario_file to use pathlib by
composing Path(ROOT) with the scenarios directory and filename; keep the os
import only if it is used elsewhere in the module.
After applying the fix, consider running `coderabbit review --agent` for local
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What was wrong
100% loss with a run length let packets through.
burst_loss_params(1.0, b)returned(1.0, r, 1.0): a two-state chain meant to "stay bad", which still leaves the bad state with probabilityr, and the packet it leaves on goes through.achievablesaid 100%, so nothing warned.The shipped
scenarios/mobile-lte-to-3g.jsonhits it at 60 s:"loss": 100inherits"loss_burst": 8from the step before, so its full outage let about one packet in nine through. A sweep of every preset and every shipped scenario step found no other case. The apply log also saidLoss will arrive in runs of about 6 packets, roughly one run every 6 packets.and the strip said100% loss, in runs of 6 packets, for runs that do not exist.With asymmetry on, the upload's runs were never described. The upload walks its own chain derived from its own loss, so it clamps on its own: 95% upload loss in runs of 5 delivered 83.45% with an empty log, and the strip showed
upload: 95% losswithout the run length.What changes
core.burst_loss_params: total loss returnsNone, the independent draw. At 1.0 it drops every packet with the same single draw per packet the chain makes, so a seed replays the same way. Checked with the function patched in memory before writing the fix: nothing below 100% changed in 42 cases (loss 0.5-99.99 x run length 0-1000, comparing verdicts, RNG state and run counter).settings.apply_settings: the burst lines are said per direction through a helper (apply_settingsgains no branch, and the lines still come before the batch opens). The upload is said only while asymmetry is on, because its values are not read otherwise. New keyslog.loss_burst_clamped_upandlog.loss_burst_gap_upin en/pl/zh. At 100% nothing is said, which is the same silence as a run length with no loss.summary: the upload half gets its run length through_loss_parts, which asksburst_loss_paramsjust as the download half does. The download half stays inline insettings_summary, and a comment there says why: that function ismax-complexity, and sharing the helper lowered it to 24, which turned the ceiling test red. Following it down would have leftdecidewith no room and doubled the near-ceiling count, so the ratchets are untouched.tips.stat_loss_runsand the READMEloss_runsrow said a 0 with a run length set means the session was too short. Both now also name 100%.Behaviour change on purpose: a stored
Reproduce:command with--loss 100and a run length now replays into a session that loses every packet.Tests
test_total_loss_does_not_divide_by_zeroasserted the buggy tuple. It is nowtest_total_loss_is_left_to_the_independent_draw.tests/test_burst_loss.py. The answer is per direction and three places read it, so each reader is driven in both directions:test_total_loss_loses_every_packet_whatever_the_run_lengthtest_total_loss_makes_one_draw_per_packet_like_the_chain_didtest_the_shipped_lte_to_3g_outage_loses_everything(scenario step ->apply_settings-> engine -> core)test_total_loss_says_nothing_about_runstest_an_upload_the_runs_cannot_carry_is_said_out_loudtest_upload_values_the_session_does_not_read_are_not_saidtest_the_summary_strip_names_the_runs_each_direction_really_getstools/mutate.py: total loss walks the chain; the upload's lines go unsaid; leftover upload values are said with asymmetry off; the upload strip loses its run length; the upload half and the download half each compare the run length instead of asking.Run locally: the guards for the changed files plus ruff and mypy (
internal_tools/guards.py --strong --run --lint, 97 files, includingtests/test_version_and_release.py,tests/test_readme_guards.pyandtests/test_i18n.py), then the tests ofsummary.pyagain after the ceiling fix. One red in that run,test_repeated_start_stop_cycles_do_not_stack_resolver_threads, is an existing timing flake: paired runs came out 0/12 on this branch and 0/12 onmaster, and no resolver code changed. Not run locally: the full suite (it runs here on Linux and Windows) and the real-network burst rig, which runs at release. The fix is in the pure decision function, on the only path step 8 takes.🤖 Generated with Claude Code
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