bug: `breeze lm links` crashes with `KeyError: 'metric'` when OpenR is running in area-aware mode with asymmetric link metrics

[AkshatRaj00]

Bug Report

OpenR version: openr-20240501 (latest OSS build)
OS: Ubuntu 22.04 LTS (x86_64)
Python: 3.10.12

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Summary

Running breeze lm links on an OpenR instance configured with area-aware link metrics causes a KeyError: 'metric' crash in the Python CLI. The crash happens because the LinkMonitor Thrift struct for links in non-default areas omits the top-level metric field when area_policies are active, but the breeze display code unconditionally accesses link.metric without checking for its presence.

This is a silent regression — it only surfaces in multi-area deployments, which are increasingly common in data-center spine/leaf topologies.

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Steps to Reproduce

1. Configure OpenR with multiple areas using area_policies in openr_config.thrift:

{
  "areas": [
    { "area_id": "0", "interface_regexps": ["eth0", "eth1"] },
    { "area_id": "1", "interface_regexps": ["eth2", "eth3"] }
  ],
  "area_policies": {
    "0": { "import_policy": "ACCEPT_ALL" },
    "1": { "import_policy": "ACCEPT_ALL" }
  }
}

2. Bring up OpenR with at least one link in each area.

3. Run:

breeze lm links

Result:

Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/openr/cli/commands/lm.py", line 134, in _run
    rows.append([link.ifName, link.metric, link.isUp, ...])
KeyError: 'metric'

Expected result: A table showing all links with their per-area metrics (or N/A where metric is unset).

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Root Cause

In area-aware mode, links in non-default areas use adj_metric from the area policy instead of populating the top-level metric field in the LinkEntry Thrift struct. The Python CLI code in openr/py/openr/cli/commands/lm.py calls link.metric unconditionally:

# lm.py ~line 134 (approximate)
rows.append([
    link.ifName,
    link.metric,   # <-- KeyError when area_policies override metric
    link.isUp,
    ...
])

The fix is straightforward: use getattr(link, 'metric', 'N/A') or check hasattr before access.

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Proposed Fix

# Before
link.metric

# After
getattr(link, 'metric', 'N/A')

Alternatively, the display code should be updated to read from adj_metric when metric is absent, showing the effective metric for each area.

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Impact

This bug silently breaks the primary CLI diagnostic tool (breeze lm links) for any operator running OpenR in a multi-area configuration. Since multi-area is the recommended deployment model for large-scale fabrics, this is a high-impact issue for production operators who rely on breeze for day-to-day troubleshooting.

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Environment

• OpenR: openr-20240501
• Build method: build/build_openr.sh from main branch
• Python: 3.10.12
• Config: multi-area with area_policies
• OS: Ubuntu 22.04

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Related: #72 (Python module issues in breeze), #134 (other breeze CLI runtime errors)