Return carrier name and country for a cell

[karlTGA]

Closes #12. Consumer side: racemap/gears#3681.

/cell and /cells now return operator, country and countryCode alongside the numeric identifiers. All three are null when the combination is unknown — never an empty string, never a guess — so clients fall back to the raw IDs.

"averageSignal": -85,
"operator": "Telekom",
"country": "Germany",
"countryCode": "DE"

Deviations from the issue

Not a MariaDB table. The issue suggested a DB table refreshed by a scheduled download, mirroring the OpenCelliD pipeline. That pipeline exists for ~40M rows changing daily; this table is ~3,600 rows changing a few times a year. A DB-backed version would cost a migration, a schema regen, a fourth background task with its own failure mode, and either a join — which would force explicit .select() into both handlers, currently absent — or a second query per request. And the data would be no fresher, since it still tracks an upstream that publishes a couple of times a year.

Instead the table is compiled into the binary via include_str! and refreshed by scripts/update-mcc-mnc.py, whose output diff is reviewed like any other change. This meets the issue's actual requirement, "scripted and repeatable", at ~50 lines of Rust and no new dependency (csv and once_cell were already in Cargo.toml).

country derives from (mcc, net), not the MCC alone. The issue states country comes from the MCC. That is wrong for 10 MCCs: 310 spans the US, Guam, the US Virgin Islands and the Northern Marianas; 255 spans Ukraine, Moldova and Russia; 425 spans Israel and Palestine. An unknown MNC still falls back to the MCC's dominant country, so the issue's intent — country survives an unknown operator — holds.

Where one MNC is genuinely registered across several territories (Airtel-Vodafone in Guernsey, Jersey and the UK; Docomo in Guam, the Northern Marianas and the USA) nothing in the cell identifiers can disambiguate it, so the table reports the umbrella country rather than guessing a territory.

Design notes

Cell is untouched. It is simultaneously the Diesel row type (Queryable/Selectable/Insertable/QueryableByName) and the wire type, so response-only fields there would break the LOAD DATA INFILE column list, the raw sql_query list, and every exhaustive Cell { … } test literal. CellWithCarrier wraps it with #[serde(flatten)] and Deref, which is why no existing test needed editing.

Its inner field is named inner, not cell — Cell has its own cell field that a matching name shadows instead of reaching through Deref.

Enrichment is applied after pagination. The ORDER BY and the five-branch cursor comparison in query_cells are unchanged.

Coverage on real data

Measured against a local import of 6.79M cells:

• 99.3% resolve to an operator name
• 100% resolve to a country

The remainder are mostly Latin American MVNO ranges (Mexico 334/3 is the largest at ~19k cells); all still get a country from the MCC fallback.

Second commit: pin the Rust toolchain

Three versions were in play — Homebrew 1.89.0 locally, 1.92.0 in the Dockerfile, and whatever ubuntu-latest ships in CI, which pinned no toolchain at all. rust-toolchain.toml pins 1.98.0 for all three, since the CI runners and the rust: images both have rustup and honor it. Note CI's first cargo call will now download that toolchain (~1 min, uncached); adding dtolnay/rust-toolchain to the workflow would make it explicit and cacheable if that is worth it.

Verified against 1.98.0 before pinning: clippy reports the same five pre-existing warnings in data.rs/mod.rs and no new ones.

Verification

• 93 tests pass, including the 17 container tests (cargo test --features integration_tests)
• 9 new tests: 6 covering the lookup (known pair, unknown MNC, unknown MCC, 2- and 3-digit source MNCs against an integer net, multi-country MCC) and 3 pinning the JSON contract (every existing key unchanged, three new camelCase keys, null emitted rather than omitted)
• clippy clean in all new and changed files; cargo fmt --check clean
• end-to-end against a live service on real data: /cell and /cells both enriched, cursor pagination still returns non-overlapping pages
• scripts/update-mcc-mnc.py is byte-deterministic on re-run

Reviewing

src/utils/mcc-mnc.csv is 3,628 generated rows — review scripts/update-mcc-mnc.py instead; it resolves duplicate keys, non-alpha-2 country codes and multi-territory MNCs at generation time so the Rust side is a plain map lookup.

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📝 Walkthrough

Walkthrough

The service adds MCC/MNC carrier lookup data and enriches single-cell and multi-cell responses with operator, country, and country-code fields. It also pins Rust 1.98.0 and updates repository documentation and tooling.

Changes

Carrier metadata enrichment

Layer / File(s)	Summary
MCC/MNC data generation and lookup scripts/update-mcc-mnc.py, src/utils/carrier.rs, src/utils/mod.rs	The generator normalizes upstream records and writes CSV data. The lookup supports exact matches, MCC-level country fallback, and unknown MCC defaults.
Cell metadata wrapper src/models.rs	CellWithCarrier flattens existing cell fields and adds optional operator, country, and countryCode values. Tests cover known and unknown carrier data.
Enriched cell responses src/handlers/cell.rs, src/handlers/cells.rs	Single-cell and multi-cell handlers return enriched cells. Pagination continues to use the original cell results.
Toolchain and API documentation CLAUDE.md, Dockerfile, rust-toolchain.toml, README.md	Repository guidance, Docker images, and local tooling use Rust 1.98.0. API examples document carrier fields and numeric changeable values.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: 🔵 Low · up to 5e871

The PR enriches cell responses with carrier and country data and standardizes the Rust toolchain. It is mergeable with explicit owner awareness because the runtime container still runs as root by default, increasing the potential impact of a service compromise; follow-up should run it as a non-root user.

Sequence Diagram(s)

sequenceDiagram
  participant CellHandler
  participant Database
  participant CellWithCarrier
  participant CarrierLookup
  CellHandler->>Database: Load Cell records
  Database-->>CellHandler: Return Cell records
  CellHandler->>CellWithCarrier: Convert cells
  CellWithCarrier->>CarrierLookup: lookup(mcc, net)
  CarrierLookup-->>CellWithCarrier: Return carrier metadata
  CellWithCarrier-->>CellHandler: Return enriched response

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary change: adding carrier name and country data to cell responses.
Description check	✅ Passed	The description directly explains the new operator, country, and countryCode response fields, fallback behavior, implementation design, and verification results.
Docstring Coverage	✅ Passed	Docstring coverage is 89.47% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 6 files. (1 skipped: 1 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 89.47% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 6 files. (1 skipped: 1 unsupported.)

✨ Finishing Touches

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• Create PR with unit tests
• Commit unit tests in branch 12-return-carrier-name-and-country-for-a-cell

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
In `@CLAUDE.md`:
- Line 28: Update the token-name note in the CONFIG startup guidance to
reference DOWNLOAD_SOURCE_TOKEN consistently with README.md and the code,
removing the stale OPENCELLID_API_KEY name while preserving the DATABASE_URL
requirement and .env setup guidance.

In `@Dockerfile`:
- Line 7: Add a dedicated non-root runtime user in the Dockerfile, grant it only
the permissions required by /run.sh and the service, and set it with a USER
instruction for the runtime stage. Ensure /run.sh remains executable and the
service can access its required files and directories.

In `@README.md`:
- Line 74: Update the DOWNLOAD_SOURCE_TOKEN entry in the README to use the
correct service name, OpenCellID, instead of OpenCellDD; leave the rest of the
documentation unchanged.
- Around line 312-318: Remove the README example documenting the unavailable
POST /cells/lookup endpoint, unless that route is actually implemented in the
relevant source; do not document a response for an unsupported endpoint.
- Line 46: Update the README statement near the null contract to distinguish
unknown network keys with a known MCC from cases without an MCC fallback:
document that the fallback may populate country and countryCode while operator
remains null, and reserve the all-null claim for lookups with no MCC fallback.

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