Summary

Found while reviewing the repo for high-value bugfixes. Two latent bugs in _walk_pages and the parallel pagination loop in get_stats_data (dataretrieval/waterdata/utils.py) cause silent or misleading failures whenever a paginated waterdata request is interrupted mid-walk.

Bug 1 — resp is stale when client.request() itself raises

while curr_url:
    try:
        resp = client.request(...)              # ← may raise ConnectionError, Timeout, …
        dfs.append(_get_resp_data(resp, geopd))
        curr_url = _next_req_url(resp)
    except Exception:
        error_text = _error_body(resp)          # ← uses *previous* page's resp
        logger.error("Request incomplete. %s", error_text)
        ...

When the network call raises before resp is reassigned, resp still references the previous successful page. The log message thus describes the wrong response, and _error_body() falls into resp.json() on a 200 OK body that wasn't an error envelope — which can itself raise and bury the original failure.

Bug 2 — no status-code check on mid-pagination responses

The initial request gate at line 615 reads if resp.status_code != 200: raise RuntimeError(_error_body(resp)). The pagination loop does not. So a 5xx response with a JSON error body that lacks numberReturned flows into _get_resp_data(), which silently returns an empty DataFrame; _next_req_url() finds no next link; and the loop exits with no error logged anywhere. The caller gets truncated data and never knows.

This affects every paginated waterdata getter: get_daily, get_continuous, get_monitoring_locations, get_time_series_metadata, get_combined_metadata, get_field_measurements, get_field_measurements_metadata, get_peaks, get_channel, get_reference_table, plus the stats getters (get_stats_por, get_stats_date_range).

Fix

Two-line change to each loop:

if resp.status_code != 200:
    raise RuntimeError(_error_body(resp))

…immediately after client.request(...) (mirrors the initial-request gate). And:

except Exception as e:
    logger.error("Request incomplete: %s", e)

…instead of _error_body(resp), so the actual exception text surfaces — works for both the network-error case (uses the exception) and the 5xx case (uses the RuntimeError(_error_body(resp)) we just raised on a fresh resp).

The "best-effort" behavior is preserved: on failure the loop still logs and returns whatever pages were collected. The change is purely to make the failure observable and the log message accurate.

Test plan

• test_walk_pages_logs_actual_exception_when_request_raises — simulates a ConnectionError mid-pagination, asserts the logged error reflects the actual exception ("boom") rather than something derived from a stale prior-page response.
• test_walk_pages_surfaces_5xx_mid_pagination — page 2 returns HTTP 503 with a JSON body, asserts the 503 / ServiceUnavailable shows up in the error log. Previously this was silently swallowed.
• Existing test_walk_pages_multiple_mocked (happy path) still passes.
• Full mocked test suite: 278 passed, ruff + format clean.

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