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Parse negative span offsets in OpenMetrics native histograms #1233

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Parse negative span offsets in OpenMetrics native histograms #1233

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2 changes: 1 addition & 1 deletion prometheus_client/openmetrics/parser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -307,7 +307,7 @@ def _parse_nh_sample(text, suffixes):

def _parse_nh_struct(text):
pattern = r'(\w+):\s*([^,}]+)'
re_spans = re.compile(r'(positive_spans|negative_spans):\[(\d+:\d+(,\d+:\d+)*)\]')
re_spans = re.compile(r'(positive_spans|negative_spans):\[(-?\d+:\d+(,-?\d+:\d+)*)\]')

@csmarchbanks csmarchbanks Nov 12, 2026

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In the most recent spec it says that only the first span in the list can be negative: https://github.com/prometheus/docs/blob/fddf99df785ab8be4275455d0f4369940520cd63/docs/specs/om/open_metrics_spec_2_0.md?plain=1#L1006. I think it would be nice to enforce that here as well.

re_deltas = re.compile(r'(positive_deltas|negative_deltas):\[(-?\d+(?:,-?\d+)*)\]')

items = dict(re.findall(pattern, text))
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12 changes: 12 additions & 0 deletions tests/openmetrics/test_parser.py
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Expand Up @@ -266,6 +266,18 @@ def test_native_histogram_three_pos_spans_no_neg_spans_or_deltas(self):
hfm.add_sample("nhsp", None, None, None, None, NativeHistogram(4, 6, 3, 2.938735877055719e-39, 1, (BucketSpan(0, 1), BucketSpan(7, 1), BucketSpan(4, 1)), None, (1, 0, 0), None))
self.assertEqual([hfm], families)

def test_native_histogram_negative_span_offsets(self):
families = text_string_to_metric_families("""# TYPE nhneg histogram
# HELP nhneg Is a native histogram whose first spans start at negative bucket indexes
nhneg {count:5,sum:-1.5,schema:0,zero_threshold:0.001,zero_count:0,positive_spans:[-2:2],negative_spans:[-1:1,2:1],positive_deltas:[1,1],negative_deltas:[1,0]}
# EOF
""")
families = list(families)

hfm = HistogramMetricFamily("nhneg", "Is a native histogram whose first spans start at negative bucket indexes")
hfm.add_sample("nhneg", None, None, None, None, NativeHistogram(5, -1.5, 0, 0.001, 0, (BucketSpan(-2, 2),), (BucketSpan(-1, 1), BucketSpan(2, 1)), (1, 1), (1, 0)))
self.assertEqual([hfm], families)

def test_native_histogram_with_labels(self):
families = text_string_to_metric_families("""# TYPE hist_w_labels histogram
# HELP hist_w_labels Is a basic example of a native histogram with labels
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