Parse the native histogram sum as a float

_parse_nh_struct parsed the sum field with int(), so a native histogram
whose sum is not integral failed to parse with

    ValueError: invalid literal for int() with base 10: '100.5'

NativeHistogram.sum_value is a float and the OpenMetrics writer emits the
sum verbatim (e.g. sum:100.5), so the library could not parse its own
output for the common case of a non-integer sum. Parse sum with float()
to match; count, schema and zero_count remain int as they are genuinely
integers.

Add test_native_histogram_float_sum, which parses a native histogram
with a fractional sum and checks it round-trips to sum_value 100.5.

Signed-off-by: Sean Kim <skim8705@gmail.com>

Author: sean-kim05

prometheus_client/openmetrics/parser.py

@@ -315,7 +315,7 @@ def _parse_nh_struct(text):
     deltas = dict(re_deltas.findall(text))
 
     count_value = int(items['count'])
-    sum_value = int(items['sum'])
+    sum_value = float(items['sum'])
     schema = int(items['schema'])
     zero_threshold = float(items['zero_threshold'])
     zero_count = int(items['zero_count'])

tests/openmetrics/test_parser.py

@@ -218,6 +218,18 @@ def test_native_histogram(self):
         hfm.add_sample("nativehistogram", None, None, None, None, NativeHistogram(24, 100, 0, 0.001, 4, (BucketSpan(0, 2), BucketSpan(1, 2)), (BucketSpan(0, 2), BucketSpan(1, 2)), (2, 1, -3, 3), (2, 1, -2, 3)))
         self.assertEqual([hfm], families)
 
+    def test_native_histogram_float_sum(self):
+        families = text_string_to_metric_families("""# TYPE nativehistogram histogram
+# HELP nativehistogram Is a basic example of a native histogram
+nativehistogram {count:24,sum:100.5,schema:0,zero_threshold:0.001,zero_count:4,positive_spans:[0:2,1:2],negative_spans:[0:2,1:2],positive_deltas:[2,1,-3,3],negative_deltas:[2,1,-2,3]}
+# EOF
+""")
+        families = list(families)
+
+        hfm = HistogramMetricFamily("nativehistogram", "Is a basic example of a native histogram")
+        hfm.add_sample("nativehistogram", None, None, None, None, NativeHistogram(24, 100.5, 0, 0.001, 4, (BucketSpan(0, 2), BucketSpan(1, 2)), (BucketSpan(0, 2), BucketSpan(1, 2)), (2, 1, -3, 3), (2, 1, -2, 3)))
+        self.assertEqual([hfm], families)
+
     def test_native_histogram_utf8(self):
         families = text_string_to_metric_families("""# TYPE "native{histogram" histogram
 # HELP "native{histogram" Is a basic example of a native histogram