Detect and backoff version in metrics exporter

Since backoff==2.0.0, the API of the expo function has changed. The
"porcelain" methods of the backoff library (the decorators
backoff.on_exception and backoff.on_predicate) send a "None" value into
the generator and discard the first yielded value. This is for
compatibility with the more general wait generator API inside the
backoff package.

This commit allows the HTTP OTLP metrics exporter to automatically
detect the behavior of the installed backoff package and adapt
accordingly.

exporter/opentelemetry-exporter-otlp-proto-http/src/opentelemetry/exporter/otlp/proto/http/metric_exporter/__init__.py

@@ -66,8 +66,8 @@
 from opentelemetry.sdk.resources import Resource as SDKResource
 from opentelemetry.util.re import parse_headers
 
+import backoff
 import requests
-from backoff import expo
 
 _logger = logging.getLogger(__name__)
 
@@ -77,6 +77,18 @@
 DEFAULT_METRICS_EXPORT_PATH = "v1/metrics"
 DEFAULT_TIMEOUT = 10  # in seconds
 
+# Work around API change between backoff 1.x and 2.x. Since 2.0.0 the backoff
+# wait generator API requires a first .send(None) before reading the backoff
+# values from the generator.
+_is_backoff_v2 = next(backoff.expo()) is None
+
+
+def _expo(*args, **kwargs):
+    gen = backoff.expo(*args, **kwargs)
+    if _is_backoff_v2:
+        gen.send(None)
+    return gen
+
 
 class OTLPMetricExporter(MetricExporter):
 
@@ -319,7 +331,7 @@ def export(
         **kwargs,
     ) -> MetricExportResult:
         serialized_data = self._translate_data(metrics_data)
-        for delay in expo(max_value=self._MAX_RETRY_TIMEOUT):
+        for delay in _expo(max_value=self._MAX_RETRY_TIMEOUT):
 
             if delay == self._MAX_RETRY_TIMEOUT:
                 return MetricExportResult.FAILURE

exporter/opentelemetry-exporter-otlp-proto-http/tests/metrics/test_otlp_metrics_exporter.py

@@ -16,6 +16,7 @@
 from unittest.mock import patch
 
 import requests
+import responses
 
 from opentelemetry.exporter.otlp.proto.http import Compression
 from opentelemetry.exporter.otlp.proto.http.metric_exporter import (
@@ -269,3 +270,30 @@ def test_serialization(self, mock_post):
             verify=exporter._certificate_file,
             timeout=exporter._timeout,
         )
+
+    @responses.activate
+    @patch("opentelemetry.exporter.otlp.proto.http.metric_exporter.backoff")
+    @patch("opentelemetry.exporter.otlp.proto.http.metric_exporter.sleep")
+    def test_handles_backoff_v2_api(self, mock_sleep, mock_backoff):
+        # In backoff ~= 2.0.0 the first value yielded from expo is None.
+        def generate_delays(*args, **kwargs):
+            yield None
+            yield 1
+
+        mock_backoff.expo.configure_mock(**{"side_effect": generate_delays})
+
+        # return a retryable error
+        responses.add(
+            responses.POST,
+            "http://metrics.example.com/export",
+            json={"error": "something exploded"},
+            status=500,
+        )
+
+        exporter = OTLPMetricExporter(
+            endpoint="http://metrics.example.com/export"
+        )
+        metrics_data = self.metrics["sum_int"]
+
+        exporter.export(metrics_data)
+        mock_sleep.assert_called_once_with(1)