feat(storage): add OpenTelemetry metrics gating and configuration module (#18407)

Introduce the foundational OpenTelemetry client metrics gating and
configuration module for Google Cloud Storage.

- Add `_opentelemetry_metrics.py` with a development gate
(`_ENABLE_METRICS_DEV_GATE`) and environment variable parsing
(`GCP_STORAGE_PYTHON_ENABLE_OTEL_METRICS`,
`GCP_STORAGE_PYTHON_ENABLE_OTEL_DEBUG_METRICS`).
- Implement `is_metrics_enabled()` and `is_advanced_metrics_enabled()`
evaluation helpers with precedence hierarchy (dev gate -> client setting
-> environment variable -> default).
- Provide `get_common_attributes()` and `get_meter()` helpers for
OpenTelemetry metrics instrumentation.
- Add unit tests in `test__opentelemetry_metrics.py` covering gating
resolution, environment variable overrides, `ImportError` fallback, and
attribute helpers.

Author: shradhakatyal

packages/google-cloud-storage/google/cloud/storage/_opentelemetry_metrics.py

@@ -0,0 +1,180 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Manages OpenTelemetry metrics instruments and gating for GCS client."""
+
+import logging
+import os
+from typing import Any, Dict, Optional
+
+from google.cloud.storage.version import __version__
+
+logger = logging.getLogger(__name__)
+
+# ---------------------------------------------------------------------------
+# 1. Hidden Development Gate
+# ---------------------------------------------------------------------------
+# Must remain False in production branches.
+# Only enabled during active development and test runs.
+_ENABLE_METRICS_DEV_GATE = False
+
+# ---------------------------------------------------------------------------
+# 2. Standardized Configuration and Environment Variable Names
+# ---------------------------------------------------------------------------
+ENABLE_OTEL_METRICS_ENV_VAR = "GCP_STORAGE_PYTHON_ENABLE_OTEL_METRICS"
+ENABLE_OTEL_DEBUG_METRICS_ENV_VAR = "GCP_STORAGE_PYTHON_ENABLE_OTEL_DEBUG_METRICS"
+
+_DEFAULT_ENABLE_METRICS = False
+_DEFAULT_ENABLE_DEBUG_METRICS = False
+
+# ---------------------------------------------------------------------------
+# 3. Optional OpenTelemetry Dependency Check
+# ---------------------------------------------------------------------------
+try:
+    from opentelemetry import metrics
+
+    HAS_OPENTELEMETRY_METRICS = True
+except ImportError:
+    HAS_OPENTELEMETRY_METRICS = False
+    logger.debug(
+        "OpenTelemetry metrics package (opentelemetry-api >= 1.12.0) is not "
+        "installed. GCS client metrics are disabled."
+    )
+
+
+_TRUTHY_ENV_VALUES = {"1", "true", "yes", "on"}
+_FALSY_ENV_VALUES = {"0", "false", "no", "off"}
+
+
+def _parse_bool_env(name: str, default: bool = False) -> bool:
+    """Parses a boolean from an environment variable."""
+    val = os.environ.get(name)
+    if val is None:
+        return default
+    normalized = val.strip().lower()
+    if not normalized:
+        return default
+    if normalized in _TRUTHY_ENV_VALUES:
+        return True
+    if normalized in _FALSY_ENV_VALUES:
+        return False
+    logger.warning(
+        "Unrecognized boolean value %r for environment variable %s; using default %s.",
+        val,
+        name,
+        default,
+    )
+    return default
+
+
+def is_metrics_enabled(enable_metrics: Optional[bool] = None) -> bool:
+    """Evaluates whether standard GCS metrics should be recorded.
+
+    Args:
+        enable_metrics: Optional boolean configured on the client instance.
+            Takes precedence over the environment variable if specified.
+
+    Returns:
+        bool: True if metrics recording is enabled, False otherwise.
+    """
+    if enable_metrics is not None and not isinstance(enable_metrics, bool):
+        raise TypeError("enable_metrics must be a boolean or None.")
+
+    if not HAS_OPENTELEMETRY_METRICS:
+        return False
+
+    if not _ENABLE_METRICS_DEV_GATE:
+        return False
+
+    if enable_metrics is not None:
+        return enable_metrics
+
+    return _parse_bool_env(ENABLE_OTEL_METRICS_ENV_VAR, _DEFAULT_ENABLE_METRICS)
+
+
+def is_debug_metrics_enabled(
+    enable_debug_metrics: Optional[bool] = None,
+) -> bool:
+    """Evaluates whether high-frequency debug metrics should be recorded.
+
+    Args:
+        enable_debug_metrics: Optional boolean configured on the client
+            instance. Takes precedence over the environment variable if
+            specified.
+
+    Returns:
+        bool: True if debug metrics recording is enabled, False otherwise.
+    """
+    if enable_debug_metrics is not None and not isinstance(enable_debug_metrics, bool):
+        raise TypeError("enable_debug_metrics must be a boolean or None.")
+
+    if not HAS_OPENTELEMETRY_METRICS:
+        return False
+
+    if not _ENABLE_METRICS_DEV_GATE:
+        return False
+
+    if enable_debug_metrics is not None:
+        return enable_debug_metrics
+
+    return _parse_bool_env(
+        ENABLE_OTEL_DEBUG_METRICS_ENV_VAR, _DEFAULT_ENABLE_DEBUG_METRICS
+    )
+
+
+# ---------------------------------------------------------------------------
+# 4. Standard Common Attributes & Meter Provider
+# ---------------------------------------------------------------------------
+_COMMON_ATTRIBUTES: Dict[str, Any] = {
+    "gcp.client.service": "storage",
+    "gcp.client.version": __version__,
+    "gcp.client.repo": "googleapis/google-cloud-python",
+    "gcp.client.artifact": "google-cloud-storage",
+}
+
+
+def get_common_attributes() -> Dict[str, Any]:
+    """Returns a copy of standard GCS client attributes for metrics."""
+    return _COMMON_ATTRIBUTES.copy()
+
+
+def get_meter(
+    enable_metrics: Optional[bool] = None,
+    enable_debug_metrics: Optional[bool] = None,
+    meter_provider: Optional[Any] = None,
+) -> Optional[Any]:
+    """Returns the OpenTelemetry Meter for Google Cloud Storage.
+
+    Args:
+        enable_metrics: Optional boolean configured on the client instance for
+            standard metrics.
+        enable_debug_metrics: Optional boolean configured on the client
+            instance for debug metrics.
+        meter_provider: Optional custom OpenTelemetry MeterProvider instance.
+            Defaults to the global MeterProvider if None.
+
+    Returns:
+        Optional[Any]: The OpenTelemetry Meter instance if standard or debug
+            metrics are enabled, or None otherwise.
+    """
+    if not (
+        is_metrics_enabled(enable_metrics)
+        or is_debug_metrics_enabled(enable_debug_metrics)
+    ):
+        return None
+    return metrics.get_meter(
+        "google.cloud.storage",
+        __version__,
+        meter_provider=meter_provider,
+    )