feat: metrics

[jpnurmi]

Summary

Implements the Sentry Metrics feature for the native SDK, allowing applications to record counter, gauge, and distribution metrics that are batched and sent to Sentry: https://develop.sentry.dev/sdk/telemetry/metrics/.

Closes #1453

Features

• Three metric types: counter, gauge, and distribution
• Batching: Metrics are buffered and sent in batches (same logic as logs - every 100 items or 5 seconds)
• Attributes: Automatic default attributes (environment, release, SDK info) plus custom user attributes
• Trace context: Metrics are automatically associated with the current trace/span
• Hook: before_send_metric callback for filtering or modifying metrics before sending
• Unit constants: Pre-defined SENTRY_UNIT_* constants for common telemetry units (byte, kilobyte, millisecond, second, etc.)
• Parallel flush/close: Logs and metrics flush and shutdown operations run in parallel for faster sentry_flush() and sentry_close()

Public API

// Enable metrics
sentry_options_set_enable_metrics(options, true);

// Record metrics
sentry_metrics_count("api.requests", 1, sentry_value_new_null());
sentry_metrics_gauge("memory.usage", 1024, SENTRY_UNIT_BYTE, sentry_value_new_null());
sentry_metrics_distribution("response.time", 150.5, SENTRY_UNIT_MILLISECOND, attributes);

Considerations

The current API requires passing sentry_value_new_null() when no custom attributes are needed. An alternative would be to provide simplified variants without the attributes parameter (e.g., sentry_metrics_count()) alongside explicit variants (e.g., sentry_metrics_count_with_attributes()). Feedback welcome on which approach is preferred.

Dependencies

• ref(logs): extract reusable batcher for metrics #1495
• ref(logs): extract attribute helpers for metrics #1497

Test plan

• Unit tests for all metric types (tests/unit/test_metrics.c)
• Integration tests for HTTP transport (tests/test_integration_http.py)
• Tests for custom attributes, before_send_metric hook, and disabled state
• Crash-safe flush behavior tested

[github-actions]

	Fails
🚫	Please consider adding a changelog entry for the next release.

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Instructions and example for changelog

Please add an entry to CHANGELOG.md to the "Unreleased" section. Make sure the entry includes this PR's number.

Example:

## Unreleased

### Features

- metrics ([#1498](https://github.com/getsentry/sentry-native/pull/1498))

If none of the above apply, you can opt out of this check by adding #skip-changelog to the PR description or adding a skip-changelog label.

Generated by 🚫 dangerJS against ca4a0e6

[JoshuaMoelans]

nice work, LGTM! just one small nit on a docstring, and a follow-up for cleaning up our integration test structure

[JoshuaMoelans]

(idea): this integration test file is becoming huge, maybe we should start splitting it up (e.g., additional files for metrics/logs/traces/proxy). I can create a follow-up PR 🧹

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}