fix(opentelemetry-exporter-prometheus): handle additional edge cases in metric name conversion

experimental/CHANGELOG.md

@@ -20,6 +20,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 * fix(sdk-node): warn and ignore zero exporter timeout in declarative config [#6711](https://github.com/open-telemetry/opentelemetry-js/pull/6711) @MikeGoldsmith
 * fix(sdk-node): pass gRPC credentials and headers to span exporter in declarative config [#6705](https://github.com/open-telemetry/opentelemetry-js/pull/6705) @MikeGoldsmith
 * fix(otlp-transformer): do not attempt to skip groups [#6704](https://github.com/open-telemetry/opentelemetry-js/pull/6704) @pichlermarc
+* fix(opentelemetry-exporter-prometheus): handle additional edge cases in metric name conversion [#6727](https://github.com/open-telemetry/opentelemetry-js/pull/6727) @cjihrig
 
 ### :books: Documentation
 
@@ -76,6 +77,9 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 * fix(instrumentation-xhr): resolve relative URLs before matching `ignoreUrls` [#6551](https://github.com/open-telemetry/opentelemetry-js/pull/6551) @Maximiliano-Zeballos
 * fix(sdk-node): fix setting of ViewOption#name from ConfigurationModel [#6620](https://github.com/open-telemetry/opentelemetry-js/pull/6620) @trentm
 * fix(web-common): add limit for timeout [#6601](https://github.com/open-telemetry/opentelemetry-js/pull/6601) @maryliag
+
+### :books: Documentation
+
 * fix(otlp-transformer): pin protobufjs@8.0.1 as protobufjs@8.0.3 is broken for browser use [#6646](https://github.com/open-telemetry/opentelemetry-js/pull/6646)
 
 ### :house: Internal

experimental/packages/opentelemetry-exporter-prometheus/src/PrometheusSerializer.ts

@@ -228,7 +228,11 @@ export class PrometheusSerializer {
   private _serializeScopeMetrics(scopeMetrics: ScopeMetrics) {
     let str = '';
     for (const metric of scopeMetrics.metrics) {
-      str += this._serializeMetricData(metric, scopeMetrics.scope) + '\n';
+      const metricStr = this._serializeMetricData(metric, scopeMetrics.scope);
+
+      if (metricStr) {
+        str += metricStr + '\n';
+      }
     }
     return str;
   }
@@ -243,6 +247,21 @@ export class PrometheusSerializer {
     if (this._prefix) {
       name = `${this._prefix}${name}`;
     }
+
+    if (name === '') {
+      diag.error(
+        `Normalization for metric "${metricData.descriptor.name}" resulted in empty name`
+      );
+      return '';
+    } else if (name === '_') {
+      diag.error(
+        `Normalization for metric "${metricData.descriptor.name}" resulted in an invalid name: "_"`
+      );
+      return '';
+    } else if (name[0] >= '0' && name[0] <= '9') {
+      name = `_${name}`;
+    }
+
     const dataPointType = metricData.dataPointType;
 
     name = enforcePrometheusNamingConvention(name, metricData);

experimental/packages/opentelemetry-exporter-prometheus/test/PrometheusSerializer.test.ts

@@ -4,6 +4,7 @@
  */
 
 import * as assert from 'assert';
+import { diag } from '@opentelemetry/api';
 import type { Attributes, UpDownCounter } from '@opentelemetry/api';
 import type { DataPoint, Histogram } from '@opentelemetry/sdk-metrics';
 import {
@@ -670,6 +671,97 @@ describe('PrometheusSerializer', () => {
 
       assert.strictEqual(result, 'test_total 1\n');
     });
+
+    it('replaces special characters with underscores when escaping is enabled', async () => {
+      const serializer = new PrometheusSerializer();
+      const result = await getCounterResult(
+        'metric@with#special$chars',
+        serializer,
+        {
+          exportAll: true,
+        }
+      );
+
+      assert.strictEqual(
+        result,
+        serializedDefaultResource +
+          '# HELP metric_with_special_chars_total description missing\n' +
+          '# TYPE metric_with_special_chars_total counter\n' +
+          'metric_with_special_chars_total{otel_scope_name="test"} 1\n'
+      );
+    });
+
+    it('metric names do not start with a digit when escaping is enabled', async () => {
+      const serializer = new PrometheusSerializer();
+      const result = await getCounterResult('123metric', serializer, {
+        exportAll: true,
+      });
+
+      assert.strictEqual(
+        result,
+        serializedDefaultResource +
+          '# HELP _123metric_total description missing\n' +
+          '# TYPE _123metric_total counter\n' +
+          '_123metric_total{otel_scope_name="test"} 1\n'
+      );
+    });
+
+    it('multiple special characters are collapsed to a single underscore when escaping is enabled', async () => {
+      const serializer = new PrometheusSerializer();
+      const result = await getCounterResult('metric@@##$$name', serializer, {
+        exportAll: true,
+      });
+
+      assert.strictEqual(
+        result,
+        serializedDefaultResource +
+          '# HELP metric_name_total description missing\n' +
+          '# TYPE metric_name_total counter\n' +
+          'metric_name_total{otel_scope_name="test"} 1\n'
+      );
+    });
+
+    it('metric names of only special characters are not serialized when escaping is enabled', async () => {
+      const serializer = new PrometheusSerializer();
+      const diagErr = diag.error;
+      const spy = sinon.spy();
+      diag.error = spy;
+      const result = await getCounterResult('@#$%', serializer, {
+        exportAll: true,
+      });
+      diag.error = diagErr;
+
+      assert.strictEqual(
+        result,
+        serializedDefaultResource + '# no registered metrics'
+      );
+      assert.strictEqual(spy.calledOnce, true);
+      sinon.assert.calledWith(
+        spy,
+        `Normalization for metric "@#$%" resulted in an invalid name: "_"`
+      );
+    });
+
+    it('metrics with empty names are not serialized', async () => {
+      const serializer = new PrometheusSerializer();
+      const diagErr = diag.error;
+      const spy = sinon.spy();
+      diag.error = spy;
+      const result = await getCounterResult('', serializer, {
+        exportAll: true,
+      });
+      diag.error = diagErr;
+
+      assert.strictEqual(
+        result,
+        serializedDefaultResource + '# no registered metrics'
+      );
+      assert.strictEqual(spy.calledOnce, true);
+      sinon.assert.calledWith(
+        spy,
+        `Normalization for metric "" resulted in empty name`
+      );
+    });
   });
 
   describe('serialize non-normalized values', () => {