add --telemetry-outfile flag (#4689)

packages/core/src/telemetry/file-exporters.ts

@@ -0,0 +1,89 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as fs from 'node:fs';
+import { ExportResult, ExportResultCode } from '@opentelemetry/core';
+import { ReadableSpan, SpanExporter } from '@opentelemetry/sdk-trace-base';
+import { ReadableLogRecord, LogRecordExporter } from '@opentelemetry/sdk-logs';
+import {
+  ResourceMetrics,
+  PushMetricExporter,
+  AggregationTemporality,
+} from '@opentelemetry/sdk-metrics';
+
+class FileExporter {
+  protected writeStream: fs.WriteStream;
+
+  constructor(filePath: string) {
+    this.writeStream = fs.createWriteStream(filePath, { flags: 'a' });
+  }
+
+  protected serialize(data: unknown): string {
+    return JSON.stringify(data, null, 2) + '\n';
+  }
+
+  shutdown(): Promise<void> {
+    return new Promise((resolve) => {
+      this.writeStream.end(resolve);
+    });
+  }
+}
+
+export class FileSpanExporter extends FileExporter implements SpanExporter {
+  export(
+    spans: ReadableSpan[],
+    resultCallback: (result: ExportResult) => void,
+  ): void {
+    const data = spans.map((span) => this.serialize(span)).join('');
+    this.writeStream.write(data, (err) => {
+      resultCallback({
+        code: err ? ExportResultCode.FAILED : ExportResultCode.SUCCESS,
+        error: err || undefined,
+      });
+    });
+  }
+}
+
+export class FileLogExporter extends FileExporter implements LogRecordExporter {
+  export(
+    logs: ReadableLogRecord[],
+    resultCallback: (result: ExportResult) => void,
+  ): void {
+    const data = logs.map((log) => this.serialize(log)).join('');
+    this.writeStream.write(data, (err) => {
+      resultCallback({
+        code: err ? ExportResultCode.FAILED : ExportResultCode.SUCCESS,
+        error: err || undefined,
+      });
+    });
+  }
+}
+
+export class FileMetricExporter
+  extends FileExporter
+  implements PushMetricExporter
+{
+  export(
+    metrics: ResourceMetrics,
+    resultCallback: (result: ExportResult) => void,
+  ): void {
+    const data = this.serialize(metrics);
+    this.writeStream.write(data, (err) => {
+      resultCallback({
+        code: err ? ExportResultCode.FAILED : ExportResultCode.SUCCESS,
+        error: err || undefined,
+      });
+    });
+  }
+
+  getPreferredAggregationTemporality(): AggregationTemporality {
+    return AggregationTemporality.CUMULATIVE;
+  }
+
+  async forceFlush(): Promise<void> {
+    return Promise.resolve();
+  }
+}