Add fs module support

All fs module usage is now automatically instrumented.

Tests are in the express-redis sample application.

Automatic instrumentation is manually suppresed in the test span
processor because it uses the fs module to handle the spans.json file.
It is done using the `supressTracing` helper provided by OpenTelemetry
core library.

.changesets/add-fs-module-support.md

@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "add"
+---
+
+Add fs module support

package.json

@@ -16,6 +16,7 @@
     "@opentelemetry/sdk-node": "^0.33.0",
     "@opentelemetry/sdk-trace-base": "^1.7.0",
     "@opentelemetry/instrumentation-fastify": "^0.30.0",
+    "@opentelemetry/instrumentation-fs": "^0.5.1",
     "@opentelemetry/instrumentation-express": "^0.31.2",
     "@opentelemetry/instrumentation-graphql": "^0.31.0",
     "@opentelemetry/instrumentation-http": "^0.32.0",

src/client.ts

@@ -15,6 +15,7 @@ import {
   ExpressLayerType
 } from "@opentelemetry/instrumentation-express"
 import { FastifyInstrumentation } from "@opentelemetry/instrumentation-fastify"
+import { FsInstrumentation } from "@opentelemetry/instrumentation-fs"
 import { GraphQLInstrumentation } from "@opentelemetry/instrumentation-graphql"
 import { HttpInstrumentation } from "@opentelemetry/instrumentation-http"
 import { IORedisInstrumentation } from "@opentelemetry/instrumentation-ioredis"
@@ -34,6 +35,7 @@ import { SpanProcessor, TestModeSpanProcessor } from "./span_processor"
 const DefaultInstrumentations = {
   "@opentelemetry/instrumentation-express": ExpressInstrumentation,
   "@opentelemetry/instrumentation-fastify": FastifyInstrumentation,
+  "@opentelemetry/instrumentation-fs": FsInstrumentation,
   "@opentelemetry/instrumentation-graphql": GraphQLInstrumentation,
   "@opentelemetry/instrumentation-http": HttpInstrumentation,
   "@opentelemetry/instrumentation-ioredis": IORedisInstrumentation,

src/span_processor.ts

@@ -1,11 +1,12 @@
 import * as fs from "fs"
 import type { Context } from "@opentelemetry/api"
-import { SpanKind } from "@opentelemetry/api"
+import { context, SpanKind } from "@opentelemetry/api"
 import type {
   Span,
   ReadableSpan,
   SpanProcessor as OpenTelemetrySpanProcessor
 } from "@opentelemetry/sdk-trace-base"
+import { suppressTracing } from "@opentelemetry/core"
 import { Client } from "./client"
 
 export class SpanProcessor implements OpenTelemetrySpanProcessor {
@@ -92,11 +93,15 @@ export class TestModeSpanProcessor implements OpenTelemetrySpanProcessor {
       endTime: span.endTime
     }
 
-    // Re-open the file for every write, as the test process might have
-    // truncated it in between writes.
-    const file = fs.openSync(this.#filePath, "a")
-    fs.appendFileSync(file, `${JSON.stringify(serializableSpan)}\n`)
-    fs.closeSync(file)
+    // As `fs` is an automatically instrumented module by default, we supress tracing during
+    // its usage here so it doesn't fail nor contaminate actual traces.
+    context.with(suppressTracing(context.active()), () => {
+      // Re-open the file for every write, as the test process might have
+      // truncated it in between writes.
+      const file = fs.openSync(this.#filePath, "a")
+      fs.appendFileSync(file, `${JSON.stringify(serializableSpan)}\n`)
+      fs.closeSync(file)
+    })
   }
 
   shutdown() {