apollo-engine-reporting: clean up SIGINT/SIGTERM handlers on stop (#3090

)

Among other things, this fixes logs in our test suite of 'Possible EventEmitter
memory leak detected'.

CHANGELOG.md

@@ -6,14 +6,14 @@ The version headers in this history reflect the versions of Apollo Server itself
 
 > The changes noted within this `vNEXT` section have not been released yet.  New PRs and commits which introduce changes should include an entry in this `vNEXT` section as part of their development.  When a release is being prepared, a new header will be (manually) created below and the the appropriate changes within that release will be moved into the new section.
 
-- _Nothing yet!_
+- `apollo-engine-reporting`: clean up `SIGINT` and `SIGTERM` handlers when `EngineReportingAgent` is stopped; fixes 'Possible EventEmitter memory leak detected' log. [PR #3090](https://github.com/apollographql/apollo-server/pull/3090)
 
 ### v2.7.1
 
 > [See complete versioning details.](https://github.com/apollographql/apollo-server/commit/2f87e4af9a6f1e3c8f4c51b4f77860bd3150c8c6)
 
 - `apollo-engine-reporting`: If an error is thrown by a custom variable transform function passed into the reporting option `sendVariableValues: { transform: ... }`, all variable values will be replaced with the string `[PREDICATE_FUNCTION_ERROR]`.
-- `apollo-server-express: Typing fix for the `connection` property, which was missing from the `ExpressContext` interface.  [PR #2959](https://github.com/apollographql/apollo-server/pull/2959)
+- `apollo-server-express`: Typing fix for the `connection` property, which was missing from the `ExpressContext` interface.  [PR #2959](https://github.com/apollographql/apollo-server/pull/2959)
 - `@apollo/gateway`: Ensure execution of correct document within multi-operation documents by including the `operationName` in the cache key used when caching query plans used in federated execution. [PR #3084](https://github.com/apollographql/apollo-server/pull/3084)
 
 ### v2.7.0

packages/apollo-engine-reporting/src/agent.ts

@@ -223,6 +223,8 @@ export class EngineReportingAgent<TContext = any> {
   );
   private signatureCache: InMemoryLRUCache<string>;
 
+  private signalHandlers = new Map<NodeJS.Signals, NodeJS.SignalsListener>();
+
   public constructor(options: EngineReportingOptions<TContext> = {}) {
     this.options = options;
     this.apiKey = options.apiKey || process.env.ENGINE_API_KEY || '';
@@ -248,11 +250,15 @@ export class EngineReportingAgent<TContext = any> {
     if (this.options.handleSignals !== false) {
       const signals: NodeJS.Signals[] = ['SIGINT', 'SIGTERM'];
       signals.forEach(signal => {
-        process.once(signal, async () => {
+        // Note: Node only started sending signal names to signal events with
+        // Node v10 so we can't use that feature here.
+        const handler: NodeJS.SignalsListener = async () => {
           this.stop();
           await this.sendAllReportsAndReportErrors();
           process.kill(process.pid, signal);
-        });
+        };
+        process.once(signal, handler);
+        this.signalHandlers.set(signal, handler);
       });
     }
 
@@ -430,6 +436,11 @@ export class EngineReportingAgent<TContext = any> {
   // size, and stop buffering new traces. You may still manually send a last
   // report by calling sendReport().
   public stop() {
+    // Clean up signal handlers so they don't accrue indefinitely.
+    this.signalHandlers.forEach((handler, signal) => {
+      process.removeListener(signal, handler);
+    });
+
     if (this.reportTimer) {
       clearInterval(this.reportTimer);
       this.reportTimer = undefined;