Proxy process.on("exit") to avoid MaxListenersExceededWarning

CHANGELOG.md

@@ -95,3 +95,4 @@
 
 - Upgrade dependencies.
 - **BREAKING:** Drop support for node 13.
+- Prevent Node.js max listeners exceeded warnings if many `fs-capacitor` `ReadStream` instances are created at the same time, fixing [#30](https://github.com/mike-marcacci/fs-capacitor/issues/30) via [#42](https://github.com/mike-marcacci/fs-capacitor/pull/42).

src/index.ts

@@ -3,6 +3,7 @@ import fs from "fs";
 import os from "os";
 import path from "path";
 import { Readable, ReadableOptions, Writable, WritableOptions } from "stream";
+import { EventEmitter } from "events";
 
 export class ReadAfterDestroyedError extends Error {}
 export class ReadAfterReleasedError extends Error {}
@@ -12,6 +13,14 @@ export interface ReadStreamOptions {
   encoding?: ReadableOptions["encoding"];
 }
 
+// Use a “proxy” event emitter configured to have an infinite maximum number of
+// listeners to prevent Node.js max listeners exceeded warnings if many
+// `fs-capacitor` `ReadStream` instances are created at the same time. See:
+// https://github.com/mike-marcacci/fs-capacitor/issues/30
+const processExitProxy = new EventEmitter();
+processExitProxy.setMaxListeners(Infinity);
+process.once("exit", () => processExitProxy.emit("exit"));
+
 export class ReadStream extends Readable {
   private _pos: number = 0;
   private _writeStream: WriteStream;
@@ -66,13 +75,13 @@ export class ReadStream extends Readable {
 
         // Otherwise, wait for the write stream to add more data or finish.
         const retry = (): void => {
-          this._writeStream.removeListener("finish", retry);
-          this._writeStream.removeListener("write", retry);
+          this._writeStream.off("finish", retry);
+          this._writeStream.off("write", retry);
           this._read(n);
         };
 
-        this._writeStream.addListener("finish", retry);
-        this._writeStream.addListener("write", retry);
+        this._writeStream.on("finish", retry);
+        this._writeStream.on("write", retry);
       }
     );
   }
@@ -117,7 +126,7 @@ export class WriteStream extends Writable {
         }
 
         // Cleanup when the process exits or is killed.
-        process.addListener("exit", this._cleanupSync);
+        processExitProxy.once("exit", this._cleanupSync);
 
         this._fd = fd;
         this.emit("ready");
@@ -126,7 +135,7 @@ export class WriteStream extends Writable {
   }
 
   _cleanupSync = (): void => {
-    process.removeListener("exit", this._cleanupSync);
+    processExitProxy.off("exit", this._cleanupSync);
 
     if (typeof this._fd === "number")
       try {
@@ -208,7 +217,7 @@ export class WriteStream extends Writable {
 
         // We avoid removing this until now in case an exit occurs while
         // asyncronously cleaning up.
-        process.removeListener("exit", this._cleanupSync);
+        processExitProxy.off("exit", this._cleanupSync);
         callback(unlinkError || closeError || error);
       });
     });
@@ -232,16 +241,13 @@ export class WriteStream extends Writable {
     const readStream = new ReadStream(this, options);
     this._readStreams.add(readStream);
 
-    const remove = (): void => {
-      readStream.removeListener("close", remove);
+    readStream.once("close", (): void => {
       this._readStreams.delete(readStream);
 
       if (this._released && this._readStreams.size === 0) {
         this.destroy();
       }
-    };
-
-    readStream.addListener("close", remove);
+    });
 
     return readStream;
   }