fix(cli-repl): do not recursively push() in LineByLineInput MONGOSH-586

packages/cli-repl/src/line-by-line-input.spec.ts

@@ -63,4 +63,22 @@ describe('LineByLineInput', () => {
       expect(forwardedChunks).to.deep.equal(['a', 'b', '\n']);
     });
   });
+
+  context('when a data listener calls nextLine() itself after Ctrl+C', () => {
+    it('does not emit data while already emitting data', () => {
+      let dataCalls = 0;
+      let insideDataCalls = 0;
+      lineByLineInput.on('data', () => {
+        expect(insideDataCalls).to.equal(0);
+        insideDataCalls++;
+        if (dataCalls++ === 0) {
+          lineByLineInput.nextLine();
+        }
+        insideDataCalls--;
+      });
+      stdinMock.emit('data', Buffer.from('foo\n\u0003'));
+      expect(dataCalls).to.equal(5);
+      expect(forwardedChunks).to.deep.equal(['\u0003', 'f', 'o', 'o', '\n']);
+    });
+  });
 });

packages/cli-repl/src/line-by-line-input.ts

@@ -27,6 +27,7 @@ export class LineByLineInput extends Readable {
   private _blockOnNewLineEnabled: boolean;
   private _charQueue: (string | null)[];
   private _decoder: StringDecoder;
+  private _insidePushCalls: number;
 
   constructor(readable: NodeJS.ReadStream) {
     super();
@@ -35,6 +36,7 @@ export class LineByLineInput extends Readable {
     this._blockOnNewLineEnabled = true;
     this._charQueue = [];
     this._decoder = new StringDecoder('utf-8');
+    this._insidePushCalls = 0;
 
     const isReadableEvent = (name: string) =>
       name === 'readable' || name === 'data' || name === 'end' || name === 'keypress';
@@ -144,7 +146,11 @@ export class LineByLineInput extends Readable {
       // have in the buffer if in the meanwhile something
       // downstream explicitly called pause(), as that may cause
       // unexpected behaviors.
-      !this._originalInput.isPaused()
+      !this._originalInput.isPaused() &&
+
+      // If we are already inside a push() call, then we do not need to flush
+      // the queue again.
+      this._insidePushCalls === 0
     ) {
       const char = this._charQueue.shift() as string | null;
 
@@ -167,4 +173,13 @@ export class LineByLineInput extends Readable {
   private _isCtrlC(char: string | null): boolean {
     return char === CTRL_C;
   }
+
+  push(chunk: Buffer | string | null): boolean {
+    this._insidePushCalls++;
+    try {
+      return super.push(chunk);
+    } finally {
+      this._insidePushCalls--;
+    }
+  }
 }