feat(smartduplex): improve backpressure handling and web/node stream interoperability

test/test.backpressure.ts

@@ -0,0 +1,56 @@
+import { tap, expect } from '@push.rocks/tapbundle';
+import { SmartDuplex } from '../ts/index.js';
+
+tap.test('Backpressure: should apply backpressure across piped streams', async (toolsArg) => {
+  const done = toolsArg.defer();
+
+  const stream1 = new SmartDuplex({
+    name: 'stream1',
+    objectMode: true,
+    writeFunction: async (chunk, tools) => {
+      await new Promise((resolve) => setTimeout(resolve, 10));
+      return chunk;
+    },
+  });
+
+  const stream2 = new SmartDuplex({
+    name: 'stream2',
+    objectMode: true,
+    writeFunction: async (chunk, tools) => {
+      await new Promise((resolve) => setTimeout(resolve, 20));
+      await tools.push(chunk);
+    },
+  });
+
+  const stream3 = new SmartDuplex({
+    objectMode: true,
+    name: 'stream3',
+    writeFunction: async (chunk, tools) => {
+      await new Promise((resolve) => setTimeout(resolve, 200));
+    },
+  });
+
+  stream1.pipe(stream2).pipe(stream3);
+
+  let backpressured = false;
+  for (let i = 0; i < 200; i++) {
+    const canContinue = stream1.write(`Chunk ${i}`, 'utf8');
+    if (!canContinue) {
+      backpressured = true;
+    }
+  }
+
+  stream1.end();
+
+  stream3.on('finish', () => {
+    if (!backpressured) {
+      throw new Error('No backpressure was observed.');
+    } else {
+      done.resolve();
+    }
+  });
+
+  await done.promise;
+});
+
+export default tap.start();