readme.md for @push.rocks/smartstream

A TypeScript-first library for creating and manipulating Node.js and Web streams with built-in backpressure handling, async transformations, and seamless Node.js ↔ Web stream interoperability.
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Install
pnpm install @push.rocks/smartstream
The package ships with two entry points:
Entry Point
Import Path
Environment
Node.js (default)
@push.rocks/smartstream
Node.js — full stream utilities, duplex, intake, wrappers, and Node↔Web helpers
Web
@push.rocks/smartstream/web
Browser & Node.js — pure Web Streams API (
WebDuplexStream)
Usage
All examples use ESM / TypeScript syntax.
📦 Importing
// Node.js — full API
import {
  SmartDuplex,
  StreamWrapper,
  StreamIntake,
  createTransformFunction,
  createPassThrough,
  nodewebhelpers,
} from '@push.rocks/smartstream';
// Web — browser-safe, zero Node.js dependencies
import { WebDuplexStream } from '@push.rocks/smartstream/web';
🔄 SmartDuplex — The Core Stream Primitive
SmartDuplex extends Node.js 
Duplex with first-class async support, built-in backpressure management, and a clean functional API. Instead of overriding 
_transform or 
_write manually, you pass a 
writeFunction that receives each chunk along with a 
tools object.
Basic Transform
import { SmartDuplex } from '@push.rocks/smartstream';
const upperCaser = new SmartDuplex<Buffer, Buffer>({
  writeFunction: async (chunk, tools) => {
    // Return a value to push it downstream
    return Buffer.from(chunk.toString().toUpperCase());
  },
});
readableStream.pipe(upperCaser).pipe(writableStream);
Using 
tools.push() for Multiple Outputs
The 
writeFunction can emit multiple chunks per input via 
tools.push():
const splitter = new SmartDuplex<string, string>({
  objectMode: true,
  writeFunction: async (chunk, tools) => {
    const words = chunk.split(' ');
    for (const word of words) {
      await tools.push(word);
    }
    // Returning nothing — output was already pushed
  },
});
Final Function
Run cleanup or emit final data when the writable side ends:
const aggregator = new SmartDuplex<number, number>({
  objectMode: true,
  writeFunction: async (chunk, tools) => {
    runningTotal += chunk;
    // Don't emit anything per-chunk
  },
  finalFunction: async (tools) => {
    return runningTotal; // Emitted as the last chunk
  },
});
Truncating a Stream Early
Call 
tools.truncate() inside 
writeFunction to signal that no more data should be read:
const limiter = new SmartDuplex<string, string>({
  objectMode: true,
  writeFunction: async (chunk, tools) => {
    if (chunk === 'STOP') {
      tools.truncate();
      return;
    }
    return chunk;
  },
});
Creating from a Buffer
const stream = SmartDuplex.fromBuffer(Buffer.from('hello world'));
stream.on('data', (chunk) => console.log(chunk.toString())); // "hello world"
Creating from a Web ReadableStream
Bridge the Web Streams API into a Node.js Duplex:
const response = await fetch('https://example.com/data');
const nodeDuplex = SmartDuplex.fromWebReadableStream(response.body);
nodeDuplex.pipe(processTransform).pipe(outputStream);
Getting Web Streams from SmartDuplex
Convert a 
SmartDuplex into Web 
ReadableStream + 
WritableStream pair:
const duplex = new SmartDuplex({
  writeFunction: async (chunk, tools) => {
    return transform(chunk);
  },
});
const { readable, writable } = await duplex.getWebStreams();
Debug Mode
Pass 
debug: true and 
name to get detailed internal logs:
const stream = new SmartDuplex({
  name: 'MyStream',
  debug: true,
  writeFunction: async (chunk, tools) => chunk,
});
🧩 StreamWrapper — Pipeline Composition
StreamWrapper takes an array of streams, pipes them together, attaches error listeners on all of them, and returns a 
Promise that resolves when the pipeline finishes:
import { StreamWrapper } from '@push.rocks/smartstream';
import fs from 'fs';
const pipeline = new StreamWrapper([
  fs.createReadStream('./input.txt'),
  new SmartDuplex({
    writeFunction: async (chunk) => Buffer.from(chunk.toString().toUpperCase()),
  }),
  fs.createWriteStream('./output.txt'),
]);
await pipeline.run();
console.log('Pipeline complete!');
Error handling is automatic — if any stream in the array errors, the returned promise rejects:
pipeline.run()
  .then(() => console.log('Done'))
  .catch((err) => console.error('Pipeline failed:', err));
You can also listen for custom events across all streams:
pipeline.onCustomEvent('progress', () => {
  console.log('Progress event fired');
});
📥 StreamIntake — Dynamic Data Injection
StreamIntake is a 
Readable stream that lets you programmatically push data into a pipeline. It operates in object mode by default and provides a reactive observable (
pushNextObservable) for demand-driven data production.
import { StreamIntake, SmartDuplex } from '@push.rocks/smartstream';
const intake = new StreamIntake<string>();
// Pipe through a transform
intake
  .pipe(new SmartDuplex({
    objectMode: true,
    writeFunction: async (chunk) => {
      console.log('Processing:', chunk);
      return chunk;
    },
  }))
  .on('data', (data) => console.log('Output:', data));
// Push data whenever it's ready
intake.pushData('Hello');
intake.pushData('World');
intake.signalEnd(); // Signal end-of-stream
Demand-driven Production with Observable
pushNextObservable emits whenever the stream is ready for more data — perfect for throttled or event-driven producers:
const intake = new StreamIntake<number>();
let counter = 0;
intake.pushNextObservable.subscribe(() => {
  if (counter < 100) {
    intake.pushData(counter++);
  } else {
    intake.signalEnd();
  }
});
intake.pipe(consumer);
Creating from Existing Streams
Wrap a Node.js 
Readable or a Web 
ReadableStream:
// From Node.js Readable
const intake = await StreamIntake.fromStream<Buffer>(fs.createReadStream('./data.bin'));
// From Web ReadableStream
const response = await fetch('https://example.com/stream');
const intake = await StreamIntake.fromStream<Uint8Array>(response.body);
⚡ Utility Functions
createTransformFunction
Quickly create a 
SmartDuplex from a simple async mapping function:
import { createTransformFunction } from '@push.rocks/smartstream';
const doubler = createTransformFunction<number, number>(async (n) => n * 2);
intakeStream.pipe(doubler).pipe(outputStream);
createPassThrough
Create an object-mode passthrough stream (useful as an intermediary or tee point):
import { createPassThrough } from '@push.rocks/smartstream';
const passThrough = createPassThrough();
source.pipe(passThrough).pipe(destination);
🌐 WebDuplexStream — Pure Web Streams API
WebDuplexStream extends 
TransformStream and works in both browsers and Node.js. Import it from the 
/web subpath for zero Node.js dependencies.
import { WebDuplexStream } from '@push.rocks/smartstream/web';
const stream = new WebDuplexStream<number, number>({
  writeFunction: async (chunk, { push }) => {
    push(chunk * 2); // Push transformed data
  },
});
const writer = stream.writable.getWriter();
const reader = stream.readable.getReader();
// Write
await writer.write(5);
await writer.write(10);
await writer.close();
// Read
const { value } = await reader.read(); // 10
const { value: v2 } = await reader.read(); // 20
From a Uint8Array
const stream = WebDuplexStream.fromUInt8Array(new Uint8Array([1, 2, 3]));
const reader = stream.readable.getReader();
const { value } = await reader.read(); // Uint8Array [1, 2, 3]
Data Production with 
readFunction
Supply data into the stream from any async source:
const stream = new WebDuplexStream<string, string>({
  readFunction: async (tools) => {
    await tools.write('chunk 1');
    await tools.write('chunk 2');
    tools.done(); // Signal end
  },
  writeFunction: async (chunk, { push }) => {
    push(chunk.toUpperCase());
  },
});
const reader = stream.readable.getReader();
// reads "CHUNK 1", "CHUNK 2"
🔀 Node ↔ Web Stream Converters
The 
nodewebhelpers namespace provides bidirectional converters between Node.js and Web Streams:
import { nodewebhelpers } from '@push.rocks/smartstream';
Function
From
To
createWebReadableStreamFromFile(path)
File path
Web 
ReadableStream<Uint8Array>
convertWebReadableToNodeReadable(webStream)
Web 
ReadableStream
Node.js 
Readable
convertNodeReadableToWebReadable(nodeStream)
Node.js 
Readable
Web 
ReadableStream
convertWebWritableToNodeWritable(webWritable)
Web 
WritableStream
Node.js 
Writable
convertNodeWritableToWebWritable(nodeWritable)
Node.js 
Writable
Web 
WritableStream
Example: Serve a File as a Web ReadableStream
const webStream = nodewebhelpers.createWebReadableStreamFromFile('./video.mp4');
// Use with fetch Response, service workers, etc.
return new Response(webStream, {
  headers: { 'Content-Type': 'video/mp4' },
});
Example: Convert Between Stream Types
import fs from 'fs';
import { nodewebhelpers } from '@push.rocks/smartstream';
// Node → Web
const nodeReadable = fs.createReadStream('./data.bin');
const webReadable = nodewebhelpers.convertNodeReadableToWebReadable(nodeReadable);
// Web → Node
const nodeReadable2 = nodewebhelpers.convertWebReadableToNodeReadable(webReadable);
nodeReadable2.pipe(fs.createWriteStream('./copy.bin'));
🏗️ Backpressure Handling
SmartDuplex uses a 
BackpressuredArray internally, bounded by 
highWaterMark (default: 1). When the downstream consumer is slow, the stream automatically pauses the upstream producer until space is available — no manual bookkeeping required.
const slow = new SmartDuplex({
  name: 'SlowConsumer',
  objectMode: true,
  highWaterMark: 1,
  writeFunction: async (chunk, tools) => {
    await new Promise((resolve) => setTimeout(resolve, 200));
    return chunk;
  },
});
const fast = new SmartDuplex({
  name: 'FastProducer',
  objectMode: true,
  writeFunction: async (chunk, tools) => {
    return chunk; // Instant processing
  },
});
// Backpressure is handled automatically between fast → slow
fast.pipe(slow).on('data', (d) => console.log(d));
for (let i = 0; i < 100; i++) {
  fast.write(`chunk-${i}`);
}
fast.end();
🎯 Real-World Example: Processing Pipeline
import fs from 'fs';
import { SmartDuplex, StreamWrapper } from '@push.rocks/smartstream';
// Read → Transform → Filter → Write
const pipeline = new StreamWrapper([
  fs.createReadStream('./access.log'),
  new SmartDuplex({
    writeFunction: async (chunk) => {
      // Parse each line
      return chunk.toString().split('\n');
    },
  }),
  new SmartDuplex({
    objectMode: true,
    writeFunction: async (lines: string[], tools) => {
      // Filter and push matching lines
      for (const line of lines) {
        if (line.includes('ERROR')) {
          await tools.push(line + '\n');
        }
      }
    },
  }),
  fs.createWriteStream('./errors.log'),
]);
await pipeline.run();
console.log('Error extraction complete');
License and Legal Information
This repository contains open-source code licensed under the MIT License. A copy of the license can be found in the LICENSE file.
Please note: The MIT License does not grant permission to use the trade names, trademarks, service marks, or product names of the project, except as required for reasonable and customary use in describing the origin of the work and reproducing the content of the NOTICE file.
Trademarks
This project is owned and maintained by Task Venture Capital GmbH. The names and logos associated with Task Venture Capital GmbH and any related products or services are trademarks of Task Venture Capital GmbH or third parties, and are not included within the scope of the MIT license granted herein.
Use of these trademarks must comply with Task Venture Capital GmbH's Trademark Guidelines or the guidelines of the respective third-party owners, and any usage must be approved in writing. Third-party trademarks used herein are the property of their respective owners and used only in a descriptive manner, e.g. for an implementation of an API or similar.
Company Information
Task Venture Capital GmbH
Registered at District Court Bremen HRB 35230 HB, Germany
For any legal inquiries or further information, please contact us via email at hello@task.vc.
By using this repository, you acknowledge that you have read this section, agree to comply with its terms, and understand that the licensing of the code does not imply endorsement by Task Venture Capital GmbH of any derivative works.