Stream Writer 🪶

Easly push data to a Stream

The Stream class extends the TransformStream interface, providing additional convenience methods for handling streams, such as writing, closing, and aborting reducing the amount of code required for those operations.

If you're interested in a simple and effective way to read streams, take a look at @alessiofrittoli/stream-reader package.

Table of Contents

• Getting started
• Key features
• API Reference
  • Importing the library
  • Properties
  • Constructor
  • Methods
    • Stream.write()
    • Stream.close()
    • Stream.abort()
• Examples
  • Writing data into a stream
  • Writing data into a stream with a custom transformer
  • Aborting the stream
• Development
  • Install depenendencies
  • Build the source code
  • ESLint
  • Jest
• Contributing
• Security
• Credits

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Getting started

Run the following command to start using stream-writer in your projects:

npm i @alessiofrittoli/stream-writer

or using pnpm

pnpm i @alessiofrittoli/stream-writer

---

Key features

Extends TransformStream

• Inherits all the functionality of the TransformStream API, allowing for custom transformations of input to output streams.
• Provides seamless integration with modern streaming APIs.

Convenient Stream Management

• write Method: A high-level abstraction for writing chunks of data into the stream. It handles readiness and ensures proper sequencing of write operations.
• close Method: Safely closes the stream while preventing multiple or concurrent close operations.
• abort Method: Gracefully aborts the stream with an optional reason, making it easier to handle errors or interruptions.

Built-In Headers for Server Responses

• The headers property contains default headers commonly used in server responses, such as:
  • Connection: keep-alive
  • Transfer-Encoding: chunked
  • Cache-Control: no-cache, no-transform
  • X-Accel-Buffering: no
  • Content-Encoding: none

Stream Writer Abstraction

• The writer property provides direct access to the underlying WritableStreamDefaultWriter, enabling fine-grained control over the writable stream.
• Ensures proper handling of stream readiness, errors, and resource management (e.g., releasing locks).

Type Safety

• Generic parameters (I for input, O for output) make the class type-safe and adaptable to various use cases, such as processing specific data types.

Designed for Robustness

• Internal mechanisms, ensure the class behaves predictably and avoids race conditions.

Chainable API

• Methods like write, close, and abort return the current Stream instance, enabling method chaining for more concise and readable code.

Compatibility and Modularity

• The Stream class can be used in both client-side and server-side applications where the TransformStream API is supported.
• Its modular design makes it easy to extend or customize further for specific application needs.

Focused on Developer Experience

• Clear and concise API with thoughtful defaults.
• Built-in documentation and examples make it easy to understand and integrate into existing projects.

These features make the Stream class a versatile and developer-friendly abstraction for working with streams in modern JavaScript and TypeScript environments.

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API Reference

Importing the library

import { Stream } from '@alessiofrittoli/stream-writer'

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Properties

Property	Type	Description
writable	WritableStream<I>	The writable stream instance.
readable	ReadableStream<O>	The readable stream instance.
writer	WritableStreamDefaultWriter<I>	The writer instance for the writable stream.
closed	boolean	Indicates whether the stream is closed.
headers	Headers	Common headers to return in a server response.

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Constructor

Constructs a new instance of the Stream class.

Parameter	Type	Description
transformer	Transformer<I, O>	(Optional) A custom transformer for the stream.
writableStrategy	QueuingStrategy<I>	(Optional) A custom strategy for the writable stream.
readableStrategy	QueuingStrategy<O>	(Optional) A custom strategy for the readable stream.

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Methods

Stream.write()

Writes data into the stream.

Parameters

Parameter	Type	Description
chunk	I	The data chunk to write to the stream.

Returns

Type: Promise<Stream>

• A Promise that resolves to the current Stream instance.

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Stream.close()

Closes the stream.

• Closes the writer if it is not already closed or in the process of closing.
• Prevents multiple close operations when .close() is not awaited.
• Releases the lock on the writer.

Returns

Type: Promise<Stream>

• A Promise that resolves to the current Stream instance.

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Stream.abort()

Aborts the stream with an optional reason.

Parameters

Parameter	Type	Description
reason	string	(Optional) The reason for aborting the stream.

Returns

Type: Promise<Stream>

• A Promise that resolves to the current Stream instance.

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Examples

Writing data into a stream

const routeHandler = () => {
  const stream = new Stream()
  
  const streamTask = async () => {
    await stream.write( 'data' )
    await stream.write( 'data 2' )
    await stream.write( 'data 3' )
    await stream.write( 'data 4' )
  }
  
  streamTask()
    .then( () => stream.close() )
  
  return new Response( stream.readable, { headers: stream.headers } )
}

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Writing data into a stream with a custom transformer

const routeHandler = () => {
  const encoder = new TextEncoder()
  const stream = (
    new Stream<string, Uint8Array>( {
      transform( chunk, controller )
      {
        controller.enqueue( encoder.encode( chunk ) )
      }
    } )
  )

  const streamTask = async () => {
    await stream.write( 'data' )
    await stream.write( 'data 2' )
    await stream.write( 'data 3' )
    await stream.write( 'data 4' )
  }

  streamTask()
    .then( () => stream.close() )

  return new Response( stream.readable, { headers: stream.headers } )
}

---

Aborting the stream

const routeHandler = request => {
  request.signal.addEventListener( 'abort', () => {
    stream.abort( 'The user aborted the request.' )
  } )
  
  const stream = new Stream()
  
  const streamTask = async () => {
    await stream.write( 'data' )
    await stream.write( 'data 2' )
    await stream.write( 'data 3' )
    await stream.write( 'data 4' )
  }
  
  streamTask()
    .catch( error => {
      if ( error.name === 'AbortError' ) {
        return console.log( 'AbortError:', error.message )
      }
      await stream.write( error.message )
    } )
    .finally( () => stream.close() )
  
  return new Response( stream.readable, { headers: stream.headers } )

}

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If you're interested in a simple and effective way to read streams, take a look at @alessiofrittoli/stream-reader package.

---

Development

Install depenendencies

npm install

or using pnpm

pnpm i

Build the source code

Run the following command to test and build code for distribution.

pnpm build

ESLint

warnings / errors check.

pnpm lint

Jest

Run all the defined test suites by running the following:

# Run tests and watch file changes.
pnpm test:watch

# Run tests in a CI environment.
pnpm test:ci

• See package.json file scripts for more info.

Run tests with coverage.

An HTTP server is then started to serve coverage files from ./coverage folder.

⚠️ You may see a blank page the first time you run this command. Simply refresh the browser to see the updates.

test:coverage:serve

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Contributing

Contributions are truly welcome!

Please refer to the Contributing Doc for more information on how to start contributing to this project.

Help keep this project up to date with GitHub Sponsor.

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Security

If you believe you have found a security vulnerability, we encourage you to responsibly disclose this and NOT open a public issue. We will investigate all legitimate reports. Email security@alessiofrittoli.it to disclose any security vulnerabilities.

Made with ☕

Alessio Frittoli https://alessiofrittoli.it | info@alessiofrittoli.it