http.IncomingMessage

Calls readable.destroy() with an AbortError and returns a promise that fulfills when the stream is finished.

The Symbol.for('nodejs.rejection') method is called in case a promise rejection happens when emitting an event and captureRejections is enabled on the emitter. It is possible to use events.captureRejectionSymbol in place of Symbol.for('nodejs.rejection').

import { EventEmitter, captureRejectionSymbol } from 'node:events';

class MyClass extends EventEmitter {
  constructor() {
    super({ captureRejections: true });
  }

  [captureRejectionSymbol](err, event, ...args) {
    console.log('rejection happened for', event, 'with', err, ...args);
    this.destroy(err);
  }

  destroy(err) {
    // Tear the resource down here.
  }
}

When the --experimental-stream-iter flag is enabled, Readable streams implement the Stream.toAsyncStreamable protocol, enabling efficient consumption by the stream/iter API.

This provides a batched async iterator that drains the stream's internal buffer into Uint8Array[] batches, amortizing the per-chunk Promise overhead of the standard Symbol.asyncIterator path. For byte-mode streams, chunks are yielded directly as Buffer instances (which are Uint8Array subclasses). For object-mode or encoded streams, each chunk is normalized to Uint8Array before batching.

The returned iterator is tagged as a validated source, so from() passes it through without additional normalization.

import { Readable } from 'node:stream';
import { text, from } from 'node:stream/iter';

const readable = new Readable({
  read() { this.push('hello'); this.push(null); },
});

// Readable is automatically consumed via toAsyncStreamable
console.log(await text(from(readable))); // 'hello'

Without the --experimental-stream-iter flag, calling this method throws ERR_STREAM_ITER_MISSING_FLAG.

import { Readable } from 'node:stream';

async function* splitToWords(source) {
  for await (const chunk of source) {
    const words = String(chunk).split(' ');

    for (const word of words) {
      yield word;
    }
  }
}

const wordsStream = Readable.from(['text passed through', 'composed stream']).compose(splitToWords);
const words = await wordsStream.toArray();

console.log(words); // prints ['text', 'passed', 'through', 'composed', 'stream']

readable.compose(s) is equivalent to stream.compose(readable, s).

This method also allows for an AbortSignal to be provided, which will destroy the composed stream when aborted.

See stream.compose(...streams) for more information.

Calls destroy() on the socket that received the IncomingMessage. If error is provided, an 'error' event is emitted on the socket and error is passed as an argument to any listeners on the event.

This method returns a new stream with the first limit chunks dropped from the start.

Returns an array listing the events for which the emitter has registered listeners.

import { EventEmitter } from 'node:events';

const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});

const sym = Symbol('symbol');
myEE.on(sym, () => {});

console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]

This method is similar to Array.prototype.every and calls fn on each chunk in the stream to check if all awaited return values are truthy value for fn. Once an fn call on a chunk awaited return value is falsy, the stream is destroyed and the promise is fulfilled with false. If all of the fn calls on the chunks return a truthy value, the promise is fulfilled with true.

This method allows filtering the stream. For each chunk in the stream the fn function will be called and if it returns a truthy value, the chunk will be passed to the result stream. If the fn function returns a promise - that promise will be awaited.

This method returns a new stream by applying the given callback to each chunk of the stream and then flattening the result.

It is possible to return a stream or another iterable or async iterable from fn and the result streams will be merged (flattened) into the returned stream.

This method allows iterating a stream. For each chunk in the stream the fn function will be called. If the fn function returns a promise - that promise will be awaited.

This method is different from for await...of loops in that it can optionally process chunks concurrently. In addition, a forEach iteration can only be stopped by having passed a signal option and aborting the related AbortController while for await...of can be stopped with break or return. In either case the stream will be destroyed.

This method is different from listening to the 'data' event in that it uses the readable event in the underlying machinary and can limit the number of concurrent fn calls.

Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to events.defaultMaxListeners.

The readable.isPaused() method returns the current operating state of the Readable. This is used primarily by the mechanism that underlies the readable.pipe() method. In most typical cases, there will be no reason to use this method directly.

const readable = new stream.Readable();

readable.isPaused(); // === false
readable.pause();
readable.isPaused(); // === true
readable.resume();
readable.isPaused(); // === false

The iterator created by this method gives users the option to cancel the destruction of the stream if the for await...of loop is exited by return, break, or throw, or if the iterator should destroy the stream if the stream emitted an error during iteration.

This method allows mapping over the stream. The fn function will be called for every chunk in the stream. If the fn function returns a promise - that promise will be awaited before being passed to the result stream.

The readable.pause() method will cause a stream in flowing mode to stop emitting 'data' events, switching out of flowing mode. Any data that becomes available will remain in the internal buffer.

const readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
  console.log(`Received ${chunk.length} bytes of data.`);
  readable.pause();
  console.log('There will be no additional data for 1 second.');
  setTimeout(() => {
    console.log('Now data will start flowing again.');
    readable.resume();
  }, 1000);
});

The readable.pause() method has no effect if there is a 'readable' event listener.

The readable.read() method reads data out of the internal buffer and returns it. If no data is available to be read, null is returned. By default, the data is returned as a Buffer object unless an encoding has been specified using the readable.setEncoding() method or the stream is operating in object mode.

The optional size argument specifies a specific number of bytes to read. If size bytes are not available to be read, null will be returned unless the stream has ended, in which case all of the data remaining in the internal buffer will be returned.

If the size argument is not specified, all of the data contained in the internal buffer will be returned.

The size argument must be less than or equal to 1 GiB.

The readable.read() method should only be called on Readable streams operating in paused mode. In flowing mode, readable.read() is called automatically until the internal buffer is fully drained.

const readable = getReadableStreamSomehow();

// 'readable' may be triggered multiple times as data is buffered in
readable.on('readable', () => {
  let chunk;
  console.log('Stream is readable (new data received in buffer)');
  // Use a loop to make sure we read all currently available data
  while (null !== (chunk = readable.read())) {
    console.log(`Read ${chunk.length} bytes of data...`);
  }
});

// 'end' will be triggered once when there is no more data available
readable.on('end', () => {
  console.log('Reached end of stream.');
});

Each call to readable.read() returns a chunk of data, or null. The chunks are not concatenated. A while loop is necessary to consume all data currently in the buffer. When reading a large file .read() may return null, having consumed all buffered content so far, but there is still more data to come not yet buffered. In this case a new 'readable' event will be emitted when there is more data in the buffer. Finally the 'end' event will be emitted when there is no more data to come.

Therefore to read a file's whole contents from a readable, it is necessary to collect chunks across multiple 'readable' events:

const chunks = [];

readable.on('readable', () => {
  let chunk;
  while (null !== (chunk = readable.read())) {
    chunks.push(chunk);
  }
});

readable.on('end', () => {
  const content = chunks.join('');
});

A Readable stream in object mode will always return a single item from a call to readable.read(size), regardless of the value of the size argument.

If the readable.read() method returns a chunk of data, a 'data' event will also be emitted.

Calling read after the 'end' event has been emitted will return null. No runtime error will be raised.

The readable.resume() method causes an explicitly paused Readable stream to resume emitting 'data' events, switching the stream into flowing mode.

The readable.resume() method can be used to fully consume the data from a stream without actually processing any of that data:

getReadableStreamSomehow()
  .resume()
  .on('end', () => {
    console.log('Reached the end, but did not read anything.');
  });

The readable.resume() method has no effect if there is a 'readable' event listener.

The readable.setEncoding() method sets the character encoding for data read from the Readable stream.

By default, no encoding is assigned and stream data will be returned as Buffer objects. Setting an encoding causes the stream data to be returned as strings of the specified encoding rather than as Buffer objects. For instance, calling readable.setEncoding('utf8') will cause the output data to be interpreted as UTF-8 data, and passed as strings. Calling readable.setEncoding('hex') will cause the data to be encoded in hexadecimal string format.

The Readable stream will properly handle multi-byte characters delivered through the stream that would otherwise become improperly decoded if simply pulled from the stream as Buffer objects.

const readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', (chunk) => {
  assert.equal(typeof chunk, 'string');
  console.log('Got %d characters of string data:', chunk.length);
});

By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.

Returns a reference to the EventEmitter, so that calls can be chained.

Calls message.socket.setTimeout(msecs, callback).

This method is similar to Array.prototype.some and calls fn on each chunk in the stream until the awaited return value is true (or any truthy value). Once an fn call on a chunk awaited return value is truthy, the stream is destroyed and the promise is fulfilled with true. If none of the fn calls on the chunks return a truthy value, the promise is fulfilled with false.

This method returns a new stream with the first limit chunks.

This method allows easily obtaining the contents of a stream.

As this method reads the entire stream into memory, it negates the benefits of streams. It's intended for interoperability and convenience, not as the primary way to consume streams.

The readable.unpipe() method detaches a Writable stream previously attached using the pipe method.

If the destination is not specified, then all pipes are detached.

If the destination is specified, but no pipe is set up for it, then the method does nothing.

import fs from 'node:fs';
const readable = getReadableStreamSomehow();
const writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second.
readable.pipe(writable);
setTimeout(() => {
  console.log('Stop writing to file.txt.');
  readable.unpipe(writable);
  console.log('Manually close the file stream.');
  writable.end();
}, 1000);

Passing chunk as null signals the end of the stream (EOF) and behaves the same as readable.push(null), after which no more data can be written. The EOF signal is put at the end of the buffer and any buffered data will still be flushed.

The readable.unshift() method pushes a chunk of data back into the internal buffer. This is useful in certain situations where a stream is being consumed by code that needs to "un-consume" some amount of data that it has optimistically pulled out of the source, so that the data can be passed on to some other party.

The stream.unshift(chunk) method cannot be called after the 'end' event has been emitted or a runtime error will be thrown.

Developers using stream.unshift() often should consider switching to use of a Transform stream instead. See the API for stream implementers section for more information.

// Pull off a header delimited by \n\n.
// Use unshift() if we get too much.
// Call the callback with (error, header, stream).
import { StringDecoder } from 'node:string_decoder';
function parseHeader(stream, callback) {
  stream.on('error', callback);
  stream.on('readable', onReadable);
  const decoder = new StringDecoder('utf8');
  let header = '';
  function onReadable() {
    let chunk;
    while (null !== (chunk = stream.read())) {
      const str = decoder.write(chunk);
      if (str.includes('\n\n')) {
        // Found the header boundary.
        const split = str.split(/\n\n/);
        header += split.shift();
        const remaining = split.join('\n\n');
        const buf = Buffer.from(remaining, 'utf8');
        stream.removeListener('error', callback);
        // Remove the 'readable' listener before unshifting.
        stream.removeListener('readable', onReadable);
        if (buf.length)
          stream.unshift(buf);
        // Now the body of the message can be read from the stream.
        callback(null, header, stream);
        return;
      }
      // Still reading the header.
      header += str;
    }
  }
}

Unlike push, stream.unshift(chunk) will not end the reading process by resetting the internal reading state of the stream. This can cause unexpected results if readable.unshift() is called during a read (i.e. from within a _read implementation on a custom stream). Following the call to readable.unshift() with an immediate push will reset the reading state appropriately, however it is best to simply avoid calling readable.unshift() while in the process of performing a read.

Prior to Node.js 0.10, streams did not implement the entire node:stream module API as it is currently defined. (See Compatibility for more information.)

When using an older Node.js library that emits 'data' events and has a pause method that is advisory only, the readable.wrap() method can be used to create a Readable stream that uses the old stream as its data source.

It will rarely be necessary to use readable.wrap() but the method has been provided as a convenience for interacting with older Node.js applications and libraries.

import { OldReader } from './old-api-module.js';
import { Readable } from 'node:stream';
const oreader = new OldReader();
const myReader = new Readable().wrap(oreader);

myReader.on('readable', () => {
  myReader.read(); // etc.
});

A utility method for creating Readable Streams out of iterators.

A utility method for creating a Readable from a web ReadableStream.

Returns whether the stream has been read from or cancelled.

A utility method for creating a web ReadableStream from a Readable.