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RetriableReadableStream class

ONLY AVAILABLE IN NODE.JS RUNTIME. A Node.js ReadableStream will internally retry when internal ReadableStream unexpected ends.

Extends

Readable

Constructors

RetriableReadableStream(Aborter, ReadableStream, ReadableStreamGetter, number, number, IRetriableReadableStreamOptions)

Creates an instance of RetriableReadableStream.

Properties

destroyed

Is true after readable.destroy() has been called.

readable

Is true if it is safe to call readable.read(), which means the stream has not been destroyed or emitted 'error' or 'end'.

readableAborted

Returns whether the stream was destroyed or errored before emitting 'end'.

readableDidRead

Returns whether 'data' has been emitted.

readableEncoding

Getter for the property encoding of a given Readable stream. The encodingproperty can be set using the readable.setEncoding() method.

readableEnded

Becomes true when 'end' event is emitted.

readableFlowing

This property reflects the current state of a Readable stream as described in the Three states section.

readableHighWaterMark

Returns the value of highWaterMark passed when creating this Readable.

readableLength

This property contains the number of bytes (or objects) in the queue ready to be read. The value provides introspection data regarding the status of the highWaterMark.

readableObjectMode

Getter for the property objectMode of a given Readable stream.

Methods

addListener("close", () => void)

Event emitter The defined events on documents including:

  1. close
  2. data
  3. end
  4. error
  5. pause
  6. readable
  7. resume
addListener("data", (chunk: any) => void)
addListener("end", () => void)
addListener("error", (err: Error) => void)
addListener("pause", () => void)
addListener("readable", () => void)
addListener("resume", () => void)
addListener(string | symbol, (args: any[]) => void)
destroy(Error)

Destroy the stream. Optionally emit an 'error' event, and emit a 'close'event (unless emitClose is set to false). After this call, the readable stream will release any internal resources and subsequent calls to push()will be ignored. Once destroy() has been called any further calls will be a no-op and no further errors except from _destroy() may be emitted as 'error'.

Implementors should not override this method, but instead implement readable._destroy().

emit("close")
emit("data", any)
emit("end")
emit("error", Error)
emit("pause")
emit("readable")
emit("resume")
emit(string | symbol, any[])
eventNames()

Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.

const EventEmitter = require('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) ]
from(Iterable<any> | AsyncIterable<any>, ReadableOptions)

A utility method for creating Readable Streams out of iterators.

getMaxListeners()

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

isDisturbed(Readable | ReadableStream)

Returns whether the stream has been read from or cancelled.

isPaused()

The readable.isPaused() method returns the current operating state of theReadable. This is used primarily by the mechanism that underlies thereadable.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
listenerCount(string | symbol)

Returns the number of listeners listening to the event named eventName.

listeners(string | symbol)

Returns a copy of the array of listeners for the event named eventName.

server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
off(string | symbol, (args: any[]) => void)

Alias for emitter.removeListener().

on("close", () => void)
on("data", (chunk: any) => void)
on("end", () => void)
on("error", (err: Error) => void)
on("pause", () => void)
on("readable", () => void)
on("resume", () => void)
on(string | symbol, (args: any[]) => void)
once("close", () => void)
once("data", (chunk: any) => void)
once("end", () => void)
once("error", (err: Error) => void)
once("pause", () => void)
once("readable", () => void)
once("resume", () => void)
once(string | symbol, (args: any[]) => void)
pause()

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.

pipe<T>(T, undefined | Object)
prependListener("close", () => void)
prependListener("data", (chunk: any) => void)
prependListener("end", () => void)
prependListener("error", (err: Error) => void)
prependListener("pause", () => void)
prependListener("readable", () => void)
prependListener("resume", () => void)
prependListener(string | symbol, (args: any[]) => void)
prependOnceListener("close", () => void)
prependOnceListener("data", (chunk: any) => void)
prependOnceListener("end", () => void)
prependOnceListener("error", (err: Error) => void)
prependOnceListener("pause", () => void)
prependOnceListener("readable", () => void)
prependOnceListener("resume", () => void)
prependOnceListener(string | symbol, (args: any[]) => void)
push(any, BufferEncoding)
rawListeners(string | symbol)

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
read(undefined | number)

The readable.read() method pulls some data out of the internal buffer and returns it. If no data available to be read, null is returned. By default, the data will be 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. Ifsize 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 thesize argument.

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

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

removeAllListeners(string | symbol)

Removes all listeners, or those of the specified eventName. It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).

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

removeListener("close", () => void)
removeListener("data", (chunk: any) => void)
removeListener("end", () => void)
removeListener("error", (err: Error) => void)
removeListener("pause", () => void)
removeListener("readable", () => void)
removeListener("resume", () => void)
removeListener(string | symbol, (args: any[]) => void)
resume()

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.

setEncoding(BufferEncoding)

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 asBuffer objects. Setting an encoding causes the stream data to be returned as strings of the specified encoding rather than as Bufferobjects. For instance, calling readable.setEncoding('utf8') will cause the output data to be interpreted as UTF-8 data, and passed as strings. Callingreadable.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);
});
setMaxListeners(number)

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 toInfinity (or 0) to indicate an unlimited number of listeners. Returns a reference to the EventEmitter, so that calls can be chained.

unpipe(NodeJS.WritableStream)

The readable.unpipe() method detaches a Writable stream previously attached using the <xref: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.

const fs = require('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);
unshift(any, BufferEncoding)

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).
const { StringDecoder } = require('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.match(/\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);
      } else {
        // Still reading the header.
        header += str;
      }
    }
  }
}

Unlike <xref: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 <xref:_read> implementation on a custom stream). Following the call to readable.unshift() with an immediate <xref: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.

wrap(ReadableStream)

Prior to Node.js 0.10, streams did not implement the entire 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 <xref:pause> method that is advisory only, thereadable.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.

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

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

Constructor Details

RetriableReadableStream(Aborter, ReadableStream, ReadableStreamGetter, number, number, IRetriableReadableStreamOptions)

Creates an instance of RetriableReadableStream.

new RetriableReadableStream(aborter: Aborter, source: ReadableStream, getter: ReadableStreamGetter, offset: number, count: number, options?: IRetriableReadableStreamOptions)

Parameters

aborter
Aborter

Create a new Aborter instance with Aborter.none or Aborter.timeout(), goto documents of Aborter for more examples about request cancellation

source

ReadableStream

The current ReadableStream returned from getter

getter
ReadableStreamGetter

A method calling downloading request returning a new ReadableStream from specified offset

offset

number

Offset position in original data source to read

count

number

How much data in original data source to read

Property Details

destroyed

Is true after readable.destroy() has been called.

destroyed: boolean

Property Value

boolean

readable

Is true if it is safe to call readable.read(), which means the stream has not been destroyed or emitted 'error' or 'end'.

readable: boolean

Property Value

boolean

readableAborted

Returns whether the stream was destroyed or errored before emitting 'end'.

readableAborted: boolean

Property Value

boolean

readableDidRead

Returns whether 'data' has been emitted.

readableDidRead: boolean

Property Value

boolean

readableEncoding

Getter for the property encoding of a given Readable stream. The encodingproperty can be set using the readable.setEncoding() method.

readableEncoding: BufferEncoding | null

Property Value

BufferEncoding | null

readableEnded

Becomes true when 'end' event is emitted.

readableEnded: boolean

Property Value

boolean

readableFlowing

This property reflects the current state of a Readable stream as described in the Three states section.

readableFlowing: boolean | null

Property Value

boolean | null

readableHighWaterMark

Returns the value of highWaterMark passed when creating this Readable.

readableHighWaterMark: number

Property Value

number

readableLength

This property contains the number of bytes (or objects) in the queue ready to be read. The value provides introspection data regarding the status of the highWaterMark.

readableLength: number

Property Value

number

readableObjectMode

Getter for the property objectMode of a given Readable stream.

readableObjectMode: boolean

Property Value

boolean

Method Details

addListener("close", () => void)

Event emitter The defined events on documents including:

  1. close
  2. data
  3. end
  4. error
  5. pause
  6. readable
  7. resume
function addListener(event: "close", listener: () => void)

Parameters

event

"close"

listener

() => void

Returns

this

addListener("data", (chunk: any) => void)

function addListener(event: "data", listener: (chunk: any) => void)

Parameters

event

"data"

listener

(chunk: any) => void

Returns

this

addListener("end", () => void)

function addListener(event: "end", listener: () => void)

Parameters

event

"end"

listener

() => void

Returns

this

addListener("error", (err: Error) => void)

function addListener(event: "error", listener: (err: Error) => void)

Parameters

event

"error"

listener

(err: Error) => void

Returns

this

addListener("pause", () => void)

function addListener(event: "pause", listener: () => void)

Parameters

event

"pause"

listener

() => void

Returns

this

addListener("readable", () => void)

function addListener(event: "readable", listener: () => void)

Parameters

event

"readable"

listener

() => void

Returns

this

addListener("resume", () => void)

function addListener(event: "resume", listener: () => void)

Parameters

event

"resume"

listener

() => void

Returns

this

addListener(string | symbol, (args: any[]) => void)

function addListener(event: string | symbol, listener: (args: any[]) => void)

Parameters

event

string | symbol

listener

(args: any[]) => void

Returns

this

destroy(Error)

Destroy the stream. Optionally emit an 'error' event, and emit a 'close'event (unless emitClose is set to false). After this call, the readable stream will release any internal resources and subsequent calls to push()will be ignored. Once destroy() has been called any further calls will be a no-op and no further errors except from _destroy() may be emitted as 'error'.

Implementors should not override this method, but instead implement readable._destroy().

function destroy(error?: Error)

Parameters

error

Error

Error which will be passed as payload in 'error' event

emit("close")

function emit(event: "close")

Parameters

event

"close"

Returns

boolean

emit("data", any)

function emit(event: "data", chunk: any)

Parameters

event

"data"

chunk

any

Returns

boolean

emit("end")

function emit(event: "end")

Parameters

event

"end"

Returns

boolean

emit("error", Error)

function emit(event: "error", err: Error)

Parameters

event

"error"

err

Error

Returns

boolean

emit("pause")

function emit(event: "pause")

Parameters

event

"pause"

Returns

boolean

emit("readable")

function emit(event: "readable")

Parameters

event

"readable"

Returns

boolean

emit("resume")

function emit(event: "resume")

Parameters

event

"resume"

Returns

boolean

emit(string | symbol, any[])

function emit(event: string | symbol, args: any[])

Parameters

event

string | symbol

args

any[]

Returns

boolean

eventNames()

Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.

const EventEmitter = require('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) ]
function eventNames()

Returns

Array<string | symbol>

from(Iterable<any> | AsyncIterable<any>, ReadableOptions)

A utility method for creating Readable Streams out of iterators.

static function from(iterable: Iterable<any> | AsyncIterable<any>, options?: ReadableOptions)

Parameters

iterable

Iterable<any> | AsyncIterable<any>

options

ReadableOptions

Returns

Readable

getMaxListeners()

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

function getMaxListeners()

Returns

number

isDisturbed(Readable | ReadableStream)

Returns whether the stream has been read from or cancelled.

static function isDisturbed(stream: Readable | ReadableStream)

Parameters

stream

Readable | ReadableStream

Returns

boolean

isPaused()

The readable.isPaused() method returns the current operating state of theReadable. This is used primarily by the mechanism that underlies thereadable.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
function isPaused()

Returns

boolean

listenerCount(string | symbol)

Returns the number of listeners listening to the event named eventName.

function listenerCount(eventName: string | symbol)

Parameters

eventName

string | symbol

The name of the event being listened for

Returns

number

listeners(string | symbol)

Returns a copy of the array of listeners for the event named eventName.

server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
function listeners(eventName: string | symbol)

Parameters

eventName

string | symbol

Returns

Function[]

off(string | symbol, (args: any[]) => void)

Alias for emitter.removeListener().

function off(eventName: string | symbol, listener: (args: any[]) => void)

Parameters

eventName

string | symbol

listener

(args: any[]) => void

Returns

this

on("close", () => void)

function on(event: "close", listener: () => void)

Parameters

event

"close"

listener

() => void

Returns

this

on("data", (chunk: any) => void)

function on(event: "data", listener: (chunk: any) => void)

Parameters

event

"data"

listener

(chunk: any) => void

Returns

this

on("end", () => void)

function on(event: "end", listener: () => void)

Parameters

event

"end"

listener

() => void

Returns

this

on("error", (err: Error) => void)

function on(event: "error", listener: (err: Error) => void)

Parameters

event

"error"

listener

(err: Error) => void

Returns

this

on("pause", () => void)

function on(event: "pause", listener: () => void)

Parameters

event

"pause"

listener

() => void

Returns

this

on("readable", () => void)

function on(event: "readable", listener: () => void)

Parameters

event

"readable"

listener

() => void

Returns

this

on("resume", () => void)

function on(event: "resume", listener: () => void)

Parameters

event

"resume"

listener

() => void

Returns

this

on(string | symbol, (args: any[]) => void)

function on(event: string | symbol, listener: (args: any[]) => void)

Parameters

event

string | symbol

listener

(args: any[]) => void

Returns

this

once("close", () => void)

function once(event: "close", listener: () => void)

Parameters

event

"close"

listener

() => void

Returns

this

once("data", (chunk: any) => void)

function once(event: "data", listener: (chunk: any) => void)

Parameters

event

"data"

listener

(chunk: any) => void

Returns

this

once("end", () => void)

function once(event: "end", listener: () => void)

Parameters

event

"end"

listener

() => void

Returns

this

once("error", (err: Error) => void)

function once(event: "error", listener: (err: Error) => void)

Parameters

event

"error"

listener

(err: Error) => void

Returns

this

once("pause", () => void)

function once(event: "pause", listener: () => void)

Parameters

event

"pause"

listener

() => void

Returns

this

once("readable", () => void)

function once(event: "readable", listener: () => void)

Parameters

event

"readable"

listener

() => void

Returns

this

once("resume", () => void)

function once(event: "resume", listener: () => void)

Parameters

event

"resume"

listener

() => void

Returns

this

once(string | symbol, (args: any[]) => void)

function once(event: string | symbol, listener: (args: any[]) => void)

Parameters

event

string | symbol

listener

(args: any[]) => void

Returns

this

pause()

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.

function pause()

Returns

this

pipe<T>(T, undefined | Object)

function pipe<T>(destination: T, options?: undefined | Object)

Parameters

destination

T

options

undefined | Object

Returns

T

prependListener("close", () => void)

function prependListener(event: "close", listener: () => void)

Parameters

event

"close"

listener

() => void

Returns

this

prependListener("data", (chunk: any) => void)

function prependListener(event: "data", listener: (chunk: any) => void)

Parameters

event

"data"

listener

(chunk: any) => void

Returns

this

prependListener("end", () => void)

function prependListener(event: "end", listener: () => void)

Parameters

event

"end"

listener

() => void

Returns

this

prependListener("error", (err: Error) => void)

function prependListener(event: "error", listener: (err: Error) => void)

Parameters

event

"error"

listener

(err: Error) => void

Returns

this

prependListener("pause", () => void)

function prependListener(event: "pause", listener: () => void)

Parameters

event

"pause"

listener

() => void

Returns

this

prependListener("readable", () => void)

function prependListener(event: "readable", listener: () => void)

Parameters

event

"readable"

listener

() => void

Returns

this

prependListener("resume", () => void)

function prependListener(event: "resume", listener: () => void)

Parameters

event

"resume"

listener

() => void

Returns

this

prependListener(string | symbol, (args: any[]) => void)

function prependListener(event: string | symbol, listener: (args: any[]) => void)

Parameters

event

string | symbol

listener

(args: any[]) => void

Returns

this

prependOnceListener("close", () => void)

function prependOnceListener(event: "close", listener: () => void)

Parameters

event

"close"

listener

() => void

Returns

this

prependOnceListener("data", (chunk: any) => void)

function prependOnceListener(event: "data", listener: (chunk: any) => void)

Parameters

event

"data"

listener

(chunk: any) => void

Returns

this

prependOnceListener("end", () => void)

function prependOnceListener(event: "end", listener: () => void)

Parameters

event

"end"

listener

() => void

Returns

this

prependOnceListener("error", (err: Error) => void)

function prependOnceListener(event: "error", listener: (err: Error) => void)

Parameters

event

"error"

listener

(err: Error) => void

Returns

this

prependOnceListener("pause", () => void)

function prependOnceListener(event: "pause", listener: () => void)

Parameters

event

"pause"

listener

() => void

Returns

this

prependOnceListener("readable", () => void)

function prependOnceListener(event: "readable", listener: () => void)

Parameters

event

"readable"

listener

() => void

Returns

this

prependOnceListener("resume", () => void)

function prependOnceListener(event: "resume", listener: () => void)

Parameters

event

"resume"

listener

() => void

Returns

this

prependOnceListener(string | symbol, (args: any[]) => void)

function prependOnceListener(event: string | symbol, listener: (args: any[]) => void)

Parameters

event

string | symbol

listener

(args: any[]) => void

Returns

this

push(any, BufferEncoding)

function push(chunk: any, encoding?: BufferEncoding)

Parameters

chunk

any

encoding

BufferEncoding

Returns

boolean

rawListeners(string | symbol)

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
function rawListeners(eventName: string | symbol)

Parameters

eventName

string | symbol

Returns

Function[]

read(undefined | number)

The readable.read() method pulls some data out of the internal buffer and returns it. If no data available to be read, null is returned. By default, the data will be 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. Ifsize 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 thesize argument.

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

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

function read(size?: undefined | number)

Parameters

size

undefined | number

Optional argument to specify how much data to read.

Returns

any

removeAllListeners(string | symbol)

Removes all listeners, or those of the specified eventName. It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).

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

function removeAllListeners(event?: string | symbol)

Parameters

event

string | symbol

Returns

this

removeListener("close", () => void)

function removeListener(event: "close", listener: () => void)

Parameters

event

"close"

listener

() => void

Returns

this

removeListener("data", (chunk: any) => void)

function removeListener(event: "data", listener: (chunk: any) => void)

Parameters

event

"data"

listener

(chunk: any) => void

Returns

this

removeListener("end", () => void)

function removeListener(event: "end", listener: () => void)

Parameters

event

"end"

listener

() => void

Returns

this

removeListener("error", (err: Error) => void)

function removeListener(event: "error", listener: (err: Error) => void)

Parameters

event

"error"

listener

(err: Error) => void

Returns

this

removeListener("pause", () => void)

function removeListener(event: "pause", listener: () => void)

Parameters

event

"pause"

listener

() => void

Returns

this

removeListener("readable", () => void)

function removeListener(event: "readable", listener: () => void)

Parameters

event

"readable"

listener

() => void

Returns

this

removeListener("resume", () => void)

function removeListener(event: "resume", listener: () => void)

Parameters

event

"resume"

listener

() => void

Returns

this

removeListener(string | symbol, (args: any[]) => void)

function removeListener(event: string | symbol, listener: (args: any[]) => void)

Parameters

event

string | symbol

listener

(args: any[]) => void

Returns

this

resume()

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.

function resume()

Returns

this

setEncoding(BufferEncoding)

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 asBuffer objects. Setting an encoding causes the stream data to be returned as strings of the specified encoding rather than as Bufferobjects. For instance, calling readable.setEncoding('utf8') will cause the output data to be interpreted as UTF-8 data, and passed as strings. Callingreadable.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);
});
function setEncoding(encoding: BufferEncoding)

Parameters

encoding

BufferEncoding

The encoding to use.

Returns

this

setMaxListeners(number)

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 toInfinity (or 0) to indicate an unlimited number of listeners. Returns a reference to the EventEmitter, so that calls can be chained.

function setMaxListeners(n: number)

Parameters

n

number

Returns

this

unpipe(NodeJS.WritableStream)

The readable.unpipe() method detaches a Writable stream previously attached using the <xref: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.

const fs = require('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);
function unpipe(destination?: NodeJS.WritableStream)

Parameters

destination
NodeJS.WritableStream

Optional specific stream to unpipe

Returns

this

unshift(any, BufferEncoding)

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).
const { StringDecoder } = require('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.match(/\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);
      } else {
        // Still reading the header.
        header += str;
      }
    }
  }
}

Unlike <xref: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 <xref:_read> implementation on a custom stream). Following the call to readable.unshift() with an immediate <xref: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.

function unshift(chunk: any, encoding?: BufferEncoding)

Parameters

chunk

any

Chunk of data to unshift onto the read queue. For streams not operating in object mode, chunk must be a string, Buffer, Uint8Array or null. For object mode streams, chunk may be any JavaScript value.

encoding

BufferEncoding

Encoding of string chunks. Must be a valid Buffer encoding, such as 'utf8' or 'ascii'.

wrap(ReadableStream)

Prior to Node.js 0.10, streams did not implement the entire 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 <xref:pause> method that is advisory only, thereadable.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.

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

myReader.on('readable', () => {
  myReader.read(); // etc.
});
function wrap(stream: ReadableStream)

Parameters

stream

ReadableStream

An "old style" readable stream

Returns

this