dots.node.fs.read-stream — io.github.dots-cljs/dots-node 20.12.12-9

Instances of fs.ReadStream are created and returned using the {@link createReadStream } function.

add-listener cljs

(add-listener read-stream event listener)

events.EventEmitter

1. open
2. close
3. ready

Parameters:

• event: string | symbol
• listener: (...args: any[]) => void

Returns: ReadStream

as-indexed-pairs cljs

(as-indexed-pairs read-stream)

(as-indexed-pairs read-stream options)

This method returns a new stream with chunks of the underlying stream paired with a counter in the form [index, chunk]. The first index value is 0 and it increases by 1 for each chunk produced.

Parameters:

• options: Pick<ArrayOptions, "signal"> | undefined

Returns: Readable - a stream of indexed pairs.

bytes-read cljs

(bytes-read read-stream)

The number of bytes that have been read so far.

close cljs

(close read-stream)

(close read-stream callback)

Parameters:

• callback: ((err?: ErrnoException | null | undefined) => void) | undefined

Returns: void

closed? cljs

(closed? read-stream)

Is true after 'close' has been emitted.

compose cljs

(compose read-stream stream)

(compose read-stream stream options)

Parameters:

• stream: T | ComposeFnParam | Iterable<T> | AsyncIterable<T>
• options: { signal: AbortSignal; } | undefined

Returns: T

destroy cljs

(destroy read-stream)

(destroy read-stream 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().

Parameters:

• error: Error | undefined - Error which will be passed as payload in 'error' event

Returns: ReadStream

destroyed? cljs

(destroyed? read-stream)

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

drop cljs

(drop read-stream limit)

(drop read-stream limit options)

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

Parameters:

• limit: number - the number of chunks to drop from the readable.
• options: Pick<ArrayOptions, "signal"> | undefined

Returns: Readable - a stream with limit chunks dropped from the start.

emit? cljs

(emit? read-stream & event)

(emit? read-stream event chunk)

(emit? read-stream event err)

(emit? read-stream event & args)

Parameters:

• event: string | symbol
• args: any[]
• chunk: any
• err: Error

Returns: boolean

errored cljs

(errored read-stream)

Returns error if the stream has been destroyed with an error.

event-names cljs

(event-names read-stream)

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

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) ]

Returns: (string | symbol)[]

every cljs

(every read-stream fn)

(every read-stream fn options)

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.

Parameters:

• fn: (data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => boolean | Promise<boolean> - a function to call on each chunk of the stream. Async or not.
• options: ArrayOptions | undefined

Returns: Promise<boolean> - a promise evaluating to true if fn returned a truthy value for every one of the chunks.

filter cljs

(filter read-stream fn)

(filter read-stream fn options)

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.

Parameters:

• fn: (data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => boolean | Promise<boolean> - a function to filter chunks from the stream. Async or not.
• options: ArrayOptions | undefined

Returns: Readable - a stream filtered with the predicate fn.

find cljs

(find read-stream fn)

(find read-stream fn options)

This method is similar to Array.prototype.find and calls fn on each chunk in the stream to find a chunk with a truthy value for fn. Once an fn call's awaited return value is truthy, the stream is destroyed and the promise is fulfilled with value for which fn returned a truthy value. If all of the fn calls on the chunks return a falsy value, the promise is fulfilled with undefined.

Parameters:

• fn: (data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => boolean | Promise<boolean>
• options: ArrayOptions | undefined

Returns: Promise<any> - a promise evaluating to the first chunk for which fn evaluated with a truthy value, or undefined if no element was found.

flat-map cljs

(flat-map read-stream fn)

(flat-map read-stream fn options)

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.

Parameters:

• fn: (data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => any - a function to map over every chunk in the stream. May be async. May be a stream or generator.
• options: ArrayOptions | undefined

Returns: Readable - a stream flat-mapped with the function fn.

for-each cljs

(for-each read-stream fn)

(for-each read-stream fn options)

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.

Parameters:

• fn: (data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => void | Promise<void> - a function to call on each chunk of the stream. Async or not.
• options: ArrayOptions | undefined

Returns: Promise<void> - a promise for when the stream has finished.

iterator cljs

(iterator read-stream)

(iterator read-stream options)

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.

Parameters:

• options: { destroyOnReturn?: boolean | undefined; } | undefined

Returns: AsyncIterableIterator<any>

listener-count cljs

(listener-count read-stream event-name)

(listener-count read-stream event-name listener)

Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.

Parameters:

• event-name: string | symbol - The name of the event being listened for
• listener: Function | undefined - The event handler function

Returns: number

listeners cljs

(listeners read-stream event-name)

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] ]

Parameters:

• event-name: string | symbol

Returns: Function[]

map cljs

(map read-stream fn)

(map read-stream fn options)

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.

Parameters:

• fn: (data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => any - a function to map over every chunk in the stream. Async or not.
• options: ArrayOptions | undefined

Returns: Readable - a stream mapped with the function fn.

max-listeners cljs

(max-listeners read-stream)

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

Returns: number

off cljs

(off read-stream event-name listener)

Alias for emitter.removeListener().

Parameters:

• event-name: string | symbol
• listener: (...args: any[]) => void

Returns: ReadStream

on cljs

(on read-stream event listener)

Parameters:

• event: string | symbol
• listener: (...args: any[]) => void

Returns: ReadStream

once cljs

(once read-stream event listener)

Parameters:

• event: string | symbol
• listener: (...args: any[]) => void

Returns: ReadStream

path cljs

(path read-stream)

The path to the file the stream is reading from as specified in the first argument to fs.createReadStream(). If path is passed as a string, thenreadStream.path will be a string. If path is passed as a Buffer, thenreadStream.path will be a Buffer. If fd is specified, thenreadStream.path will be undefined.

pause cljs

(pause read-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.

Returns: ReadStream

paused? cljs

(paused? read-stream)

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

Returns: boolean

pending? cljs

(pending? read-stream)

This property is true if the underlying file has not been opened yet, i.e. before the 'ready' event is emitted.

pipe cljs

(pipe read-stream destination)

(pipe read-stream destination options)

Parameters:

• destination: T
• options: { end?: boolean | undefined; } | undefined

Returns: T

prepend-listener cljs

(prepend-listener read-stream event listener)

Parameters:

• event: string | symbol
• listener: (...args: any[]) => void

Returns: ReadStream

prepend-once-listener cljs

(prepend-once-listener read-stream event listener)

Parameters:

• event: string | symbol
• listener: (...args: any[]) => void

Returns: ReadStream

push? cljs

(push? read-stream chunk)

(push? read-stream chunk encoding)

Parameters:

• chunk: any
• encoding: BufferEncoding | undefined

Returns: boolean

raw-listeners cljs

(raw-listeners read-stream event-name)

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

import { EventEmitter } from 'node:events';
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');

Parameters:

• event-name: string | symbol

Returns: Function[]

read cljs

(read read-stream)

(read read-stream size)

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 {@link read } after the 'end' event has been emitted will return null. No runtime error will be raised.

Parameters:

• size: number | undefined - Optional argument to specify how much data to read.

Returns: any

readable-aborted? cljs

(readable-aborted? read-stream)

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

readable-did-read? cljs

(readable-did-read? read-stream)

Returns whether 'data' has been emitted.

readable-encoding cljs

(readable-encoding read-stream)

Getter for the property encoding of a given Readable stream. The encoding property can be set using the {@link setEncoding } method.

readable-ended? cljs

(readable-ended? read-stream)

Becomes true when 'end' event is emitted.

readable-flowing? cljs

(readable-flowing? read-stream)

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

readable-high-water-mark cljs

(readable-high-water-mark read-stream)

Returns the value of highWaterMark passed when creating this Readable.

readable-length cljs

(readable-length read-stream)

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.

readable-object-mode? cljs

(readable-object-mode? read-stream)

Getter for the property objectMode of a given Readable stream.

readable? cljs

(readable? read-stream)

Is true if it is safe to call {@link read }, which means the stream has not been destroyed or emitted 'error' or 'end'.

reduce cljs

(reduce read-stream fn)

(reduce read-stream fn initial)

(reduce read-stream fn initial options)

This method calls fn on each chunk of the stream in order, passing it the result from the calculation on the previous element. It returns a promise for the final value of the reduction.

If no initial value is supplied the first chunk of the stream is used as the initial value. If the stream is empty, the promise is rejected with a TypeError with the ERR_INVALID_ARGS code property.

The reducer function iterates the stream element-by-element which means that there is no concurrency parameter or parallelism. To perform a reduce concurrently, you can extract the async function to readable.map method.

Parameters:

• fn: (previous: T, data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => T
• initial: T
• options: Pick<ArrayOptions, "signal"> | undefined

Returns: Promise<T> - a promise for the final value of the reduction.

remove-all-listeners cljs

(remove-all-listeners read-stream)

(remove-all-listeners read-stream event-name)

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.

Parameters:

• event-name: string | symbol | undefined

Returns: ReadStream

remove-listener cljs

(remove-listener read-stream event listener)

Parameters:

• event: string | symbol
• listener: (...args: any[]) => void

Returns: ReadStream

resume cljs

(resume read-stream)

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.

Returns: ReadStream

set-bytes-read! cljs

(set-bytes-read! read-stream value)

The number of bytes that have been read so far.

set-destroyed! cljs

(set-destroyed! read-stream value)

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

set-encoding cljs

(set-encoding read-stream encoding)

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);
});

Parameters:

• encoding: BufferEncoding - The encoding to use.

Returns: ReadStream

set-max-listeners cljs

(set-max-listeners read-stream n)

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.

Parameters:

• n: number

Returns: ReadStream

set-path! cljs

(set-path! read-stream value)

The path to the file the stream is reading from as specified in the first argument to fs.createReadStream(). If path is passed as a string, thenreadStream.path will be a string. If path is passed as a Buffer, thenreadStream.path will be a Buffer. If fd is specified, thenreadStream.path will be undefined.

set-pending! cljs

(set-pending! read-stream value)

This property is true if the underlying file has not been opened yet, i.e. before the 'ready' event is emitted.

set-readable! cljs

(set-readable! read-stream value)

Is true if it is safe to call {@link read }, which means the stream has not been destroyed or emitted 'error' or 'end'.

some cljs

(some read-stream fn)

(some read-stream fn options)

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.

Parameters:

• fn: (data: any, options?: Pick<ArrayOptions, "signal"> | undefined) => boolean | Promise<boolean> - a function to call on each chunk of the stream. Async or not.
• options: ArrayOptions | undefined

Returns: Promise<boolean> - a promise evaluating to true if fn returned a truthy value for at least one of the chunks.

take cljs

(take read-stream limit)

(take read-stream limit options)

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

Parameters:

• limit: number - the number of chunks to take from the readable.
• options: Pick<ArrayOptions, "signal"> | undefined

Returns: Readable - a stream with limit chunks taken.

to-array cljs

(to-array read-stream)

(to-array read-stream options)

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.

Parameters:

• options: Pick<ArrayOptions, "signal"> | undefined

Returns: Promise<any[]> - a promise containing an array with the contents of the stream.

unpipe cljs

(unpipe read-stream)

(unpipe read-stream destination)

The readable.unpipe() method detaches a Writable stream previously attached using the {@link 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('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);

Parameters:

• destination: WritableStream | undefined - Optional specific stream to unpipe

Returns: ReadStream

unshift cljs

(unshift read-stream chunk)

(unshift read-stream chunk encoding)

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('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 {@link 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 {@link _read } implementation on a custom stream). Following the call to readable.unshift() with an immediate {@link 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.

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

Returns: void

wrap cljs

(wrap read-stream stream)

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 {@link 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.

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

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

Parameters:

• stream: ReadableStream - An "old style" readable stream

Returns: ReadStream