Streams

A stream is an abstract interface implemented by various objects in Node. For example a request to an HTTP server is a stream, as is stdout. Streams are readable, writable, or both. All streams are instances of EventEmitter.

Readable Stream

A Readable Stream has the following methods, members, and events.

Table of Contents #

Event: 'data' #

function (data) { }

The 'data' event emits either a Buffer (by default) or a string if setEncoding() was used.

Event: 'end' #

function () { }

Emitted when the stream has received an EOF (FIN in TCP terminology). Indicates that no more 'data' events will happen. If the stream is also writable, it may be possible to continue writing.

Event: 'error' #

function (exception) { }

Emitted if there was an error receiving data.

Event: 'close' #

function () { }

Emitted when the underlying file descriptor has been closed. Not all streams will emit this. (For example, an incoming HTTP request will not emit 'close'.)

stream.readable #

A boolean that is true by default, but turns false after an 'error' occurred, the stream came to an 'end', or destroy() was called.

stream.setEncoding(encoding) #

Makes the data event emit a string instead of a Buffer. encoding can be 'utf8', 'ascii', or 'base64'.

stream.pause() #

Pauses the incoming 'data' events.

stream.resume() #

Resumes the incoming 'data' events after a pause().

stream.destroy() #

Closes the underlying file descriptor. Stream will not emit any more events.

stream.destroySoon() #

After the write queue is drained, close the file descriptor.

stream.pipe(destination, [options]) #

This is a Stream.prototype method available on all Streams.

Connects this read stream to destination WriteStream. Incoming data on this stream gets written to destination. The destination and source streams are kept in sync by pausing and resuming as necessary.

This function returns the destination stream.

Emulating the Unix cat command:

process.stdin.resume();
process.stdin.pipe(process.stdout);

By default end() is called on the destination when the source stream emits end, so that destination is no longer writable. Pass { end: false } as options to keep the destination stream open.

This keeps process.stdout open so that "Goodbye" can be written at the end.

process.stdin.resume();

process.stdin.pipe(process.stdout, { end: false });

process.stdin.on("end", function() {
  process.stdout.write("Goodbye\n");
});

Writable Stream

A Writable Stream has the following methods, members, and events.

Event: 'drain' #

function () { }

After a write() method returned false, this event is emitted to indicate that it is safe to write again.

Event: 'error' #

function (exception) { }

Emitted on error with the exception exception.

Event: 'close' #

function () { }

Emitted when the underlying file descriptor has been closed.

Event: 'pipe' #

function (src) { }

Emitted when the stream is passed to a readable stream's pipe method.

stream.writable #

A boolean that is true by default, but turns false after an 'error' occurred or end() / destroy() was called.

stream.write(string, encoding='utf8', [fd]) #

Writes string with the given encoding to the stream. Returns true if the string has been flushed to the kernel buffer. Returns false to indicate that the kernel buffer is full, and the data will be sent out in the future. The 'drain' event will indicate when the kernel buffer is empty again. The encoding defaults to 'utf8'.

If the optional fd parameter is specified, it is interpreted as an integral file descriptor to be sent over the stream. This is only supported for UNIX streams, and is silently ignored otherwise. When writing a file descriptor in this manner, closing the descriptor before the stream drains risks sending an invalid (closed) FD.

stream.write(buffer) #

Same as the above except with a raw buffer.

stream.end() #

Terminates the stream with EOF or FIN. This call will allow queued write data to be sent before closing the stream.

stream.end(string, encoding) #

Sends string with the given encoding and terminates the stream with EOF or FIN. This is useful to reduce the number of packets sent.

stream.end(buffer) #

Same as above but with a buffer.

stream.destroy() #

Closes the underlying file descriptor. Stream will not emit any more events. Any queued write data will not be sent.

stream.destroySoon() #

After the write queue is drained, close the file descriptor. destroySoon() can still destroy straight away, as long as there is no data left in the queue for writes.

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