--- /dev/null
+# Stream
+
+ Stability: 2 - Stable
+
+A stream is an abstract interface implemented by various objects in
+Node.js. For example a [request to an HTTP server][http-incoming-message] is a
+stream, as is [`process.stdout`][]. Streams are readable, writable, or both. All
+streams are instances of [`EventEmitter`][].
+
+You can load the Stream base classes by doing `require('stream')`.
+There are base classes provided for [Readable][] streams, [Writable][]
+streams, [Duplex][] streams, and [Transform][] streams.
+
+This document is split up into 3 sections:
+
+1. The first section explains the parts of the API that you need to be
+ aware of to use streams in your programs.
+2. The second section explains the parts of the API that you need to
+ use if you implement your own custom streams yourself. The API is designed to
+ make this easy for you to do.
+3. The third section goes into more depth about how streams work,
+ including some of the internal mechanisms and functions that you
+ should probably not modify unless you definitely know what you are
+ doing.
+
+
+## API for Stream Consumers
+
+<!--type=misc-->
+
+Streams can be either [Readable][], [Writable][], or both ([Duplex][]).
+
+All streams are EventEmitters, but they also have other custom methods
+and properties depending on whether they are Readable, Writable, or
+Duplex.
+
+If a stream is both Readable and Writable, then it implements all of
+the methods and events. So, a [Duplex][] or [Transform][] stream is
+fully described by this API, though their implementation may be
+somewhat different.
+
+It is not necessary to implement Stream interfaces in order to consume
+streams in your programs. If you **are** implementing streaming
+interfaces in your own program, please also refer to
+[API for Stream Implementors][].
+
+Almost all Node.js programs, no matter how simple, use Streams in some
+way. Here is an example of using Streams in an Node.js program:
+
+```js
+const http = require('http');
+
+var server = http.createServer( (req, res) => {
+ // req is an http.IncomingMessage, which is a Readable Stream
+ // res is an http.ServerResponse, which is a Writable Stream
+
+ var body = '';
+ // we want to get the data as utf8 strings
+ // If you don't set an encoding, then you'll get Buffer objects
+ req.setEncoding('utf8');
+
+ // Readable streams emit 'data' events once a listener is added
+ req.on('data', (chunk) => {
+ body += chunk;
+ });
+
+ // the end event tells you that you have entire body
+ req.on('end', () => {
+ try {
+ var data = JSON.parse(body);
+ } catch (er) {
+ // uh oh! bad json!
+ res.statusCode = 400;
+ return res.end(`error: ${er.message}`);
+ }
+
+ // write back something interesting to the user:
+ res.write(typeof data);
+ res.end();
+ });
+});
+
+server.listen(1337);
+
+// $ curl localhost:1337 -d '{}'
+// object
+// $ curl localhost:1337 -d '"foo"'
+// string
+// $ curl localhost:1337 -d 'not json'
+// error: Unexpected token o
+```
+
+### Class: stream.Duplex
+
+Duplex streams are streams that implement both the [Readable][] and
+[Writable][] interfaces.
+
+Examples of Duplex streams include:
+
+* [TCP sockets][]
+* [zlib streams][zlib]
+* [crypto streams][crypto]
+
+### Class: stream.Readable
+
+<!--type=class-->
+
+The Readable stream interface is the abstraction for a *source* of
+data that you are reading from. In other words, data comes *out* of a
+Readable stream.
+
+A Readable stream will not start emitting data until you indicate that
+you are ready to receive it.
+
+Readable streams have two "modes": a **flowing mode** and a **paused
+mode**. When in flowing mode, data is read from the underlying system
+and provided to your program as fast as possible. In paused mode, you
+must explicitly call [`stream.read()`][stream-read] to get chunks of data out.
+Streams start out in paused mode.
+
+**Note**: If no data event handlers are attached, and there are no
+[`stream.pipe()`][] destinations, and the stream is switched into flowing
+mode, then data will be lost.
+
+You can switch to flowing mode by doing any of the following:
+
+* Adding a [`'data'`][] event handler to listen for data.
+* Calling the [`stream.resume()`][stream-resume] method to explicitly open the
+ flow.
+* Calling the [`stream.pipe()`][] method to send the data to a [Writable][].
+
+You can switch back to paused mode by doing either of the following:
+
+* If there are no pipe destinations, by calling the
+ [`stream.pause()`][stream-pause] method.
+* If there are pipe destinations, by removing any [`'data'`][] event
+ handlers, and removing all pipe destinations by calling the
+ [`stream.unpipe()`][] method.
+
+Note that, for backwards compatibility reasons, removing [`'data'`][]
+event handlers will **not** automatically pause the stream. Also, if
+there are piped destinations, then calling [`stream.pause()`][stream-pause] will
+not guarantee that the stream will *remain* paused once those
+destinations drain and ask for more data.
+
+Examples of readable streams include:
+
+* [HTTP responses, on the client][http-incoming-message]
+* [HTTP requests, on the server][http-incoming-message]
+* [fs read streams][]
+* [zlib streams][zlib]
+* [crypto streams][crypto]
+* [TCP sockets][]
+* [child process stdout and stderr][]
+* [`process.stdin`][]
+
+#### Event: 'close'
+
+Emitted when the stream and any of its underlying resources (a file
+descriptor, for example) have been closed. The event indicates that
+no more events will be emitted, and no further computation will occur.
+
+Not all streams will emit the `'close'` event.
+
+#### Event: 'data'
+
+* `chunk` {Buffer|String} The chunk of data.
+
+Attaching a `'data'` event listener to a stream that has not been
+explicitly paused will switch the stream into flowing mode. Data will
+then be passed as soon as it is available.
+
+If you just want to get all the data out of the stream as fast as
+possible, this is the best way to do so.
+
+```js
+var readable = getReadableStreamSomehow();
+readable.on('data', (chunk) => {
+ console.log('got %d bytes of data', chunk.length);
+});
+```
+
+#### Event: 'end'
+
+This event fires when there will be no more data to read.
+
+Note that the `'end'` event **will not fire** unless the data is
+completely consumed. This can be done by switching into flowing mode,
+or by calling [`stream.read()`][stream-read] repeatedly until you get to the
+end.
+
+```js
+var readable = getReadableStreamSomehow();
+readable.on('data', (chunk) => {
+ console.log('got %d bytes of data', chunk.length);
+});
+readable.on('end', () => {
+ console.log('there will be no more data.');
+});
+```
+
+#### Event: 'error'
+
+* {Error Object}
+
+Emitted if there was an error receiving data.
+
+#### Event: 'readable'
+
+When a chunk of data can be read from the stream, it will emit a
+`'readable'` event.
+
+In some cases, listening for a `'readable'` event will cause some data
+to be read into the internal buffer from the underlying system, if it
+hadn't already.
+
+```javascript
+var readable = getReadableStreamSomehow();
+readable.on('readable', () => {
+ // there is some data to read now
+});
+```
+
+Once the internal buffer is drained, a `'readable'` event will fire
+again when more data is available.
+
+The `'readable'` event is not emitted in the "flowing" mode with the
+sole exception of the last one, on end-of-stream.
+
+The `'readable'` event indicates that the stream has new information:
+either new data is available or the end of the stream has been reached.
+In the former case, [`stream.read()`][stream-read] will return that data. In the
+latter case, [`stream.read()`][stream-read] will return null. For instance, in
+the following example, `foo.txt` is an empty file:
+
+```js
+const fs = require('fs');
+var rr = fs.createReadStream('foo.txt');
+rr.on('readable', () => {
+ console.log('readable:', rr.read());
+});
+rr.on('end', () => {
+ console.log('end');
+});
+```
+
+The output of running this script is:
+
+```
+$ node test.js
+readable: null
+end
+```
+
+#### readable.isPaused()
+
+* Return: {Boolean}
+
+This method returns whether or not the `readable` has been **explicitly**
+paused by client code (using [`stream.pause()`][stream-pause] without a
+corresponding [`stream.resume()`][stream-resume]).
+
+```js
+var readable = new stream.Readable
+
+readable.isPaused() // === false
+readable.pause()
+readable.isPaused() // === true
+readable.resume()
+readable.isPaused() // === false
+```
+
+#### readable.pause()
+
+* Return: `this`
+
+This 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.
+
+```js
+var readable = getReadableStreamSomehow();
+readable.on('data', (chunk) => {
+ console.log('got %d bytes of data', chunk.length);
+ readable.pause();
+ console.log('there will be no more data for 1 second');
+ setTimeout(() => {
+ console.log('now data will start flowing again');
+ readable.resume();
+ }, 1000);
+});
+```
+
+#### readable.pipe(destination[, options])
+
+* `destination` {stream.Writable} The destination for writing data
+* `options` {Object} Pipe options
+ * `end` {Boolean} End the writer when the reader ends. Default = `true`
+
+This method pulls all the data out of a readable stream, and writes it
+to the supplied destination, automatically managing the flow so that
+the destination is not overwhelmed by a fast readable stream.
+
+Multiple destinations can be piped to safely.
+
+```js
+var readable = getReadableStreamSomehow();
+var writable = fs.createWriteStream('file.txt');
+// All the data from readable goes into 'file.txt'
+readable.pipe(writable);
+```
+
+This function returns the destination stream, so you can set up pipe
+chains like so:
+
+```js
+var r = fs.createReadStream('file.txt');
+var z = zlib.createGzip();
+var w = fs.createWriteStream('file.txt.gz');
+r.pipe(z).pipe(w);
+```
+
+For example, emulating the Unix `cat` command:
+
+```js
+process.stdin.pipe(process.stdout);
+```
+
+By default [`stream.end()`][stream-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 `writer` open so that "Goodbye" can be written at the
+end.
+
+```js
+reader.pipe(writer, { end: false });
+reader.on('end', () => {
+ writer.end('Goodbye\n');
+});
+```
+
+Note that [`process.stderr`][] and [`process.stdout`][] are never closed until
+the process exits, regardless of the specified options.
+
+#### readable.read([size])
+
+* `size` {Number} Optional argument to specify how much data to read.
+* Return {String|Buffer|Null}
+
+The `read()` method pulls some data out of the internal buffer and
+returns it. If there is no data available, then it will return
+`null`.
+
+If you pass in a `size` argument, then it will return that many
+bytes. If `size` bytes are not available, then it will return `null`,
+unless we've ended, in which case it will return the data remaining
+in the buffer.
+
+If you do not specify a `size` argument, then it will return all the
+data in the internal buffer.
+
+This method should only be called in paused mode. In flowing mode,
+this method is called automatically until the internal buffer is
+drained.
+
+```js
+var readable = getReadableStreamSomehow();
+readable.on('readable', () => {
+ var chunk;
+ while (null !== (chunk = readable.read())) {
+ console.log('got %d bytes of data', chunk.length);
+ }
+});
+```
+
+If this method returns a data chunk, then it will also trigger the
+emission of a [`'data'`][] event.
+
+Note that calling [`stream.read([size])`][stream-read] after the [`'end'`][]
+event has been triggered will return `null`. No runtime error will be raised.
+
+#### readable.resume()
+
+* Return: `this`
+
+This method will cause the readable stream to resume emitting [`'data'`][]
+events.
+
+This method will switch the stream into flowing mode. If you do *not*
+want to consume the data from a stream, but you *do* want to get to
+its [`'end'`][] event, you can call [`stream.resume()`][stream-resume] to open
+the flow of data.
+
+```js
+var readable = getReadableStreamSomehow();
+readable.resume();
+readable.on('end', () => {
+ console.log('got to the end, but did not read anything');
+});
+```
+
+#### readable.setEncoding(encoding)
+
+* `encoding` {String} The encoding to use.
+* Return: `this`
+
+Call this function to cause the stream to return strings of the specified
+encoding instead of Buffer objects. For example, if you do
+`readable.setEncoding('utf8')`, then the output data will be interpreted as
+UTF-8 data, and returned as strings. If you do `readable.setEncoding('hex')`,
+then the data will be encoded in hexadecimal string format.
+
+This properly handles multi-byte characters that would otherwise be
+potentially mangled if you simply pulled the Buffers directly and
+called [`buf.toString(encoding)`][] on them. If you want to read the data
+as strings, always use this method.
+
+Also you can disable any encoding at all with `readable.setEncoding(null)`.
+This approach is very useful if you deal with binary data or with large
+multi-byte strings spread out over multiple chunks.
+
+```js
+var readable = getReadableStreamSomehow();
+readable.setEncoding('utf8');
+readable.on('data', (chunk) => {
+ assert.equal(typeof chunk, 'string');
+ console.log('got %d characters of string data', chunk.length);
+});
+```
+
+#### readable.unpipe([destination])
+
+* `destination` {stream.Writable} Optional specific stream to unpipe
+
+This method will remove the hooks set up for a previous [`stream.pipe()`][]
+call.
+
+If the destination is not specified, then all pipes are removed.
+
+If the destination is specified, but no pipe is set up for it, then
+this is a no-op.
+
+```js
+var readable = getReadableStreamSomehow();
+var 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);
+```
+
+#### readable.unshift(chunk)
+
+* `chunk` {Buffer|String} Chunk of data to unshift onto the read queue
+
+This is useful in certain cases where a stream is being consumed by a
+parser, which needs to "un-consume" some data that it has
+optimistically pulled out of the source, so that the stream can be
+passed on to some other party.
+
+Note that `stream.unshift(chunk)` cannot be called after the [`'end'`][] event
+has been triggered; a runtime error will be raised.
+
+If you find that you must often call `stream.unshift(chunk)` in your
+programs, consider implementing a [Transform][] stream instead. (See [API
+for Stream Implementors][].)
+
+```js
+// 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').StringDecoder;
+function parseHeader(stream, callback) {
+ stream.on('error', callback);
+ stream.on('readable', onReadable);
+ var decoder = new StringDecoder('utf8');
+ var header = '';
+ function onReadable() {
+ var chunk;
+ while (null !== (chunk = stream.read())) {
+ var str = decoder.write(chunk);
+ if (str.match(/\n\n/)) {
+ // found the header boundary
+ var split = str.split(/\n\n/);
+ header += split.shift();
+ var remaining = split.join('\n\n');
+ var buf = new Buffer(remaining, 'utf8');
+ if (buf.length)
+ stream.unshift(buf);
+ stream.removeListener('error', callback);
+ stream.removeListener('readable', onReadable);
+ // now the body of the message can be read from the stream.
+ callback(null, header, stream);
+ } else {
+ // still reading the header.
+ header += str;
+ }
+ }
+ }
+}
+```
+
+Note that, unlike [`stream.push(chunk)`][stream-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 `unshift()` is called during a
+read (i.e. from within a [`stream._read()`][stream-_read] implementation on a
+custom stream). Following the call to `unshift()` with an immediate
+[`stream.push('')`][stream-push] will reset the reading state appropriately,
+however it is best to simply avoid calling `unshift()` while in the process of
+performing a read.
+
+#### readable.wrap(stream)
+
+* `stream` {Stream} An "old style" readable stream
+
+Versions of Node.js prior to v0.10 had streams that did not implement the
+entire Streams API as it is today. (See [Compatibility][] for
+more information.)
+
+If you are using an older Node.js library that emits [`'data'`][] events and
+has a [`stream.pause()`][stream-pause] method that is advisory only, then you
+can use the `wrap()` method to create a [Readable][] stream that uses the old
+stream as its data source.
+
+You will very rarely ever need to call this function, but it exists
+as a convenience for interacting with old Node.js programs and libraries.
+
+For example:
+
+```js
+const OldReader = require('./old-api-module.js').OldReader;
+const Readable = require('stream').Readable;
+const oreader = new OldReader;
+const myReader = new Readable().wrap(oreader);
+
+myReader.on('readable', () => {
+ myReader.read(); // etc.
+});
+```
+
+### Class: stream.Transform
+
+Transform streams are [Duplex][] streams where the output is in some way
+computed from the input. They implement both the [Readable][] and
+[Writable][] interfaces.
+
+Examples of Transform streams include:
+
+* [zlib streams][zlib]
+* [crypto streams][crypto]
+
+### Class: stream.Writable
+
+<!--type=class-->
+
+The Writable stream interface is an abstraction for a *destination*
+that you are writing data *to*.
+
+Examples of writable streams include:
+
+* [HTTP requests, on the client][]
+* [HTTP responses, on the server][]
+* [fs write streams][]
+* [zlib streams][zlib]
+* [crypto streams][crypto]
+* [TCP sockets][]
+* [child process stdin][]
+* [`process.stdout`][], [`process.stderr`][]
+
+#### Event: 'drain'
+
+If a [`stream.write(chunk)`][stream-write] call returns `false`, then the
+`'drain'` event will indicate when it is appropriate to begin writing more data
+to the stream.
+
+```js
+// Write the data to the supplied writable stream one million times.
+// Be attentive to back-pressure.
+function writeOneMillionTimes(writer, data, encoding, callback) {
+ var i = 1000000;
+ write();
+ function write() {
+ var ok = true;
+ do {
+ i -= 1;
+ if (i === 0) {
+ // last time!
+ writer.write(data, encoding, callback);
+ } else {
+ // see if we should continue, or wait
+ // don't pass the callback, because we're not done yet.
+ ok = writer.write(data, encoding);
+ }
+ } while (i > 0 && ok);
+ if (i > 0) {
+ // had to stop early!
+ // write some more once it drains
+ writer.once('drain', write);
+ }
+ }
+}
+```
+
+#### Event: 'error'
+
+* {Error}
+
+Emitted if there was an error when writing or piping data.
+
+#### Event: 'finish'
+
+When the [`stream.end()`][stream-end] method has been called, and all data has
+been flushed to the underlying system, this event is emitted.
+
+```javascript
+var writer = getWritableStreamSomehow();
+for (var i = 0; i < 100; i ++) {
+ writer.write('hello, #${i}!\n');
+}
+writer.end('this is the end\n');
+writer.on('finish', () => {
+ console.error('all writes are now complete.');
+});
+```
+
+#### Event: 'pipe'
+
+* `src` {stream.Readable} source stream that is piping to this writable
+
+This is emitted whenever the [`stream.pipe()`][] method is called on a readable
+stream, adding this writable to its set of destinations.
+
+```js
+var writer = getWritableStreamSomehow();
+var reader = getReadableStreamSomehow();
+writer.on('pipe', (src) => {
+ console.error('something is piping into the writer');
+ assert.equal(src, reader);
+});
+reader.pipe(writer);
+```
+
+#### Event: 'unpipe'
+
+* `src` {[Readable][] Stream} The source stream that
+ [unpiped][`stream.unpipe()`] this writable
+
+This is emitted whenever the [`stream.unpipe()`][] method is called on a
+readable stream, removing this writable from its set of destinations.
+
+```js
+var writer = getWritableStreamSomehow();
+var reader = getReadableStreamSomehow();
+writer.on('unpipe', (src) => {
+ console.error('something has stopped piping into the writer');
+ assert.equal(src, reader);
+});
+reader.pipe(writer);
+reader.unpipe(writer);
+```
+
+#### writable.cork()
+
+Forces buffering of all writes.
+
+Buffered data will be flushed either at [`stream.uncork()`][] or at
+[`stream.end()`][stream-end] call.
+
+#### writable.end([chunk][, encoding][, callback])
+
+* `chunk` {String|Buffer} Optional data to write
+* `encoding` {String} The encoding, if `chunk` is a String
+* `callback` {Function} Optional callback for when the stream is finished
+
+Call this method when no more data will be written to the stream. If supplied,
+the callback is attached as a listener on the [`'finish'`][] event.
+
+Calling [`stream.write()`][stream-write] after calling
+[`stream.end()`][stream-end] will raise an error.
+
+```js
+// write 'hello, ' and then end with 'world!'
+var file = fs.createWriteStream('example.txt');
+file.write('hello, ');
+file.end('world!');
+// writing more now is not allowed!
+```
+
+#### writable.setDefaultEncoding(encoding)
+
+* `encoding` {String} The new default encoding
+
+Sets the default encoding for a writable stream.
+
+#### writable.uncork()
+
+Flush all data, buffered since [`stream.cork()`][] call.
+
+#### writable.write(chunk[, encoding][, callback])
+
+* `chunk` {String|Buffer} The data to write
+* `encoding` {String} The encoding, if `chunk` is a String
+* `callback` {Function} Callback for when this chunk of data is flushed
+* Returns: {Boolean} `true` if the data was handled completely.
+
+This method writes some data to the underlying system, and calls the
+supplied callback once the data has been fully handled.
+
+The return value indicates if you should continue writing right now.
+If the data had to be buffered internally, then it will return
+`false`. Otherwise, it will return `true`.
+
+This return value is strictly advisory. You MAY continue to write,
+even if it returns `false`. However, writes will be buffered in
+memory, so it is best not to do this excessively. Instead, wait for
+the [`'drain'`][] event before writing more data.
+
+
+## API for Stream Implementors
+
+<!--type=misc-->
+
+To implement any sort of stream, the pattern is the same:
+
+1. Extend the appropriate parent class in your own subclass. (The
+ [`util.inherits()`][] method is particularly helpful for this.)
+2. Call the appropriate parent class constructor in your constructor,
+ to be sure that the internal mechanisms are set up properly.
+3. Implement one or more specific methods, as detailed below.
+
+The class to extend and the method(s) to implement depend on the sort
+of stream class you are writing:
+
+<table>
+ <thead>
+ <tr>
+ <th>
+ <p>Use-case</p>
+ </th>
+ <th>
+ <p>Class</p>
+ </th>
+ <th>
+ <p>Method(s) to implement</p>
+ </th>
+ </tr>
+ </thead>
+ <tr>
+ <td>
+ <p>Reading only</p>
+ </td>
+ <td>
+ <p>[Readable](#stream_class_stream_readable_1)</p>
+ </td>
+ <td>
+ <p><code>[_read][stream-_read]</code></p>
+ </td>
+ </tr>
+ <tr>
+ <td>
+ <p>Writing only</p>
+ </td>
+ <td>
+ <p>[Writable](#stream_class_stream_writable_1)</p>
+ </td>
+ <td>
+ <p><code>[_write][stream-_write]</code>, <code>[_writev][stream-_writev]</code></p>
+ </td>
+ </tr>
+ <tr>
+ <td>
+ <p>Reading and writing</p>
+ </td>
+ <td>
+ <p>[Duplex](#stream_class_stream_duplex_1)</p>
+ </td>
+ <td>
+ <p><code>[_read][stream-_read]</code>, <code>[_write][stream-_write]</code>, <code>[_writev][stream-_writev]</code></p>
+ </td>
+ </tr>
+ <tr>
+ <td>
+ <p>Operate on written data, then read the result</p>
+ </td>
+ <td>
+ <p>[Transform](#stream_class_stream_transform_1)</p>
+ </td>
+ <td>
+ <p><code>[_transform][stream-_transform]</code>, <code>[_flush][stream-_flush]</code></p>
+ </td>
+ </tr>
+</table>
+
+In your implementation code, it is very important to never call the methods
+described in [API for Stream Consumers][]. Otherwise, you can potentially cause
+adverse side effects in programs that consume your streaming interfaces.
+
+### Class: stream.Duplex
+
+<!--type=class-->
+
+A "duplex" stream is one that is both Readable and Writable, such as a TCP
+socket connection.
+
+Note that `stream.Duplex` is an abstract class designed to be extended
+with an underlying implementation of the [`stream._read(size)`][stream-_read]
+and [`stream._write(chunk, encoding, callback)`][stream-_write] methods as you
+would with a Readable or Writable stream class.
+
+Since JavaScript doesn't have multiple prototypal inheritance, this class
+prototypally inherits from Readable, and then parasitically from Writable. It is
+thus up to the user to implement both the low-level
+[`stream._read(n)`][stream-_read] method as well as the low-level
+[`stream._write(chunk, encoding, callback)`][stream-_write] method on extension
+duplex classes.
+
+#### new stream.Duplex(options)
+
+* `options` {Object} Passed to both Writable and Readable
+ constructors. Also has the following fields:
+ * `allowHalfOpen` {Boolean} Default = `true`. If set to `false`, then
+ the stream will automatically end the readable side when the
+ writable side ends and vice versa.
+ * `readableObjectMode` {Boolean} Default = `false`. Sets `objectMode`
+ for readable side of the stream. Has no effect if `objectMode`
+ is `true`.
+ * `writableObjectMode` {Boolean} Default = `false`. Sets `objectMode`
+ for writable side of the stream. Has no effect if `objectMode`
+ is `true`.
+
+In classes that extend the Duplex class, make sure to call the
+constructor so that the buffering settings can be properly
+initialized.
+
+### Class: stream.PassThrough
+
+This is a trivial implementation of a [Transform][] stream that simply
+passes the input bytes across to the output. Its purpose is mainly
+for examples and testing, but there are occasionally use cases where
+it can come in handy as a building block for novel sorts of streams.
+
+### Class: stream.Readable
+
+<!--type=class-->
+
+`stream.Readable` is an abstract class designed to be extended with an
+underlying implementation of the [`stream._read(size)`][stream-_read] method.
+
+Please see [API for Stream Consumers][] for how to consume
+streams in your programs. What follows is an explanation of how to
+implement Readable streams in your programs.
+
+#### new stream.Readable([options])
+
+* `options` {Object}
+ * `highWaterMark` {Number} The maximum number of bytes to store in
+ the internal buffer before ceasing to read from the underlying
+ resource. Default = `16384` (16kb), or `16` for `objectMode` streams
+ * `encoding` {String} If specified, then buffers will be decoded to
+ strings using the specified encoding. Default = `null`
+ * `objectMode` {Boolean} Whether this stream should behave
+ as a stream of objects. Meaning that [`stream.read(n)`][stream-read] returns
+ a single value instead of a Buffer of size n. Default = `false`
+ * `read` {Function} Implementation for the [`stream._read()`][stream-_read]
+ method.
+
+In classes that extend the Readable class, make sure to call the
+Readable constructor so that the buffering settings can be properly
+initialized.
+
+#### readable.\_read(size)
+
+* `size` {Number} Number of bytes to read asynchronously
+
+Note: **Implement this method, but do NOT call it directly.**
+
+This method is prefixed with an underscore because it is internal to the
+class that defines it and should only be called by the internal Readable
+class methods. All Readable stream implementations must provide a \_read
+method to fetch data from the underlying resource.
+
+When `_read()` is called, if data is available from the resource, the `_read()`
+implementation should start pushing that data into the read queue by calling
+[`this.push(dataChunk)`][stream-push]. `_read()` should continue reading from
+the resource and pushing data until push returns `false`, at which point it
+should stop reading from the resource. Only when `_read()` is called again after
+it has stopped should it start reading more data from the resource and pushing
+that data onto the queue.
+
+Note: once the `_read()` method is called, it will not be called again until
+the [`stream.push()`][stream-push] method is called.
+
+The `size` argument is advisory. Implementations where a "read" is a
+single call that returns data can use this to know how much data to
+fetch. Implementations where that is not relevant, such as TCP or
+TLS, may ignore this argument, and simply provide data whenever it
+becomes available. There is no need, for example to "wait" until
+`size` bytes are available before calling [`stream.push(chunk)`][stream-push].
+
+#### readable.push(chunk[, encoding])
+
+
+* `chunk` {Buffer|Null|String} Chunk of data to push into the read queue
+* `encoding` {String} Encoding of String chunks. Must be a valid
+ Buffer encoding, such as `'utf8'` or `'ascii'`
+* return {Boolean} Whether or not more pushes should be performed
+
+Note: **This method should be called by Readable implementors, NOT
+by consumers of Readable streams.**
+
+If a value other than null is passed, The `push()` method adds a chunk of data
+into the queue for subsequent stream processors to consume. If `null` is
+passed, it signals the end of the stream (EOF), after which no more data
+can be written.
+
+The data added with `push()` can be pulled out by calling the
+[`stream.read()`][stream-read] method when the [`'readable'`][] event fires.
+
+This API is designed to be as flexible as possible. For example,
+you may be wrapping a lower-level source which has some sort of
+pause/resume mechanism, and a data callback. In those cases, you
+could wrap the low-level source object by doing something like this:
+
+```js
+// source is an object with readStop() and readStart() methods,
+// and an `ondata` member that gets called when it has data, and
+// an `onend` member that gets called when the data is over.
+
+util.inherits(SourceWrapper, Readable);
+
+function SourceWrapper(options) {
+ Readable.call(this, options);
+
+ this._source = getLowlevelSourceObject();
+
+ // Every time there's data, we push it into the internal buffer.
+ this._source.ondata = (chunk) => {
+ // if push() returns false, then we need to stop reading from source
+ if (!this.push(chunk))
+ this._source.readStop();
+ };
+
+ // When the source ends, we push the EOF-signaling `null` chunk
+ this._source.onend = () => {
+ this.push(null);
+ };
+}
+
+// _read will be called when the stream wants to pull more data in
+// the advisory size argument is ignored in this case.
+SourceWrapper.prototype._read = function(size) {
+ this._source.readStart();
+};
+```
+
+#### Example: A Counting Stream
+
+<!--type=example-->
+
+This is a basic example of a Readable stream. It emits the numerals
+from 1 to 1,000,000 in ascending order, and then ends.
+
+```js
+const Readable = require('stream').Readable;
+const util = require('util');
+util.inherits(Counter, Readable);
+
+function Counter(opt) {
+ Readable.call(this, opt);
+ this._max = 1000000;
+ this._index = 1;
+}
+
+Counter.prototype._read = function() {
+ var i = this._index++;
+ if (i > this._max)
+ this.push(null);
+ else {
+ var str = '' + i;
+ var buf = new Buffer(str, 'ascii');
+ this.push(buf);
+ }
+};
+```
+
+#### Example: SimpleProtocol v1 (Sub-optimal)
+
+This is similar to the `parseHeader` function described
+[here](#stream_readable_unshift_chunk), but implemented as a custom stream.
+Also, note that this implementation does not convert the incoming data to a
+string.
+
+However, this would be better implemented as a [Transform][] stream. See
+[SimpleProtocol v2][] for a better implementation.
+
+```js
+// A parser for a simple data protocol.
+// The "header" is a JSON object, followed by 2 \n characters, and
+// then a message body.
+//
+// NOTE: This can be done more simply as a Transform stream!
+// Using Readable directly for this is sub-optimal. See the
+// alternative example below under the Transform section.
+
+const Readable = require('stream').Readable;
+const util = require('util');
+
+util.inherits(SimpleProtocol, Readable);
+
+function SimpleProtocol(source, options) {
+ if (!(this instanceof SimpleProtocol))
+ return new SimpleProtocol(source, options);
+
+ Readable.call(this, options);
+ this._inBody = false;
+ this._sawFirstCr = false;
+
+ // source is a readable stream, such as a socket or file
+ this._source = source;
+
+ var self = this;
+ source.on('end', () => {
+ self.push(null);
+ });
+
+ // give it a kick whenever the source is readable
+ // read(0) will not consume any bytes
+ source.on('readable', () => {
+ self.read(0);
+ });
+
+ this._rawHeader = [];
+ this.header = null;
+}
+
+SimpleProtocol.prototype._read = function(n) {
+ if (!this._inBody) {
+ var chunk = this._source.read();
+
+ // if the source doesn't have data, we don't have data yet.
+ if (chunk === null)
+ return this.push('');
+
+ // check if the chunk has a \n\n
+ var split = -1;
+ for (var i = 0; i < chunk.length; i++) {
+ if (chunk[i] === 10) { // '\n'
+ if (this._sawFirstCr) {
+ split = i;
+ break;
+ } else {
+ this._sawFirstCr = true;
+ }
+ } else {
+ this._sawFirstCr = false;
+ }
+ }
+
+ if (split === -1) {
+ // still waiting for the \n\n
+ // stash the chunk, and try again.
+ this._rawHeader.push(chunk);
+ this.push('');
+ } else {
+ this._inBody = true;
+ var h = chunk.slice(0, split);
+ this._rawHeader.push(h);
+ var header = Buffer.concat(this._rawHeader).toString();
+ try {
+ this.header = JSON.parse(header);
+ } catch (er) {
+ this.emit('error', new Error('invalid simple protocol data'));
+ return;
+ }
+ // now, because we got some extra data, unshift the rest
+ // back into the read queue so that our consumer will see it.
+ var b = chunk.slice(split);
+ this.unshift(b);
+ // calling unshift by itself does not reset the reading state
+ // of the stream; since we're inside _read, doing an additional
+ // push('') will reset the state appropriately.
+ this.push('');
+
+ // and let them know that we are done parsing the header.
+ this.emit('header', this.header);
+ }
+ } else {
+ // from there on, just provide the data to our consumer.
+ // careful not to push(null), since that would indicate EOF.
+ var chunk = this._source.read();
+ if (chunk) this.push(chunk);
+ }
+};
+
+// Usage:
+// var parser = new SimpleProtocol(source);
+// Now parser is a readable stream that will emit 'header'
+// with the parsed header data.
+```
+
+### Class: stream.Transform
+
+A "transform" stream is a duplex stream where the output is causally
+connected in some way to the input, such as a [zlib][] stream or a
+[crypto][] stream.
+
+There is no requirement that the output be the same size as the input,
+the same number of chunks, or arrive at the same time. For example, a
+Hash stream will only ever have a single chunk of output which is
+provided when the input is ended. A zlib stream will produce output
+that is either much smaller or much larger than its input.
+
+Rather than implement the [`stream._read()`][stream-_read] and
+[`stream._write()`][stream-_write] methods, Transform classes must implement the
+[`stream._transform()`][stream-_transform] method, and may optionally
+also implement the [`stream._flush()`][stream-_flush] method. (See below.)
+
+#### new stream.Transform([options])
+
+* `options` {Object} Passed to both Writable and Readable
+ constructors. Also has the following fields:
+ * `transform` {Function} Implementation for the
+ [`stream._transform()`][stream-_transform] method.
+ * `flush` {Function} Implementation for the [`stream._flush()`][stream-_flush]
+ method.
+
+In classes that extend the Transform class, make sure to call the
+constructor so that the buffering settings can be properly
+initialized.
+
+#### Events: 'finish' and 'end'
+
+The [`'finish'`][] and [`'end'`][] events are from the parent Writable
+and Readable classes respectively. The `'finish'` event is fired after
+[`stream.end()`][stream-end] is called and all chunks have been processed by
+[`stream._transform()`][stream-_transform], `'end'` is fired after all data has
+been output which is after the callback in [`stream._flush()`][stream-_flush]
+has been called.
+
+#### transform.\_flush(callback)
+
+* `callback` {Function} Call this function (optionally with an error
+ argument) when you are done flushing any remaining data.
+
+Note: **This function MUST NOT be called directly.** It MAY be implemented
+by child classes, and if so, will be called by the internal Transform
+class methods only.
+
+In some cases, your transform operation may need to emit a bit more
+data at the end of the stream. For example, a `Zlib` compression
+stream will store up some internal state so that it can optimally
+compress the output. At the end, however, it needs to do the best it
+can with what is left, so that the data will be complete.
+
+In those cases, you can implement a `_flush()` method, which will be
+called at the very end, after all the written data is consumed, but
+before emitting [`'end'`][] to signal the end of the readable side. Just
+like with [`stream._transform()`][stream-_transform], call
+`transform.push(chunk)` zero or more times, as appropriate, and call `callback`
+when the flush operation is complete.
+
+This method is prefixed with an underscore because it is internal to
+the class that defines it, and should not be called directly by user
+programs. However, you **are** expected to override this method in
+your own extension classes.
+
+#### transform.\_transform(chunk, encoding, callback)
+
+* `chunk` {Buffer|String} The chunk to be transformed. Will **always**
+ be a buffer unless the `decodeStrings` option was set to `false`.
+* `encoding` {String} If the chunk is a string, then this is the
+ encoding type. If chunk is a buffer, then this is the special
+ value - 'buffer', ignore it in this case.
+* `callback` {Function} Call this function (optionally with an error
+ argument and data) when you are done processing the supplied chunk.
+
+Note: **This function MUST NOT be called directly.** It should be
+implemented by child classes, and called by the internal Transform
+class methods only.
+
+All Transform stream implementations must provide a `_transform()`
+method to accept input and produce output.
+
+`_transform()` should do whatever has to be done in this specific
+Transform class, to handle the bytes being written, and pass them off
+to the readable portion of the interface. Do asynchronous I/O,
+process things, and so on.
+
+Call `transform.push(outputChunk)` 0 or more times to generate output
+from this input chunk, depending on how much data you want to output
+as a result of this chunk.
+
+Call the callback function only when the current chunk is completely
+consumed. Note that there may or may not be output as a result of any
+particular input chunk. If you supply a second argument to the callback
+it will be passed to the push method. In other words the following are
+equivalent:
+
+```js
+transform.prototype._transform = function (data, encoding, callback) {
+ this.push(data);
+ callback();
+};
+
+transform.prototype._transform = function (data, encoding, callback) {
+ callback(null, data);
+};
+```
+
+This method is prefixed with an underscore because it is internal to
+the class that defines it, and should not be called directly by user
+programs. However, you **are** expected to override this method in
+your own extension classes.
+
+#### Example: `SimpleProtocol` parser v2
+
+The example [here](#stream_example_simpleprotocol_v1_sub_optimal) of a simple
+protocol parser can be implemented simply by using the higher level
+[Transform][] stream class, similar to the `parseHeader` and `SimpleProtocol
+v1` examples.
+
+In this example, rather than providing the input as an argument, it
+would be piped into the parser, which is a more idiomatic Node.js stream
+approach.
+
+```javascript
+const util = require('util');
+const Transform = require('stream').Transform;
+util.inherits(SimpleProtocol, Transform);
+
+function SimpleProtocol(options) {
+ if (!(this instanceof SimpleProtocol))
+ return new SimpleProtocol(options);
+
+ Transform.call(this, options);
+ this._inBody = false;
+ this._sawFirstCr = false;
+ this._rawHeader = [];
+ this.header = null;
+}
+
+SimpleProtocol.prototype._transform = function(chunk, encoding, done) {
+ if (!this._inBody) {
+ // check if the chunk has a \n\n
+ var split = -1;
+ for (var i = 0; i < chunk.length; i++) {
+ if (chunk[i] === 10) { // '\n'
+ if (this._sawFirstCr) {
+ split = i;
+ break;
+ } else {
+ this._sawFirstCr = true;
+ }
+ } else {
+ this._sawFirstCr = false;
+ }
+ }
+
+ if (split === -1) {
+ // still waiting for the \n\n
+ // stash the chunk, and try again.
+ this._rawHeader.push(chunk);
+ } else {
+ this._inBody = true;
+ var h = chunk.slice(0, split);
+ this._rawHeader.push(h);
+ var header = Buffer.concat(this._rawHeader).toString();
+ try {
+ this.header = JSON.parse(header);
+ } catch (er) {
+ this.emit('error', new Error('invalid simple protocol data'));
+ return;
+ }
+ // and let them know that we are done parsing the header.
+ this.emit('header', this.header);
+
+ // now, because we got some extra data, emit this first.
+ this.push(chunk.slice(split));
+ }
+ } else {
+ // from there on, just provide the data to our consumer as-is.
+ this.push(chunk);
+ }
+ done();
+};
+
+// Usage:
+// var parser = new SimpleProtocol();
+// source.pipe(parser)
+// Now parser is a readable stream that will emit 'header'
+// with the parsed header data.
+```
+
+### Class: stream.Writable
+
+<!--type=class-->
+
+`stream.Writable` is an abstract class designed to be extended with an
+underlying implementation of the
+[`stream._write(chunk, encoding, callback)`][stream-_write] method.
+
+Please see [API for Stream Consumers][] for how to consume
+writable streams in your programs. What follows is an explanation of
+how to implement Writable streams in your programs.
+
+#### new stream.Writable([options])
+
+* `options` {Object}
+ * `highWaterMark` {Number} Buffer level when
+ [`stream.write()`][stream-write] starts returning `false`. Default = `16384`
+ (16kb), or `16` for `objectMode` streams.
+ * `decodeStrings` {Boolean} Whether or not to decode strings into
+ Buffers before passing them to [`stream._write()`][stream-_write].
+ Default = `true`
+ * `objectMode` {Boolean} Whether or not the
+ [`stream.write(anyObj)`][stream-write] is a valid operation. If set you can
+ write arbitrary data instead of only `Buffer` / `String` data.
+ Default = `false`
+ * `write` {Function} Implementation for the
+ [`stream._write()`][stream-_write] method.
+ * `writev` {Function} Implementation for the
+ [`stream._writev()`][stream-_writev] method.
+
+In classes that extend the Writable class, make sure to call the
+constructor so that the buffering settings can be properly
+initialized.
+
+#### writable.\_write(chunk, encoding, callback)
+
+* `chunk` {Buffer|String} The chunk to be written. Will **always**
+ be a buffer unless the `decodeStrings` option was set to `false`.
+* `encoding` {String} If the chunk is a string, then this is the
+ encoding type. If chunk is a buffer, then this is the special
+ value - 'buffer', ignore it in this case.
+* `callback` {Function} Call this function (optionally with an error
+ argument) when you are done processing the supplied chunk.
+
+All Writable stream implementations must provide a
+[`stream._write()`][stream-_write] method to send data to the underlying
+resource.
+
+Note: **This function MUST NOT be called directly.** It should be
+implemented by child classes, and called by the internal Writable
+class methods only.
+
+Call the callback using the standard `callback(error)` pattern to
+signal that the write completed successfully or with an error.
+
+If the `decodeStrings` flag is set in the constructor options, then
+`chunk` may be a string rather than a Buffer, and `encoding` will
+indicate the sort of string that it is. This is to support
+implementations that have an optimized handling for certain string
+data encodings. If you do not explicitly set the `decodeStrings`
+option to `false`, then you can safely ignore the `encoding` argument,
+and assume that `chunk` will always be a Buffer.
+
+This method is prefixed with an underscore because it is internal to
+the class that defines it, and should not be called directly by user
+programs. However, you **are** expected to override this method in
+your own extension classes.
+
+#### writable.\_writev(chunks, callback)
+
+* `chunks` {Array} The chunks to be written. Each chunk has following
+ format: `{ chunk: ..., encoding: ... }`.
+* `callback` {Function} Call this function (optionally with an error
+ argument) when you are done processing the supplied chunks.
+
+Note: **This function MUST NOT be called directly.** It may be
+implemented by child classes, and called by the internal Writable
+class methods only.
+
+This function is completely optional to implement. In most cases it is
+unnecessary. If implemented, it will be called with all the chunks
+that are buffered in the write queue.
+
+
+## Simplified Constructor API
+
+<!--type=misc-->
+
+In simple cases there is now the added benefit of being able to construct a
+stream without inheritance.
+
+This can be done by passing the appropriate methods as constructor options:
+
+Examples:
+
+### Duplex
+
+```js
+var duplex = new stream.Duplex({
+ read: function(n) {
+ // sets this._read under the hood
+
+ // push data onto the read queue, passing null
+ // will signal the end of the stream (EOF)
+ this.push(chunk);
+ },
+ write: function(chunk, encoding, next) {
+ // sets this._write under the hood
+
+ // An optional error can be passed as the first argument
+ next()
+ }
+});
+
+// or
+
+var duplex = new stream.Duplex({
+ read: function(n) {
+ // sets this._read under the hood
+
+ // push data onto the read queue, passing null
+ // will signal the end of the stream (EOF)
+ this.push(chunk);
+ },
+ writev: function(chunks, next) {
+ // sets this._writev under the hood
+
+ // An optional error can be passed as the first argument
+ next()
+ }
+});
+```
+
+### Readable
+
+```js
+var readable = new stream.Readable({
+ read: function(n) {
+ // sets this._read under the hood
+
+ // push data onto the read queue, passing null
+ // will signal the end of the stream (EOF)
+ this.push(chunk);
+ }
+});
+```
+
+### Transform
+
+```js
+var transform = new stream.Transform({
+ transform: function(chunk, encoding, next) {
+ // sets this._transform under the hood
+
+ // generate output as many times as needed
+ // this.push(chunk);
+
+ // call when the current chunk is consumed
+ next();
+ },
+ flush: function(done) {
+ // sets this._flush under the hood
+
+ // generate output as many times as needed
+ // this.push(chunk);
+
+ done();
+ }
+});
+```
+
+### Writable
+
+```js
+var writable = new stream.Writable({
+ write: function(chunk, encoding, next) {
+ // sets this._write under the hood
+
+ // An optional error can be passed as the first argument
+ next()
+ }
+});
+
+// or
+
+var writable = new stream.Writable({
+ writev: function(chunks, next) {
+ // sets this._writev under the hood
+
+ // An optional error can be passed as the first argument
+ next()
+ }
+});
+```
+
+## Streams: Under the Hood
+
+<!--type=misc-->
+
+### Buffering
+
+<!--type=misc-->
+
+Both Writable and Readable streams will buffer data on an internal
+object which can be retrieved from `_writableState.getBuffer()` or
+`_readableState.buffer`, respectively.
+
+The amount of data that will potentially be buffered depends on the
+`highWaterMark` option which is passed into the constructor.
+
+Buffering in Readable streams happens when the implementation calls
+[`stream.push(chunk)`][stream-push]. If the consumer of the Stream does not
+call [`stream.read()`][stream-read], then the data will sit in the internal
+queue until it is consumed.
+
+Buffering in Writable streams happens when the user calls
+[`stream.write(chunk)`][stream-write] repeatedly, even when it returns `false`.
+
+The purpose of streams, especially with the [`stream.pipe()`][] method, is to
+limit the buffering of data to acceptable levels, so that sources and
+destinations of varying speed will not overwhelm the available memory.
+
+### Compatibility with Older Node.js Versions
+
+<!--type=misc-->
+
+In versions of Node.js prior to v0.10, the Readable stream interface was
+simpler, but also less powerful and less useful.
+
+* Rather than waiting for you to call the [`stream.read()`][stream-read] method,
+ [`'data'`][] events would start emitting immediately. If you needed to do
+ some I/O to decide how to handle data, then you had to store the chunks
+ in some kind of buffer so that they would not be lost.
+* The [`stream.pause()`][stream-pause] method was advisory, rather than
+ guaranteed. This meant that you still had to be prepared to receive
+ [`'data'`][] events even when the stream was in a paused state.
+
+In Node.js v0.10, the [Readable][] class was added.
+For backwards compatibility with older Node.js programs, Readable streams
+switch into "flowing mode" when a [`'data'`][] event handler is added, or
+when the [`stream.resume()`][stream-resume] method is called. The effect is
+that, even if you are not using the new [`stream.read()`][stream-read] method
+and [`'readable'`][] event, you no longer have to worry about losing
+[`'data'`][] chunks.
+
+Most programs will continue to function normally. However, this
+introduces an edge case in the following conditions:
+
+* No [`'data'`][] event handler is added.
+* The [`stream.resume()`][stream-resume] method is never called.
+* The stream is not piped to any writable destination.
+
+For example, consider the following code:
+
+```js
+// WARNING! BROKEN!
+net.createServer((socket) => {
+
+ // we add an 'end' method, but never consume the data
+ socket.on('end', () => {
+ // It will never get here.
+ socket.end('I got your message (but didnt read it)\n');
+ });
+
+}).listen(1337);
+```
+
+In versions of Node.js prior to v0.10, the incoming message data would be
+simply discarded. However, in Node.js v0.10 and beyond,
+the socket will remain paused forever.
+
+The workaround in this situation is to call the
+[`stream.resume()`][stream-resume] method to start the flow of data:
+
+```js
+// Workaround
+net.createServer((socket) => {
+
+ socket.on('end', () => {
+ socket.end('I got your message (but didnt read it)\n');
+ });
+
+ // start the flow of data, discarding it.
+ socket.resume();
+
+}).listen(1337);
+```
+
+In addition to new Readable streams switching into flowing mode,
+pre-v0.10 style streams can be wrapped in a Readable class using the
+[`stream.wrap()`][] method.
+
+
+### Object Mode
+
+<!--type=misc-->
+
+Normally, Streams operate on Strings and Buffers exclusively.
+
+Streams that are in **object mode** can emit generic JavaScript values
+other than Buffers and Strings.
+
+A Readable stream in object mode will always return a single item from
+a call to [`stream.read(size)`][stream-read], regardless of what the size
+argument is.
+
+A Writable stream in object mode will always ignore the `encoding`
+argument to [`stream.write(data, encoding)`][stream-write].
+
+The special value `null` still retains its special value for object
+mode streams. That is, for object mode readable streams, `null` as a
+return value from [`stream.read()`][stream-read] indicates that there is no more
+data, and [`stream.push(null)`][stream-push] will signal the end of stream data
+(`EOF`).
+
+No streams in Node.js core are object mode streams. This pattern is only
+used by userland streaming libraries.
+
+You should set `objectMode` in your stream child class constructor on
+the options object. Setting `objectMode` mid-stream is not safe.
+
+For Duplex streams `objectMode` can be set exclusively for readable or
+writable side with `readableObjectMode` and `writableObjectMode`
+respectively. These options can be used to implement parsers and
+serializers with Transform streams.
+
+```js
+const util = require('util');
+const StringDecoder = require('string_decoder').StringDecoder;
+const Transform = require('stream').Transform;
+util.inherits(JSONParseStream, Transform);
+
+// Gets \n-delimited JSON string data, and emits the parsed objects
+function JSONParseStream() {
+ if (!(this instanceof JSONParseStream))
+ return new JSONParseStream();
+
+ Transform.call(this, { readableObjectMode : true });
+
+ this._buffer = '';
+ this._decoder = new StringDecoder('utf8');
+}
+
+JSONParseStream.prototype._transform = function(chunk, encoding, cb) {
+ this._buffer += this._decoder.write(chunk);
+ // split on newlines
+ var lines = this._buffer.split(/\r?\n/);
+ // keep the last partial line buffered
+ this._buffer = lines.pop();
+ for (var l = 0; l < lines.length; l++) {
+ var line = lines[l];
+ try {
+ var obj = JSON.parse(line);
+ } catch (er) {
+ this.emit('error', er);
+ return;
+ }
+ // push the parsed object out to the readable consumer
+ this.push(obj);
+ }
+ cb();
+};
+
+JSONParseStream.prototype._flush = function(cb) {
+ // Just handle any leftover
+ var rem = this._buffer.trim();
+ if (rem) {
+ try {
+ var obj = JSON.parse(rem);
+ } catch (er) {
+ this.emit('error', er);
+ return;
+ }
+ // push the parsed object out to the readable consumer
+ this.push(obj);
+ }
+ cb();
+};
+```
+
+### `stream.read(0)`
+
+There are some cases where you want to trigger a refresh of the
+underlying readable stream mechanisms, without actually consuming any
+data. In that case, you can call `stream.read(0)`, which will always
+return null.
+
+If the internal read buffer is below the `highWaterMark`, and the
+stream is not currently reading, then calling `stream.read(0)` will trigger
+a low-level [`stream._read()`][stream-_read] call.
+
+There is almost never a need to do this. However, you will see some
+cases in Node.js's internals where this is done, particularly in the
+Readable stream class internals.
+
+### `stream.push('')`
+
+Pushing a zero-byte string or Buffer (when not in [Object mode][]) has an
+interesting side effect. Because it *is* a call to
+[`stream.push()`][stream-push], it will end the `reading` process. However, it
+does *not* add any data to the readable buffer, so there's nothing for
+a user to consume.
+
+Very rarely, there are cases where you have no data to provide now,
+but the consumer of your stream (or, perhaps, another bit of your own
+code) will know when to check again, by calling [`stream.read(0)`][stream-read].
+In those cases, you *may* call `stream.push('')`.
+
+So far, the only use case for this functionality is in the
+[`tls.CryptoStream`][] class, which is deprecated in Node.js/io.js v1.0. If you
+find that you have to use `stream.push('')`, please consider another
+approach, because it almost certainly indicates that something is
+horribly wrong.
+
+[`'data'`]: #stream_event_data
+[`'drain'`]: #stream_event_drain
+[`'end'`]: #stream_event_end
+[`'finish'`]: #stream_event_finish
+[`'readable'`]: #stream_event_readable
+[`buf.toString(encoding)`]: https://nodejs.org/docs/v5.8.0/api/buffer.html#buffer_buf_tostring_encoding_start_end
+[`EventEmitter`]: https://nodejs.org/docs/v5.8.0/api/events.html#events_class_eventemitter
+[`process.stderr`]: https://nodejs.org/docs/v5.8.0/api/process.html#process_process_stderr
+[`process.stdin`]: https://nodejs.org/docs/v5.8.0/api/process.html#process_process_stdin
+[`process.stdout`]: https://nodejs.org/docs/v5.8.0/api/process.html#process_process_stdout
+[`stream.cork()`]: #stream_writable_cork
+[`stream.pipe()`]: #stream_readable_pipe_destination_options
+[`stream.uncork()`]: #stream_writable_uncork
+[`stream.unpipe()`]: #stream_readable_unpipe_destination
+[`stream.wrap()`]: #stream_readable_wrap_stream
+[`tls.CryptoStream`]: https://nodejs.org/docs/v5.8.0/api/tls.html#tls_class_cryptostream
+[`util.inherits()`]: https://nodejs.org/docs/v5.8.0/api/util.html#util_util_inherits_constructor_superconstructor
+[API for Stream Consumers]: #stream_api_for_stream_consumers
+[API for Stream Implementors]: #stream_api_for_stream_implementors
+[child process stdin]: https://nodejs.org/docs/v5.8.0/api/child_process.html#child_process_child_stdin
+[child process stdout and stderr]: https://nodejs.org/docs/v5.8.0/api/child_process.html#child_process_child_stdout
+[Compatibility]: #stream_compatibility_with_older_node_js_versions
+[crypto]: crypto.html
+[Duplex]: #stream_class_stream_duplex
+[fs read streams]: https://nodejs.org/docs/v5.8.0/api/fs.html#fs_class_fs_readstream
+[fs write streams]: https://nodejs.org/docs/v5.8.0/api/fs.html#fs_class_fs_writestream
+[HTTP requests, on the client]: https://nodejs.org/docs/v5.8.0/api/http.html#http_class_http_clientrequest
+[HTTP responses, on the server]: https://nodejs.org/docs/v5.8.0/api/http.html#http_class_http_serverresponse
+[http-incoming-message]: https://nodejs.org/docs/v5.8.0/api/http.html#http_class_http_incomingmessage
+[Object mode]: #stream_object_mode
+[Readable]: #stream_class_stream_readable
+[SimpleProtocol v2]: #stream_example_simpleprotocol_parser_v2
+[stream-_flush]: #stream_transform_flush_callback
+[stream-_read]: #stream_readable_read_size_1
+[stream-_transform]: #stream_transform_transform_chunk_encoding_callback
+[stream-_write]: #stream_writable_write_chunk_encoding_callback_1
+[stream-_writev]: #stream_writable_writev_chunks_callback
+[stream-end]: #stream_writable_end_chunk_encoding_callback
+[stream-pause]: #stream_readable_pause
+[stream-push]: #stream_readable_push_chunk_encoding
+[stream-read]: #stream_readable_read_size
+[stream-resume]: #stream_readable_resume
+[stream-write]: #stream_writable_write_chunk_encoding_callback
+[TCP sockets]: https://nodejs.org/docs/v5.8.0/api/net.html#net_class_net_socket
+[Transform]: #stream_class_stream_transform
+[Writable]: #stream_class_stream_writable
+[zlib]: zlib.html
projects / yaffs-website / blobdiff