readable-stream
Advanced tools
Comparing version 1.1.10 to 1.1.11-1
@@ -29,2 +29,8 @@ // Copyright Joyent, Inc. and other Node contributors. | ||
var util = require('util'); | ||
if (!util.isUndefined) { | ||
var utilIs = require('core-util-is'); | ||
for (var f in utilIs) { | ||
util[f] = utilIs[f]; | ||
} | ||
} | ||
var Readable = require('./_stream_readable'); | ||
@@ -31,0 +37,0 @@ var Writable = require('./_stream_writable'); |
@@ -30,2 +30,8 @@ // Copyright Joyent, Inc. and other Node contributors. | ||
var util = require('util'); | ||
if (!util.isUndefined) { | ||
var utilIs = require('core-util-is'); | ||
for (var f in utilIs) { | ||
util[f] = utilIs[f]; | ||
} | ||
} | ||
util.inherits(PassThrough, Transform); | ||
@@ -32,0 +38,0 @@ |
@@ -39,2 +39,3 @@ // Copyright Joyent, Inc. and other Node contributors. | ||
var util = require('util'); | ||
var Buffer = require('buffer').Buffer; | ||
if (!util.isUndefined) { | ||
@@ -410,3 +411,3 @@ var utilIs = require('core-util-is'); | ||
function onEofChunk(stream, state) { | ||
if (state.decoder && !state.ended && state.decoder.end) { | ||
if (state.decoder && !state.ended) { | ||
var chunk = state.decoder.end(); | ||
@@ -413,0 +414,0 @@ if (chunk && chunk.length) { |
@@ -30,2 +30,3 @@ // Copyright Joyent, Inc. and other Node contributors. | ||
var util = require('util'); | ||
var Buffer = require('buffer').Buffer; | ||
if (!util.isUndefined) { | ||
@@ -125,8 +126,13 @@ var utilIs = require('core-util-is'); | ||
this.prefinished = false; | ||
// Internal, used in net.js and _tls_wrap.js | ||
this._errorEmitted = false; | ||
} | ||
function Writable(options) { | ||
var Duplex = require('./_stream_duplex'); | ||
// Writable ctor is applied to Duplexes, though they're not | ||
// instanceof Writable, they're instanceof Readable. | ||
if (!(this instanceof Writable) && !(this instanceof require('./_stream_duplex'))) | ||
if (!(this instanceof Writable) && !(this instanceof Duplex)) | ||
return new Writable(options); | ||
@@ -247,3 +253,5 @@ | ||
var ret = state.length < state.highWaterMark; | ||
state.needDrain = !ret; | ||
// we must ensure that previous needDrain will not be reset to false. | ||
if (!ret) | ||
state.needDrain = true; | ||
@@ -282,2 +290,3 @@ if (state.writing || state.corked) | ||
stream.emit('error', er); | ||
stream._errorEmitted = true; | ||
} | ||
@@ -284,0 +293,0 @@ |
{ | ||
"name": "readable-stream", | ||
"version": "1.1.10", | ||
"version": "1.1.11-1", | ||
"description": "An exploration of a new kind of readable streams for Node.js", | ||
@@ -5,0 +5,0 @@ "main": "readable.js", |
767
README.md
# readable-stream | ||
A new class of streams for Node.js | ||
***Node-core streams for userland*** | ||
This module provides the new Stream base classes introduced in Node | ||
v0.10, for use in Node v0.8. You can use it to have programs that | ||
have to work with node v0.8, while being forward-compatible for v0.10 | ||
and beyond. When you drop support for v0.8, you can remove this | ||
module, and only use the native streams. | ||
[![NPM](https://nodei.co/npm/readable-stream.png?downloads=true)](https://nodei.co/npm/readable-stream/) | ||
[![NPM](https://nodei.co/npm-dl/readable-stream.png)](https://nodei.co/npm/readable-stream/) | ||
This is almost exactly the same codebase as appears in Node v0.10. | ||
However: | ||
This package is a mirror of the Streams2 and Streams3 implementations in Node-core. | ||
1. The exported object is actually the Readable class. Decorating the | ||
native `stream` module would be global pollution. | ||
2. In v0.10, you can safely use `base64` as an argument to | ||
`setEncoding` in Readable streams. However, in v0.8, the | ||
StringDecoder class has no `end()` method, which is problematic for | ||
Base64. So, don't use that, because it'll break and be weird. | ||
If you want to guarantee a stable streams base, regardless of what version of Node you, or the users of your libraries are using, use **readable-stream** *only* and avoid the *"stream"* module in Node-core. | ||
Other than that, the API is the same as `require('stream')` in v0.10, | ||
so the API docs are reproduced below. | ||
**readable-stream** comes in two major versions, v1.0.x and v1.1.x. The former tracks the Streams2 implementation in Node 0.10, including bug-fixes and minor improvements as they are added. The latter tracks Streams3 as it develops in Node 0.11; we will likely see a v1.2.x branch for Node 0.12. | ||
---------- | ||
**readable-stream** uses proper patch-level versioning so if you pin to `"~1.0.0"` you’ll get the latest Node 0.10 Streams2 implementation, including any fixes and minor non-breaking improvements. The patch-level versions of 1.0.x and 1.1.x should mirror the patch-level versions of Node-core releases. You should prefer the **1.0.x** releases for now and when you’re ready to start using Streams3, pin to `"~1.1.0"` | ||
Stability: 2 - Unstable | ||
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][] | ||
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. | ||
## Compatibility | ||
In earlier versions of Node, the Readable stream interface was | ||
simpler, but also less powerful and less useful. | ||
* Rather than waiting for you to call the `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 `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 v0.10, the Readable class described below was added. For | ||
backwards compatibility with older Node programs, Readable streams | ||
switch into "old mode" when a `'data'` event handler is added, or when | ||
the `pause()` or `resume()` methods are called. The effect is that, | ||
even if you are not using the new `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 `pause()` and `resume()` methods are never called. | ||
For example, consider the following code: | ||
```javascript | ||
// WARNING! BROKEN! | ||
net.createServer(function(socket) { | ||
// we add an 'end' method, but never consume the data | ||
socket.on('end', function() { | ||
// It will never get here. | ||
socket.end('I got your message (but didnt read it)\n'); | ||
}); | ||
}).listen(1337); | ||
``` | ||
In versions of node prior to v0.10, the incoming message data would be | ||
simply discarded. However, in Node v0.10 and beyond, the socket will | ||
remain paused forever. | ||
The workaround in this situation is to call the `resume()` method to | ||
trigger "old mode" behavior: | ||
```javascript | ||
// Workaround | ||
net.createServer(function(socket) { | ||
socket.on('end', function() { | ||
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 old-mode, pre-v0.10 | ||
style streams can be wrapped in a Readable class using the `wrap()` | ||
method. | ||
## Class: stream.Readable | ||
<!--type=class--> | ||
A `Readable Stream` has the following methods, members, and events. | ||
Note that `stream.Readable` is an abstract class designed to be | ||
extended with an underlying implementation of the `_read(size)` | ||
method. (See below.) | ||
### 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=16kb | ||
* `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) returns | ||
a single value instead of a Buffer of size n | ||
In classes that extend the Readable class, make sure to call the | ||
constructor so that the buffering settings can be properly | ||
initialized. | ||
### readable.\_read(size) | ||
* `size` {Number} Number of bytes to read asynchronously | ||
Note: **This function should NOT be called directly.** It should be | ||
implemented by child classes, and called by the internal Readable | ||
class methods only. | ||
All Readable stream implementations must provide a `_read` method | ||
to fetch data from the underlying resource. | ||
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. | ||
When data is available, put it into the read queue by calling | ||
`readable.push(chunk)`. If `push` returns false, then you should stop | ||
reading. When `_read` is called again, you should start pushing more | ||
data. | ||
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)`. | ||
### readable.push(chunk) | ||
* `chunk` {Buffer | null | String} Chunk of data to push into the read queue | ||
* return {Boolean} Whether or not more pushes should be performed | ||
Note: **This function should be called by Readable implementors, NOT | ||
by consumers of Readable subclasses.** The `_read()` function will not | ||
be called again until at least one `push(chunk)` call is made. If no | ||
data is available, then you MAY call `push('')` (an empty string) to | ||
allow a future `_read` call, without adding any data to the queue. | ||
The `Readable` class works by putting data into a read queue to be | ||
pulled out later by calling the `read()` method when the `'readable'` | ||
event fires. | ||
The `push()` method will explicitly insert some data into the read | ||
queue. If it is called with `null` then it will signal the end of the | ||
data. | ||
In some cases, 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: | ||
```javascript | ||
// 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. | ||
var stream = new Readable(); | ||
source.ondata = function(chunk) { | ||
// if push() returns false, then we need to stop reading from source | ||
if (!stream.push(chunk)) | ||
source.readStop(); | ||
}; | ||
source.onend = function() { | ||
stream.push(null); | ||
}; | ||
// _read will be called when the stream wants to pull more data in | ||
// the advisory size argument is ignored in this case. | ||
stream._read = function(n) { | ||
source.readStart(); | ||
}; | ||
``` | ||
### readable.unshift(chunk) | ||
* `chunk` {Buffer | null | String} Chunk of data to unshift onto the read queue | ||
* return {Boolean} Whether or not more pushes should be performed | ||
This is the corollary of `readable.push(chunk)`. Rather than putting | ||
the data at the *end* of the read queue, it puts it at the *front* of | ||
the read queue. | ||
This is useful in certain use-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. | ||
```javascript | ||
// 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. See below. | ||
function SimpleProtocol(source, options) { | ||
if (!(this instanceof SimpleProtocol)) | ||
return new SimpleProtocol(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', function() { | ||
self.push(null); | ||
}); | ||
// give it a kick whenever the source is readable | ||
// read(0) will not consume any bytes | ||
source.on('readable', function() { | ||
self.read(0); | ||
}); | ||
this._rawHeader = []; | ||
this.header = null; | ||
} | ||
SimpleProtocol.prototype = Object.create( | ||
Readable.prototype, { constructor: { value: SimpleProtocol }}); | ||
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); | ||
// 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. | ||
``` | ||
### readable.wrap(stream) | ||
* `stream` {Stream} An "old style" readable stream | ||
If you are using an older Node library that emits `'data'` events and | ||
has a `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. | ||
For example: | ||
```javascript | ||
var OldReader = require('./old-api-module.js').OldReader; | ||
var oreader = new OldReader; | ||
var Readable = require('stream').Readable; | ||
var myReader = new Readable().wrap(oreader); | ||
myReader.on('readable', function() { | ||
myReader.read(); // etc. | ||
}); | ||
``` | ||
### Event: 'readable' | ||
When there is data ready to be consumed, this event will fire. | ||
When this event emits, call the `read()` method to consume the data. | ||
### Event: 'end' | ||
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: 'data' | ||
The `'data'` event emits either a `Buffer` (by default) or a string if | ||
`setEncoding()` was used. | ||
Note that adding a `'data'` event listener will switch the Readable | ||
stream into "old mode", where data is emitted as soon as it is | ||
available, rather than waiting for you to call `read()` to consume it. | ||
### Event: 'error' | ||
Emitted if there was an error receiving data. | ||
### Event: 'close' | ||
Emitted when the underlying resource (for example, the backing file | ||
descriptor) has been closed. Not all streams will emit this. | ||
### readable.setEncoding(encoding) | ||
Makes the `'data'` event emit a string instead of a `Buffer`. `encoding` | ||
can be `'utf8'`, `'utf16le'` (`'ucs2'`), `'ascii'`, or `'hex'`. | ||
The encoding can also be set by specifying an `encoding` field to the | ||
constructor. | ||
### readable.read([size]) | ||
* `size` {Number | null} Optional number of bytes to read. | ||
* Return: {Buffer | String | null} | ||
Note: **This function SHOULD be called by Readable stream users.** | ||
Call this method to consume data once the `'readable'` event is | ||
emitted. | ||
The `size` argument will set a minimum number of bytes that you are | ||
interested in. If not set, then the entire content of the internal | ||
buffer is returned. | ||
If there is no data to consume, or if there are fewer bytes in the | ||
internal buffer than the `size` argument, then `null` is returned, and | ||
a future `'readable'` event will be emitted when more is available. | ||
Calling `stream.read(0)` will always return `null`, and will trigger a | ||
refresh of the internal buffer, but otherwise be a no-op. | ||
### readable.pipe(destination, [options]) | ||
* `destination` {Writable Stream} | ||
* `options` {Object} Optional | ||
* `end` {Boolean} Default=true | ||
Connects this readable stream to `destination` WriteStream. Incoming | ||
data on this stream gets written to `destination`. Properly manages | ||
back-pressure so that a slow destination will not be overwhelmed by a | ||
fast readable stream. | ||
This function returns the `destination` stream. | ||
For example, emulating the Unix `cat` command: | ||
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 `writer` open so that "Goodbye" can be written at the | ||
end. | ||
reader.pipe(writer, { end: false }); | ||
reader.on("end", function() { | ||
writer.end("Goodbye\n"); | ||
}); | ||
Note that `process.stderr` and `process.stdout` are never closed until | ||
the process exits, regardless of the specified options. | ||
### readable.unpipe([destination]) | ||
* `destination` {Writable Stream} Optional | ||
Undo a previously established `pipe()`. If no destination is | ||
provided, then all previously established pipes are removed. | ||
### readable.pause() | ||
Switches the readable stream into "old mode", where data is emitted | ||
using a `'data'` event rather than being buffered for consumption via | ||
the `read()` method. | ||
Ceases the flow of data. No `'data'` events are emitted while the | ||
stream is in a paused state. | ||
### readable.resume() | ||
Switches the readable stream into "old mode", where data is emitted | ||
using a `'data'` event rather than being buffered for consumption via | ||
the `read()` method. | ||
Resumes the incoming `'data'` events after a `pause()`. | ||
## Class: stream.Writable | ||
<!--type=class--> | ||
A `Writable` Stream has the following methods, members, and events. | ||
Note that `stream.Writable` is an abstract class designed to be | ||
extended with an underlying implementation of the | ||
`_write(chunk, encoding, cb)` method. (See below.) | ||
### new stream.Writable([options]) | ||
* `options` {Object} | ||
* `highWaterMark` {Number} Buffer level when `write()` starts | ||
returning false. Default=16kb | ||
* `decodeStrings` {Boolean} Whether or not to decode strings into | ||
Buffers before passing them to `_write()`. Default=true | ||
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. Ignore chunk is a buffer. Note that chunk will | ||
**always** be a buffer unless the `decodeStrings` option is | ||
explicitly set to `false`. | ||
* `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 `_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.write(chunk, [encoding], [callback]) | ||
* `chunk` {Buffer | String} Data to be written | ||
* `encoding` {String} Optional. If `chunk` is a string, then encoding | ||
defaults to `'utf8'` | ||
* `callback` {Function} Optional. Called when this chunk is | ||
successfully written. | ||
* Returns {Boolean} | ||
Writes `chunk` to the stream. Returns `true` if the data has been | ||
flushed to the underlying resource. Returns `false` to indicate that | ||
the buffer is full, and the data will be sent out in the future. The | ||
`'drain'` event will indicate when the buffer is empty again. | ||
The specifics of when `write()` will return false, is determined by | ||
the `highWaterMark` option provided to the constructor. | ||
### writable.end([chunk], [encoding], [callback]) | ||
* `chunk` {Buffer | String} Optional final data to be written | ||
* `encoding` {String} Optional. If `chunk` is a string, then encoding | ||
defaults to `'utf8'` | ||
* `callback` {Function} Optional. Called when the final chunk is | ||
successfully written. | ||
Call this method to signal the end of the data being written to the | ||
stream. | ||
### Event: 'drain' | ||
Emitted when the stream's write queue empties and it's safe to write | ||
without buffering again. Listen for it when `stream.write()` returns | ||
`false`. | ||
### Event: 'close' | ||
Emitted when the underlying resource (for example, the backing file | ||
descriptor) has been closed. Not all streams will emit this. | ||
### Event: 'finish' | ||
When `end()` is called and there are no more chunks to write, this | ||
event is emitted. | ||
### Event: 'pipe' | ||
* `source` {Readable Stream} | ||
Emitted when the stream is passed to a readable stream's pipe method. | ||
### Event 'unpipe' | ||
* `source` {Readable Stream} | ||
Emitted when a previously established `pipe()` is removed using the | ||
source Readable stream's `unpipe()` method. | ||
## 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 `_read(size)` | ||
and `_write(chunk, encoding, callback)` 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 lowlevel | ||
`_read(n)` method as well as the lowlevel `_write(chunk, encoding, cb)` 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. | ||
In classes that extend the Duplex class, make sure to call the | ||
constructor so that the buffering settings can be properly | ||
initialized. | ||
## 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 either produce | ||
much smaller or much larger than its input. | ||
Rather than implement the `_read()` and `_write()` methods, Transform | ||
classes must implement the `_transform()` method, and may optionally | ||
also implement the `_flush()` method. (See below.) | ||
### new stream.Transform([options]) | ||
* `options` {Object} Passed to both Writable and Readable | ||
constructors. | ||
In classes that extend the Transform class, make sure to call the | ||
constructor so that the buffering settings can be properly | ||
initialized. | ||
### 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. (Ignore if `decodeStrings` chunk is a buffer.) | ||
* `callback` {Function} Call this function (optionally with an error | ||
argument) 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. | ||
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.\_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 `_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. | ||
### Example: `SimpleProtocol` parser | ||
The example above of a simple protocol parser can be implemented much | ||
more simply by using the higher level `Transform` stream class. | ||
In this example, rather than providing the input as an argument, it | ||
would be piped into the parser, which is a more idiomatic Node stream | ||
approach. | ||
```javascript | ||
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 = Object.create( | ||
Transform.prototype, { constructor: { value: SimpleProtocol }}); | ||
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(b); | ||
} | ||
} else { | ||
// from there on, just provide the data to our consumer as-is. | ||
this.push(b); | ||
} | ||
done(); | ||
}; | ||
var parser = new SimpleProtocol(); | ||
source.pipe(parser) | ||
// Now parser is a readable stream that will emit 'header' | ||
// with the parsed header data. | ||
``` | ||
## 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. | ||
[EventEmitter]: events.html#events_class_events_eventemitter |
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