// Copyright Joyent, Inc. and other Node contributors.
|
//
|
// Permission is hereby granted, free of charge, to any person obtaining a
|
// copy of this software and associated documentation files (the
|
// "Software"), to deal in the Software without restriction, including
|
// without limitation the rights to use, copy, modify, merge, publish,
|
// distribute, sublicense, and/or sell copies of the Software, and to permit
|
// persons to whom the Software is furnished to do so, subject to the
|
// following conditions:
|
//
|
// The above copyright notice and this permission notice shall be included
|
// in all copies or substantial portions of the Software.
|
//
|
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
|
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
|
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
|
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
|
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
|
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
|
// USE OR OTHER DEALINGS IN THE SOFTWARE.
|
// a transform stream is a readable/writable stream where you do
|
// something with the data. Sometimes it's called a "filter",
|
// but that's not a great name for it, since that implies a thing where
|
// some bits pass through, and others are simply ignored. (That would
|
// be a valid example of a transform, of course.)
|
//
|
// While the output is causally related to the input, it's not a
|
// necessarily symmetric or synchronous transformation. For example,
|
// a zlib stream might take multiple plain-text writes(), and then
|
// emit a single compressed chunk some time in the future.
|
//
|
// Here's how this works:
|
//
|
// The Transform stream has all the aspects of the readable and writable
|
// stream classes. When you write(chunk), that calls _write(chunk,cb)
|
// internally, and returns false if there's a lot of pending writes
|
// buffered up. When you call read(), that calls _read(n) until
|
// there's enough pending readable data buffered up.
|
//
|
// In a transform stream, the written data is placed in a buffer. When
|
// _read(n) is called, it transforms the queued up data, calling the
|
// buffered _write cb's as it consumes chunks. If consuming a single
|
// written chunk would result in multiple output chunks, then the first
|
// outputted bit calls the readcb, and subsequent chunks just go into
|
// the read buffer, and will cause it to emit 'readable' if necessary.
|
//
|
// This way, back-pressure is actually determined by the reading side,
|
// since _read has to be called to start processing a new chunk. However,
|
// a pathological inflate type of transform can cause excessive buffering
|
// here. For example, imagine a stream where every byte of input is
|
// interpreted as an integer from 0-255, and then results in that many
|
// bytes of output. Writing the 4 bytes {ff,ff,ff,ff} would result in
|
// 1kb of data being output. In this case, you could write a very small
|
// amount of input, and end up with a very large amount of output. In
|
// such a pathological inflating mechanism, there'd be no way to tell
|
// the system to stop doing the transform. A single 4MB write could
|
// cause the system to run out of memory.
|
//
|
// However, even in such a pathological case, only a single written chunk
|
// would be consumed, and then the rest would wait (un-transformed) until
|
// the results of the previous transformed chunk were consumed.
|
'use strict';
|
|
module.exports = Transform;
|
|
var _require$codes = require('../errors').codes,
|
ERR_METHOD_NOT_IMPLEMENTED = _require$codes.ERR_METHOD_NOT_IMPLEMENTED,
|
ERR_MULTIPLE_CALLBACK = _require$codes.ERR_MULTIPLE_CALLBACK,
|
ERR_TRANSFORM_ALREADY_TRANSFORMING = _require$codes.ERR_TRANSFORM_ALREADY_TRANSFORMING,
|
ERR_TRANSFORM_WITH_LENGTH_0 = _require$codes.ERR_TRANSFORM_WITH_LENGTH_0;
|
|
var Duplex = require('./_stream_duplex');
|
|
require('inherits')(Transform, Duplex);
|
|
function afterTransform(er, data) {
|
var ts = this._transformState;
|
ts.transforming = false;
|
var cb = ts.writecb;
|
|
if (cb === null) {
|
return this.emit('error', new ERR_MULTIPLE_CALLBACK());
|
}
|
|
ts.writechunk = null;
|
ts.writecb = null;
|
if (data != null) // single equals check for both `null` and `undefined`
|
this.push(data);
|
cb(er);
|
var rs = this._readableState;
|
rs.reading = false;
|
|
if (rs.needReadable || rs.length < rs.highWaterMark) {
|
this._read(rs.highWaterMark);
|
}
|
}
|
|
function Transform(options) {
|
if (!(this instanceof Transform)) return new Transform(options);
|
Duplex.call(this, options);
|
this._transformState = {
|
afterTransform: afterTransform.bind(this),
|
needTransform: false,
|
transforming: false,
|
writecb: null,
|
writechunk: null,
|
writeencoding: null
|
}; // start out asking for a readable event once data is transformed.
|
|
this._readableState.needReadable = true; // we have implemented the _read method, and done the other things
|
// that Readable wants before the first _read call, so unset the
|
// sync guard flag.
|
|
this._readableState.sync = false;
|
|
if (options) {
|
if (typeof options.transform === 'function') this._transform = options.transform;
|
if (typeof options.flush === 'function') this._flush = options.flush;
|
} // When the writable side finishes, then flush out anything remaining.
|
|
|
this.on('prefinish', prefinish);
|
}
|
|
function prefinish() {
|
var _this = this;
|
|
if (typeof this._flush === 'function' && !this._readableState.destroyed) {
|
this._flush(function (er, data) {
|
done(_this, er, data);
|
});
|
} else {
|
done(this, null, null);
|
}
|
}
|
|
Transform.prototype.push = function (chunk, encoding) {
|
this._transformState.needTransform = false;
|
return Duplex.prototype.push.call(this, chunk, encoding);
|
}; // This is the part where you do stuff!
|
// override this function in implementation classes.
|
// 'chunk' is an input chunk.
|
//
|
// Call `push(newChunk)` to pass along transformed output
|
// to the readable side. You may call 'push' zero or more times.
|
//
|
// Call `cb(err)` when you are done with this chunk. If you pass
|
// an error, then that'll put the hurt on the whole operation. If you
|
// never call cb(), then you'll never get another chunk.
|
|
|
Transform.prototype._transform = function (chunk, encoding, cb) {
|
cb(new ERR_METHOD_NOT_IMPLEMENTED('_transform()'));
|
};
|
|
Transform.prototype._write = function (chunk, encoding, cb) {
|
var ts = this._transformState;
|
ts.writecb = cb;
|
ts.writechunk = chunk;
|
ts.writeencoding = encoding;
|
|
if (!ts.transforming) {
|
var rs = this._readableState;
|
if (ts.needTransform || rs.needReadable || rs.length < rs.highWaterMark) this._read(rs.highWaterMark);
|
}
|
}; // Doesn't matter what the args are here.
|
// _transform does all the work.
|
// That we got here means that the readable side wants more data.
|
|
|
Transform.prototype._read = function (n) {
|
var ts = this._transformState;
|
|
if (ts.writechunk !== null && !ts.transforming) {
|
ts.transforming = true;
|
|
this._transform(ts.writechunk, ts.writeencoding, ts.afterTransform);
|
} else {
|
// mark that we need a transform, so that any data that comes in
|
// will get processed, now that we've asked for it.
|
ts.needTransform = true;
|
}
|
};
|
|
Transform.prototype._destroy = function (err, cb) {
|
Duplex.prototype._destroy.call(this, err, function (err2) {
|
cb(err2);
|
});
|
};
|
|
function done(stream, er, data) {
|
if (er) return stream.emit('error', er);
|
if (data != null) // single equals check for both `null` and `undefined`
|
stream.push(data); // TODO(BridgeAR): Write a test for these two error cases
|
// if there's nothing in the write buffer, then that means
|
// that nothing more will ever be provided
|
|
if (stream._writableState.length) throw new ERR_TRANSFORM_WITH_LENGTH_0();
|
if (stream._transformState.transforming) throw new ERR_TRANSFORM_ALREADY_TRANSFORMING();
|
return stream.push(null);
|
}
|
