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