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node_modules/readable-stream/lib/_stream_transform.js

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+// 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 Duplex = require('./_stream_duplex');
+
+/*<replacement>*/
+var util = require('core-util-is');
+util.inherits = require('inherits');
+/*</replacement>*/
+
+util.inherits(Transform, Duplex);
+
+function afterTransform(er, data) {
+  var ts = this._transformState;
+  ts.transforming = false;
+
+  var cb = ts.writecb;
+
+  if (!cb) {
+    return this.emit('error', new Error('write callback called multiple times'));
+  }
+
+  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._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) {
+  throw new Error('_transform() is not implemented');
+};
+
+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.writecb && !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) {
+  var _this2 = this;
+
+  Duplex.prototype._destroy.call(this, err, function (err2) {
+    cb(err2);
+    _this2.emit('close');
+  });
+};
+
+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);
+
+  // if there's nothing in the write buffer, then that means
+  // that nothing more will ever be provided
+  if (stream._writableState.length) throw new Error('Calling transform done when ws.length != 0');
+
+  if (stream._transformState.transforming) throw new Error('Calling transform done when still transforming');
+
+  return stream.push(null);
+}