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EDIT :: _stream_writable.js

// 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 bit simpler than readable streams.
// Implement an async ._write(chunk, encoding, cb), and it'll handle all
// the drain event emission and buffering.

'use strict';

/*<replacement>*/

var pna = require('process-nextick-args');
/*</replacement>*/

module.exports = Writable;

/* <replacement> */
function WriteReq(chunk, encoding, cb) {
  this.chunk = chunk;
  this.encoding = encoding;
  this.callback = cb;
  this.next = null;
}

// It seems a linked list but it is not
// there will be only 2 of these for each stream
function CorkedRequest(state) {
  var _this = this;

this.next = null;
  this.entry = null;
  this.finish = function () {
    onCorkedFinish(_this, state);
  };
}
/* </replacement> */

/*<replacement>*/
var asyncWrite = !process.browser && ['v0.10', 'v0.9.'].indexOf(process.version.slice(0, 5)) > -1 ? setImmediate : pna.nextTick;
/*</replacement>*/

/*<replacement>*/
var Duplex;
/*</replacement>*/

Writable.WritableState = WritableState;

/*<replacement>*/
var util = require('core-util-is');
util.inherits = require('inherits');
/*</replacement>*/

/*<replacement>*/
var internalUtil = {
  deprecate: require('util-deprecate')
};
/*</replacement>*/

/*<replacement>*/
var Stream = require('./internal/streams/stream');
/*</replacement>*/

/*<replacement>*/

/*</replacement>*/

var destroyImpl = require('./internal/streams/destroy');

util.inherits(Writable, Stream);

function nop() {}

function WritableState(options, stream) {
  Duplex = Duplex || require('./_stream_duplex');

options = options || {};

// Duplex streams are both readable and writable, but share
  // the same options object.
  // However, some cases require setting options to different
  // values for the readable and the writable sides of the duplex stream.
  // These options can be provided separately as readableXXX and writableXXX.
  var isDuplex = stream instanceof Duplex;

// object stream flag to indicate whether or not this stream
  // contains buffers or objects.
  this.objectMode = !!options.objectMode;

if (isDuplex) this.objectMode = this.objectMode || !!options.writableObjectMode;

// the point at which write() starts returning false
  // Note: 0 is a valid value, means that we always return false if
  // the entire buffer is not flushed immediately on write()
  var hwm = options.highWaterMark;
  var writableHwm = options.writableHighWaterMark;
  var defaultHwm = this.objectMode ? 16 : 16 * 1024;

if (hwm || hwm === 0) this.highWaterMark = hwm;else if (isDuplex && (writableHwm || writableHwm === 0)) this.highWaterMark = writableHwm;else this.highWaterMark = defaultHwm;

// cast to ints.
  this.highWaterMark = Math.floor(this.highWaterMark);

// if _final has been called
  this.finalCalled = false;

// drain event flag.
  this.needDrain = false;
  // at the start of calling end()
  this.ending = false;
  // when end() has been called, and returned
  this.ended = false;
  // when 'finish' is emitted
  this.finished = false;

// has it been destroyed
  this.destroyed = false;

// should we decode strings into buffers before passing to _write?
  // this is here so that some node-core streams can optimize string
  // handling at a lower level.
  var noDecode = options.decodeStrings === false;
  this.decodeStrings = !noDecode;

// Crypto is kind of old and crusty.  Historically, its default string
  // encoding is 'binary' so we have to make this configurable.
  // Everything else in the universe uses 'utf8', though.
  this.defaultEncoding = options.defaultEncoding || 'utf8';

// not an actual buffer we keep track of, but a measurement
  // of how much we're waiting to get pushed to some underlying
  // socket or file.
  this.length = 0;

// a flag to see when we're in the middle of a write.
  this.writing = false;

// when true all writes will be buffered until .uncork() call
  this.corked = 0;

// a flag to be able to tell if the onwrite cb is called immediately,
  // or on a later tick.  We set this to true at first, because any
  // actions that shouldn't happen until "later" should generally also
  // not happen before the first write call.
  this.sync = true;

// a flag to know if we're processing previously buffered items, which
  // may call the _write() callback in the same tick, so that we don't
  // end up in an overlapped onwrite situation.
  this.bufferProcessing = false;

// the callback that's passed to _write(chunk,cb)
  this.onwrite = function (er) {
    onwrite(stream, er);
  };

// the callback that the user supplies to write(chunk,encoding,cb)
  this.writecb = null;

// the amount that is being written when _write is called.
  this.writelen = 0;

this.bufferedRequest = null;
  this.lastBufferedRequest = null;

// number of pending user-supplied write callbacks
  // this must be 0 before 'finish' can be emitted
  this.pendingcb = 0;

// emit prefinish if the only thing we're waiting for is _write cbs
  // This is relevant for synchronous Transform streams
  this.prefinished = false;

// True if the error was already emitted and should not be thrown again
  this.errorEmitted = false;

// count buffered requests
  this.bufferedRequestCount = 0;

// allocate the first CorkedRequest, there is always
  // one allocated and free to use, and we maintain at most two
  this.corkedRequestsFree = new CorkedRequest(this);
}

WritableState.prototype.getBuffer = function getBuffer() {
  var current = this.bufferedRequest;
  var out = [];
  while (current) {
    out.push(current);
    current = current.next;
  }
  return out;
};

// Test _writableState for inheritance to account for Duplex streams,
// whose prototype chain only points to Readable.
var realHasInstance;
if (typeof Symbol === 'function' && Symbol.hasInstance && typeof Function.prototype[Symbol.hasInstance] === 'function') {
  realHasInstance = Function.prototype[Symbol.hasInstance];
  Object.defineProperty(Writable, Symbol.hasInstance, {
    value: function (object) {
      if (realHasInstance.call(this, object)) return true;
      if (this !== Writable) return false;

return object && object._writableState instanceof WritableState;
    }
  });
} else {
  realHasInstance = function (object) {
    return object instanceof this;
  };
}

function Writable(options) {
  Duplex = Duplex || require('./_stream_duplex');

// Writable ctor is applied to Duplexes, too.
  // `realHasInstance` is necessary because using plain `instanceof`
  // would return false, as no `_writableState` property is attached.

// Trying to use the custom `instanceof` for Writable here will also break the
  // Node.js LazyTransform implementation, which has a non-trivial getter for
  // `_writableState` that would lead to infinite recursion.
  if (!realHasInstance.call(Writable, this) && !(this instanceof Duplex)) {
    return new Writable(options);
  }

this._writableState = new WritableState(options, this);

// legacy.
  this.writable = true;

if (options) {
    if (typeof options.write === 'function') this._write = options.write;

if (typeof options.writev === 'function') this._writev = options.writev;

if (typeof options.destroy === 'function') this._destroy = options.destroy;

if (typeof options.final === 'function') this._final = options.final;
  }

Stream.call(this);
}

// Otherwise people can pipe Writable streams, which is just wrong.
Writable.prototype.pipe = function () {
  this.emit('error', new Error('Cannot pipe, not readable'));
};

function writeAfterEnd(stream, cb) {
  var er = new Error('write after end');
  // TODO: defer error events consistently everywhere, not just the cb
  stream.emit('error', er);
  pna.nextTick(cb, er);
}

// Checks that a user-supplied chunk is valid, especially for the particular
// mode the stream is in. Currently this means that `null` is never accepted
// and undefined/non-string values are only allowed in object mode.
function validChunk(stream, state, chunk, cb) {
  var valid = true;
  var er = false;

if (chunk === null) {
    er = new TypeError('May not write null values to stream');
  } else if (typeof chunk !== 'string' && chunk !== undefined && !state.objectMode) {
    er = new TypeError('Invalid non-string/buffer chunk');
  }
  if (er) {
    stream.emit('error', er);
    pna.nextTick(cb, er);
    valid = false;
  }
  return valid;
}

Writable.prototype.write = function (chunk, encoding, cb) {
  var state = this._writableState;
  var ret = false;
  var isBuf = !state.objectMode && _isUint8Array(chunk);

if (isBuf && !Buffer.isBuffer(chunk)) {
    chunk = _uint8ArrayToBuffer(chunk);
  }

if (typeof encoding === 'function') {
    cb = encoding;
    encoding = null;
  }

if (isBuf) encoding = 'buffer';else if (!encoding) encoding = state.defaultEncoding;

if (typeof cb !== 'function') cb = nop;

if (state.ended) writeAfterEnd(this, cb);else if (isBuf || validChunk(this, state, chunk, cb)) {
    state.pendingcb++;
    ret = writeOrBuffer(this, state, isBuf, chunk, encoding, cb);
  }

return ret;
};

Writable.prototype.cork = function () {
  var state = this._writableState;

state.corked++;
};

Writable.prototype.uncork = function () {
  var state = this._writableState;

if (state.corked) {
    state.corked--;

if (!state.writing && !state.corked && !state.finished && !state.bufferProcessing && state.bufferedRequest) clearBuffer(this, state);
  }
};

Writable.prototype.setDefaultEncoding = function setDefaultEncoding(encoding) {
  // node::ParseEncoding() requires lower case.
  if (typeof encoding === 'string') encoding = encoding.toLowerCase();
  if (!(['hex', 'utf8', 'utf-8', 'ascii', 'binary', 'base64', 'ucs2', 'ucs-2', 'utf16le', 'utf-16le', 'raw'].indexOf((encoding + '').toLowerCase()) > -1)) throw new TypeError('Unknown encoding: ' + encoding);
  this._writableState.defaultEncoding = encoding;
  return this;
};

function decodeChunk(state, chunk, encoding) {
  if (!state.objectMode && state.decodeStrings !== false && typeof chunk === 'string') {
    chunk = Buffer.from(chunk, encoding);
  }
  return chunk;
}

Object.defineProperty(Writable.prototype, 'writableHighWaterMark', {
  // making it explicit this property is not enumerable
  // because otherwise some prototype manipulation in
  // userland will fail
  enumerable: false,
  get: function () {
    return this._writableState.highWaterMark;
  }
});

// if we're already writing something, then just put this
// in the queue, and wait our turn.  Otherwise, call _write
// If we return false, then we need a drain event, so set that flag.
function writeOrBuffer(stream, state, isBuf, chunk, encoding, cb) {
  if (!isBuf) {
    var newChunk = decodeChunk(state, chunk, encoding);
    if (chunk !== newChunk) {
      isBuf = true;
      encoding = 'buffer';
      chunk = newChunk;
    }
  }
  var len = state.objectMode ? 1 : chunk.length;

state.length += len;

var ret = state.length < state.highWaterMark;
  // we must ensure that previous needDrain will not be reset to false.
  if (!ret) state.needDrain = true;

if (state.writing || state.corked) {
    var last = state.lastBufferedRequest;
    state.lastBufferedRequest = {
      chunk: chunk,
      encoding: encoding,
      isBuf: isBuf,
      callback: cb,
      next: null
    };
    if (last) {
      last.next = state.lastBufferedRequest;
    } else {
      state.bufferedRequest = state.lastBufferedRequest;
    }
    state.bufferedRequestCount += 1;
  } else {
    doWrite(stream, state, false, len, chunk, encoding, cb);
  }

return ret;
}

function doWrite(stream, state, writev, len, chunk, encoding, cb) {
  state.writelen = len;
  state.writecb = cb;
  state.writing = true;
  state.sync = true;
  if (writev) stream._writev(chunk, state.onwrite);else stream._write(chunk, encoding, state.onwrite);
  state.sync = false;
}

function onwriteError(stream, state, sync, er, cb) {
  --state.pendingcb;

if (sync) {
    // defer the callback if we are being called synchronously
    // to avoid piling up things on the stack
    pna.nextTick(cb, er);
    // this can emit finish, and it will always happen
    // after error
    pna.nextTick(finishMaybe, stream, state);
    stream._writableState.errorEmitted = true;
    stream.emit('error', er);
  } else {
    // the caller expect this to happen before if
    // it is async
    cb(er);
    stream._writableState.errorEmitted = true;
    stream.emit('error', er);
    // this can emit finish, but finish must
    // always follow error
    finishMaybe(stream, state);
  }
}

function onwriteStateUpdate(state) {
  state.writing = false;
  state.writecb = null;
  state.length -= state.writelen;
  state.writelen = 0;
}

function onwrite(stream, er) {
  var state = stream._writableState;
  var sync = state.sync;
  var cb = state.writecb;

onwriteStateUpdate(state);

if (er) onwriteError(stream, state, sync, er, cb);else {
    // Check if we're actually ready to finish, but don't emit yet
    var finished = needFinish(state);

if (!finished && !state.corked && !state.bufferProcessing && state.bufferedRequest) {
      clearBuffer(stream, state);
    }

if (sync) {
      /*<replacement>*/
      asyncWrite(afterWrite, stream, state, finished, cb);
      /*</replacement>*/
    } else {
      afterWrite(stream, state, finished, cb);
    }
  }
}

function afterWrite(stream, state, finished, cb) {
  if (!finished) onwriteDrain(stream, state);
  state.pendingcb--;
  cb();
  finishMaybe(stream, state);
}

// Must force callback to be called on nextTick, so that we don't
// emit 'drain' before the write() consumer gets the 'false' return
// value, and has a chance to attach a 'drain' listener.
function onwriteDrain(stream, state) {
  if (state.length === 0 && state.needDrain) {
    state.needDrain = false;
    stream.emit('drain');
  }
}

// if there's something in the buffer waiting, then process it
function clearBuffer(stream, state) {
  state.bufferProcessing = true;
  var entry = state.bufferedRequest;

if (stream._writev && entry && entry.next) {
    // Fast case, write everything using _writev()
    var l = state.bufferedRequestCount;
    var buffer = new Array(l);
    var holder = state.corkedRequestsFree;
    holder.entry = entry;

var count = 0;
    var allBuffers = true;
    while (entry) {
      buffer[count] = entry;
      if (!entry.isBuf) allBuffers = false;
      entry = entry.next;
      count += 1;
    }
    buffer.allBuffers = allBuffers;

doWrite(stream, state, true, state.length, buffer, '', holder.finish);

// doWrite is almost always async, defer these to save a bit of time
    // as the hot path ends with doWrite
    state.pendingcb++;
    state.lastBufferedRequest = null;
    if (holder.next) {
      state.corkedRequestsFree = holder.next;
      holder.next = null;
    } else {
      state.corkedRequestsFree = new CorkedRequest(state);
    }
    state.bufferedRequestCount = 0;
  } else {
    // Slow case, write chunks one-by-one
    while (entry) {
      var chunk = entry.chunk;
      var encoding = entry.encoding;
      var cb = entry.callback;
      var len = state.objectMode ? 1 : chunk.length;

doWrite(stream, state, false, len, chunk, encoding, cb);
      entry = entry.next;
      state.bufferedRequestCount--;
      // if we didn't call the onwrite immediately, then
      // it means that we need to wait until it does.
      // also, that means that the chunk and cb are currently
      // being processed, so move the buffer counter past them.
      if (state.writing) {
        break;
      }
    }

if (entry === null) state.lastBufferedRequest = null;
  }

state.bufferedRequest = entry;
  state.bufferProcessing = false;
}

Writable.prototype._write = function (chunk, encoding, cb) {
  cb(new Error('_write() is not implemented'));
};

Writable.prototype._writev = null;

Writable.prototype.end = function (chunk, encoding, cb) {
  var state = this._writableState;

if (typeof chunk === 'function') {
    cb = chunk;
    chunk = null;
    encoding = null;
  } else if (typeof encoding === 'function') {
    cb = encoding;
    encoding = null;
  }

if (chunk !== null && chunk !== undefined) this.write(chunk, encoding);

// .end() fully uncorks
  if (state.corked) {
    state.corked = 1;
    this.uncork();
  }

// ignore unnecessary end() calls.
  if (!state.ending && !state.finished) endWritable(this, state, cb);
};

function endWritable(stream, state, cb) {
  state.ending = true;
  finishMaybe(stream, state);
  if (cb) {
    if (state.finished) pna.nextTick(cb);else stream.once('finish', cb);
  }
  state.ended = true;
  stream.writable = false;
}

Object.defineProperty(Writable.prototype, 'destroyed', {
  get: function () {
    if (this._writableState === undefined) {
      return false;
    }
    return this._writableState.destroyed;
  },
  set: function (value) {
    // we ignore the value if the stream
    // has not been initialized yet
    if (!this._writableState) {
      return;
    }

// backward compatibility, the user is explicitly
    // managing destroyed
    this._writableState.destroyed = value;
  }
});

Writable.prototype.destroy = destroyImpl.destroy;
Writable.prototype._undestroy = destroyImpl.undestroy;
Writable.prototype._destroy = function (err, cb) {
  this.end();
  cb(err);
};

CANCEL

// SYSTEM PANEL //

EDIT :: _stream_writable.js