text: 'use strict';
  
  // 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.
  
  module.exports = Readable;
  
  /*<replacement>*/
  var isArray = require('isarray');
  /*</replacement>*/
  
  /*<replacement>*/
  var Buffer = require('buffer').Buffer;
  /*</replacement>*/
  
  Readable.ReadableState = ReadableState;
  
  var EE = require('events').EventEmitter;
  
  /*<replacement>*/
  if (!EE.listenerCount) EE.listenerCount = function (emitter, type) {
    return emitter.listeners(type).length;
  };
  /*</replacement>*/
  
  var Stream = require('stream');
  
  /*<replacement>*/
  var util = require('core-util-is');
  util.inherits = require('inherits');
  /*</replacement>*/
  
  var StringDecoder;
  
  /*<replacement>*/
  var debug = require('util');
  if (debug && debug.debuglog) {
    debug = debug.debuglog('stream');
  } else {
    debug = function debug() {};
  }
  /*</replacement>*/
  
  util.inherits(Readable, Stream);
  
  function ReadableState(options, stream) {
    var Duplex = require('./_stream_duplex');
  
    options = options || {};
  
    // the point at which it stops calling _read() to fill the buffer
    // Note: 0 is a valid value, means "don't call _read preemptively ever"
    var hwm = options.highWaterMark;
    var defaultHwm = options.objectMode ? 16 : 16 * 1024;
    this.highWaterMark = hwm || hwm === 0 ? hwm : defaultHwm;
  
    // cast to ints.
    this.highWaterMark = ~~this.highWaterMark;
  
    this.buffer = [];
    this.length = 0;
    this.pipes = null;
    this.pipesCount = 0;
    this.flowing = null;
    this.ended = false;
    this.endEmitted = false;
    this.reading = false;
  
    // 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;
  
    // whenever we return null, then we set a flag to say
    // that we're awaiting a 'readable' event emission.
    this.needReadable = false;
    this.emittedReadable = false;
    this.readableListening = false;
  
    // object stream flag. Used to make read(n) ignore n and to
    // make all the buffer merging and length checks go away
    this.objectMode = !!options.objectMode;
  
    if (stream instanceof Duplex) this.objectMode = this.objectMode || !!options.readableObjectMode;
  
    // 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';
  
    // when piping, we only care about 'readable' events that happen
    // after read()ing all the bytes and not getting any pushback.
    this.ranOut = false;
  
    // the number of writers that are awaiting a drain event in .pipe()s
    this.awaitDrain = 0;
  
    // if true, a maybeReadMore has been scheduled
    this.readingMore = false;
  
    this.decoder = null;
    this.encoding = null;
    if (options.encoding) {
      if (!StringDecoder) StringDecoder = require('string_decoder/').StringDecoder;
      this.decoder = new StringDecoder(options.encoding);
      this.encoding = options.encoding;
    }
  }
  
  function Readable(options) {
    var Duplex = require('./_stream_duplex');
  
    if (!(this instanceof Readable)) return new Readable(options);
  
    this._readableState = new ReadableState(options, this);
  
    // legacy
    this.readable = true;
  
    Stream.call(this);
  }
  
  // Manually shove something into the read() buffer.
  // This returns true if the highWaterMark has not been hit yet,
  // similar to how Writable.write() returns true if you should
  // write() some more.
  Readable.prototype.push = function (chunk, encoding) {
    var state = this._readableState;
  
    if (util.isString(chunk) && !state.objectMode) {
      encoding = encoding || state.defaultEncoding;
      if (encoding !== state.encoding) {
        chunk = new Buffer(chunk, encoding);
        encoding = '';
      }
    }
  
    return readableAddChunk(this, state, chunk, encoding, false);
  };
  
  // Unshift should *always* be something directly out of read()
  Readable.prototype.unshift = function (chunk) {
    var state = this._readableState;
    return readableAddChunk(this, state, chunk, '', true);
  };
  
  function readableAddChunk(stream, state, chunk, encoding, addToFront) {
    var er = chunkInvalid(state, chunk);
    if (er) {
      stream.emit('error', er);
    } else if (util.isNullOrUndefined(chunk)) {
      state.reading = false;
      if (!state.ended) onEofChunk(stream, state);
    } else if (state.objectMode || chunk && chunk.length > 0) {
      if (state.ended && !addToFront) {
        var e = new Error('stream.push() after EOF');
        stream.emit('error', e);
      } else if (state.endEmitted && addToFront) {
        var e = new Error('stream.unshift() after end event');
        stream.emit('error', e);
      } else {
        if (state.decoder && !addToFront && !encoding) chunk = state.decoder.write(chunk);
  
        if (!addToFront) state.reading = false;
  
        // if we want the data now, just emit it.
        if (state.flowing && state.length === 0 && !state.sync) {
          stream.emit('data', chunk);
          stream.read(0);
        } else {
          // update the buffer info.
          state.length += state.objectMode ? 1 : chunk.length;
          if (addToFront) state.buffer.unshift(chunk);else state.buffer.push(chunk);
  
          if (state.needReadable) emitReadable(stream);
        }
  
        maybeReadMore(stream, state);
      }
    } else if (!addToFront) {
      state.reading = false;
    }
  
    return needMoreData(state);
  }
  
  // if it's past the high water mark, we can push in some more.
  // Also, if we have no data yet, we can stand some
  // more bytes.  This is to work around cases where hwm=0,
  // such as the repl.  Also, if the push() triggered a
  // readable event, and the user called read(largeNumber) such that
  // needReadable was set, then we ought to push more, so that another
  // 'readable' event will be triggered.
  function needMoreData(state) {
    return !state.ended && (state.needReadable || state.length < state.highWaterMark || state.length === 0);
  }
  
  // backwards compatibility.
  Readable.prototype.setEncoding = function (enc) {
    if (!StringDecoder) StringDecoder = require('string_decoder/').StringDecoder;
    this._readableState.decoder = new StringDecoder(enc);
    this._readableState.encoding = enc;
    return this;
  };
  
  // Don't raise the hwm > 128MB
  var MAX_HWM = 0x800000;
  function roundUpToNextPowerOf2(n) {
    if (n >= MAX_HWM) {
      n = MAX_HWM;
    } else {
      // Get the next highest power of 2
      n--;
      for (var p = 1; p < 32; p <<= 1) {
        n |= n >> p;
      }n++;
    }
    return n;
  }
  
  function howMuchToRead(n, state) {
    if (state.length === 0 && state.ended) return 0;
  
    if (state.objectMode) return n === 0 ? 0 : 1;
  
    if (isNaN(n) || util.isNull(n)) {
      // only flow one buffer at a time
      if (state.flowing && state.buffer.length) return state.buffer[0].length;else return state.length;
    }
  
    if (n <= 0) return 0;
  
    // If we're asking for more than the target buffer level,
    // then raise the water mark.  Bump up to the next highest
    // power of 2, to prevent increasing it excessively in tiny
    // amounts.
    if (n > state.highWaterMark) state.highWaterMark = roundUpToNextPowerOf2(n);
  
    // don't have that much.  return null, unless we've ended.
    if (n > state.length) {
      if (!state.ended) {
        state.needReadable = true;
        return 0;
      } else return state.length;
    }
  
    return n;
  }
  
  // you can override either this method, or the async _read(n) below.
  Readable.prototype.read = function (n) {
    debug('read', n);
    var state = this._readableState;
    var nOrig = n;
  
    if (!util.isNumber(n) || n > 0) state.emittedReadable = false;
  
    // if we're doing read(0) to trigger a readable event, but we
    // already have a bunch of data in the buffer, then just trigger
    // the 'readable' event and move on.
    if (n === 0 && state.needReadable && (state.length >= state.highWaterMark || state.ended)) {
      debug('read: emitReadable', state.length, state.ended);
      if (state.length === 0 && state.ended) endReadable(this);else emitReadable(this);
      return null;
    }
  
    n = howMuchToRead(n, state);
  
    // if we've ended, and we're now clear, then finish it up.
    if (n === 0 && state.ended) {
      if (state.length === 0) endReadable(this);
      return null;
    }
  
    // All the actual chunk generation logic needs to be
    // *below* the call to _read.  The reason is that in certain
    // synthetic stream cases, such as passthrough streams, _read
    // may be a completely synchronous operation which may change
    // the state of the read buffer, providing enough data when
    // before there was *not* enough.
    //
    // So, the steps are:
    // 1. Figure out what the state of things will be after we do
    // a read from the buffer.
    //
    // 2. If that resulting state will trigger a _read, then call _read.
    // Note that this may be asynchronous, or synchronous.  Yes, it is
    // deeply ugly to write APIs this way, but that still doesn't mean
    // that the Readable class should behave improperly, as streams are
    // designed to be sync/async agnostic.
    // Take note if the _read call is sync or async (ie, if the read call
    // has returned yet), so that we know whether or not it's safe to emit
    // 'readable' etc.
    //
    // 3. Actually pull the requested chunks out of the buffer and return.
  
    // if we need a readable event, then we need to do some reading.
    var doRead = state.needReadable;
    debug('need readable', doRead);
  
    // if we currently have less than the highWaterMark, then also read some
    if (state.length === 0 || state.length - n < state.highWaterMark) {
      doRead = true;
      debug('length less than watermark', doRead);
    }
  
    // however, if we've ended, then there's no point, and if we're already
    // reading, then it's unnecessary.
    if (state.ended || state.reading) {
      doRead = false;
      debug('reading or ended', doRead);
    }
  
    if (doRead) {
      debug('do read');
      state.reading = true;
      state.sync = true;
      // if the length is currently zero, then we *need* a readable event.
      if (state.length === 0) state.needReadable = true;
      // call internal read method
      this._read(state.highWaterMark);
      state.sync = false;
    }
  
    // If _read pushed data synchronously, then `reading` will be false,
    // and we need to re-evaluate how much data we can return to the user.
    if (doRead && !state.reading) n = howMuchToRead(nOrig, state);
  
    var ret;
    if (n > 0) ret = fromList(n, state);else ret = null;
  
    if (util.isNull(ret)) {
      state.needReadable = true;
      n = 0;
    }
  
    state.length -= n;
  
    // If we have nothing in the buffer, then we want to know
    // as soon as we *do* get something into the buffer.
    if (state.length === 0 && !state.ended) state.needReadable = true;
  
    // If we tried to read() past the EOF, then emit end on the next tick.
    if (nOrig !== n && state.ended && state.length === 0) endReadable(this);
  
    if (!util.isNull(ret)) this.emit('data', ret);
  
    return ret;
  };
  
  function chunkInvalid(state, chunk) {
    var er = null;
    if (!util.isBuffer(chunk) && !util.isString(chunk) && !util.isNullOrUndefined(chunk) && !state.objectMode) {
      er = new TypeError('Invalid non-string/buffer chunk');
    }
    return er;
  }
  
  function onEofChunk(stream, state) {
    if (state.decoder && !state.ended) {
      var chunk = state.decoder.end();
      if (chunk && chunk.length) {
        state.buffer.push(chunk);
        state.length += state.objectMode ? 1 : chunk.length;
      }
    }
    state.ended = true;
  
    // emit 'readable' now to make sure it gets picked up.
    emitReadable(stream);
  }
  
  // Don't emit readable right away in sync mode, because this can trigger
  // another read() call => stack overflow.  This way, it might trigger
  // a nextTick recursion warning, but that's not so bad.
  function emitReadable(stream) {
    var state = stream._readableState;
    state.needReadable = false;
    if (!state.emittedReadable) {
      debug('emitReadable', state.flowing);
      state.emittedReadable = true;
      if (state.sync) process.nextTick(function () {
        emitReadable_(stream);
      });else emitReadable_(stream);
    }
  }
  
  function emitReadable_(stream) {
    debug('emit readable');
    stream.emit('readable');
    flow(stream);
  }
  
  // at this point, the user has presumably seen the 'readable' event,
  // and called read() to consume some data.  that may have triggered
  // in turn another _read(n) call, in which case reading = true if
  // it's in progress.
  // However, if we're not ended, or reading, and the length < hwm,
  // then go ahead and try to read some more preemptively.
  function maybeReadMore(stream, state) {
    if (!state.readingMore) {
      state.readingMore = true;
      process.nextTick(function () {
        maybeReadMore_(stream, state);
      });
    }
  }
  
  function maybeReadMore_(stream, state) {
    var len = state.length;
    while (!state.reading && !state.flowing && !state.ended && state.length < state.highWaterMark) {
      debug('maybeReadMore read 0');
      stream.read(0);
      if (len === state.length)
        // didn't get any data, stop spinning.
        break;else len = state.length;
    }
    state.readingMore = false;
  }
  
  // abstract method.  to be overridden in specific implementation classes.
  // call cb(er, data) where data is <= n in length.
  // for virtual (non-string, non-buffer) streams, "length" is somewhat
  // arbitrary, and perhaps not very meaningful.
  Readable.prototype._read = function (n) {
    this.emit('error', new Error('not implemented'));
  };
  
  Readable.prototype.pipe = function (dest, pipeOpts) {
    var src = this;
    var state = this._readableState;
  
    switch (state.pipesCount) {
      case 0:
        state.pipes = dest;
        break;
      case 1:
        state.pipes = [state.pipes, dest];
        break;
      default:
        state.pipes.push(dest);
        break;
    }
    state.pipesCount += 1;
    debug('pipe count=%d opts=%j', state.pipesCount, pipeOpts);
  
    var doEnd = (!pipeOpts || pipeOpts.end !== false) && dest !== process.stdout && dest !== process.stderr;
  
    var endFn = doEnd ? onend : cleanup;
    if (state.endEmitted) process.nextTick(endFn);else src.once('end', endFn);
  
    dest.on('unpipe', onunpipe);
    function onunpipe(readable) {
      debug('onunpipe');
      if (readable === src) {
        cleanup();
      }
    }
  
    function onend() {
      debug('onend');
      dest.end();
    }
  
    // when the dest drains, it reduces the awaitDrain counter
    // on the source.  This would be more elegant with a .once()
    // handler in flow(), but adding and removing repeatedly is
    // too slow.
    var ondrain = pipeOnDrain(src);
    dest.on('drain', ondrain);
  
    function cleanup() {
      debug('cleanup');
      // cleanup event handlers once the pipe is broken
      dest.removeListener('close', onclose);
      dest.removeListener('finish', onfinish);
      dest.removeListener('drain', ondrain);
      dest.removeListener('error', onerror);
      dest.removeListener('unpipe', onunpipe);
      src.removeListener('end', onend);
      src.removeListener('end', cleanup);
      src.removeListener('data', ondata);
  
      // if the reader is waiting for a drain event from this
      // specific writer, then it would cause it to never start
      // flowing again.
      // So, if this is awaiting a drain, then we just call it now.
      // If we don't know, then assume that we are waiting for one.
      if (state.awaitDrain && (!dest._writableState || dest._writableState.needDrain)) ondrain();
    }
  
    src.on('data', ondata);
    function ondata(chunk) {
      debug('ondata');
      var ret = dest.write(chunk);
      if (false === ret) {
        debug('false write response, pause', src._readableState.awaitDrain);
        src._readableState.awaitDrain++;
        src.pause();
      }
    }
  
    // if the dest has an error, then stop piping into it.
    // however, don't suppress the throwing behavior for this.
    function onerror(er) {
      debug('onerror', er);
      unpipe();
      dest.removeListener('error', onerror);
      if (EE.listenerCount(dest, 'error') === 0) dest.emit('error', er);
    }
    // This is a brutally ugly hack to make sure that our error handler
    // is attached before any userland ones.  NEVER DO THIS.
    if (!dest._events || !dest._events.error) dest.on('error', onerror);else if (isArray(dest._events.error)) dest._events.error.unshift(onerror);else dest._events.error = [onerror, dest._events.error];
  
    // Both close and finish should trigger unpipe, but only once.
    function onclose() {
      dest.removeListener('finish', onfinish);
      unpipe();
    }
    dest.once('close', onclose);
    function onfinish() {
      debug('onfinish');
      dest.removeListener('close', onclose);
      unpipe();
    }
    dest.once('finish', onfinish);
  
    function unpipe() {
      debug('unpipe');
      src.unpipe(dest);
    }
  
    // tell the dest that it's being piped to
    dest.emit('pipe', src);
  
    // start the flow if it hasn't been started already.
    if (!state.flowing) {
      debug('pipe resume');
      src.resume();
    }
  
    return dest;
  };
  
  function pipeOnDrain(src) {
    return function () {
      var state = src._readableState;
      debug('pipeOnDrain', state.awaitDrain);
      if (state.awaitDrain) state.awaitDrain--;
      if (state.awaitDrain === 0 && EE.listenerCount(src, 'data')) {
        state.flowing = true;
        flow(src);
      }
    };
  }
  
  Readable.prototype.unpipe = function (dest) {
    var state = this._readableState;
  
    // if we're not piping anywhere, then do nothing.
    if (state.pipesCount === 0) return this;
  
    // just one destination.  most common case.
    if (state.pipesCount === 1) {
      // passed in one, but it's not the right one.
      if (dest && dest !== state.pipes) return this;
  
      if (!dest) dest = state.pipes;
  
      // got a match.
      state.pipes = null;
      state.pipesCount = 0;
      state.flowing = false;
      if (dest) dest.emit('unpipe', this);
      return this;
    }
  
    // slow case. multiple pipe destinations.
  
    if (!dest) {
      // remove all.
      var dests = state.pipes;
      var len = state.pipesCount;
      state.pipes = null;
      state.pipesCount = 0;
      state.flowing = false;
  
      for (var i = 0; i < len; i++) {
        dests[i].emit('unpipe', this);
      }return this;
    }
  
    // try to find the right one.
    var i = indexOf(state.pipes, dest);
    if (i === -1) return this;
  
    state.pipes.splice(i, 1);
    state.pipesCount -= 1;
    if (state.pipesCount === 1) state.pipes = state.pipes[0];
  
    dest.emit('unpipe', this);
  
    return this;
  };
  
  // set up data events if they are asked for
  // Ensure readable listeners eventually get something
  Readable.prototype.on = function (ev, fn) {
    var res = Stream.prototype.on.call(this, ev, fn);
  
    // If listening to data, and it has not explicitly been paused,
    // then call resume to start the flow of data on the next tick.
    if (ev === 'data' && false !== this._readableState.flowing) {
      this.resume();
    }
  
    if (ev === 'readable' && this.readable) {
      var state = this._readableState;
      if (!state.readableListening) {
        state.readableListening = true;
        state.emittedReadable = false;
        state.needReadable = true;
        if (!state.reading) {
          var self = this;
          process.nextTick(function () {
            debug('readable nexttick read 0');
            self.read(0);
          });
        } else if (state.length) {
          emitReadable(this, state);
        }
      }
    }
  
    return res;
  };
  Readable.prototype.addListener = Readable.prototype.on;
  
  // pause() and resume() are remnants of the legacy readable stream API
  // If the user uses them, then switch into old mode.
  Readable.prototype.resume = function () {
    var state = this._readableState;
    if (!state.flowing) {
      debug('resume');
      state.flowing = true;
      if (!state.reading) {
        debug('resume read 0');
        this.read(0);
      }
      resume(this, state);
    }
    return this;
  };
  
  function resume(stream, state) {
    if (!state.resumeScheduled) {
      state.resumeScheduled = true;
      process.nextTick(function () {
        resume_(stream, state);
      });
    }
  }
  
  function resume_(stream, state) {
    state.resumeScheduled = false;
    stream.emit('resume');
    flow(stream);
    if (state.flowing && !state.reading) stream.read(0);
  }
  
  Readable.prototype.pause = function () {
    debug('call pause flowing=%j', this._readableState.flowing);
    if (false !== this._readableState.flowing) {
      debug('pause');
      this._readableState.flowing = false;
      this.emit('pause');
    }
    return this;
  };
  
  function flow(stream) {
    var state = stream._readableState;
    debug('flow', state.flowing);
    if (state.flowing) {
      do {
        var chunk = stream.read();
      } while (null !== chunk && state.flowing);
    }
  }
  
  // wrap an old-style stream as the async data source.
  // This is *not* part of the readable stream interface.
  // It is an ugly unfortunate mess of history.
  Readable.prototype.wrap = function (stream) {
    var state = this._readableState;
    var paused = false;
  
    var self = this;
    stream.on('end', function () {
      debug('wrapped end');
      if (state.decoder && !state.ended) {
        var chunk = state.decoder.end();
        if (chunk && chunk.length) self.push(chunk);
      }
  
      self.push(null);
    });
  
    stream.on('data', function (chunk) {
      debug('wrapped data');
      if (state.decoder) chunk = state.decoder.write(chunk);
      if (!chunk || !state.objectMode && !chunk.length) return;
  
      var ret = self.push(chunk);
      if (!ret) {
        paused = true;
        stream.pause();
      }
    });
  
    // proxy all the other methods.
    // important when wrapping filters and duplexes.
    for (var i in stream) {
      if (util.isFunction(stream[i]) && util.isUndefined(this[i])) {
        this[i] = function (method) {
          return function () {
            return stream[method].apply(stream, arguments);
          };
        }(i);
      }
    }
  
    // proxy certain important events.
    var events = ['error', 'close', 'destroy', 'pause', 'resume'];
    forEach(events, function (ev) {
      stream.on(ev, self.emit.bind(self, ev));
    });
  
    // when we try to consume some more bytes, simply unpause the
    // underlying stream.
    self._read = function (n) {
      debug('wrapped _read', n);
      if (paused) {
        paused = false;
        stream.resume();
      }
    };
  
    return self;
  };
  
  // exposed for testing purposes only.
  Readable._fromList = fromList;
  
  // Pluck off n bytes from an array of buffers.
  // Length is the combined lengths of all the buffers in the list.
  function fromList(n, state) {
    var list = state.buffer;
    var length = state.length;
    var stringMode = !!state.decoder;
    var objectMode = !!state.objectMode;
    var ret;
  
    // nothing in the list, definitely empty.
    if (list.length === 0) return null;
  
    if (length === 0) ret = null;else if (objectMode) ret = list.shift();else if (!n || n >= length) {
      // read it all, truncate the array.
      if (stringMode) ret = list.join('');else ret = Buffer.concat(list, length);
      list.length = 0;
    } else {
      // read just some of it.
      if (n < list[0].length) {
        // just take a part of the first list item.
        // slice is the same for buffers and strings.
        var buf = list[0];
        ret = buf.slice(0, n);
        list[0] = buf.slice(n);
      } else if (n === list[0].length) {
        // first list is a perfect match
        ret = list.shift();
      } else {
        // complex case.
        // we have enough to cover it, but it spans past the first buffer.
        if (stringMode) ret = '';else ret = new Buffer(n);
  
        var c = 0;
        for (var i = 0, l = list.length; i < l && c < n; i++) {
          var buf = list[0];
          var cpy = Math.min(n - c, buf.length);
  
          if (stringMode) ret += buf.slice(0, cpy);else buf.copy(ret, c, 0, cpy);
  
          if (cpy < buf.length) list[0] = buf.slice(cpy);else list.shift();
  
          c += cpy;
        }
      }
    }
  
    return ret;
  }
  
  function endReadable(stream) {
    var state = stream._readableState;
  
    // If we get here before consuming all the bytes, then that is a
    // bug in node.  Should never happen.
    if (state.length > 0) throw new Error('endReadable called on non-empty stream');
  
    if (!state.endEmitted) {
      state.ended = true;
      process.nextTick(function () {
        // Check that we didn't get one last unshift.
        if (!state.endEmitted && state.length === 0) {
          state.endEmitted = true;
          stream.readable = false;
          stream.emit('end');
        }
      });
    }
  }
  
  function forEach(xs, f) {
    for (var i = 0, l = xs.length; i < l; i++) {
      f(xs[i], i);
    }
  }
  
  function indexOf(xs, x) {
    for (var i = 0, l = xs.length; i < l; i++) {
      if (xs[i] === x) return i;
    }
    return -1;
  }