text: // 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;
  Readable.ReadableState = ReadableState;
  
  var Stream = require('stream');
  var util = require('util');
  var StringDecoder;
  
  util.inherits(Readable, Stream);
  
  function ReadableState(options, stream) {
    options = options || {};
  
    // the argument passed to this._read(n,cb)
    this.bufferSize = options.bufferSize || 16 * 1024;
  
    // 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;
    this.highWaterMark = (hwm || hwm === 0) ? hwm : 16 * 1024;
  
    // the minimum number of bytes to buffer before emitting 'readable'
    // default to pushing everything out as fast as possible.
    this.lowWaterMark = options.lowWaterMark || 0;
  
    // cast to ints.
    this.bufferSize = ~~this.bufferSize;
    this.lowWaterMark = ~~this.lowWaterMark;
    this.highWaterMark = ~~this.highWaterMark;
  
    if (this.lowWaterMark > this.highWaterMark)
      throw new Error('lowWaterMark cannot be higher than highWaterMark');
  
    this.buffer = [];
    this.length = 0;
    this.pipes = null;
    this.pipesCount = 0;
    this.flowing = false;
    this.ended = false;
    this.endEmitted = false;
    this.reading = false;
    this.sync = false;
    this.onread = function(er, data) {
      onread(stream, er, data);
    };
  
    // 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;
  
  
    // 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;
  
    // 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;
    this.pipeChunkSize = null;
  
    this.decoder = null;
    if (options.encoding) {
      if (!StringDecoder)
        StringDecoder = require('string_decoder').StringDecoder;
      this.decoder = new StringDecoder(options.encoding);
    }
  }
  
  function Readable(options) {
    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) {
    var rs = this._readableState;
    rs.onread(null, chunk);
  
    // if it's past the high water mark, we can push in some more.
    // Also, if it's still within the lowWaterMark, we can stand some
    // more bytes.  This is to work around cases where hwm=0 and
    // lwm=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.
    return rs.needReadable ||
           rs.length < rs.highWaterMark ||
           rs.length <= rs.lowWaterMark;
  };
  
  // backwards compatibility.
  Readable.prototype.setEncoding = function(enc) {
    if (!StringDecoder)
      StringDecoder = require('string_decoder').StringDecoder;
    this._readableState.decoder = new StringDecoder(enc);
  };
  
  
  function howMuchToRead(n, state) {
    if (state.length === 0 && state.ended)
      return 0;
  
    if (state.objectMode)
      return n === 0 ? 0 : 1;
  
    if (isNaN(n) || n === null) {
      // 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;
  
    // 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 _read(n, cb) below.
  Readable.prototype.read = function(n) {
    var state = this._readableState;
    var nOrig = n;
  
    if (typeof n !== 'number' || 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) {
      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;
  
    // if we currently have less than the highWaterMark, then also read some
    if (state.length - n <= state.highWaterMark)
      doRead = true;
  
    // 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;
  
    if (doRead) {
      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.bufferSize, state.onread);
      state.sync = false;
    }
  
    // If _read called its callback 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 (ret === null) {
      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 happened to read() exactly the remaining amount in the
    // buffer, and the EOF has been seen at this point, then make sure
    // that we emit 'end' on the very next tick.
    if (state.ended && !state.endEmitted && state.length === 0)
      endReadable(this);
  
    return ret;
  };
  
  function onread(stream, er, chunk) {
    var state = stream._readableState;
    var sync = state.sync;
  
    // If we get something that is not a buffer, string, null, or undefined,
    // then switch into objectMode.  Now stream chunks are all considered
    // to be of length=1, and the watermarks determine how many objects to
    // keep in the buffer, rather than how many bytes or characters.
    if (!Buffer.isBuffer(chunk) &&
        'string' !== typeof chunk &&
        chunk !== null &&
        chunk !== undefined) {
      state.objectMode = true;
      state.length = state.buffer.length;
      state.decoder = null;
    }
  
    state.reading = false;
    if (er)
      return stream.emit('error', er);
  
    if (chunk === null || chunk === undefined) {
      // eof
      state.ended = true;
      if (state.decoder) {
        chunk = state.decoder.end();
        if (chunk && chunk.length) {
          state.buffer.push(chunk);
          state.length += state.objectMode ? 1 : chunk.length;
        }
      }
  
      // if we've ended and we have some data left, then emit
      // 'readable' now to make sure it gets picked up.
      if (state.length > 0)
        emitReadable(stream);
      else
        endReadable(stream);
      return;
    }
  
    // at this point, if we got a zero-length buffer or string,
    // and we're not in object-mode, then there's really no point
    // continuing.  it means that there is nothing to read right
    // now, but as we have not received the EOF-signaling null,
    // we're not ended.  we've already unset the reading flag,
    // so just get out of here.
    if (!state.objectMode &&
        (chunk || typeof chunk === 'string') &&
        0 === chunk.length)
      return;
  
    if (state.decoder)
      chunk = state.decoder.write(chunk);
  
    // update the buffer info.
    state.length += state.objectMode ? 1 : chunk.length;
    state.buffer.push(chunk);
  
    // if we haven't gotten enough to pass the lowWaterMark,
    // and we haven't ended, then don't bother telling the user
    // that it's time to read more data.  Otherwise, emitting 'readable'
    // probably will trigger another stream.read(), which can trigger
    // another _read(n,cb) before this one returns!
    if (state.length <= state.lowWaterMark) {
      state.reading = true;
      stream._read(state.bufferSize, state.onread);
      return;
    }
  
    // 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.
    if (state.needReadable) {
      if (!sync)
        emitReadable(stream);
      else
        process.nextTick(function() {
          emitReadable(stream);
        });
    }
  }
  
  function emitReadable(stream) {
    var state = stream._readableState;
    state.needReadable = false;
    if (state.emittedReadable)
      return;
  
    state.emittedReadable = true;
    stream.emit('readable');
  }
  
  // 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, cb) {
    process.nextTick(function() {
      cb(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;
  
    if ((!pipeOpts || pipeOpts.end !== false) &&
        dest !== process.stdout &&
        dest !== process.stderr) {
      src.once('end', onend);
    } else {
      src.once('end', cleanup);
    }
  
    dest.on('unpipe', onunpipe);
    function onunpipe(readable) {
      if (readable !== src) return;
      cleanup();
    }
  
    if (pipeOpts && pipeOpts.chunkSize)
      state.pipeChunkSize = pipeOpts.chunkSize;
  
    function 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() {
      // 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);
  
      // 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 (!dest._writableState || dest._writableState.needDrain)
        ondrain();
    }
  
    // if the dest has an error, then stop piping into it.
    // however, don't suppress the throwing behavior for this.
    function onerror(er) {
      unpipe();
      if (dest.listeners('error').length === 0)
        dest.emit('error', er);
    }
    dest.once('error', onerror);
  
    // Both close and finish should trigger unpipe, but only once.
    function onclose() {
      dest.removeListener('finish', onfinish);
      unpipe();
    }
    dest.once('close', onclose);
    function onfinish() {
      dest.removeListener('close', onclose);
      unpipe();
    }
    dest.once('finish', onfinish);
  
    function 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) {
      // the handler that waits for readable events after all
      // the data gets sucked out in flow.
      // This would be easier to follow with a .once() handler
      // in flow(), but that is too slow.
      this.on('readable', pipeOnReadable);
  
      state.flowing = true;
      process.nextTick(function() {
        flow(src);
      });
    }
  
    return dest;
  };
  
  function pipeOnDrain(src) {
    return function() {
      var dest = this;
      var state = src._readableState;
      state.awaitDrain--;
      if (state.awaitDrain === 0)
        flow(src);
    };
  }
  
  function flow(src) {
    var state = src._readableState;
    var chunk;
    state.awaitDrain = 0;
  
    function write(dest, i, list) {
      var written = dest.write(chunk);
      if (false === written) {
        state.awaitDrain++;
      }
    }
  
    while (state.pipesCount &&
           null !== (chunk = src.read(state.pipeChunkSize))) {
  
      if (state.pipesCount === 1)
        write(state.pipes, 0, null);
      else
        state.pipes.forEach(write);
  
      src.emit('data', chunk);
  
      // if anyone needs a drain, then we have to wait for that.
      if (state.awaitDrain > 0)
        return;
    }
  
    // if every destination was unpiped, either before entering this
    // function, or in the while loop, then stop flowing.
    //
    // NB: This is a pretty rare edge case.
    if (state.pipesCount === 0) {
      state.flowing = false;
  
      // if there were data event listeners added, then switch to old mode.
      if (src.listeners('data').length)
        emitDataEvents(src);
      return;
    }
  
    // at this point, no one needed a drain, so we just ran out of data
    // on the next readable event, start it over again.
    state.ranOut = true;
  }
  
  function pipeOnReadable() {
    if (this._readableState.ranOut) {
      this._readableState.ranOut = false;
      flow(this);
    }
  }
  
  
  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;
      this.removeListener('readable', pipeOnReadable);
      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;
      this.removeListener('readable', pipeOnReadable);
      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 = state.pipes.indexOf(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;
  };
  
  // kludge for on('data', fn) consumers.  Sad.
  // This is *not* part of the new readable stream interface.
  // It is an ugly unfortunate mess of history.
  Readable.prototype.on = function(ev, fn) {
    var res = Stream.prototype.on.call(this, ev, fn);
  
    // https://github.com/isaacs/readable-stream/issues/16
    // if we're already flowing, then no need to set up data events.
    if (ev === 'data' && !this._readableState.flowing)
      emitDataEvents(this);
  
    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() {
    emitDataEvents(this);
    this.read(0);
    this.emit('resume');
  };
  
  Readable.prototype.pause = function() {
    emitDataEvents(this, true);
    this.emit('pause');
  };
  
  function emitDataEvents(stream, startPaused) {
    var state = stream._readableState;
  
    if (state.flowing) {
      // https://github.com/isaacs/readable-stream/issues/16
      throw new Error('Cannot switch to old mode now.');
    }
  
    var paused = startPaused || false;
    var readable = false;
  
    // convert to an old-style stream.
    stream.readable = true;
    stream.pipe = Stream.prototype.pipe;
    stream.on = stream.addListener = Stream.prototype.on;
  
    stream.on('readable', function() {
      readable = true;
  
      var c;
      while (!paused && (null !== (c = stream.read())))
        stream.emit('data', c);
  
      if (c === null) {
        readable = false;
        stream._readableState.needReadable = true;
      }
    });
  
    stream.pause = function() {
      paused = true;
      this.emit('pause');
    };
  
    stream.resume = function() {
      paused = false;
      if (readable)
        process.nextTick(function() {
          stream.emit('readable');
        });
      else
        this.read(0);
      this.emit('resume');
    };
  
    // now make it start, just in case it hadn't already.
    stream.emit('readable');
  }
  
  // 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() {
      state.ended = true;
      if (state.decoder) {
        var chunk = state.decoder.end();
        if (chunk && chunk.length)
          self.push(chunk);
      }
  
      self.push(null);
    });
  
    stream.on('data', function(chunk) {
      if (state.decoder)
        chunk = state.decoder.write(chunk);
      if (!chunk || !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 (typeof stream[i] === 'function' &&
          typeof this[i] === 'undefined') {
        this[i] = function(method) { return function() {
          return stream[method].apply(stream, arguments);
        }}(i);
      }
    }
  
    // proxy certain important events.
    var events = ['error', 'close', 'destroy', 'pause', 'resume'];
    events.forEach(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, cb) {
      if (paused) {
        stream.resume();
        paused = false;
      }
    };
  };
  
  
  
  // 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)
      return;
    state.ended = true;
    state.endEmitted = true;
    process.nextTick(function() {
      stream.readable = false;
      stream.emit('end');
    });
  }
  