time-to-botec

_stream_readable.js (31324B)

---

 // 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.
 
 'use strict';
 
 /*<replacement>*/
 
 var pna = require('process-nextick-args');
 /*</replacement>*/
 
 module.exports = Readable;
 
 /*<replacement>*/
 var isArray = require('isarray');
 /*</replacement>*/
 
 /*<replacement>*/
 var Duplex;
 /*</replacement>*/
 
 Readable.ReadableState = ReadableState;
 
 /*<replacement>*/
 var EE = require('events').EventEmitter;
 
 var EElistenerCount = function (emitter, type) {
   return emitter.listeners(type).length;
 };
 /*</replacement>*/
 
 /*<replacement>*/
 var Stream = require('./internal/streams/stream');
 /*</replacement>*/
 
 /*<replacement>*/
 
 var Buffer = require('safe-buffer').Buffer;
 var OurUint8Array = global.Uint8Array || function () {};
 function _uint8ArrayToBuffer(chunk) {
   return Buffer.from(chunk);
 }
 function _isUint8Array(obj) {
   return Buffer.isBuffer(obj) || obj instanceof OurUint8Array;
 }
 
 /*</replacement>*/
 
 /*<replacement>*/
 var util = Object.create(require('core-util-is'));
 util.inherits = require('inherits');
 /*</replacement>*/
 
 /*<replacement>*/
 var debugUtil = require('util');
 var debug = void 0;
 if (debugUtil && debugUtil.debuglog) {
   debug = debugUtil.debuglog('stream');
 } else {
   debug = function () {};
 }
 /*</replacement>*/
 
 var BufferList = require('./internal/streams/BufferList');
 var destroyImpl = require('./internal/streams/destroy');
 var StringDecoder;
 
 util.inherits(Readable, Stream);
 
 var kProxyEvents = ['error', 'close', 'destroy', 'pause', 'resume'];
 
 function prependListener(emitter, event, fn) {
   // Sadly this is not cacheable as some libraries bundle their own
   // event emitter implementation with them.
   if (typeof emitter.prependListener === 'function') return emitter.prependListener(event, fn);
 
   // This is a hack to make sure that our error handler is attached before any
   // userland ones.  NEVER DO THIS. This is here only because this code needs
   // to continue to work with older versions of Node.js that do not include
   // the prependListener() method. The goal is to eventually remove this hack.
   if (!emitter._events || !emitter._events[event]) emitter.on(event, fn);else if (isArray(emitter._events[event])) emitter._events[event].unshift(fn);else emitter._events[event] = [fn, emitter._events[event]];
 }
 
 function ReadableState(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. Used to make read(n) ignore n and to
   // make all the buffer merging and length checks go away
   this.objectMode = !!options.objectMode;
 
   if (isDuplex) this.objectMode = this.objectMode || !!options.readableObjectMode;
 
   // 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 readableHwm = options.readableHighWaterMark;
   var defaultHwm = this.objectMode ? 16 : 16 * 1024;
 
   if (hwm || hwm === 0) this.highWaterMark = hwm;else if (isDuplex && (readableHwm || readableHwm === 0)) this.highWaterMark = readableHwm;else this.highWaterMark = defaultHwm;
 
   // cast to ints.
   this.highWaterMark = Math.floor(this.highWaterMark);
 
   // A linked list is used to store data chunks instead of an array because the
   // linked list can remove elements from the beginning faster than
   // array.shift()
   this.buffer = new BufferList();
   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 event 'readable'/'data' is emitted
   // 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 read 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;
   this.resumeScheduled = false;
 
   // has it been destroyed
   this.destroyed = false;
 
   // 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';
 
   // 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) {
   Duplex = Duplex || require('./_stream_duplex');
 
   if (!(this instanceof Readable)) return new Readable(options);
 
   this._readableState = new ReadableState(options, this);
 
   // legacy
   this.readable = true;
 
   if (options) {
     if (typeof options.read === 'function') this._read = options.read;
 
     if (typeof options.destroy === 'function') this._destroy = options.destroy;
   }
 
   Stream.call(this);
 }
 
 Object.defineProperty(Readable.prototype, 'destroyed', {
   get: function () {
     if (this._readableState === undefined) {
       return false;
     }
     return this._readableState.destroyed;
   },
   set: function (value) {
     // we ignore the value if the stream
     // has not been initialized yet
     if (!this._readableState) {
       return;
     }
 
     // backward compatibility, the user is explicitly
     // managing destroyed
     this._readableState.destroyed = value;
   }
 });
 
 Readable.prototype.destroy = destroyImpl.destroy;
 Readable.prototype._undestroy = destroyImpl.undestroy;
 Readable.prototype._destroy = function (err, cb) {
   this.push(null);
   cb(err);
 };
 
 // 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;
   var skipChunkCheck;
 
   if (!state.objectMode) {
     if (typeof chunk === 'string') {
       encoding = encoding || state.defaultEncoding;
       if (encoding !== state.encoding) {
         chunk = Buffer.from(chunk, encoding);
         encoding = '';
       }
       skipChunkCheck = true;
     }
   } else {
     skipChunkCheck = true;
   }
 
   return readableAddChunk(this, chunk, encoding, false, skipChunkCheck);
 };
 
 // Unshift should *always* be something directly out of read()
 Readable.prototype.unshift = function (chunk) {
   return readableAddChunk(this, chunk, null, true, false);
 };
 
 function readableAddChunk(stream, chunk, encoding, addToFront, skipChunkCheck) {
   var state = stream._readableState;
   if (chunk === null) {
     state.reading = false;
     onEofChunk(stream, state);
   } else {
     var er;
     if (!skipChunkCheck) er = chunkInvalid(state, chunk);
     if (er) {
       stream.emit('error', er);
     } else if (state.objectMode || chunk && chunk.length > 0) {
       if (typeof chunk !== 'string' && !state.objectMode && Object.getPrototypeOf(chunk) !== Buffer.prototype) {
         chunk = _uint8ArrayToBuffer(chunk);
       }
 
       if (addToFront) {
         if (state.endEmitted) stream.emit('error', new Error('stream.unshift() after end event'));else addChunk(stream, state, chunk, true);
       } else if (state.ended) {
         stream.emit('error', new Error('stream.push() after EOF'));
       } else {
         state.reading = false;
         if (state.decoder && !encoding) {
           chunk = state.decoder.write(chunk);
           if (state.objectMode || chunk.length !== 0) addChunk(stream, state, chunk, false);else maybeReadMore(stream, state);
         } else {
           addChunk(stream, state, chunk, false);
         }
       }
     } else if (!addToFront) {
       state.reading = false;
     }
   }
 
   return needMoreData(state);
 }
 
 function addChunk(stream, state, chunk, addToFront) {
   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);
 }
 
 function chunkInvalid(state, chunk) {
   var er;
   if (!_isUint8Array(chunk) && typeof chunk !== 'string' && chunk !== undefined && !state.objectMode) {
     er = new TypeError('Invalid non-string/buffer chunk');
   }
   return er;
 }
 
 // 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);
 }
 
 Readable.prototype.isPaused = function () {
   return this._readableState.flowing === false;
 };
 
 // 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 > 8MB
 var MAX_HWM = 0x800000;
 function computeNewHighWaterMark(n) {
   if (n >= MAX_HWM) {
     n = MAX_HWM;
   } else {
     // Get the next highest power of 2 to prevent increasing hwm excessively in
     // tiny amounts
     n--;
     n |= n >>> 1;
     n |= n >>> 2;
     n |= n >>> 4;
     n |= n >>> 8;
     n |= n >>> 16;
     n++;
   }
   return n;
 }
 
 // This function is designed to be inlinable, so please take care when making
 // changes to the function body.
 function howMuchToRead(n, state) {
   if (n <= 0 || state.length === 0 && state.ended) return 0;
   if (state.objectMode) return 1;
   if (n !== n) {
     // Only flow one buffer at a time
     if (state.flowing && state.length) return state.buffer.head.data.length;else return state.length;
   }
   // If we're asking for more than the current hwm, then raise the hwm.
   if (n > state.highWaterMark) state.highWaterMark = computeNewHighWaterMark(n);
   if (n <= state.length) return n;
   // Don't have enough
   if (!state.ended) {
     state.needReadable = true;
     return 0;
   }
   return state.length;
 }
 
 // you can override either this method, or the async _read(n) below.
 Readable.prototype.read = function (n) {
   debug('read', n);
   n = parseInt(n, 10);
   var state = this._readableState;
   var nOrig = n;
 
   if (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);
   } else 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 (!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;
   } else {
     state.length -= n;
   }
 
   if (state.length === 0) {
     // If we have nothing in the buffer, then we want to know
     // as soon as we *do* get something into the buffer.
     if (!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) endReadable(this);
   }
 
   if (ret !== null) this.emit('data', ret);
 
   return ret;
 };
 
 function onEofChunk(stream, state) {
   if (state.ended) return;
   if (state.decoder) {
     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) pna.nextTick(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;
     pna.nextTick(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('_read() is 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 : unpipe;
   if (state.endEmitted) pna.nextTick(endFn);else src.once('end', endFn);
 
   dest.on('unpipe', onunpipe);
   function onunpipe(readable, unpipeInfo) {
     debug('onunpipe');
     if (readable === src) {
       if (unpipeInfo && unpipeInfo.hasUnpiped === false) {
         unpipeInfo.hasUnpiped = true;
         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);
 
   var cleanedUp = false;
   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', unpipe);
     src.removeListener('data', ondata);
 
     cleanedUp = true;
 
     // 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();
   }
 
   // If the user pushes more data while we're writing to dest then we'll end up
   // in ondata again. However, we only want to increase awaitDrain once because
   // dest will only emit one 'drain' event for the multiple writes.
   // => Introduce a guard on increasing awaitDrain.
   var increasedAwaitDrain = false;
   src.on('data', ondata);
   function ondata(chunk) {
     debug('ondata');
     increasedAwaitDrain = false;
     var ret = dest.write(chunk);
     if (false === ret && !increasedAwaitDrain) {
       // If the user unpiped during `dest.write()`, it is possible
       // to get stuck in a permanently paused state if that write
       // also returned false.
       // => Check whether `dest` is still a piping destination.
       if ((state.pipesCount === 1 && state.pipes === dest || state.pipesCount > 1 && indexOf(state.pipes, dest) !== -1) && !cleanedUp) {
         debug('false write response, pause', src._readableState.awaitDrain);
         src._readableState.awaitDrain++;
         increasedAwaitDrain = true;
       }
       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 (EElistenerCount(dest, 'error') === 0) dest.emit('error', er);
   }
 
   // Make sure our error handler is attached before userland ones.
   prependListener(dest, '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() {
     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 && EElistenerCount(src, 'data')) {
       state.flowing = true;
       flow(src);
     }
   };
 }
 
 Readable.prototype.unpipe = function (dest) {
   var state = this._readableState;
   var unpipeInfo = { hasUnpiped: false };
 
   // 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, unpipeInfo);
     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, unpipeInfo);
     }return this;
   }
 
   // try to find the right one.
   var index = indexOf(state.pipes, dest);
   if (index === -1) return this;
 
   state.pipes.splice(index, 1);
   state.pipesCount -= 1;
   if (state.pipesCount === 1) state.pipes = state.pipes[0];
 
   dest.emit('unpipe', this, unpipeInfo);
 
   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 (ev === 'data') {
     // Start flowing on next tick if stream isn't explicitly paused
     if (this._readableState.flowing !== false) this.resume();
   } else if (ev === 'readable') {
     var state = this._readableState;
     if (!state.endEmitted && !state.readableListening) {
       state.readableListening = state.needReadable = true;
       state.emittedReadable = false;
       if (!state.reading) {
         pna.nextTick(nReadingNextTick, this);
       } else if (state.length) {
         emitReadable(this);
       }
     }
   }
 
   return res;
 };
 Readable.prototype.addListener = Readable.prototype.on;
 
 function nReadingNextTick(self) {
   debug('readable nexttick read 0');
   self.read(0);
 }
 
 // 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;
     resume(this, state);
   }
   return this;
 };
 
 function resume(stream, state) {
   if (!state.resumeScheduled) {
     state.resumeScheduled = true;
     pna.nextTick(resume_, stream, state);
   }
 }
 
 function resume_(stream, state) {
   if (!state.reading) {
     debug('resume read 0');
     stream.read(0);
   }
 
   state.resumeScheduled = false;
   state.awaitDrain = 0;
   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);
   while (state.flowing && stream.read() !== null) {}
 }
 
 // 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 _this = this;
 
   var state = this._readableState;
   var paused = false;
 
   stream.on('end', function () {
     debug('wrapped end');
     if (state.decoder && !state.ended) {
       var chunk = state.decoder.end();
       if (chunk && chunk.length) _this.push(chunk);
     }
 
     _this.push(null);
   });
 
   stream.on('data', function (chunk) {
     debug('wrapped data');
     if (state.decoder) chunk = state.decoder.write(chunk);
 
     // don't skip over falsy values in objectMode
     if (state.objectMode && (chunk === null || chunk === undefined)) return;else if (!state.objectMode && (!chunk || !chunk.length)) return;
 
     var ret = _this.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 (this[i] === undefined && typeof stream[i] === 'function') {
       this[i] = function (method) {
         return function () {
           return stream[method].apply(stream, arguments);
         };
       }(i);
     }
   }
 
   // proxy certain important events.
   for (var n = 0; n < kProxyEvents.length; n++) {
     stream.on(kProxyEvents[n], this.emit.bind(this, kProxyEvents[n]));
   }
 
   // when we try to consume some more bytes, simply unpause the
   // underlying stream.
   this._read = function (n) {
     debug('wrapped _read', n);
     if (paused) {
       paused = false;
       stream.resume();
     }
   };
 
   return this;
 };
 
 Object.defineProperty(Readable.prototype, 'readableHighWaterMark', {
   // making it explicit this property is not enumerable
   // because otherwise some prototype manipulation in
   // userland will fail
   enumerable: false,
   get: function () {
     return this._readableState.highWaterMark;
   }
 });
 
 // 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.
 // This function is designed to be inlinable, so please take care when making
 // changes to the function body.
 function fromList(n, state) {
   // nothing buffered
   if (state.length === 0) return null;
 
   var ret;
   if (state.objectMode) ret = state.buffer.shift();else if (!n || n >= state.length) {
     // read it all, truncate the list
     if (state.decoder) ret = state.buffer.join('');else if (state.buffer.length === 1) ret = state.buffer.head.data;else ret = state.buffer.concat(state.length);
     state.buffer.clear();
   } else {
     // read part of list
     ret = fromListPartial(n, state.buffer, state.decoder);
   }
 
   return ret;
 }
 
 // Extracts only enough buffered data to satisfy the amount requested.
 // This function is designed to be inlinable, so please take care when making
 // changes to the function body.
 function fromListPartial(n, list, hasStrings) {
   var ret;
   if (n < list.head.data.length) {
     // slice is the same for buffers and strings
     ret = list.head.data.slice(0, n);
     list.head.data = list.head.data.slice(n);
   } else if (n === list.head.data.length) {
     // first chunk is a perfect match
     ret = list.shift();
   } else {
     // result spans more than one buffer
     ret = hasStrings ? copyFromBufferString(n, list) : copyFromBuffer(n, list);
   }
   return ret;
 }
 
 // Copies a specified amount of characters from the list of buffered data
 // chunks.
 // This function is designed to be inlinable, so please take care when making
 // changes to the function body.
 function copyFromBufferString(n, list) {
   var p = list.head;
   var c = 1;
   var ret = p.data;
   n -= ret.length;
   while (p = p.next) {
     var str = p.data;
     var nb = n > str.length ? str.length : n;
     if (nb === str.length) ret += str;else ret += str.slice(0, n);
     n -= nb;
     if (n === 0) {
       if (nb === str.length) {
         ++c;
         if (p.next) list.head = p.next;else list.head = list.tail = null;
       } else {
         list.head = p;
         p.data = str.slice(nb);
       }
       break;
     }
     ++c;
   }
   list.length -= c;
   return ret;
 }
 
 // Copies a specified amount of bytes from the list of buffered data chunks.
 // This function is designed to be inlinable, so please take care when making
 // changes to the function body.
 function copyFromBuffer(n, list) {
   var ret = Buffer.allocUnsafe(n);
   var p = list.head;
   var c = 1;
   p.data.copy(ret);
   n -= p.data.length;
   while (p = p.next) {
     var buf = p.data;
     var nb = n > buf.length ? buf.length : n;
     buf.copy(ret, ret.length - n, 0, nb);
     n -= nb;
     if (n === 0) {
       if (nb === buf.length) {
         ++c;
         if (p.next) list.head = p.next;else list.head = list.tail = null;
       } else {
         list.head = p;
         p.data = buf.slice(nb);
       }
       break;
     }
     ++c;
   }
   list.length -= c;
   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;
     pna.nextTick(endReadableNT, state, stream);
   }
 }
 
 function endReadableNT(state, stream) {
   // 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 indexOf(xs, x) {
   for (var i = 0, l = xs.length; i < l; i++) {
     if (xs[i] === x) return i;
   }
   return -1;
 }