readable.js

// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
// Copyright Joyent and Node contributors. All rights reserved. MIT license.
// deno-lint-ignore-file

import { addAbortSignalNoValidate } from "./add-abort-signal.js";
import { Buffer } from "../../buffer.ts";
import { debuglog } from "../util/debuglog.ts";
import { getDefaultHighWaterMark, getHighWaterMark } from "./state.js";
import { prependListener, Stream } from "./legacy.js";
import { StringDecoder } from "../../string_decoder.ts";
import { validateObject } from "../validators.js";
import {
  ERR_INVALID_ARG_TYPE,
  ERR_METHOD_NOT_IMPLEMENTED,
  ERR_STREAM_PUSH_AFTER_EOF,
  ERR_STREAM_UNSHIFT_AFTER_END_EVENT,
} from "../errors.ts";
import { nextTick } from "../../_next_tick.ts";
import { stdio } from "../../_process/stdio.js";
import _from from "./from.js";
import BufferList from "./buffer_list.js";
import destroyImpl from "./destroy.js";
import EE from "../../events.ts";

let debug = debuglog("stream", (fn) => {
  debug = fn;
});

const kPaused = Symbol("kPaused");

Object.setPrototypeOf(Readable.prototype, Stream.prototype);
Object.setPrototypeOf(Readable, Stream);
const nop = () => {};

const { errorOrDestroy } = destroyImpl;

function ReadableState(options, stream, isDuplex) {
  // 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.
  if (typeof isDuplex !== "boolean") {
    isDuplex = stream instanceof Stream.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 && options.objectMode);

  if (isDuplex) {
    this.objectMode = this.objectMode ||
      !!(options && 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"
  this.highWaterMark = options
    ? getHighWaterMark(this, options, "readableHighWaterMark", isDuplex)
    : getDefaultHighWaterMark(false);

  // 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 = [];
  this.flowing = null;
  this.ended = false;
  this.endEmitted = false;
  this.reading = false;

  // Stream is still being constructed and cannot be
  // destroyed until construction finished or failed.
  // Async construction is opt in, therefore we start as
  // constructed.
  this.constructed = true;

  // 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;
  this[kPaused] = null;

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

  // Should close be emitted on destroy. Defaults to true.
  this.emitClose = !options || options.emitClose !== false;

  // Should .destroy() be called after 'end' (and potentially 'finish').
  this.autoDestroy = !options || options.autoDestroy !== false;

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

  // Indicates whether the stream has errored. When true no further
  // _read calls, 'data' or 'readable' events should occur. This is needed
  // since when autoDestroy is disabled we need a way to tell whether the
  // stream has failed.
  this.errored = null;

  // Indicates whether the stream has finished destroying.
  this.closed = false;

  // True if close has been emitted or would have been emitted
  // depending on emitClose.
  this.closeEmitted = 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 && options.defaultEncoding) || "utf8";

  // Ref the piped dest which we need a drain event on it
  // type: null | Writable | Set<Writable>.
  this.awaitDrainWriters = null;
  this.multiAwaitDrain = false;

  // If true, a maybeReadMore has been scheduled.
  this.readingMore = false;

  this.dataEmitted = false;

  this.decoder = null;
  this.encoding = null;
  if (options && options.encoding) {
    this.decoder = new StringDecoder(options.encoding);
    this.encoding = options.encoding;
  }
}

function Readable(options) {
  if (!(this instanceof Readable)) {
    return new Readable(options);
  }

  // Checking for a Stream.Duplex instance is faster here instead of inside
  // the ReadableState constructor, at least with V8 6.5.
  const isDuplex = this instanceof Stream.Duplex;

  this._readableState = new ReadableState(options, this, isDuplex);

  if (options) {
    if (typeof options.read === "function") {
      this._read = options.read;
    }

    if (typeof options.destroy === "function") {
      this._destroy = options.destroy;
    }

    if (typeof options.construct === "function") {
      this._construct = options.construct;
    }
    if (options.signal && !isDuplex) {
      addAbortSignalNoValidate(options.signal, this);
    }
  }

  Stream.call(this, options);

  destroyImpl.construct(this, () => {
    if (this._readableState.needReadable) {
      maybeReadMore(this, this._readableState);
    }
  });
}

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

Readable.prototype[EE.captureRejectionSymbol] = function (err) {
  this.destroy(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) {
  return readableAddChunk(this, chunk, encoding, false);
};

// Unshift should *always* be something directly out of read().
Readable.prototype.unshift = function (chunk, encoding) {
  return readableAddChunk(this, chunk, encoding, true);
};

function readableAddChunk(stream, chunk, encoding, addToFront) {
  debug("readableAddChunk", chunk);
  const state = stream._readableState;

  let err;
  if (!state.objectMode) {
    if (typeof chunk === "string") {
      encoding = encoding || state.defaultEncoding;
      if (state.encoding !== encoding) {
        if (addToFront && state.encoding) {
          // When unshifting, if state.encoding is set, we have to save
          // the string in the BufferList with the state encoding.
          chunk = Buffer.from(chunk, encoding).toString(state.encoding);
        } else {
          chunk = Buffer.from(chunk, encoding);
          encoding = "";
        }
      }
    } else if (chunk instanceof Buffer) {
      encoding = "";
    } else if (Stream._isUint8Array(chunk)) {
      chunk = Stream._uint8ArrayToBuffer(chunk);
      encoding = "";
    } else if (chunk != null) {
      err = new ERR_INVALID_ARG_TYPE(
        "chunk",
        ["string", "Buffer", "Uint8Array"],
        chunk,
      );
    }
  }

  if (err) {
    errorOrDestroy(stream, err);
  } else if (chunk === null) {
    state.reading = false;
    onEofChunk(stream, state);
  } else if (state.objectMode || (chunk && chunk.length > 0)) {
    if (addToFront) {
      if (state.endEmitted) {
        errorOrDestroy(stream, new ERR_STREAM_UNSHIFT_AFTER_END_EVENT());
      } else {
        addChunk(stream, state, chunk, true);
      }
    } else if (state.ended) {
      errorOrDestroy(stream, new ERR_STREAM_PUSH_AFTER_EOF());
    } else if (state.destroyed || state.errored) {
      return false;
    } 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;
    maybeReadMore(stream, state);
  }

  // We can push more data if we are below the highWaterMark.
  // 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.
  return !state.ended &&
    (state.length < state.highWaterMark || state.length === 0);
}

function addChunk(stream, state, chunk, addToFront) {
  if (
    state.flowing && state.length === 0 && !state.sync &&
    stream.listenerCount("data") > 0
  ) {
    // Use the guard to avoid creating `Set()` repeatedly
    // when we have multiple pipes.
    if (state.multiAwaitDrain) {
      state.awaitDrainWriters.clear();
    } else {
      state.awaitDrainWriters = null;
    }
    state.dataEmitted = true;
    stream.emit("data", chunk);
  } 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);
}

Readable.prototype.isPaused = function () {
  const state = this._readableState;
  return state[kPaused] === true || state.flowing === false;
};

// Backwards compatibility.
Readable.prototype.setEncoding = function (enc) {
  const decoder = new StringDecoder(enc);
  this._readableState.decoder = decoder;
  // If setEncoding(null), decoder.encoding equals utf8.
  this._readableState.encoding = this._readableState.decoder.encoding;

  const buffer = this._readableState.buffer;
  // Iterate over current buffer to convert already stored Buffers:
  let content = "";
  for (const data of buffer) {
    content += decoder.write(data);
  }
  buffer.clear();
  if (content !== "") {
    buffer.push(content);
  }
  this._readableState.length = content.length;
  return this;
};

// Don't raise the hwm > 1GB.
const MAX_HWM = 0x40000000;
function computeNewHighWaterMark(n) {
  if (n >= MAX_HWM) {
    // TODO(ronag): Throw ERR_VALUE_OUT_OF_RANGE.
    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 (Number.isNaN(n)) {
    // Only flow one buffer at a time.
    if (state.flowing && state.length) {
      return state.buffer.first().length;
    }
    return state.length;
  }
  if (n <= state.length) {
    return n;
  }
  return state.ended ? state.length : 0;
}

// You can override either this method, or the async _read(n) below.
Readable.prototype.read = function (n) {
  debug("read", n);
  // Same as parseInt(undefined, 10), however V8 7.3 performance regressed
  // in this scenario, so we are doing it manually.
  if (n === undefined) {
    n = NaN;
  } else if (!Number.isInteger(n)) {
    n = Number.parseInt(n, 10);
  }
  const state = this._readableState;
  const nOrig = n;

  // If we're asking for more than the current hwm, then raise the hwm.
  if (n > state.highWaterMark) {
    state.highWaterMark = computeNewHighWaterMark(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.highWaterMark !== 0
      ? state.length >= state.highWaterMark
      : state.length > 0) ||
      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.
  let 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, if we're already
  // reading, then it's unnecessary, if we're constructing we have to wait,
  // and if we're destroyed or errored, then it's not allowed,
  if (
    state.ended || state.reading || state.destroyed || state.errored ||
    !state.constructed
  ) {
    doRead = false;
    debug("reading, ended or constructing", 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);
    }
  }

  let ret;
  if (n > 0) {
    ret = fromList(n, state);
  } else {
    ret = null;
  }

  if (ret === null) {
    state.needReadable = state.length <= state.highWaterMark;
    n = 0;
  } else {
    state.length -= n;
    if (state.multiAwaitDrain) {
      state.awaitDrainWriters.clear();
    } else {
      state.awaitDrainWriters = null;
    }
  }

  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) {
    state.dataEmitted = true;
    this.emit("data", ret);
  }

  return ret;
};

function onEofChunk(stream, state) {
  debug("onEofChunk");
  if (state.ended) return;
  if (state.decoder) {
    const chunk = state.decoder.end();
    if (chunk && chunk.length) {
      state.buffer.push(chunk);
      state.length += state.objectMode ? 1 : chunk.length;
    }
  }
  state.ended = true;

  if (state.sync) {
    // If we are sync, wait until next tick to emit the data.
    // Otherwise we risk emitting data in the flow()
    // the readable code triggers during a read() call.
    emitReadable(stream);
  } else {
    // Emit 'readable' now to make sure it gets picked up.
    state.needReadable = false;
    state.emittedReadable = true;
    // We have to emit readable now that we are EOF. Modules
    // in the ecosystem (e.g. dicer) rely on this event being sync.
    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) {
  const state = stream._readableState;
  debug("emitReadable", state.needReadable, state.emittedReadable);
  state.needReadable = false;
  if (!state.emittedReadable) {
    debug("emitReadable", state.flowing);
    state.emittedReadable = true;
    nextTick(emitReadable_, stream);
  }
}

function emitReadable_(stream) {
  const state = stream._readableState;
  debug("emitReadable_", state.destroyed, state.length, state.ended);
  if (!state.destroyed && !state.errored && (state.length || state.ended)) {
    stream.emit("readable");
    state.emittedReadable = false;
  }

  // The stream needs another readable event if:
  // 1. It is not flowing, as the flow mechanism will take
  //    care of it.
  // 2. It is not ended.
  // 3. It is below the highWaterMark, so we can schedule
  //    another readable later.
  state.needReadable = !state.flowing &&
    !state.ended &&
    state.length <= state.highWaterMark;
  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.constructed) {
    state.readingMore = true;
    nextTick(maybeReadMore_, stream, state);
  }
}

function maybeReadMore_(stream, state) {
  // Attempt to read more data if we should.
  //
  // The conditions for reading more data are (one of):
  // - Not enough data buffered (state.length < state.highWaterMark). The loop
  //   is responsible for filling the buffer with enough data if such data
  //   is available. If highWaterMark is 0 and we are not in the flowing mode
  //   we should _not_ attempt to buffer any extra data. We'll get more data
  //   when the stream consumer calls read() instead.
  // - No data in the buffer, and the stream is in flowing mode. In this mode
  //   the loop below is responsible for ensuring read() is called. Failing to
  //   call read here would abort the flow and there's no other mechanism for
  //   continuing the flow if the stream consumer has just subscribed to the
  //   'data' event.
  //
  // In addition to the above conditions to keep reading data, the following
  // conditions prevent the data from being read:
  // - The stream has ended (state.ended).
  // - There is already a pending 'read' operation (state.reading). This is a
  //   case where the stream has called the implementation defined _read()
  //   method, but they are processing the call asynchronously and have _not_
  //   called push() with new data. In this case we skip performing more
  //   read()s. The execution ends in this method again after the _read() ends
  //   up calling push() with more data.
  while (
    !state.reading && !state.ended &&
    (state.length < state.highWaterMark ||
      (state.flowing && state.length === 0))
  ) {
    const len = state.length;
    debug("maybeReadMore read 0");
    stream.read(0);
    if (len === state.length) {
      // Didn't get any data, stop spinning.
      break;
    }
  }
  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) {
  throw new ERR_METHOD_NOT_IMPLEMENTED("_read()");
};

Readable.prototype.pipe = function (dest, pipeOpts) {
  const src = this;
  const state = this._readableState;

  if (state.pipes.length === 1) {
    if (!state.multiAwaitDrain) {
      state.multiAwaitDrain = true;
      state.awaitDrainWriters = new Set(
        state.awaitDrainWriters ? [state.awaitDrainWriters] : [],
      );
    }
  }

  state.pipes.push(dest);
  debug("pipe count=%d opts=%j", state.pipes.length, pipeOpts);

  const doEnd = (!pipeOpts || pipeOpts.end !== false) &&
    dest !== stdio.stdout &&
    dest !== stdio.stderr;

  const endFn = doEnd ? onend : unpipe;
  if (state.endEmitted) {
    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();
  }

  let ondrain;

  let cleanedUp = false;
  function cleanup() {
    debug("cleanup");
    // Cleanup event handlers once the pipe is broken.
    dest.removeListener("close", onclose);
    dest.removeListener("finish", onfinish);
    if (ondrain) {
      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 (
      ondrain && state.awaitDrainWriters &&
      (!dest._writableState || dest._writableState.needDrain)
    ) {
      ondrain();
    }
  }

  function pause() {
    // 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 (!cleanedUp) {
      if (state.pipes.length === 1 && state.pipes[0] === dest) {
        debug("false write response, pause", 0);
        state.awaitDrainWriters = dest;
        state.multiAwaitDrain = false;
      } else if (state.pipes.length > 1 && state.pipes.includes(dest)) {
        debug("false write response, pause", state.awaitDrainWriters.size);
        state.awaitDrainWriters.add(dest);
      }
      src.pause();
    }
    if (!ondrain) {
      // 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.
      ondrain = pipeOnDrain(src, dest);
      dest.on("drain", ondrain);
    }
  }

  src.on("data", ondata);
  function ondata(chunk) {
    debug("ondata");
    const ret = dest.write(chunk);
    debug("dest.write", ret);
    if (ret === false) {
      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) {
      const s = dest._writableState || dest._readableState;
      if (s && !s.errorEmitted) {
        // User incorrectly emitted 'error' directly on the stream.
        errorOrDestroy(dest, er);
      } else {
        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 (dest.writableNeedDrain === true) {
    if (state.flowing) {
      pause();
    }
  } else if (!state.flowing) {
    debug("pipe resume");
    src.resume();
  }

  return dest;
};

function pipeOnDrain(src, dest) {
  return function pipeOnDrainFunctionResult() {
    const state = src._readableState;

    // `ondrain` will call directly,
    // `this` maybe not a reference to dest,
    // so we use the real dest here.
    if (state.awaitDrainWriters === dest) {
      debug("pipeOnDrain", 1);
      state.awaitDrainWriters = null;
    } else if (state.multiAwaitDrain) {
      debug("pipeOnDrain", state.awaitDrainWriters.size);
      state.awaitDrainWriters.delete(dest);
    }

    if (
      (!state.awaitDrainWriters || state.awaitDrainWriters.size === 0) &&
      EE.listenerCount(src, "data")
    ) {
      state.flowing = true;
      flow(src);
    }
  };
}

Readable.prototype.unpipe = function (dest) {
  const state = this._readableState;
  const unpipeInfo = { hasUnpiped: false };

  // If we're not piping anywhere, then do nothing.
  if (state.pipes.length === 0) {
    return this;
  }

  if (!dest) {
    // remove all.
    const dests = state.pipes;
    state.pipes = [];
    this.pause();

    for (let i = 0; i < dests.length; i++) {
      dests[i].emit("unpipe", this, { hasUnpiped: false });
    }
    return this;
  }

  // Try to find the right one.
  const index = state.pipes.indexOf(dest);
  if (index === -1) {
    return this;
  }

  state.pipes.splice(index, 1);
  if (state.pipes.length === 0) {
    this.pause();
  }

  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) {
  const res = Stream.prototype.on.call(this, ev, fn);
  const state = this._readableState;

  if (ev === "data") {
    // Update readableListening so that resume() may be a no-op
    // a few lines down. This is needed to support once('readable').
    state.readableListening = this.listenerCount("readable") > 0;

    // Try start flowing on next tick if stream isn't explicitly paused.
    if (state.flowing !== false) {
      this.resume();
    }
  } else if (ev === "readable") {
    if (!state.endEmitted && !state.readableListening) {
      state.readableListening = state.needReadable = true;
      state.flowing = false;
      state.emittedReadable = false;
      debug("on readable", state.length, state.reading);
      if (state.length) {
        emitReadable(this);
      } else if (!state.reading) {
        nextTick(nReadingNextTick, this);
      }
    }
  }

  return res;
};
Readable.prototype.addListener = Readable.prototype.on;

Readable.prototype.removeListener = function (ev, fn) {
  const res = Stream.prototype.removeListener.call(this, ev, fn);

  if (ev === "readable") {
    // We need to check if there is someone still listening to
    // readable and reset the state. However this needs to happen
    // after readable has been emitted but before I/O (nextTick) to
    // support once('readable', fn) cycles. This means that calling
    // resume within the same tick will have no
    // effect.
    nextTick(updateReadableListening, this);
  }

  return res;
};
Readable.prototype.off = Readable.prototype.removeListener;

Readable.prototype.removeAllListeners = function (ev) {
  const res = Stream.prototype.removeAllListeners.apply(this, arguments);

  if (ev === "readable" || ev === undefined) {
    // We need to check if there is someone still listening to
    // readable and reset the state. However this needs to happen
    // after readable has been emitted but before I/O (nextTick) to
    // support once('readable', fn) cycles. This means that calling
    // resume within the same tick will have no
    // effect.
    nextTick(updateReadableListening, this);
  }

  return res;
};

function updateReadableListening(self) {
  const state = self._readableState;
  state.readableListening = self.listenerCount("readable") > 0;

  if (state.resumeScheduled && state[kPaused] === false) {
    // Flowing needs to be set to true now, otherwise
    // the upcoming resume will not flow.
    state.flowing = true;

    // Crude way to check if we should resume.
  } else if (self.listenerCount("data") > 0) {
    self.resume();
  } else if (!state.readableListening) {
    state.flowing = null;
  }
}

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 () {
  const state = this._readableState;
  if (!state.flowing) {
    debug("resume");
    // We flow only if there is no one listening
    // for readable, but we still have to call
    // resume().
    state.flowing = !state.readableListening;
    resume(this, state);
  }
  state[kPaused] = false;
  return this;
};

function resume(stream, state) {
  if (!state.resumeScheduled) {
    state.resumeScheduled = true;
    nextTick(resume_, stream, state);
  }
}

function resume_(stream, state) {
  debug("resume", state.reading);
  if (!state.reading) {
    stream.read(0);
  }

  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 (this._readableState.flowing !== false) {
    debug("pause");
    this._readableState.flowing = false;
    this.emit("pause");
  }
  this._readableState[kPaused] = true;
  return this;
};

function flow(stream) {
  const 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) {
  let paused = false;

  // TODO (ronag): Should this.destroy(err) emit
  // 'error' on the wrapped stream? Would require
  // a static factory method, e.g. Readable.wrap(stream).

  stream.on("data", (chunk) => {
    if (!this.push(chunk) && stream.pause) {
      paused = true;
      stream.pause();
    }
  });

  stream.on("end", () => {
    this.push(null);
  });

  stream.on("error", (err) => {
    errorOrDestroy(this, err);
  });

  stream.on("close", () => {
    this.destroy();
  });

  stream.on("destroy", () => {
    this.destroy();
  });

  this._read = () => {
    if (paused && stream.resume) {
      paused = false;
      stream.resume();
    }
  };

  // Proxy all the other methods. Important when wrapping filters and duplexes.
  const streamKeys = Object.keys(stream);
  for (let j = 1; j < streamKeys.length; j++) {
    const i = streamKeys[j];
    if (this[i] === undefined && typeof stream[i] === "function") {
      this[i] = stream[i].bind(stream);
    }
  }

  return this;
};

Readable.prototype[Symbol.asyncIterator] = function () {
  return streamToAsyncIterator(this);
};

Readable.prototype.iterator = function (options) {
  if (options !== undefined) {
    validateObject(options, "options");
  }
  return streamToAsyncIterator(this, options);
};

function streamToAsyncIterator(stream, options) {
  if (typeof stream.read !== "function") {
    stream = Readable.wrap(stream, { objectMode: true });
  }

  const iter = createAsyncIterator(stream, options);
  iter.stream = stream;
  return iter;
}

async function* createAsyncIterator(stream, options) {
  let callback = nop;

  const opts = {
    destroyOnReturn: true,
    destroyOnError: true,
    ...options,
  };

  function next(resolve) {
    if (this === stream) {
      callback();
      callback = nop;
    } else {
      callback = resolve;
    }
  }

  const state = stream._readableState;

  let error = state.errored;
  let errorEmitted = state.errorEmitted;
  let endEmitted = state.endEmitted;
  let closeEmitted = state.closeEmitted;

  stream
    .on("readable", next)
    .on("error", function (err) {
      error = err;
      errorEmitted = true;
      next.call(this);
    })
    .on("end", function () {
      endEmitted = true;
      next.call(this);
    })
    .on("close", function () {
      closeEmitted = true;
      next.call(this);
    });

  let errorThrown = false;
  try {
    while (true) {
      const chunk = stream.destroyed ? null : stream.read();
      if (chunk !== null) {
        yield chunk;
      } else if (errorEmitted) {
        throw error;
      } else if (endEmitted) {
        break;
      } else if (closeEmitted) {
        break;
      } else {
        await new Promise(next);
      }
    }
  } catch (err) {
    if (opts.destroyOnError) {
      destroyImpl.destroyer(stream, err);
    }
    errorThrown = true;
    throw err;
  } finally {
    if (!errorThrown && opts.destroyOnReturn) {
      if (state.autoDestroy || !endEmitted) {
        // TODO(ronag): ERR_PREMATURE_CLOSE?
        destroyImpl.destroyer(stream, null);
      }
    }
  }
}

// Making it explicit these properties are not enumerable
// because otherwise some prototype manipulation in
// userland will fail.
Object.defineProperties(Readable.prototype, {
  readable: {
    get() {
      const r = this._readableState;
      // r.readable === false means that this is part of a Duplex stream
      // where the readable side was disabled upon construction.
      // Compat. The user might manually disable readable side through
      // deprecated setter.
      return !!r && r.readable !== false && !r.destroyed && !r.errorEmitted &&
        !r.endEmitted;
    },
    set(val) {
      // Backwards compat.
      if (this._readableState) {
        this._readableState.readable = !!val;
      }
    },
  },

  readableDidRead: {
    enumerable: false,
    get: function () {
      return this._readableState.dataEmitted;
    },
  },

  readableAborted: {
    enumerable: false,
    get: function () {
      return !!(this._readableState.destroyed || this._readableState.errored) &&
        !this._readableState.endEmitted;
    },
  },

  readableHighWaterMark: {
    enumerable: false,
    get: function () {
      return this._readableState.highWaterMark;
    },
  },

  readableBuffer: {
    enumerable: false,
    get: function () {
      return this._readableState && this._readableState.buffer;
    },
  },

  readableFlowing: {
    enumerable: false,
    get: function () {
      return this._readableState.flowing;
    },
    set: function (state) {
      if (this._readableState) {
        this._readableState.flowing = state;
      }
    },
  },

  readableLength: {
    enumerable: false,
    get() {
      return this._readableState.length;
    },
  },

  readableObjectMode: {
    enumerable: false,
    get() {
      return this._readableState ? this._readableState.objectMode : false;
    },
  },

  readableEncoding: {
    enumerable: false,
    get() {
      return this._readableState ? this._readableState.encoding : null;
    },
  },

  destroyed: {
    enumerable: false,
    get() {
      if (this._readableState === undefined) {
        return false;
      }
      return this._readableState.destroyed;
    },
    set(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;
    },
  },

  readableEnded: {
    enumerable: false,
    get() {
      return this._readableState ? this._readableState.endEmitted : false;
    },
  },
});

Object.defineProperties(ReadableState.prototype, {
  // Legacy getter for `pipesCount`.
  pipesCount: {
    get() {
      return this.pipes.length;
    },
  },

  // Legacy property for `paused`.
  paused: {
    get() {
      return this[kPaused] !== false;
    },
    set(value) {
      this[kPaused] = !!value;
    },
  },
});

// 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;
  }

  let 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.first();
    } else {
      ret = state.buffer.concat(state.length);
    }
    state.buffer.clear();
  } else {
    // read part of list.
    ret = state.buffer.consume(n, state.decoder);
  }

  return ret;
}

function endReadable(stream) {
  const state = stream._readableState;

  debug("endReadable", state.endEmitted);
  if (!state.endEmitted) {
    state.ended = true;
    nextTick(endReadableNT, state, stream);
  }
}

function endReadableNT(state, stream) {
  debug("endReadableNT", state.endEmitted, state.length);

  // Check that we didn't get one last unshift.
  if (
    !state.errorEmitted && !state.closeEmitted &&
    !state.endEmitted && state.length === 0
  ) {
    state.endEmitted = true;
    stream.emit("end");

    if (stream.writable && stream.allowHalfOpen === false) {
      nextTick(endWritableNT, stream);
    } else if (state.autoDestroy) {
      // In case of duplex streams we need a way to detect
      // if the writable side is ready for autoDestroy as well.
      const wState = stream._writableState;
      const autoDestroy = !wState || (
        wState.autoDestroy &&
        // We don't expect the writable to ever 'finish'
        // if writable is explicitly set to false.
        (wState.finished || wState.writable === false)
      );

      if (autoDestroy) {
        stream.destroy();
      }
    }
  }
}

function endWritableNT(stream) {
  const writable = stream.writable && !stream.writableEnded &&
    !stream.destroyed;
  if (writable) {
    stream.end();
  }
}

function readableFrom(iterable, opts) {
  return _from(Readable, iterable, opts);
}

function wrap(src, options) {
  return new Readable({
    objectMode: src.readableObjectMode ?? src.objectMode ?? true,
    ...options,
    destroy(err, callback) {
      destroyImpl.destroyer(src, err);
      callback(err);
    },
  }).wrap(src);
}

// Exposed for testing purposes only.
Readable._fromList = fromList;
Readable.ReadableState = ReadableState;
Readable.from = readableFrom;
Readable.wrap = wrap;

export default Readable;
export { fromList as _fromList, readableFrom as from, ReadableState, wrap };