Function ReadableState

lib/internal/streams/readable.js:269–319

(options, stream, isDuplex)

function ReadableState(options, stream, isDuplex) {
  // Bit map field to store ReadableState more efficiently with 1 bit per field
  // instead of a V8 slot per field.
  this[kState] = kEmitClose | kAutoDestroy | kConstructed | kSync;

  // Object stream flag. Used to make read(n) ignore n and to
  // make all the buffer merging and length checks go away.
  if (options?.objectMode)
    this[kState] |= kObjectMode;

  if (isDuplex && options?.readableObjectMode)
    this[kState] |= kObjectMode;

  // 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);

  this.buffer = [];
  this.bufferIndex = 0;
  this.length = 0;
  this.pipes = [];

  // Should close be emitted on destroy. Defaults to true.
  if (options && options.emitClose === false) this[kState] &= ~kEmitClose;

  // Should .destroy() be called after 'end' (and potentially 'finish').
  if (options && options.autoDestroy === false) this[kState] &= ~kAutoDestroy;

  // 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.
  const defaultEncoding = options?.defaultEncoding;
  if (defaultEncoding == null || defaultEncoding === 'utf8' || defaultEncoding === 'utf-8') {
    this[kState] |= kDefaultUTF8Encoding;
  } else if (Buffer.isEncoding(defaultEncoding)) {
    this.defaultEncoding = defaultEncoding;
  } else {
    throw new ERR_UNKNOWN_ENCODING(defaultEncoding);
  }

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

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

ReadableState.prototype[kOnConstructed] = function onConstructed(stream) {
  if ((this[kState] & kNeedReadable) !== 0) {