Function maybeReadMore_

lib/internal/streams/readable.js:878–913

(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[kState] & (kReading | kEnded)) === 0 &&
         (state.length < state.highWaterMark ||
          ((state[kState] & kFlowing) !== 0 && 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[kState] &= ~kReadingMore;
}

// Abstract method.  to be overridden in specific implementation classes.
// call cb(er, data) where data is <= n in length.