tongchengred/node_modules/pngjs/lib/sync-reader.js

'use strict';

var SyncReader = module.exports = function(buffer) {

  this._buffer = buffer;
  this._reads = [];
};

SyncReader.prototype.read = function(length, callback) {

  this._reads.push({
    length: Math.abs(length), // if length < 0 then at most this length
    allowLess: length < 0,
    func: callback
  });
};

SyncReader.prototype.process = function() {

  // as long as there is any data and read requests
  while (this._reads.length > 0 && this._buffer.length) {

    var read = this._reads[0];

    if (this._buffer.length && (this._buffer.length >= read.length || read.allowLess)) {

      // ok there is any data so that we can satisfy this request
      this._reads.shift(); // == read

      var buf = this._buffer;

      this._buffer = buf.slice(read.length);

      read.func.call(this, buf.slice(0, read.length));

    }
    else {
      break;
    }

  }

  if (this._reads.length > 0) {
    return new Error('There are some read requests waitng on finished stream');
  }

  if (this._buffer.length > 0) {
    return new Error('unrecognised content at end of stream');
  }

};