pngjs/lib/sync-reader.js

// Copyright (c) 2012 Kuba Niegowski
//
// 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';

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');
  }

};