pngjs/lib/parser.js

"use strict";

let constants = require("./constants");
let CrcCalculator = require("./crc");

let Parser = (module.exports = function (options, dependencies) {
  this._options = options;
  options.checkCRC = options.checkCRC !== false;

  this._hasIHDR = false;
  this._hasIEND = false;
  this._emittedHeadersFinished = false;

  // input flags/metadata
  this._palette = [];
  this._colorType = 0;

  this._chunks = {};
  this._chunks[constants.TYPE_IHDR] = this._handleIHDR.bind(this);
  this._chunks[constants.TYPE_IEND] = this._handleIEND.bind(this);
  this._chunks[constants.TYPE_IDAT] = this._handleIDAT.bind(this);
  this._chunks[constants.TYPE_PLTE] = this._handlePLTE.bind(this);
  this._chunks[constants.TYPE_tRNS] = this._handleTRNS.bind(this);
  this._chunks[constants.TYPE_gAMA] = this._handleGAMA.bind(this);

  this.read = dependencies.read;
  this.error = dependencies.error;
  this.metadata = dependencies.metadata;
  this.gamma = dependencies.gamma;
  this.transColor = dependencies.transColor;
  this.palette = dependencies.palette;
  this.parsed = dependencies.parsed;
  this.inflateData = dependencies.inflateData;
  this.finished = dependencies.finished;
  this.simpleTransparency = dependencies.simpleTransparency;
  this.headersFinished = dependencies.headersFinished || function () {};
});

Parser.prototype.start = function () {
  this.read(constants.PNG_SIGNATURE.length, this._parseSignature.bind(this));
};

Parser.prototype._parseSignature = function (data) {
  let signature = constants.PNG_SIGNATURE;

  for (let i = 0; i < signature.length; i++) {
    if (data[i] !== signature[i]) {
      this.error(new Error("Invalid file signature"));
      return;
    }
  }
  this.read(8, this._parseChunkBegin.bind(this));
};

Parser.prototype._parseChunkBegin = function (data) {
  // chunk content length
  let length = data.readUInt32BE(0);

  // chunk type
  let type = data.readUInt32BE(4);
  let name = "";
  for (let i = 4; i < 8; i++) {
    name += String.fromCharCode(data[i]);
  }

  //console.log('chunk ', name, length);

  // chunk flags
  let ancillary = Boolean(data[4] & 0x20); // or critical
  //    priv = Boolean(data[5] & 0x20), // or public
  //    safeToCopy = Boolean(data[7] & 0x20); // or unsafe

  if (!this._hasIHDR && type !== constants.TYPE_IHDR) {
    this.error(new Error("Expected IHDR on beggining"));
    return;
  }

  this._crc = new CrcCalculator();
  this._crc.write(Buffer.from(name));

  if (this._chunks[type]) {
    return this._chunks[type](length);
  }

  if (!ancillary) {
    this.error(new Error("Unsupported critical chunk type " + name));
    return;
  }

  this.read(length + 4, this._skipChunk.bind(this));
};

Parser.prototype._skipChunk = function (/*data*/) {
  this.read(8, this._parseChunkBegin.bind(this));
};

Parser.prototype._handleChunkEnd = function () {
  this.read(4, this._parseChunkEnd.bind(this));
};

Parser.prototype._parseChunkEnd = function (data) {
  let fileCrc = data.readInt32BE(0);
  let calcCrc = this._crc.crc32();

  // check CRC
  if (this._options.checkCRC && calcCrc !== fileCrc) {
    this.error(new Error("Crc error - " + fileCrc + " - " + calcCrc));
    return;
  }

  if (!this._hasIEND) {
    this.read(8, this._parseChunkBegin.bind(this));
  }
};

Parser.prototype._handleIHDR = function (length) {
  this.read(length, this._parseIHDR.bind(this));
};
Parser.prototype._parseIHDR = function (data) {
  this._crc.write(data);

  let width = data.readUInt32BE(0);
  let height = data.readUInt32BE(4);
  let depth = data[8];
  let colorType = data[9]; // bits: 1 palette, 2 color, 4 alpha
  let compr = data[10];
  let filter = data[11];
  let interlace = data[12];

  // console.log('    width', width, 'height', height,
  //     'depth', depth, 'colorType', colorType,
  //     'compr', compr, 'filter', filter, 'interlace', interlace
  // );

  if (
    depth !== 8 &&
    depth !== 4 &&
    depth !== 2 &&
    depth !== 1 &&
    depth !== 16
  ) {
    this.error(new Error("Unsupported bit depth " + depth));
    return;
  }
  if (!(colorType in constants.COLORTYPE_TO_BPP_MAP)) {
    this.error(new Error("Unsupported color type"));
    return;
  }
  if (compr !== 0) {
    this.error(new Error("Unsupported compression method"));
    return;
  }
  if (filter !== 0) {
    this.error(new Error("Unsupported filter method"));
    return;
  }
  if (interlace !== 0 && interlace !== 1) {
    this.error(new Error("Unsupported interlace method"));
    return;
  }

  this._colorType = colorType;

  let bpp = constants.COLORTYPE_TO_BPP_MAP[this._colorType];

  this._hasIHDR = true;

  this.metadata({
    width: width,
    height: height,
    depth: depth,
    interlace: Boolean(interlace),
    palette: Boolean(colorType & constants.COLORTYPE_PALETTE),
    color: Boolean(colorType & constants.COLORTYPE_COLOR),
    alpha: Boolean(colorType & constants.COLORTYPE_ALPHA),
    bpp: bpp,
    colorType: colorType,
  });

  this._handleChunkEnd();
};

Parser.prototype._handlePLTE = function (length) {
  this.read(length, this._parsePLTE.bind(this));
};
Parser.prototype._parsePLTE = function (data) {
  this._crc.write(data);

  let entries = Math.floor(data.length / 3);
  // console.log('Palette:', entries);

  for (let i = 0; i < entries; i++) {
    this._palette.push([data[i * 3], data[i * 3 + 1], data[i * 3 + 2], 0xff]);
  }

  this.palette(this._palette);

  this._handleChunkEnd();
};

Parser.prototype._handleTRNS = function (length) {
  this.simpleTransparency();
  this.read(length, this._parseTRNS.bind(this));
};
Parser.prototype._parseTRNS = function (data) {
  this._crc.write(data);

  // palette
  if (this._colorType === constants.COLORTYPE_PALETTE_COLOR) {
    if (this._palette.length === 0) {
      this.error(new Error("Transparency chunk must be after palette"));
      return;
    }
    if (data.length > this._palette.length) {
      this.error(new Error("More transparent colors than palette size"));
      return;
    }
    for (let i = 0; i < data.length; i++) {
      this._palette[i][3] = data[i];
    }
    this.palette(this._palette);
  }

  // for colorType 0 (grayscale) and 2 (rgb)
  // there might be one gray/color defined as transparent
  if (this._colorType === constants.COLORTYPE_GRAYSCALE) {
    // grey, 2 bytes
    this.transColor([data.readUInt16BE(0)]);
  }
  if (this._colorType === constants.COLORTYPE_COLOR) {
    this.transColor([
      data.readUInt16BE(0),
      data.readUInt16BE(2),
      data.readUInt16BE(4),
    ]);
  }

  this._handleChunkEnd();
};

Parser.prototype._handleGAMA = function (length) {
  this.read(length, this._parseGAMA.bind(this));
};
Parser.prototype._parseGAMA = function (data) {
  this._crc.write(data);
  this.gamma(data.readUInt32BE(0) / constants.GAMMA_DIVISION);

  this._handleChunkEnd();
};

Parser.prototype._handleIDAT = function (length) {
  if (!this._emittedHeadersFinished) {
    this._emittedHeadersFinished = true;
    this.headersFinished();
  }
  this.read(-length, this._parseIDAT.bind(this, length));
};
Parser.prototype._parseIDAT = function (length, data) {
  this._crc.write(data);

  if (
    this._colorType === constants.COLORTYPE_PALETTE_COLOR &&
    this._palette.length === 0
  ) {
    throw new Error("Expected palette not found");
  }

  this.inflateData(data);
  let leftOverLength = length - data.length;

  if (leftOverLength > 0) {
    this._handleIDAT(leftOverLength);
  } else {
    this._handleChunkEnd();
  }
};

Parser.prototype._handleIEND = function (length) {
  this.read(length, this._parseIEND.bind(this));
};
Parser.prototype._parseIEND = function (data) {
  this._crc.write(data);

  this._hasIEND = true;
  this._handleChunkEnd();

  if (this.finished) {
    this.finished();
  }
};