xmp.js

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * This Source Code Form is "Incompatible With Secondary Licenses", as
 * defined by the Mozilla Public License, v. 2.0.
 */

/*
 *  Interpreter for XML XMP data.
 */

function xmpClass()
{
  var fxifUtils = new fxifUtilsClass();

  var NodeTypes = {
    ELEMENT_NODE:1, ATTRIBUTE_NODE:2, TEXT_NODE:3, CDATA_SECTION_NODE:4,
    ENTITY_REFERENCE_NODE:5, ENTITY_NODE:6, PROCESSING_INSTRUCTION_NODE:7,
    COMMENT_NODE:8, DOCUMENT_NODE:9, DOCUMENT_TYPE_NODE:10,
    DOCUMENT_FRAGMENT_NODE:11, NOTATION_NODE:12
  };


  // Parses and reads through the XMP document within the file.
  this.parseXML = function (dataObj, xml)
  {
    var parser = new DOMParser();
    // There is at least one programm which includes a null byte at the end of the document.
    // The parser doesn't like this, so shorten the length by one byte of the last one is null.
    var doclength = xml.length;
    if (xml.length > 1 && xml[xml.length - 1] == 0)
      doclength--;
    var dom = parser.parseFromBuffer(xml, doclength, 'text/xml');

    if (dom.documentElement.nodeName == 'parsererror') {
      // parsererror might have been caused by incorrect encoding of characters.
      // XMP documents in JPEG files have been reported with characters as ISO-8859-1
      // (while containing an UTF-8 BOM) or even illegal not UTF-8 encoded "BOM" like
      // xpacket begin="i»?" which.
      // So just go on and try to save the situation converting from a single byte encoding to Unicode.
      // I used iso-8859-1 here which will give wrong characters if the source is encoded differently,
      // but getting correct characters isn’t the objective here, just to be able reading the document
      // somehow. The document is corrupt anyway.

      // XXX: Not usable in a WebExtension
      // var converter = Components.classes["@mozilla.org/intl/scriptableunicodeconverter"].createInstance(Components.interfaces.nsIScriptableUnicodeConverter);
      // converter.charset = 'iso-8859-1';
      // var xmlString = converter.convertFromByteArray(xml, doclength);
      // dom = parser.parseFromString(xmlString, 'text/xml');

      if (dom.documentElement.nodeName == 'parsererror') {
        console.error("Error parsing XML");
        // no known remedy, so don’t throw this problem
        return;
      }
    }

    var val;

    // Creators come in an ordered list. Get them all.
    val = getXMPOrderedArray(dom, "http://purl.org/dc/elements/1.1/", "creator", "");
    if (val && val.length) {
      dataObj.Creator = val.join(", ");
    }

    val = getXMPValue(dom, "http://ns.adobe.com/photoshop/1.0/", "City");
    if (val)
      dataObj.City = val;

    val = getXMPValue(dom, "http://iptc.org/std/Iptc4xmpCore/1.0/xmlns/", "Location");
    if (val)
      dataObj.Sublocation = val;

    val = getXMPValue(dom, "http://ns.adobe.com/photoshop/1.0/", "State");
    if (val)
      dataObj.ProvinceState = val;

    val = getXMPValue(dom, "http://ns.adobe.com/photoshop/1.0/", "Country");
    if (val)
      dataObj.CountryName = val;

    val = getXMPValue(dom, "http://ns.adobe.com/photoshop/1.0/", "Headline");
    if (val)
      dataObj.Headline = val;

    val = getXMPValue(dom, "http://ns.adobe.com/photoshop/1.0/", "Instructions");
    if (val)
      dataObj.Instructions = val;

    // only use if not already set
    if (!dataObj.Software)
    {
      val = getXMPValue(dom, "http://ns.adobe.com/xap/1.0/", "CreatorTool");
      if (val)
        dataObj.Software = val;
    }

    val = getXMPOrderedArray(dom, "http://ns.adobe.com/xap/1.0/mm/", "History", "http://ns.adobe.com/xap/1.0/sType/ResourceEvent#", "softwareAgent");
    if(val && val.length) {
      dataObj.Software = val[val.length - 1];
    }


    var lang = fxifUtils.getLang();
    // Build a regular expression to be used to test the language
    // alternatives available in the XMP.
    var langTest = new RegExp("^"+lang.match(/^[a-z]{2,3}/i), "i")

    if (!dataObj.Headline)
    {
      val = getXMPAltValue(dom, "http://purl.org/dc/elements/1.1/", "title", langTest);
      if(val) {
        dataObj.Headline = val;
      }
    }

//    val = getXMPAltValue(dom, "dc:description", langTest);
    val = getXMPAltValue(dom, "http://purl.org/dc/elements/1.1/", "description", langTest);
    if(val) {
      dataObj.Caption = val;
    }

//    val = getXMPAltValue(dom, "dc:rights", langTest);
    val = getXMPAltValue(dom, "http://purl.org/dc/elements/1.1/", "rights", langTest);
    if(val)
      dataObj.Copyright = val;
    else
    {
      val = getXMPAltValue(dom, "http://ns.adobe.com/xap/1.0/rights/", "UsageTerms ", langTest);
      if(val)
        dataObj.Copyright = val;
      else
        val = getXMPValue(dom, "http://creativecommons.org/ns#", "license");
    }
    if(val)
      dataObj.Copyright = val;



    // XMP:EXIF

    val = getXMPValue(dom, "http://ns.adobe.com/tiff/1.0/", "Make");
    if (val)
      dataObj.Make = val;

    val = getXMPValue(dom, "http://ns.adobe.com/tiff/1.0/", "Model");
    if (val)
      dataObj.Model = val;

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/aux/", "Lens");
    if (val)
      dataObj.Lens = val;

    if(!dataObj.Date)
    {
      val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "DateTimeDigitized");
      if (val) {
        var date = readAndFormatISODate(val);
        if (date)
          dataObj.Date = date;
      }
    }

    val = getXMPValue(dom, "http://ns.adobe.com/photoshop/1.0/", "CreateDate");
    if (val) {
      var date = readAndFormatISODate(val);
      if (date)
        dataObj.Date = date;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "DateTimeOriginal");
    if (val) {
      var date = readAndFormatISODate(val);
      if (date)
        dataObj.Date = date;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "FNumber");  // expects a rational (eg. "5/1")
    if (!val)
      val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "ApertureValue");  // expects a rational (eg. "4643856/1000000")
    if (val)
    {
      try
      {
        dataObj.ApertureFNumber = "ƒ/" + parseRational(val).toFixed(1);
      }
      catch (ex)
      {
        if (!dataObj.ApertureFNumber)
          dataObj.ApertureFNumber = val;
      }
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "FocalLength"); // expects a rational (eg. "2000/10")
    if (val)
      try
      {
        dataObj.FocalLength = parseRational(val).toFixed(1);
      }
      catch (ex)
      {
        if (!dataObj.FocalLength)
          dataObj.FocalLength = val;
      }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "FocalLengthIn35mmFilm");
    if (!val)
      // this name is no official one, but written by some applications
      val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "FocalLengthIn35mmFormat");
    if (val)
      dataObj.FocalLength35mmEquiv = val;

    if (dataObj.FocalLength) {
      var fl = stringBundle.getFormattedString("millimeters", [dataObj.FocalLength]);
      if (dataObj.FocalLength35mmEquiv) {
        dataObj.FocalLength35mmEquiv = parseFloat(dataObj.FocalLength35mmEquiv);
        fl += " " + stringBundle.getFormattedString("35mmequiv", [dataObj.FocalLength35mmEquiv.toFixed(0)]);
      }

      dataObj.FocalLengthText = fl;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "SubjectDistance");
    if (val)
    {
      try
      {
        var distance = parseRational(val).toFixed(2);
        if (distance < 0)
          dataObj.Distance = stringBundle.getString("infinite");
        else
          dataObj.Distance = stringBundle.getFormattedString("meters", [distance]);
      }
      catch (ex)
      {
        if (!dataObj.Distance)
          dataObj.Distance = val;
      }
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "ExposureTime");
    if (val)
    {
      try
      {
        var et = "";
        val = parseRational(val);
        if (val < 0.010)
          et = stringBundle.getFormattedString("seconds", [val.toFixed(4)]);
        else
          et = stringBundle.getFormattedString("seconds", [val.toFixed(3)]);
        if (val <= 0.5)
          et += " (1/" + Math.floor(0.5 + 1/val).toFixed(0) + ")";
        dataObj.ExposureTime = et;
      }
      catch (ex)
      {
        if (!dataObj.ExposureTime)
          dataObj.ExposureTime = val;
      }
    }

    var el = dom.getElementsByTagNameNS("http://ns.adobe.com/exif/1.0/", "Flash");
    var flashFired = 0;
    var flashFunction = 0;
    var flashMode = 0;
    var redEyeMode = 0;
    var flashReturn = 0;
    if (el.length) {
      // Flash values can occur in two ways, as attribute values of flash
      // like <Flash Fired="True"/>
      // and as child values, e.g. <Flash><Fired>True</Fired></Flash>
      // We've to deal with both and also mixed as a bonus.
      flashFired = getSubvalues(el[0], "http://ns.adobe.com/exif/1.0/", "Fired");
      if (!flashFired)
        flashFired = el[0].getAttributeNS("http://ns.adobe.com/exif/1.0/", "Fired");
      flashFunction = getSubvalues(el[0], "http://ns.adobe.com/exif/1.0/", "Function");
      if (!flashFunction)
        flashFunction = el[0].getAttributeNS("http://ns.adobe.com/exif/1.0/", "Function");
      flashMode = Number(getSubvalues(el[0], "http://ns.adobe.com/exif/1.0/", "Mode"));
      if (!flashMode)
        flashMode = Number(el[0].getAttributeNS("http://ns.adobe.com/exif/1.0/", "Mode"));
      redEyeMode = getSubvalues(el[0], "http://ns.adobe.com/exif/1.0/", "RedEyeMode");
      if (!redEyeMode)
        redEyeMode = el[0].getAttributeNS("http://ns.adobe.com/exif/1.0/", "RedEyeMode");
      flashReturn = Number(getSubvalues(el[0], "http://ns.adobe.com/exif/1.0/", "Return"));
      if (!flashReturn)
        flashReturn = Number(el[0].getAttributeNS("http://ns.adobe.com/exif/1.0/", "Return"));

      var fu;
      var addfunc = new Array();
      if (flashFired && flashFired.match(/^true$/i)) {
        fu = stringBundle.getString("yes");

        if (flashMode == 3)
          addfunc.push(stringBundle.getString("auto"));
        else
          if (flashMode == 1)
            addfunc.push(stringBundle.getString("enforced"));

        if (redEyeMode && redEyeMode.match(/^true$/i))
          addfunc.push(stringBundle.getString("redeye"));

        if (flashReturn == 3)
          addfunc.push(stringBundle.getString("returnlight"));
        else
          if (flashReturn == 2)
            addfunc.push(stringBundle.getString("noreturnlight"));
      }
      else {
        fu = stringBundle.getString("no");
        if (flashFunction && flashFunction.match(/^true$/i))
            addfunc.push(stringBundle.getString("noflash"));
        else
          if (flashMode == 2)
            addfunc.push(stringBundle.getString("enforced"));
          else
            if (flashMode == 3)
              addfunc.push(stringBundle.getString("auto"));
      }

      if (addfunc.length)
        fu += " (" + addfunc.join(", ") + ")";

      dataObj.FlashUsed = fu;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/tiff/1.0/", "Orientation");
    if (!dataObj.Orientation && val && val > 0) {
        if (val <= 8)
          dataObj.Orientation = stringBundle.getString("orientation" + val);
        else
          dataObj.Orientation = stringBundle.getString("unknown") + " (" + val + ")";
    }

    val = getXMPValue(dom, "http://ns.adobe.com/tiff/1.0/", "ImageHeight");
    if (val)
      dataObj.Length = val;

    val = getXMPValue(dom, "http://ns.adobe.com/tiff/1.0/", "ImageWidth");
    if (val)
      dataObj.Width = val;

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "FocalPlaneXResolution");
    if (val)
      dataObj.FocalPlaneXRes = val;

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "FocalPlaneResolutionUnit");
    if (val) {
      if (val.search(/^\d+$/) != -1) // Unfortunately there are applications which write non-number values
      {
        switch(Number(val)) {
          case 1: dataObj.FocalPlaneUnits = 25.4; break; // inches
          case 2:
            // According to the information I was using, 2 means meters.
            // But looking at the Canon powershot's files, inches is the only
            // sensible value.
            dataObj.FocalPlaneUnits = 25.4;
            break;
          case 3: dataObj.FocalPlaneUnits = 10;   break;  // centimeter
          case 4: dataObj.FocalPlaneUnits = 1;    break;  // millimeter
          case 5: dataObj.FocalPlaneUnits = .001; break;  // micrometer
        }
      }
      else
        if (!dataObj.FocalPlaneUnits)
            dataObj.FocalPlaneUnits = val;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "ExposureBiasValue");
    if (val) {
      try
      {
        val = parseRational(val).toFixed(2);
        if (val == 0)
          dataObj.ExposureBias = stringBundle.getString("none");
        else
          // add a + sign before positive values
          dataObj.ExposureBias = (val > 0 ? '+' : '') + stringBundle.getFormattedString("ev", [val]);
      }
      catch (ex)
      {
        if (!dataObj.ExposureBias)
          dataObj.ExposureBias = val;
      }
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "WhiteBalance");
    if (val) {
      if (val.search(/^\d+$/) != -1) // Unfortunately there are applications which write non-number values
      {
        switch(Number(val)) {
          case 0:
            dataObj.WhiteBalance = stringBundle.getString("auto");
            break;
          case 1:
            dataObj.WhiteBalance = stringBundle.getString("manual");
            break;
        }
      }
      else
        if (!dataObj.WhiteBalance)
            dataObj.WhiteBalance = val;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "LightSource");
    if (val) {
      if (val.search(/^\d+$/) != -1) // Unfortunately there are applications which write non-number values
      {
        switch(Number(val)) {
          case 0:
            dataObj.LightSource = stringBundle.getString("unknown");
            break;
          case 1:
            dataObj.LightSource = stringBundle.getString("daylight");
            break;
          case 2:
            dataObj.LightSource = stringBundle.getString("fluorescent");
            break;
          case 3:
            dataObj.LightSource = stringBundle.getString("incandescent");
            break;
          case 4:
            dataObj.LightSource = stringBundle.getString("flash");
            break;
          case 9:
            dataObj.LightSource = stringBundle.getString("fineweather");
            break;
          case 10:
            dataObj.LightSource = stringBundle.getString("cloudy");
            break;
          case 11:
            dataObj.LightSource = stringBundle.getString("shade");
            break;
          case 12:
            dataObj.LightSource = stringBundle.getString("daylightfluorescent");
            break;
          case 13:
            dataObj.LightSource = stringBundle.getString("daywhitefluorescent");
            break;
          case 14:
            dataObj.LightSource = stringBundle.getString("coolwhitefluorescent");
            break;
          case 15:
            dataObj.LightSource = stringBundle.getString("whitefluorescent");
            break;
          case 24:
            dataObj.LightSource = stringBundle.getString("studiotungsten");
            break;
          default:; //Quercus: 17-1-2004 There are many more modes for this, check Exif2.2 specs
          // If it just says 'unknown' or we don't know it, then
          // don't bother showing it - it doesn't add any useful information.
        }
      }
      else
        if (!dataObj.LightSource)
            dataObj.LightSource = val;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "MeteringMode");
    if (val) {
      if (val.search(/^\d+$/) != -1) // Unfortunately there are applications which write non-number values
      {
        switch(Number(val)) {
          case 0:
            dataObj.MeteringMode = stringBundle.getString("unknown");
            break;
          case 1:
            dataObj.MeteringMode = stringBundle.getString("average");
            break;
          case 2:
            dataObj.MeteringMode = stringBundle.getString("centerweight");
            break;
          case 3:
            dataObj.MeteringMode = stringBundle.getString("spot");
            break;
          case 3:
            dataObj.MeteringMode = stringBundle.getString("multispot");
            break;
          case 5:
            dataObj.MeteringMode = stringBundle.getString("matrix");
            break;
          case 6:
            dataObj.MeteringMode = stringBundle.getString("partial");
            break;
        }
      }
      else
        if (!dataObj.MeteringMode)
            dataObj.MeteringMode = val;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "ExposureProgram");
    if (val) {
      if (val.search(/^\d+$/) != -1) // Unfortunately there are applications which write non-number values
      {
        switch(Number(val)) {
          case 1:
            dataObj.ExposureProgram = stringBundle.getString("manual");
            break;
          case 2:
            dataObj.ExposureProgram = stringBundle.getString("program") + " ("
              + stringBundle.getString("auto") + ")";
            break;
          case 3:
            dataObj.ExposureProgram = stringBundle.getString("apriority")
              + " (" + stringBundle.getString("semiauto") + ")";
            break;
          case 4:
            dataObj.ExposureProgram = stringBundle.getString("spriority")
              + " (" + stringBundle.getString("semiauto") +")";
            break;
          case 5:
            dataObj.ExposureProgram = stringBundle.getString("creative");
            break;
          case 6:
            dataObj.ExposureProgram = stringBundle.getString("action");
            break;
          case 7:
            dataObj.ExposureProgram = stringBundle.getString("portrait");
            break;
          case 8:
            dataObj.ExposureProgram = stringBundle.getString("landscape");
            break;
          default:
          break;
        }
      }
      else
        if (!dataObj.ExposureProgram)
            dataObj.ExposureProgram = val;
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "ExposureIndex");
    if (val) {
      if (!dataObj.ExposureIndex)
        try
        {
          dataObj.ExposureIndex = parseRational(val).toFixed(0);
        }
        catch (ex)
        {
          dataObj.ExposureIndex = val;
        }
    }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "ExposureMode");
    if (val) {
      if (val.search(/^\d+$/) != -1) // Unfortunately there are applications which write non-number values
      {
        switch(Number(val)) {
          case 0: // Automatic
            break;
          case 1:
            dataObj.ExposureMode = stringBundle.getString("manual");
            break;
          case 2:
            dataObj.ExposureMode = stringBundle.getString("autobracketing");
            break;
        }
      }
      else
        if (!dataObj.ExposureProgram)
            dataObj.ExposureProgram = val;
    }

    val = getXMPOrderedArray(dom, "http://ns.adobe.com/exif/1.0/", "ISOSpeedRatings");
    if(val && val.length)
      dataObj.ISOequivalent = val.join(", ");

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "DigitalZoomRatio");
    if (val)
      try
      {
        var floatVal = parseRational(val);
        if (floatVal > 1)
          dataObj.DigitalZoomRatio = floatVal.toFixed(3) + "x";
      }
      catch (ex)
      {
        if (!dataObj.DigitalZoomRatio)
          dataObj.DigitalZoomRatio = val;
      }

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "ColorSpace");
    if (val)
    {
      if(val == 1)
        dataObj.ColorSpace = "sRGB";
      else if(val == 2)
        dataObj.ColorSpace = "Adobe RGB";
    }

    if (!dataObj.ColorSpace)
    {
      // At least Photoshop writes ColorSpace "uncalibrated" though it uses
      // a defined colorspace which is documented in ICCProfile
      val = getXMPValue(dom, "http://ns.adobe.com/photoshop/1.0/", "ICCProfile");
      if(val)
        dataObj.ColorSpace = val;
    }

    // GPS stuff

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "GPSAltitude");
    var gpsAlt;
    if (val)
      gpsAlt = parseRational(val);

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "GPSAltitudeRef");
    var gpsAltRef = 0;
    if (val)
      gpsAltRef = Number(val);

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "GPSImgDirection");
    var gpsImgDir;
    if (val)
      gpsImgDir = parseRational(val);

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "GPSImgDirectionRef");
    var gpsImgDirRef = 'M';
    if (val)
      gpsImgDirRef = val;

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "GPSLatitude");
    var gpsLat;
    if (val)
      gpsLat = parseGPSPos(val);

    val = getXMPValue(dom, "http://ns.adobe.com/exif/1.0/", "GPSLongitude");
    var gpsLon;
    if (val)
      gpsLon = parseGPSPos(val);


    // use dms format by default
    var degFormat = "dms";
    var degFormatter = fxifUtils.dd2dms;
    try {
      // 0 = DMS, 1 = DD, 2 = DM
      if (fxifUtils.getPreferences().getIntPref("gpsFormat") == 1)
      {
        // but dd if the user wants that
        degFormat = "dd";
        degFormatter = fxifUtils.dd2dd;
      }
      else if (fxifUtils.getPreferences().getIntPref("gpsFormat") == 2)
      {
        // but dd if the user wants that
        degFormat = "dm";
        degFormatter = fxifUtils.dd2dm;
      }
    } catch(e){}

    if (gpsLat != undefined) {
      var gpsArr = degFormatter(Math.abs(gpsLat));
      gpsArr.push(gpsLat < 0 ? 'S' : 'N');
      dataObj.GPSLat = stringBundle.getFormattedString("latlon"+degFormat, gpsArr);
    }
    if (gpsLon != undefined) {
      var gpsArr = degFormatter(Math.abs(gpsLon));
      gpsArr.push(gpsLon < 0 ? 'W' : 'E');
      dataObj.GPSLon = stringBundle.getFormattedString("latlon"+degFormat, gpsArr);
    }
    if (gpsAlt != undefined) {
      dataObj.GPSAlt = stringBundle.getFormattedString("meters", [gpsAlt * (gpsAltRef ? -1.0 : 1.0)]);
    }
    if (gpsImgDir != undefined && (gpsImgDirRef == 'M' || gpsImgDirRef == 'T')) {
      dataObj.GPSImgDir = stringBundle.getFormattedString("dir"+gpsImgDirRef, [gpsImgDir]);
    }

    // Get the straight decimal values without rounding.
    // For creating links to map services.
    if (gpsLat != undefined &&
        gpsLon != undefined) {
      dataObj.GPSPureDdLat = gpsLat / 3600;
      dataObj.GPSPureDdLon = gpsLon / 3600;
    }
  }

  // Parse a GPS datum.
  // It's stored like 49,9.8672N
  function parseGPSPos(gpsstring)
  {
    var matches = gpsstring.match(/^(\d{1,3}).([0-9.]+) ?([NSEW])$/);
    if (matches)
    {
      var val = matches[1] * 3600 + matches[2] * 60;
      val = val * (matches[3] == 'N' || matches[3] == 'E' ? 1.0 : -1.0);
      return val;
    }
  }


  // Parse rational numbers. They consist of two
  // integers separated by a "/".
  // Throws an exception if ratstring contains to rational
  // (yes, this happens, e.g. GIMP 2.8.10 writes "f/3,5" for FNumber)?
  function parseRational(ratstring)
  {
    var matches = ratstring.match(/^([+-]?\d+)\/(\d+)$/);
    if (matches)
    {
      var val = matches[1] / matches[2];
      return val;
    }
    else
      throw ("ratstring contains no rational");
  }

  // Since JS can't really parse dates and keep timezone informations,
  // I only break the string up and reformat it without any JS functions.
  // Input format is YYYY-MM-DD[THH:MM[:SS[.SS]][+/-HH:MM|Z]] and
  // Output format is YYYY-MM-DD HH:MM:SS [+/-HH:MM]
  // It’s a bit more relaxted than the specification in that
  // the time zone information is optional
  function readAndFormatISODate(datestring)
  {
    var exploded_date = datestring.match(/^(\d{4}-\d{2}-\d{2})(?:[T ](\d{2}:\d{2})(?:(:\d{2})(?:\.\d+)?)?([+-]\d{2}:\d{2}|Z)?)?$/);
    if (exploded_date)
    {
      date = exploded_date[1];
      if (typeof exploded_date[2] != 'undefined' && exploded_date[2].length > 0)
      {
        date += ' ' + exploded_date[2];
        if (typeof exploded_date[3] != 'undefined' && exploded_date[3].length > 0)
          date += exploded_date[3];
        if (typeof exploded_date[4] != 'undefined' && exploded_date[4].length > 0)
        {
          if (exploded_date[4] == 'Z')
            date += ' UTC';
          else
            date += ' ' + exploded_date[4];
        }
        else
          date += ' ' + stringBundle.getString("noTZ");
      }
      return date;
    }
  }


  // Retrieves a property stored somewhere in the XMP data.
  // Unfortunately there are at least two common ways a property
  // value can be stored.
  // 1. As property value of an element
  // 2. As content of an element with name of the property
  // This function looks for both and returns the first one found.
  // ns "http://ns.adobe.com/exif/1.0/"
  // property "FNumber"
  function getXMPValue(dom, ns, property)
  {
    var el = dom.getElementsByTagNameNS(ns, property);
    if(el.length && el[0].hasChildNodes())
      return el[0].firstChild.nodeValue;

    var list = dom.getElementsByTagNameNS("http://www.w3.org/1999/02/22-rdf-syntax-ns#", "Description");
    var val = "";

    for(var i = 0; i < list.length; i++)
    {
      var attr = list[i].getAttributeNS(ns, property);
      if(attr)
        return attr;
    }
  }

  // Gets names and descriptions that can be available
  // in multiple alternative languages.
  // But only those in the first structure with the
  // given property name is fetched.
  function getXMPAltValue(dom, ns, property, langTest)
  {
    var val;

    var propertyList = dom.getElementsByTagNameNS(ns, property);

    // go through all the property elements (though there should
    // only be one)
    for(var i = 0; i < propertyList.length && !val; i++)
    {
      var entriesList = propertyList[0].getElementsByTagNameNS("http://www.w3.org/1999/02/22-rdf-syntax-ns#", "li");

      for(var j = 0; j < entriesList.length; j++)
      {
        // found a non empty entry with fitting language
        if(entriesList[j].hasChildNodes() &&
           langTest.test(entriesList[j].getAttribute("xml:lang"))) {
          val = entriesList[j].firstChild.nodeValue;
          break;
        }
      }
    }
    // our language wasn't found or its entry was empty
    for(var i = 0; i < propertyList.length && !val; i++)
    {
      var entriesList = propertyList[0].getElementsByTagNameNS("http://www.w3.org/1999/02/22-rdf-syntax-ns#", "li");

      for(var j = 0; j < entriesList.length; j++)
      {
        // found a non empty entry with fitting language
        if(entriesList[j].hasChildNodes() &&
           entriesList[j].getAttribute("xml:lang") == "x-default") {
          val = entriesList[j].firstChild.nodeValue;
          break;
        }
      }
    }

    return val;
  }

  function getSubvalues(dom, ns, property)
  {
    var val;
    var list = dom.getElementsByTagNameNS(ns, property);
    if(list.length) {
      if (list[0].hasChildNodes()) {
        var fc = list[0].firstChild;
        if(fc.nodeType == NodeTypes.TEXT_NODE)
          val = fc.nodeValue;
      }
    }

    return val;
  }

  // Get all entries from an ordered array.
  // Elements might be straight text nodes or come
  // with a property qualifier in a more complex organisation like
  // values as properties of the li element.
  // Currently the getElementsByTagNameNS() methods are used
  // for Firefox 2 (Gecko 1.8) compatibility. These are ugly and
  // complicated. Should remove this when Firefox 3 is widespread.
  //function getXMPOrderedArray(dom, property)
  function getXMPOrderedArray(dom, ns, property, attrNS, attrName)
  {
    var valarray = new Array();

    var el = dom.getElementsByTagNameNS(ns, property);
    if(el.length) {
      var list = el[0].getElementsByTagNameNS("http://www.w3.org/1999/02/22-rdf-syntax-ns#", "li");
      for(var i = 0; i < list.length; i++) {
        if (list[i].hasChildNodes()) {
          var el;
          var tmp = list[i].getElementsByTagNameNS(attrNS, attrName);
          if (tmp.length && tmp[0].hasChildNodes())
            el = tmp[0].firstChild;
          else
            el = list[i].firstChild;
          if (el.nodeType == NodeTypes.TEXT_NODE)
            valarray.push(el.nodeValue);
        }
        else
        // supposedly one element with values as properties
        {
          var test = list[i].getAttributeNS(attrNS, attrName);
          if (test)
            valarray.push(test);
        }
      }
    }

    return valarray;
  }
}