iTextSharp.text.io.RandomAccessSourceFactory.CreateBestSource C# (CSharp) Метод

        public IRandomAccessSource CreateBestSource(String filename) {
            if (!File.Exists(filename)) {
                if (filename.StartsWith("file:/")
                        || filename.StartsWith("http://") 
                        || filename.StartsWith("https://")) {
                    return CreateSource(new Uri(filename));
                } else {
                    return CreateByReadingToMemory(filename);
                }
            }
                
            if (forceRead){
                return CreateByReadingToMemory(new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read));
            }
            return new RAFRandomAccessSource(new FileStream(filename, FileMode.Open, FileAccess.Read, exclusivelyLockFile ? FileShare.None : FileShare.Read));
        }
        

        /// <summary>
        /// Gets an instance of an Image.
        /// </summary>
        /// <param name="url">an URL</param>
        /// <returns>an object of type Gif, Jpeg or Png</returns>
        public static Image GetInstance(Uri url, bool recoverFromImageError) {
            Stream istr = null;
            RandomAccessSourceFactory randomAccessSourceFactory = new RandomAccessSourceFactory();
            try {
                WebRequest w = WebRequest.Create(url);
                w.Credentials = CredentialCache.DefaultCredentials;
                istr = w.GetResponse().GetResponseStream();
                int c1 = istr.ReadByte();
                int c2 = istr.ReadByte();
                int c3 = istr.ReadByte();
                int c4 = istr.ReadByte();
			    // jbig2
			    int c5 = istr.ReadByte();
			    int c6 = istr.ReadByte();
			    int c7 = istr.ReadByte();
			    int c8 = istr.ReadByte();
                istr.Close();

                istr = null;
                if (c1 == 'G' && c2 == 'I' && c3 == 'F') {
                    GifImage gif = new GifImage(url);
                    Image img = gif.GetImage(1);
                    return img;
                }
                if (c1 == 0xFF && c2 == 0xD8) {
                    return new Jpeg(url);
                }
			    if (c1 == 0x00 && c2 == 0x00 && c3 == 0x00 && c4 == 0x0c) {
				    return new Jpeg2000(url);
			    }
			    if (c1 == 0xff && c2 == 0x4f && c3 == 0xff && c4 == 0x51) {
				    return new Jpeg2000(url);
			    }
                if (c1 == PngImage.PNGID[0] && c2 == PngImage.PNGID[1]
                        && c3 == PngImage.PNGID[2] && c4 == PngImage.PNGID[3]) {
                    Image img = PngImage.GetImage(url);
                    return img;
                }
                if (c1 == 0xD7 && c2 == 0xCD) {
                    Image img = new ImgWMF(url);
                    return img;
                }
                if (c1 == 'B' && c2 == 'M') {
                    Image img = BmpImage.GetImage(url);
                    return img;
                }
                if ((c1 == 'M' && c2 == 'M' && c3 == 0 && c4 == 42)
                        || (c1 == 'I' && c2 == 'I' && c3 == 42 && c4 == 0)) {
                    RandomAccessFileOrArray ra = null;
                    try {
                        if (url.IsFile) {
                            String file = url.LocalPath;
                            ra = new RandomAccessFileOrArray(randomAccessSourceFactory.CreateBestSource(file));
                        } else
                            ra = new RandomAccessFileOrArray(randomAccessSourceFactory.CreateSource(url));
                        Image img = TiffImage.GetTiffImage(ra, 1);
                        img.url = url;
                        return img;
                    } catch (Exception e) {
                        if (recoverFromImageError) {
                            // reruns the getTiffImage() with several error recovering workarounds in place
                            // not guaranteed to work with every TIFF
                            Image img = TiffImage.GetTiffImage(ra, recoverFromImageError, 1);
                            img.url = url;
                            return img;
                        }
                        throw e;
                    }
                    finally {
                        if (ra != null)
                            ra.Close();
                    }

                }
                if ( c1 == 0x97 && c2 == 'J' && c3 == 'B' && c4 == '2' &&
                        c5 == '\r' && c6 == '\n' && c7 == 0x1a && c8 == '\n' ) {
                    RandomAccessFileOrArray ra = null;
                    try {
                        if (url.IsFile) {
                            String file = url.LocalPath;
                            ra = new RandomAccessFileOrArray(randomAccessSourceFactory.CreateBestSource(file));
                        } else
                            ra = new RandomAccessFileOrArray(randomAccessSourceFactory.CreateSource(url));
                        Image img = JBIG2Image.GetJbig2Image(ra, 1);
                        img.url = url;
                        return img;
                    } finally {
                        if (ra != null)
                            ra.Close();
                    }
                }
                throw new IOException(MessageLocalization.GetComposedMessage("unknown.image.format", url.ToString()));
            } finally {
                if (istr != null) {
                    istr.Close();
                }
            }
        }