242 lines
7.2 KiB
C#
242 lines
7.2 KiB
C#
/*
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* Copyright (c) 2023 ETH Zürich, Educational Development and Technology (LET)
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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using System;
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using System.Collections.Generic;
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using System.IO;
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using System.Linq;
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using System.Security.Cryptography;
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using System.Text;
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using System.Xml.Linq;
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using SafeExamBrowser.Configuration.Contracts;
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using SafeExamBrowser.Logging.Contracts;
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using SafeExamBrowser.Proctoring.ScreenProctoring.Data;
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using SafeExamBrowser.Proctoring.ScreenProctoring.Imaging;
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using SafeExamBrowser.Settings.Proctoring;
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namespace SafeExamBrowser.Proctoring.ScreenProctoring
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{
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internal class Cache
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{
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private const string DATA_FILE_EXTENSION = "xml";
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private readonly AppConfig appConfig;
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private readonly ILogger logger;
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private readonly Queue<(string fileName, int checksum, string hash)> queue;
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private string Directory { get; set; }
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public Cache(AppConfig appConfig, ILogger logger)
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{
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this.appConfig = appConfig;
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this.logger = logger;
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this.queue = new Queue<(string, int, string)>();
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}
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internal bool Any()
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{
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return false;
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}
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internal bool TryEnqueue(MetaData metaData, ScreenShot screenShot)
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{
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var fileName = $"{screenShot.CaptureTime:yyyy-MM-dd HH\\hmm\\mss\\sfff\\m\\s}";
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var success = false;
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try
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{
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InitializeDirectory();
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SaveData(fileName, metaData, screenShot);
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SaveImage(fileName, screenShot);
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Enqueue(fileName, metaData, screenShot);
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success = true;
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logger.Debug($"Cached data for '{fileName}'.");
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}
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catch (Exception e)
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{
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logger.Error($"Failed to cache data for '{fileName}'!", e);
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}
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return success;
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}
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internal bool TryDequeue(out MetaData metaData, out ScreenShot screenShot)
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{
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var success = false;
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metaData = default;
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screenShot = default;
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if (queue.Any())
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{
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var (fileName, checksum, hash) = queue.Peek();
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try
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{
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LoadData(fileName, out metaData, out screenShot);
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LoadImage(fileName, screenShot);
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Dequeue(fileName, checksum, hash, metaData, screenShot);
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success = true;
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logger.Debug($"Uncached data for '{fileName}'.");
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}
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catch (Exception e)
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{
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logger.Error($"Failed to uncache data for '{fileName}'!", e);
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}
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}
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return success;
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}
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private void Dequeue(string fileName, int checksum, string hash, MetaData metaData, ScreenShot screenShot)
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{
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var dataPath = Path.Combine(Directory, $"{fileName}.{DATA_FILE_EXTENSION}");
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var extension = screenShot.Format.ToString().ToLower();
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var imagePath = Path.Combine(Directory, $"{fileName}.{extension}");
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if (checksum != GenerateChecksum(screenShot))
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{
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logger.Warn($"The checksum for '{fileName}' does not match, the image data may be manipulated!");
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}
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if (hash != GenerateHash(metaData, screenShot))
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{
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logger.Warn($"The hash for '{fileName}' does not match, the metadata may be manipulated!");
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}
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File.Delete(dataPath);
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File.Delete(imagePath);
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queue.Dequeue();
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}
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private void Enqueue(string fileName, MetaData metaData, ScreenShot screenShot)
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{
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var checksum = GenerateChecksum(screenShot);
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var hash = GenerateHash(metaData, screenShot);
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queue.Enqueue((fileName, checksum, hash));
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}
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private int GenerateChecksum(ScreenShot screenShot)
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{
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var checksum = default(int);
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foreach (var data in screenShot.Data)
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{
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unchecked
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{
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checksum += data;
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}
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}
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return checksum;
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}
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private string GenerateHash(MetaData metaData, ScreenShot screenShot)
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{
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var hash = default(string);
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using (var algorithm = new SHA256Managed())
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{
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var input = metaData.ToJson() + screenShot.CaptureTime + screenShot.Format + screenShot.Height + screenShot.Width;
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var bytes = Encoding.UTF8.GetBytes(input);
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var result = algorithm.ComputeHash(bytes);
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hash = string.Join(string.Empty, result.Select(b => $"{b:x2}"));
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}
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return hash;
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}
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private void InitializeDirectory()
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{
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if (Directory == default)
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{
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Directory = Path.Combine(appConfig.TemporaryDirectory, nameof(ScreenProctoring));
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}
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if (!System.IO.Directory.Exists(Directory))
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{
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System.IO.Directory.CreateDirectory(Directory);
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logger.Debug($"Created caching directory '{Directory}'.");
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}
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}
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private void LoadData(string fileName, out MetaData metaData, out ScreenShot screenShot)
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{
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var dataPath = Path.Combine(Directory, $"{fileName}.{DATA_FILE_EXTENSION}");
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var document = XDocument.Load(dataPath);
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var xml = document.Descendants(nameof(MetaData)).First();
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metaData = new MetaData();
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screenShot = new ScreenShot();
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metaData.ApplicationInfo = xml.Descendants(nameof(MetaData.ApplicationInfo)).First().Value;
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metaData.BrowserInfo = xml.Descendants(nameof(MetaData.BrowserInfo)).First().Value;
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metaData.Elapsed = TimeSpan.Parse(xml.Descendants(nameof(MetaData.Elapsed)).First().Value);
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metaData.TriggerInfo = xml.Descendants(nameof(MetaData.TriggerInfo)).First().Value;
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metaData.Urls = xml.Descendants(nameof(MetaData.Urls)).First().Value;
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metaData.WindowTitle = xml.Descendants(nameof(MetaData.WindowTitle)).First().Value;
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xml = document.Descendants(nameof(ScreenShot)).First();
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screenShot.CaptureTime = DateTime.Parse(xml.Descendants(nameof(ScreenShot.CaptureTime)).First().Value);
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screenShot.Format = (ImageFormat) Enum.Parse(typeof(ImageFormat), xml.Descendants(nameof(ScreenShot.Format)).First().Value);
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screenShot.Height = int.Parse(xml.Descendants(nameof(ScreenShot.Height)).First().Value);
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screenShot.Width = int.Parse(xml.Descendants(nameof(ScreenShot.Width)).First().Value);
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}
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private void LoadImage(string fileName, ScreenShot screenShot)
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{
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var extension = screenShot.Format.ToString().ToLower();
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var imagePath = Path.Combine(Directory, $"{fileName}.{extension}");
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screenShot.Data = File.ReadAllBytes(imagePath);
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}
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private void SaveData(string fileName, MetaData metaData, ScreenShot screenShot)
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{
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var data = new XDocument(new XDeclaration("1.0", "utf-8", "yes"));
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var dataPath = Path.Combine(Directory, $"{fileName}.{DATA_FILE_EXTENSION}");
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data.Add(
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new XElement("Data",
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new XElement(nameof(MetaData),
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new XElement(nameof(MetaData.ApplicationInfo), metaData.ApplicationInfo),
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new XElement(nameof(MetaData.BrowserInfo), metaData.BrowserInfo),
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new XElement(nameof(MetaData.Elapsed), metaData.Elapsed.ToString()),
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new XElement(nameof(MetaData.TriggerInfo), metaData.TriggerInfo),
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new XElement(nameof(MetaData.Urls), metaData.Urls),
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new XElement(nameof(MetaData.WindowTitle), metaData.WindowTitle)
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),
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new XElement(nameof(ScreenShot),
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new XElement(nameof(ScreenShot.CaptureTime), screenShot.CaptureTime.ToString()),
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new XElement(nameof(ScreenShot.Format), screenShot.Format),
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new XElement(nameof(ScreenShot.Height), screenShot.Height),
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new XElement(nameof(ScreenShot.Width), screenShot.Width)
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)
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)
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);
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data.Save(dataPath);
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}
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private void SaveImage(string fileName, ScreenShot screenShot)
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{
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var extension = screenShot.Format.ToString().ToLower();
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var imagePath = Path.Combine(Directory, $"{fileName}.{extension}");
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File.WriteAllBytes(imagePath, screenShot.Data);
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}
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}
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}
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