Restore SEBPatch
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301
SafeExamBrowser.Configuration/DataFormats/XmlParser.cs
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301
SafeExamBrowser.Configuration/DataFormats/XmlParser.cs
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/*
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* Copyright (c) 2024 ETH Zürich, IT Services
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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.Globalization;
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using System.IO;
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using System.Text;
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using System.Xml;
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using System.Xml.Linq;
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using SafeExamBrowser.Configuration.Contracts;
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using SafeExamBrowser.Configuration.Contracts.Cryptography;
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using SafeExamBrowser.Configuration.Contracts.DataCompression;
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using SafeExamBrowser.Configuration.Contracts.DataFormats;
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using SafeExamBrowser.Logging.Contracts;
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namespace SafeExamBrowser.Configuration.DataFormats
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{
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public class XmlParser : IDataParser
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{
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private const string XML_PREFIX = "<?xm";
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private readonly IDataCompressor compressor;
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private readonly ILogger logger;
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public XmlParser(IDataCompressor compressor, ILogger logger)
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{
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this.compressor = compressor;
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this.logger = logger;
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}
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public bool CanParse(Stream data)
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{
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try
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{
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var longEnough = data.Length > XML_PREFIX.Length;
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if (longEnough)
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{
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var prefix = ReadPrefix(data);
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var isValid = XML_PREFIX.Equals(prefix, StringComparison.OrdinalIgnoreCase);
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logger.Debug($"'{data}' starting with '{prefix}' {(isValid ? "matches" : "does not match")} the {FormatType.Xml} format.");
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return isValid;
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}
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logger.Debug($"'{data}' is not long enough ({data.Length} bytes) to match the {FormatType.Xml} format.");
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}
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catch (Exception e)
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{
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logger.Error($"Failed to determine whether '{data}' with {data?.Length / 1000.0} KB data matches the {FormatType.Xml} format!", e);
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}
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return false;
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}
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public ParseResult TryParse(Stream data, PasswordParameters password = null)
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{
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var prefix = ReadPrefix(data);
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var isValid = XML_PREFIX.Equals(prefix, StringComparison.OrdinalIgnoreCase);
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var result = new ParseResult { Status = LoadStatus.InvalidData };
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if (isValid)
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{
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data = compressor.IsCompressed(data) ? compressor.Decompress(data) : data;
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data.Seek(0, SeekOrigin.Begin);
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using (var reader = XmlReader.Create(data, new XmlReaderSettings { DtdProcessing = DtdProcessing.Ignore }))
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{
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var hasRoot = reader.ReadToFollowing(XmlElement.Root);
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var hasDictionary = reader.ReadToDescendant(XmlElement.Dictionary);
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if (hasRoot && hasDictionary)
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{
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logger.Debug($"Found root node, starting to parse data...");
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result.Status = ParseDictionary(reader, out var rawData);
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result.RawData = rawData;
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logger.Debug($"Finished parsing -> Result: {result.Status}.");
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}
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else
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{
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logger.Error($"Could not find root {(!hasRoot ? $"node '{XmlElement.Root}'" : $"dictionary '{XmlElement.Dictionary}'")}!");
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}
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}
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result.Format = FormatType.Xml;
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}
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else
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{
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logger.Error($"'{data}' starting with '{prefix}' does not match the {FormatType.Xml} format!");
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}
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return result;
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}
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private LoadStatus ParseArray(XmlReader reader, out List<object> array)
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{
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array = new List<object>();
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if (reader.IsEmptyElement)
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{
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reader.Read();
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reader.MoveToContent();
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return LoadStatus.Success;
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}
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reader.Read();
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reader.MoveToContent();
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while (reader.NodeType == XmlNodeType.Element)
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{
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var status = ParseElement(reader, out object element);
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if (status == LoadStatus.Success)
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{
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array.Add(element);
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}
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else
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{
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return status;
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}
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reader.MoveToContent();
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}
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if (reader.NodeType == XmlNodeType.EndElement && reader.Name == XmlElement.Array)
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{
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reader.Read();
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reader.MoveToContent();
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return LoadStatus.Success;
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}
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logger.Error($"Expected closing tag for '{XmlElement.Array}', but found '{reader.Name}{reader.Value}'!");
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return LoadStatus.InvalidData;
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}
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private LoadStatus ParseDictionary(XmlReader reader, out Dictionary<string, object> dictionary)
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{
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dictionary = new Dictionary<string, object>();
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if (reader.IsEmptyElement)
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{
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reader.Read();
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reader.MoveToContent();
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return LoadStatus.Success;
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}
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reader.Read();
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reader.MoveToContent();
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while (reader.NodeType == XmlNodeType.Element)
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{
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var status = ParseKeyValuePair(reader, out var pair);
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if (status == LoadStatus.Success)
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{
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dictionary[pair.Key] = pair.Value;
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}
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else
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{
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return status;
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}
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reader.MoveToContent();
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}
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if (reader.NodeType == XmlNodeType.EndElement && reader.Name == XmlElement.Dictionary)
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{
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reader.Read();
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reader.MoveToContent();
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return LoadStatus.Success;
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}
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logger.Error($"Expected closing tag for '{XmlElement.Dictionary}', but found '{reader.Name}{reader.Value}'!");
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return LoadStatus.InvalidData;
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}
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private LoadStatus ParseKeyValuePair(XmlReader reader, out KeyValuePair<string, object> pair)
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{
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var status = LoadStatus.InvalidData;
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var key = XNode.ReadFrom(reader) as XElement;
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pair = default(KeyValuePair<string, object>);
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if (key.Name.LocalName == XmlElement.Key)
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{
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reader.MoveToContent();
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status = ParseElement(reader, out object value);
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if (status == LoadStatus.Success)
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{
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pair = new KeyValuePair<string, object>(key.Value, value);
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}
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}
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else
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{
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logger.Error($"Expected element '{XmlElement.Key}', but found '{key}'!");
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}
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return status;
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}
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private LoadStatus ParseElement(XmlReader reader, out object element)
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{
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var array = default(List<object>);
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var dictionary = default(Dictionary<string, object>);
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var status = default(LoadStatus);
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var value = default(object);
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if (reader.Name == XmlElement.Array)
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{
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status = ParseArray(reader, out array);
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}
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else if (reader.Name == XmlElement.Dictionary)
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{
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status = ParseDictionary(reader, out dictionary);
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}
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else
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{
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status = ParseSimpleType(XNode.ReadFrom(reader) as XElement, out value);
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}
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element = array ?? dictionary ?? value;
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return status;
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}
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private LoadStatus ParseSimpleType(XElement element, out object value)
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{
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var status = LoadStatus.Success;
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value = null;
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switch (element.Name.LocalName)
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{
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case XmlElement.Data:
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value = Convert.FromBase64String(element.Value);
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break;
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case XmlElement.Date:
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value = XmlConvert.ToDateTime(element.Value, XmlDateTimeSerializationMode.Utc);
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break;
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case XmlElement.False:
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value = false;
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break;
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case XmlElement.Integer:
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value = Convert.ToInt32(element.Value);
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break;
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case XmlElement.Real:
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value = Convert.ToDouble(element.Value, CultureInfo.InvariantCulture);
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break;
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case XmlElement.String:
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value = element.IsEmpty ? null : element.Value;
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break;
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case XmlElement.True:
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value = true;
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break;
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default:
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status = LoadStatus.InvalidData;
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break;
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}
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if (status != LoadStatus.Success)
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{
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logger.Error($"Element '{element}' is not a supported value type!");
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}
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return status;
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}
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private string ReadPrefix(Stream data)
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{
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var prefixData = new byte[XML_PREFIX.Length];
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if (compressor.IsCompressed(data))
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{
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prefixData = compressor.Peek(data, XML_PREFIX.Length);
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}
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else
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{
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data.Seek(0, SeekOrigin.Begin);
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data.Read(prefixData, 0, XML_PREFIX.Length);
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}
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return Encoding.UTF8.GetString(prefixData);
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}
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}
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}
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