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ResourceHandler.cs
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ResourceHandler.cs
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/*
* Copyright (c) 2024 ETH Zürich, IT Services
*
* 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/.
*/
using System;
using System.Collections.Specialized;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Mime;
using System.Threading.Tasks;
using CefSharp;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using SafeExamBrowser.Browser.Content;
using SafeExamBrowser.Browser.Contracts.Events;
using SafeExamBrowser.Browser.Contracts.Filters;
using SafeExamBrowser.Configuration.Contracts;
using SafeExamBrowser.Configuration.Contracts.Cryptography;
using SafeExamBrowser.I18n.Contracts;
using SafeExamBrowser.Logging.Contracts;
using SafeExamBrowser.Settings;
using SafeExamBrowser.Settings.Browser;
using SafeExamBrowser.Settings.Browser.Filter;
using BrowserSettings = SafeExamBrowser.Settings.Browser.BrowserSettings;
using Request = SafeExamBrowser.Browser.Contracts.Filters.Request;
namespace SafeExamBrowser.Browser.Handlers
{
internal class ResourceHandler : CefSharp.Handler.ResourceRequestHandler
{
private readonly AppConfig appConfig;
private readonly ContentLoader contentLoader;
private readonly IRequestFilter filter;
private readonly IKeyGenerator keyGenerator;
private readonly ILogger logger;
private readonly SessionMode sessionMode;
private readonly BrowserSettings settings;
private readonly WindowSettings windowSettings;
private IResourceHandler contentHandler;
private IResourceHandler pageHandler;
private string userIdentifier;
internal event UserIdentifierDetectedEventHandler UserIdentifierDetected;
internal ResourceHandler(
AppConfig appConfig,
IRequestFilter filter,
IKeyGenerator keyGenerator,
ILogger logger,
SessionMode sessionMode,
BrowserSettings settings,
WindowSettings windowSettings,
IText text)
{
this.appConfig = appConfig;
this.filter = filter;
this.contentLoader = new ContentLoader(text);
this.keyGenerator = keyGenerator;
this.logger = logger;
this.sessionMode = sessionMode;
this.settings = settings;
this.windowSettings = windowSettings;
}
protected override IResourceHandler GetResourceHandler(IWebBrowser webBrowser, IBrowser browser, IFrame frame, IRequest request)
{
if (Block(request))
{
return ResourceHandlerFor(request.ResourceType);
}
return base.GetResourceHandler(webBrowser, browser, frame, request);
}
protected override CefReturnValue OnBeforeResourceLoad(IWebBrowser webBrowser, IBrowser browser, IFrame frame, IRequest request, IRequestCallback callback)
{
if (IsMailtoUrl(request.Url))
{
return CefReturnValue.Cancel;
}
AppendCustomHeaders(webBrowser, request);
ReplaceSebScheme(request);
return base.OnBeforeResourceLoad(webBrowser, browser, frame, request, callback);
}
protected override bool OnProtocolExecution(IWebBrowser webBrowser, IBrowser browser, IFrame frame, IRequest request)
{
return true;
}
protected override void OnResourceRedirect(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, IResponse response, ref string newUrl)
{
if (sessionMode == SessionMode.Server)
{
SearchUserIdentifier(request, response);
}
base.OnResourceRedirect(chromiumWebBrowser, browser, frame, request, response, ref newUrl);
}
protected override bool OnResourceResponse(IWebBrowser webBrowser, IBrowser browser, IFrame frame, IRequest request, IResponse response)
{
if (RedirectToDisablePdfReaderToolbar(request, response, out var url))
{
frame?.LoadUrl(url);
return true;
}
if (sessionMode == SessionMode.Server)
{
SearchUserIdentifier(request, response);
}
return base.OnResourceResponse(webBrowser, browser, frame, request, response);
}
private void AppendCustomHeaders(IWebBrowser webBrowser, IRequest request)
{
Uri.TryCreate(webBrowser.Address, UriKind.Absolute, out var pageUrl);
Uri.TryCreate(request.Url, UriKind.Absolute, out var requestUrl);
if (request.ResourceType == ResourceType.MainFrame || pageUrl?.Host?.Equals(requestUrl?.Host) == true)
{
var headers = new NameValueCollection(request.Headers);
if (settings.SendConfigurationKey)
{
headers["X-SafeExamBrowser-ConfigKeyHash"] = keyGenerator.CalculateConfigurationKeyHash(settings.ConfigurationKey, request.Url);
}
if (settings.SendBrowserExamKey)
{
headers["X-SafeExamBrowser-RequestHash"] = keyGenerator.CalculateBrowserExamKeyHash(settings.ConfigurationKey, settings.BrowserExamKeySalt, request.Url);
}
request.Headers = headers;
}
}
private bool Block(IRequest request)
{
var block = false;
var url = WebUtility.UrlDecode(request.Url);
var isValidUri = Uri.TryCreate(url, UriKind.Absolute, out _);
if (settings.Filter.ProcessContentRequests && isValidUri)
{
var result = filter.Process(new Request { Url = url });
if (result == FilterResult.Block)
{
block = true;
logger.Info($"Blocked content request{(windowSettings.UrlPolicy.CanLog() ? $" for '{url}'" : "")} ({request.ResourceType}, {request.TransitionType}).");
}
}
else if (!isValidUri)
{
logger.Warn($"Filter could not process request{(windowSettings.UrlPolicy.CanLog() ? $" for '{url}'" : "")} ({request.ResourceType}, {request.TransitionType})!");
}
return block;
}
private bool IsMailtoUrl(string url)
{
return url.StartsWith(Uri.UriSchemeMailto);
}
private bool RedirectToDisablePdfReaderToolbar(IRequest request, IResponse response, out string url)
{
const string DISABLE_PDF_READER_TOOLBAR = "#toolbar=0";
var isPdf = response.Headers["Content-Type"] == MediaTypeNames.Application.Pdf;
var isMainFrame = request.ResourceType == ResourceType.MainFrame;
var hasFragment = request.Url.Contains(DISABLE_PDF_READER_TOOLBAR);
var redirect = settings.AllowPdfReader && !settings.AllowPdfReaderToolbar && isPdf && isMainFrame && !hasFragment;
url = request.Url + DISABLE_PDF_READER_TOOLBAR;
if (redirect)
{
logger.Info($"Redirecting{(windowSettings.UrlPolicy.CanLog() ? $" to '{url}'" : "")} to disable PDF reader toolbar.");
}
return redirect;
}
private void ReplaceSebScheme(IRequest request)
{
if (Uri.IsWellFormedUriString(request.Url, UriKind.RelativeOrAbsolute))
{
var uri = new Uri(request.Url);
if (uri.Scheme == appConfig.SebUriScheme)
{
request.Url = new UriBuilder(uri) { Scheme = Uri.UriSchemeHttp }.Uri.AbsoluteUri;
}
else if (uri.Scheme == appConfig.SebUriSchemeSecure)
{
request.Url = new UriBuilder(uri) { Scheme = Uri.UriSchemeHttps }.Uri.AbsoluteUri;
}
}
}
private IResourceHandler ResourceHandlerFor(ResourceType resourceType)
{
if (contentHandler == default(IResourceHandler))
{
contentHandler = CefSharp.ResourceHandler.FromString(contentLoader.LoadBlockedContent());
}
if (pageHandler == default(IResourceHandler))
{
pageHandler = CefSharp.ResourceHandler.FromString(contentLoader.LoadBlockedPage());
}
switch (resourceType)
{
case ResourceType.MainFrame:
case ResourceType.SubFrame:
return pageHandler;
default:
return contentHandler;
}
}
private void SearchUserIdentifier(IRequest request, IResponse response)
{
var success = TrySearchGenericUserIdentifier(response);
if (!success)
{
success = TrySearchEdxUserIdentifier(response);
}
if (!success)
{
TrySearchMoodleUserIdentifier(request, response);
}
}
private bool TrySearchGenericUserIdentifier(IResponse response)
{
var ids = response.Headers.GetValues("X-LMS-USER-ID");
var success = false;
if (ids != default(string[]))
{
var userId = ids.FirstOrDefault();
if (userId != default && userIdentifier != userId)
{
userIdentifier = userId;
Task.Run(() => UserIdentifierDetected?.Invoke(userIdentifier));
logger.Info("Generic LMS user identifier detected.");
success = true;
}
}
return success;
}
private bool TrySearchEdxUserIdentifier(IResponse response)
{
var cookies = response.Headers.GetValues("Set-Cookie");
var success = false;
if (cookies != default(string[]))
{
try
{
var userInfo = cookies.FirstOrDefault(c => c.Contains("edx-user-info"));
if (userInfo != default)
{
var start = userInfo.IndexOf("=") + 1;
var end = userInfo.IndexOf("; expires");
var cookie = userInfo.Substring(start, end - start);
var sanitized = cookie.Replace("\\\"", "\"").Replace("\\054", ",").Trim('"');
var json = JsonConvert.DeserializeObject(sanitized) as JObject;
var userName = json["username"].Value<string>();
if (userIdentifier != userName)
{
userIdentifier = userName;
Task.Run(() => UserIdentifierDetected?.Invoke(userIdentifier));
logger.Info("EdX user identifier detected.");
success = true;
}
}
}
catch (Exception e)
{
logger.Error("Failed to parse edX user identifier!", e);
}
}
return success;
}
private bool TrySearchMoodleUserIdentifier(IRequest request, IResponse response)
{
var success = TrySearchMoodleUserIdentifierByLocation(response);
if (!success)
{
success = TrySearchMoodleUserIdentifierByRequest(MoodleRequestType.Plugin, request, response);
}
if (!success)
{
success = TrySearchMoodleUserIdentifierByRequest(MoodleRequestType.Theme, request, response);
}
return success;
}
private bool TrySearchMoodleUserIdentifierByLocation(IResponse response)
{
var locations = response.Headers.GetValues("Location");
if (locations != default(string[]))
{
try
{
var location = locations.FirstOrDefault(l => l.Contains("/login/index.php?testsession"));
if (location != default)
{
var userId = location.Substring(location.IndexOf("=") + 1);
if (userIdentifier != userId)
{
userIdentifier = userId;
Task.Run(() => UserIdentifierDetected?.Invoke(userIdentifier));
logger.Info("Moodle user identifier detected by location.");
}
return true;
}
}
catch (Exception e)
{
logger.Error("Failed to parse Moodle user identifier by location!", e);
}
}
return false;
}
private bool TrySearchMoodleUserIdentifierByRequest(MoodleRequestType type, IRequest request, IResponse response)
{
var cookies = response.Headers.GetValues("Set-Cookie");
var success = false;
if (cookies != default(string[]))
{
var session = cookies.FirstOrDefault(c => c.Contains("MoodleSession"));
if (session != default)
{
var userId = ExecuteMoodleUserIdentifierRequest(request.Url, session, type);
if (int.TryParse(userId, out var id) && id > 0 && userIdentifier != userId)
{
userIdentifier = userId;
Task.Run(() => UserIdentifierDetected?.Invoke(userIdentifier));
logger.Info($"Moodle user identifier detected by request ({type}).");
success = true;
}
}
}
return success;
}
private string ExecuteMoodleUserIdentifierRequest(string requestUrl, string session, MoodleRequestType type)
{
var userId = default(string);
try
{
Task.Run(async () =>
{
try
{
var endpointUrl = default(string);
var start = session.IndexOf("=") + 1;
var end = session.IndexOf(";");
var name = session.Substring(0, start - 1);
var value = session.Substring(start, end - start);
var uri = new Uri(requestUrl);
if (type == MoodleRequestType.Plugin)
{
endpointUrl = $"{uri.Scheme}{Uri.SchemeDelimiter}{uri.Host}/mod/quiz/accessrule/sebserver/classes/external/user.php";
}
else
{
endpointUrl = $"{uri.Scheme}{Uri.SchemeDelimiter}{uri.Host}/theme/boost_ethz/sebuser.php";
}
var message = new HttpRequestMessage(HttpMethod.Get, endpointUrl);
using (var handler = new HttpClientHandler { UseCookies = false })
using (var client = new HttpClient(handler))
{
message.Headers.Add("Cookie", $"{name}={value}");
var result = await client.SendAsync(message);
if (result.IsSuccessStatusCode)
{
userId = await result.Content.ReadAsStringAsync();
}
else if (result.StatusCode != HttpStatusCode.NotFound)
{
logger.Error($"Failed to retrieve Moodle user identifier by request ({type})! Response: {(int) result.StatusCode} {result.ReasonPhrase}");
}
}
}
catch (Exception e)
{
logger.Error($"Failed to parse Moodle user identifier by request ({type})!", e);
}
}).GetAwaiter().GetResult();
}
catch (Exception e)
{
logger.Error($"Failed to execute Moodle user identifier request ({type})!", e);
}
return userId;
}
private enum MoodleRequestType
{
Plugin,
Theme
}
}
}