Develop Reference

MongoDB Serialization C# - Adding Additional Encrypted Field Properties

I am trying to write a MongoDb serializer in c# that will allow me to decorate properties via a [Encrypt()] attribute and then at runtime it would allow me to generate an additional property called PropertyName_Encrypted which would contain the encrypted value.
On deserialization, the encrypted property value would be set in the parent property so that the default GET for the property always returns the encrypted value. Users will then call an optional Decrypt() method on the object to get decrypted values.
In doing so, I'm running into some interesting challenges:
How do I add Additional properties to the document when I am serializing current Element? How do I get the current element's name?
Is there a way I can read a specific property from the document/object? For e.g. say I want to pass a symmetric encryption key and read that to encrypt the data while serializing the current element? Is there any way I can do that?
Here are things I have done so far:
I've built an Encrypt Attribute as follows:
[AttributeUsage(AttributeTargets.Property)]
public class EncryptAttribute : Attribute
{
private readonly EncryptedFieldType _fieldType;
private readonly bool _tokenizeDisplay;
private readonly string _encryptedFieldName;
/// <summary>
///
/// </summary>
/// <param name="fieldType">The field type to encrypt. Useful if display needs to show some formatting. If no formatting is necessary, simply set to "Other".</param>
/// <param name="tokenizeDisplay">If set to true, will persist the tokenized value in the original field for display purposes.</param>
/// <param name="encryptedFieldName">Optional. If set, will save the encrypted value in the field name specified. By default all encrypted field values are stored in the corresponding _Encrypted field name. So EmailAddress field if encrypted, would have value under EmailAddress_Encrypted.</param>
public EncryptAttribute(EncryptedFieldType fieldType, bool tokenizeDisplay, string encryptedFieldName = "")
{
_fieldType = fieldType;
_tokenizeDisplay = tokenizeDisplay;
_encryptedFieldName = encryptedFieldName;
}
}
I read this Attribute on Startup and add an Encryption Serializer to the properties that are decorated using this attribute. The code that does that is like so:
var assemblies = AppDomain.CurrentDomain.GetAssemblies()
.Where(x => x.FullName.StartsWith("MongoCustomSerializer"))
.ToList();
var mapper = new Mapper();
foreach (var assembly in assemblies)
{
mapper.Map(assembly);
}
The mapper simply checks which properties in the document have the Encrypt attribute to add the serializer:
public sealed class Mapper
{
public void Map(Assembly assembly)
{
var encryptableTypes = assembly.GetTypes().Where(p =>
typeof(IEncryptable).IsAssignableFrom(p) && p.IsClass && !p.IsInterface && !p.IsValueType &&
!p.IsAbstract).ToList();
if (encryptableTypes.Any())
{
foreach (var encryptableType in encryptableTypes)
{
Map(encryptableType);
}
}
}
private void Map(Type documentType)
{
var properties =
documentType.GetProperties(BindingFlags.Public | BindingFlags.Instance);
if (properties.Length <= 0)
{
return;
}
foreach (var property in properties)
{
RegisterEncrpytionSerializer(property, typeof(EncryptAttribute), documentType);
}
}
private void RegisterEncrpytionSerializer(PropertyInfo property, Type encryptAttributeType, Type documentType)
{
var encryptAttributes = property.GetCustomAttributes(encryptAttributeType, false).ToList();
if (!encryptAttributes.Any()) return;
var memberMap = BsonClassMap.LookupClassMap(documentType).GetMemberMap(property.Name);
memberMap?.SetSerializer(new EncryptionSerializer());
}
}
In my unit tests, I'm getting an error stating that the Bson Class Map is already frozen. Even if I were to figure out a way to bypass that, how would this EncryptionSerializer class work to where I could write an additional property?
Would love to see if someone can assist!
UPDATE 1 - I was able to get the FREEZE error taken care of. It would appear that the LookupClassMap freezes the Member and Class Map info.
This change from the link allows me to take care of that issue:
private void RegisterEncrpytionSerializer(PropertyInfo property, Type encryptAttributeType, Type documentType)
{
var encryptAttributes = property.GetCustomAttributes(encryptAttributeType, false).ToList();
if (!encryptAttributes.Any()) return;
var classMapDefinition = typeof(BsonClassMap<>);
var classMapType = classMapDefinition.MakeGenericType(documentType);
var classMap = (BsonClassMap)Activator.CreateInstance(classMapType);
classMap.AutoMap();
var memberMap = classMap.GetMemberMap(property.Name);
memberMap?.SetSerializer(new KeyVaultEncryptionSerializer(memberMap.ElementName));
}

Are you using a service for saving/retrieving your items that actually call the DB?
I believe you should move the responsibility for writing/reading encrypted values to the calling service (i.e a repository implementation) instead of the BsonSerializer.
It would make sense to me that encryption/decryption is part of the persistence layer and something not handled in the application when needed.
Your implementation targets only the specified property you want to serialize. It doesn't make sense that it creates another property.
A second thought is that your suggested approach with properties that change value based on Decrypt() probably isn't a good idea since it makes your code unpredictable and hard to read. Make your properties dead simple.
What extra security in your code does it really give you if you can decrypt properties by just calling a method anyway?
If you still need to have a Decrypt() would suggest that you create methods for decrypting that return the decrypted value like GetUnencryptedCode() etc, it could just as well be an extension method but still not a readable property.
You should also be looking into using SecureString depending on your use case.

How can I modify steps/tags with a specflow generator plugin?

I am trying to write a generator plugin for specflow to modify the steps or tags that end up in the generated feature.cs files.
I have tried to follow the method described here:
SpecFlow- is it possible to programmatically add lines to a scenario?
relevant code:
public new CodeNamespace GenerateUnitTestFixture(Feature feature, string testClassName, string targetNamespace)
{
foreach (var scenario in feature.Scenarios)
{
scenario.Steps.Insert(0, new Given { Text = "Given I have <Theme> set as my current theme" });
//add any other steps you need....
}
return base.GenerateUnitTestFixture(feature, testClassName, targetNamespace);
}
The definition of GenerateUnitTestFixture has since changed in UnitTestFeatureGenerator, but using roughly the same method I am unable to insert steps as the entire GherkinDocument argument passed in to the function is readonly including steps so they cannot be modified or added to.
public new CodeNamespace GenerateUnitTestFixture(SpecFlowDocument document, string testClassName, string targetNamespace)
{
var feature = document.Feature;
foreach (ScenarioDefinition scenarioDefinition in feature.Children)
{
scenarioDefinition.Steps.///Cannot insert
}
return base.GenerateUnitTestFixture(document, testClassName, targetNamespace);
}
The same problem occurs for tags. I cant find much up-to-date documentation on this stuff, is it still possible to modify steps/tags or is it no longer supported?

Can I save the contents of an ObservableCollection so that the list is still intact when I restart my app?

What I want to do is have the user add items to the list. Then when they add an item I need the list to save, so that when the user closes the app and opens it again, the list they've created is still there.
Right now, I can add items to my list, but as soon as i close the app they will be gone.
private static ObservableCollection<ViewModels.ZoneViewModel> Zones = new ObservableCollection<ViewModels.ZoneViewModel>();
public void PopulateListView(string image, string name, string address)
{
if (name != "" && address != "")
{
Zones.Add(new ViewModels.ZoneViewModel { Image = image, Name = name, Address = address });
Application.Current.Properties["zoneslist"] = Zones;
}
}
protected override void OnAppearing()
{
if (Application.Current.Properties.ContainsKey("zoneslist"))
{
// Put the contents of the "zoneslist" key into a variable as a string.
var savedZones = Application.Current.Properties["zoneslist"] as ObservableCollection<ViewModels.ZoneViewModel>;
// Set the listviews' itemssource to the savedzones list.
zonesList.ItemsSource = savedZones;
}
}
Here's the code I use right now, I thought this could work to save it but that doesn't work.
EDIT: So I've tried what #Alessandro Calario suggested and after using json serialization the listview just gives me a ton of empty list items(even though i only added one). But an item is added and is saved, even when the app is closed. Progress, at least, but I'm not quite there yet. Anyone know a solution?
my code:
public void PopulateListView(string image, string name, string address)
{
if (name != "" && address != "")
{
Zones.Add(new ViewModels.ZoneViewModel { Image = image, Name = name, Address = address });
//Serialize to json string
var json = JsonConvert.SerializeObject(Zones);
Application.Current.Properties["zoneslist"] = json;
}
}
protected override void OnAppearing()
{
if (Application.Current.Properties.ContainsKey("zoneslist"))
{
// Put the contents of the "zoneslist" key into a variable as a string.
var savedZones = Application.Current.Properties["zoneslist"] as string; //ObservableCollection<ViewModels.ZoneViewModel>
JsonConvert.DeserializeObject<ObservableCollection<ViewModels.ZoneViewModel>>(savedZones);
// Set the listviews' itemssource to the savedzones list.
zonesList.ItemsSource = savedZones;
}
}

I think you can Serialize your List of Objects to a json String and save it to Application Properties

If using 3rd parties libraries is not a thing for your project I highly recommend you to use Akavache. This is an Async, persistent key-value store.
Once setup is very simple to use.
//To Insert your object
IObservable<Unit> InsertObject<T>(string key, T value, DateTimeOffset? absoluteExpiration = null);
//To Get your object
IObservable<T> GetObject<T>(string key);
where T can be your whole list.
Of course it's a little more than this but trust me just a little. Read the full documentation and hope it fits your needs.

The Application Properties only stores primitive types.
Note: the Properties dictionary can only serialize primitive types for
storage. Attempting to store other types (such as List can
fail silently).
Source: https://developer.xamarin.com/guides/xamarin-forms/application-fundamentals/application-class/
Either set it up so you are using the properties as a primitive storage, or go for another local storage mechanism such as Sqlite (a good guide here: https://developer.xamarin.com/guides/xamarin-forms/application-fundamentals/databases/)

How can I load only specific elements in AngleSharp?

I'm using AngleSharp to parse HTML5 at the moment what I'm doing is wrapping the elements I want to parse with a little bit of HTML to make it a valid HTML5 and then use the parser on that, is there a better of doing it? meaning, parsing specific elements directly and validate that the structure is indeed HTML5?

Hm, a little example would be nice. But AngleSharp does support fragment parsing, which sounds like the thing you want. In general fragment parsing is also applied when you set properties like InnerHtml, which transform strings to DOM nodes.
You can use the ParseFragment method of the HtmlParser class to get a list of nodes contained in the given source code. An example:
using AngleSharp.Parser.Html;
// ...
var source = "<div><span class=emphasized>Works!</span></div>";
var parser = new HtmlParser();
var nodes = parser.ParseFragment(source, null);//null = no context given
if (nodes.Length == 0)
Debug.WriteLine("Apparently something bad happened...");
foreach (var node in nodes)
{
// Examine the node
}
Usually all nodes will be IText or IElement types. Also comments (IComment) are possible. You will never see IDocument or IDocumentFragment nodes attached to such an INodeList. However, since HTML5 is quite robust it is very likely that you will never experience "errors" using this method.
What you can do is to look for (parsing) errors. You need to provide an IConfiguration that exposes an event aggregator, which collects such events. The simplest implementation for aggregating only such events (without possibility of adding / removing multiple handlers) is the following:
using AngleSharp.Events;
// ...
class SimpleEventAggregator : IEventAggregator
{
readonly List<HtmlParseErrorEvent> _errors = new List<HtmlParseErrorEvent>();
public void Publish<TEvent>(TEvent data)
{
var error = data as HtmlParseErrorEvent;
if (error != null)
_errors.Add(error);
}
public List<HtmlParseErrorEvent> Errors
{
get { return _errors; }
}
public void Subscribe<TEvent>(ISubscriber<TEvent> listener) { }
public void Unsubscribe<TEvent>(ISubscriber<TEvent> listener) { }
}
The simplest way to use the event aggregator with a configuration is to instantiate a new (provided) Configuration. Here as a sample snippet.
using AngleSharp;
// ...
var errorEvents = new SimpleEventAggregator();
var config = new Configuration(events: errorEvents);
Please note: Every error that is reported is an "official" error (according to W3C spec.). These errors do not indicate that the provided code is malicious or invalid, just that something is not following the spec and that a fallback had to be applied.
Hope this answers your question. If not, then please let me know.
Update Updated the answer for the latest version of AngleSharp.

Manage/Update Records in ASP.NET With Redis using ServiceStack

I'm coming from a SQL Server background, and experimenting with Redis in .NET using ServiceStack. I don't mean for Redis to be a full replacement for SQL Server, but I just wanted to get a basic idea of how to use it so I could see where we might make good use of it.
I'm struggling with what I think is a pretty basic issue. We have a list of items that are maintained in a couple of different data stores. For the sake of simplicity, assume the definition of the item is basic: an integer id and a string name. I'm trying to do the following:
Store an item
Retrieve an item if we only know its id
Overwrite an existing item if we only know its id
Show all the items for that specific type
And here's some of the code I've put together:
public class DocumentRepositoryRedis
{
private static string DOCUMENT_ID_KEY_BASE = "document::id::";
public IQueryable<Document> GetAllDocuments()
{
IEnumerable<Document> documentsFromRedis;
using (var documents = new RedisClient("localhost").As<Document>())
{
documentsFromRedis = documents.GetAll();
}
return documentsFromRedis.AsQueryable();
}
public Document GetDocument(int id)
{
Document document = null;
using (var redisDocuments = new RedisClient("localhost").As<Document>())
{
var documentKey = GetKeyByID(document.ID);
if (documentKey != null)
document = redisDocuments.GetValue(documentKey);
}
return document;
}
public void SaveDocument(Document document)
{
using (var redisDocuments = new RedisClient("localhost").As<Document>())
{
var documentKey = GetKeyByID(document.ID);
redisDocuments.SetEntry(documentKey, document);
}
}
private string GetKeyByID(int id)
{
return DOCUMENT_ID_KEY_BASE + id.ToString();
}
}
It all seems to work - except for GetAllDocuments. That's returning 0 documents, regardless of how many documents I have stored. What am I doing wrong?

The typed Redis client also gives you access to the non-typed methods - since Redis ultimately doesn't know or care about your object types. So when you use the client.SetEntry() method, it bypasses some of the typed client's features and just stores the object by a key. You'll want to use the client.Store method since it goes ahead and creates a SET in Redis with all the object IDs related to your type. This SET is important because it's what the GetAll method relies on to serve back all the objects to you. The client.Store method does infer the ID automatically so you'll want to play around with it.
You'd change your GetDocument(int id) and SaveDocument(Document document) methods to use the client.GetById(string id) method, and you'd use client.Store(T value) method. You won't need your GetKeyByID() method anymore. I believe your Document object will need an "Id" property for the typed client to infer your object ID.