Use MessagePack Hub Protocol in SignalR for ASP.NET Core

This article assumes the reader is familiar with the topics covered in Get started with ASP.NET Core SignalR.

What is MessagePack?

MessagePack is a fast and compact binary serialization format. It's useful when performance and bandwidth are a concern because it creates smaller messages than JSON. The binary messages are unreadable when looking at network traces and logs unless the bytes are passed through a MessagePack parser. SignalR has built-in support for the MessagePack format and provides APIs for the client and server to use.

Configure MessagePack on the server

To enable the MessagePack Hub Protocol on the server, install the Microsoft.AspNetCore.SignalR.Protocols.MessagePack package in your app. In the Startup.ConfigureServices method, add AddMessagePackProtocol to the AddSignalR call to enable MessagePack support on the server.

services.AddSignalR()
    .AddMessagePackProtocol();

Note

JSON is enabled by default. Adding MessagePack enables support for both JSON and MessagePack clients.

To customize how MessagePack formats data, AddMessagePackProtocol takes a delegate for configuring options. In that delegate, the SerializerOptions property is used to configure MessagePack serialization options. For more information on how the resolvers work, visit the MessagePack library at MessagePack-CSharp. Attributes can be used on the objects you want to serialize to define how they should be handled.

services.AddSignalR()
    .AddMessagePackProtocol(options =>
    {
        options.SerializerOptions = MessagePackSerializerOptions.Standard
            .WithResolver(new CustomResolver())
            .WithSecurity(MessagePackSecurity.UntrustedData);
    });

Warning

We strongly recommend reviewing CVE-2020-5234 and applying the recommended patches. For example, calling .WithSecurity(MessagePackSecurity.UntrustedData) when replacing the SerializerOptions.

Configure MessagePack on the client

Note

JSON is enabled by default for the supported clients. Clients can only support a single protocol. Adding MessagePack support replaces any previously configured protocols.

.NET client

To enable MessagePack in the .NET Client, install the Microsoft.AspNetCore.SignalR.Protocols.MessagePack package and call AddMessagePackProtocol on HubConnectionBuilder.

using Microsoft.AspNetCore.SignalR.Client;
using Microsoft.Extensions.DependencyInjection;

var hubConnection = new HubConnectionBuilder()
                        .WithUrl("/chathub")
                        .AddMessagePackProtocol()
                        .Build();

Note

This AddMessagePackProtocol call takes a delegate for configuring options just like the server.

JavaScript client

MessagePack support for the JavaScript client is provided by the @microsoft/signalr-protocol-msgpack npm package. Install the package by executing the following command in a command shell:

npm install @microsoft/signalr-protocol-msgpack

After installing the npm package, the module can be used directly via a JavaScript module loader or imported into the browser by referencing the following file:

node_modules\@microsoft\signalr-protocol-msgpack\dist\browser\signalr-protocol-msgpack.js

The following required javaScript files must be referenced in the order shown below:

<script src="~/lib/signalr/signalr.js"></script>
<script src="~/lib/signalr/signalr-protocol-msgpack.js"></script>

Adding .withHubProtocol(new signalR.protocols.msgpack.MessagePackHubProtocol()) to the HubConnectionBuilder configures the client to use the MessagePack protocol when connecting to a server.

const connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub")
    .withHubProtocol(new signalR.protocols.msgpack.MessagePackHubProtocol())
    .build();

At this time, there are no configuration options for the MessagePack protocol on the JavaScript client.

Java client

To enable MessagePack with Java, install the com.microsoft.signalr.messagepack package. When using Gradle, add the following line to the dependencies section of the build.gradle file:

implementation 'com.microsoft.signalr.messagepack:signalr-messagepack:5.0.0'

When using Maven, add the following lines inside the <dependencies> element of the pom.xml file:

<dependency>
    <groupId>com.microsoft.signalr.messagepack</groupId>
    <artifactId>signalr</artifactId>
    <version>5.0.0</version>
</dependency>

Call withHubProtocol(new MessagePackHubProtocol()) on HubConnectionBuilder.

HubConnection messagePackConnection = HubConnectionBuilder.create("YOUR HUB URL HERE")
    .withHubProtocol(new MessagePackHubProtocol())
    .build();

MessagePack considerations

There are a few issues to be aware of when using the MessagePack Hub Protocol.

MessagePack is case-sensitive

The MessagePack protocol is case-sensitive. For example, consider the following C# class:

public class ChatMessage
{
    public string Sender { get; }
    public string Message { get; }
}

When sending from the JavaScript client, you must use PascalCased property names, since the casing must match the C# class exactly. For example:

connection.invoke("SomeMethod", { Sender: "Sally", Message: "Hello!" });

Using camelCased names won't properly bind to the C# class. You can work around this by using the Key attribute to specify a different name for the MessagePack property. For more information, see the MessagePack-CSharp documentation.

DateTime.Kind is not preserved when serializing/deserializing

The MessagePack protocol doesn't provide a way to encode the Kind value of a DateTime. As a result, when deserializing a date, the MessagePack Hub Protocol will convert to the UTC format if the DateTime.Kind is DateTimeKind.Local otherwise it will not touch the time and pass it as is. If you're working with DateTime values, we recommend converting to UTC before sending them. Convert them from UTC to local time when you receive them.

MessagePack support in "ahead-of-time" compilation environment

The MessagePack-CSharp library used by the .NET client and server uses code generation to optimize serialization. As a result, it isn't supported by default on environments that use "ahead-of-time" compilation (such as Xamarin iOS or Unity). It's possible to use MessagePack in these environments by "pre-generating" the serializer/deserializer code. For more information, see the MessagePack-CSharp documentation. Once you have pre-generated the serializers, you can register them using the configuration delegate passed to AddMessagePackProtocol:

services.AddSignalR()
    .AddMessagePackProtocol(options =>
    {
        StaticCompositeResolver.Instance.Register(
            MessagePack.Resolvers.GeneratedResolver.Instance,
            MessagePack.Resolvers.StandardResolver.Instance
        );
        options.SerializerOptions = MessagePackSerializerOptions.Standard
            .WithResolver(StaticCompositeResolver.Instance)
            .WithSecurity(MessagePackSecurity.UntrustedData);
    });

Type checks are more strict in MessagePack

The JSON Hub Protocol will perform type conversions during deserialization. For example, if the incoming object has a property value that is a number ({ foo: 42 }) but the property on the .NET class is of type string, the value will be converted. However, MessagePack doesn't perform this conversion and will throw an exception that can be seen in server-side logs (and in the console):

InvalidDataException: Error binding arguments. Make sure that the types of the provided values match the types of the hub method being invoked.

For more information on this limitation, see GitHub issue aspnet/SignalR#2937.

Chars and Strings in Java

In the java client, char objects will be serialized as one-character String objects. This is in contrast with the C# and JavaScript client, which serialize them as short objects. The MessagePack spec itself does not define behavior for char objects, so it is up to the library author to determine how to serialize them. The difference in behavior between our clients is a result of the libraries we used for our implementations.

Additional resources

• ASP.NET Core SignalR .NET Client
• ASP.NET Core SignalR JavaScript client