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Migrate to MessagePack (binary)

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MessagePack is a compact binary serialization format, resulting in smaller message sizes compared to JSON and XML. The open source MessagePack for C# library is highly performant and offers built-in super-fast LZ4 compression for an even smaller data size. It works best when data types are annotated with either DataContractSerializer or the library's own attributes. It can be configured to support AOT environments, non-public types and members, and read-only types and members.

Some behaviors and features of MessagePack for C# will be notable during migrations from BinaryFormatter, especially if changes to the serialized types' APIs cannot be made or need to be minimized.

  • By default, only public types are serializable. Private and internal structs and classes can be serialized only when StandardResolverAllowPrivate.Options is provided as an argument to MessagePackSerializer.Serialize and MessagePackSerializer.Deserialize methods.

  • MessagePack requires each serializable type to be annotated with the [MessagePackObject] attribute. It's possible to avoid that by using the ContractlessStandardResolver, but it might cause issues with versioning in the future.

  • Every serializable non-static field and a property needs to be annotated with the [Key] attribute. If you annotate the type with the [MessagePackObject(keyAsPropertyName: true)] attribute, then members don't require explicit annotations. In such case, to ignore certain public members, use the [IgnoreMember] attribute.

  • To serialize private members, use StandardResolverAllowPrivate.

  • System.Runtime.Serialization annotations can be used instead of MessagePack annotations: [DataContract] instead of [MessagePackObject], [DataMember] instead of [Key], and [IgnoreDataMember] instead of [IgnoreMember]. These annotations can be useful if you want to avoid a dependency on MessagePack in the library that defines serializable types.

  • It supports readonly/immutable types and members. The serializer will try to use the public constructor with the best matched argument list. The constructor can be specified in an explicit way by using [SerializationConstructor] attribute.

  • Serialization of arbitrary types are supported via custom formatters that are simple to author. This removes all requirements for attributes and specific constructor or member patterns.

  • The serializer supports most frequently used built-in types and collections provided by the .NET base class libraries. You can find the full list in official docs. It has extension points that allow for customization.

Warning

MessagePack has APIs to allow for deserializing data without type restrictions. Per MessagePack Security Notes, these APIs should be avoided.

Warning

Some MessagePack APIs have behavior that is customizable via mutable statics, meaning your code may succeed or fail based on what other code in the same process, AssemblyLoadContext or AppDomain might do. You can keep your code resilient by also referencing the MessagePackAnalyzer package and enabling the MsgPack001 and MsgPack002 analyzers, which call out any uses of APIs with changeable behavior.