I'm looking to use the MsmqIntegrationBinding to integrate with a legacy queue which has a serialized object as the message body. Has anyone come up with a way to obtain the "metadata" of the message body and create a service side class to use within the service?
For example, if I put in a serialized Product object from System A and my service needs to consume it, how do I provide MsmqMessage the type if I do not have the Product class on my side? I was thinking of reading off a message in a separate program, deserializing, and then emitting via the code dom. Ideas?
I wholeheartedly recommend against attempting to emit the deserialized type at runtime in the message destination. Either work with the XML at the destination to obtain the data you desire, or build data contracts that both the source and destination can adhere to.
Hmm... in WCF, you can define service methods which take (and optionally return) an untyped Message type. This seems to fit your bill quite nicely.
Other than with strongly typed messages, you'll have to do all the putting together of the message on the client and the taking apart on the server by means of reading the raw XML - but that seems to be what you're looking for, right?
Find more information and samples here:
WCF - Handling Generic Messages
How to pass a generic object through WCF
Untyped messages on WCF
Untyped messages have some restrictions, e.g. you can only read them once on the server, but you should be able to manage your scenario with this, I think.
Marc
Related
I have a consumer with generic argument IEvent. This type is a base interface for all messages, and child interfaces of IEvent have some other properties. I'd like to have access to the raw message with all properties of nested types instead of only IEvent scope. These properties can be seen through RMQ admin dashboard and I think there should be a way to put them out.
You could use context.TryGetMessage<T>() to request the specific type, which essentially attempts to deserialize the message into the specified type (as long as it is in the list of messageTypes serialized into the header).
Otherwise, you can use context.TryGetMessage<JToken>(), and get the JToken from JSON.NET, which can be used to navigate the message body.
Honestly, this isn't the best approach to properly handling events, etc., so I'd refer to the documentation to see how to properly consume the various message types (and let MassTransit do the hard work).
In the context of a WCF project, I need to handle in the same way xml and non-xml messages (eg. Standard SOAP, WS-Attachments, etc..). The normal flow of WCF creates a Message object which can handle an Xml message, this is done by the encoder, so if one wants to handle different messages, it's needed to implement different kind of message-handling...
My needs is to create a message derivation class, which represent the concept of "received message" but not "handled" in the form of special data handling, but , about real data-handling, deferred in a secondary step.
so in the catch-all service I will get a Message messageObject as parameter, so the signature of the service will be Message Accept(Message messageObject)
Any idea?
thanks in advance
There is only single base Message type in WCF. This is a core type which is used by WCF infrastructure. The type is abstract so generally you can create your custom implementation but in such case you will probably have to replace some WCF channels to correctly use your new type.
If you need to transport message in custom format you are probably not looking for replacing Message type but either replacing encoder, serializer or both.
I am still confused when it is appropriate to use the Message type in WCF like below
[ServiceContract]
public interface IMyService
{
[OperationContract]
Message GetData();
[OperationContract]
void PutData(Message m);
}
Why would you want to use it?
Can you use it for streaming?
Thanks
MSDN lists the follow reasons for using the message class directly:
When you need an alternative way of creating outgoing message contents (for example, creating a message directly from a file on disk) instead of serializing .NET Framework objects.
When you need an alternative way of using incoming message contents (for example, when you want to apply an XSLT transformation to the raw XML contents) instead of deserializing into .NET Framework objects.
When you need to deal with messages in a general way regardless of message contents (for example, when routing or forwarding messages when building a router, load-balancer, or a publish-subscribe system).
See Using the Message Class for more detailed information.
Edit to address the streaming question
I didn't find a definitive answer in my quick scan via google, but the article above states "All communication between clients and services ultimately results in Message instances being sent and received" - so I would assume it could be used directly in streaming.
While the reasons listed by Tim are valid, we use messages directly in our services to create one uber routing service.
we have one service that can take any method call you throw at it, Clients are generated by wsdls supplied from multiple sources.
This service would take the message, examine its content and route it accordingly.
So in my opinion if you want to get closer to the wire, or when you dont know the type of incoming messages, you can use the message in the signature directly.
Streaming is a separate concept than message signature, streaming is supported by wcf under very specific bindings and security mechanism and the method signature has to be very specific (i.e it should return/accept stream). Also in streaming the actual stream of data travels outside the scope of soap message.
Consider this scenario that two WCF clients connect to one WCF service(server), this service will receive an object from one client and send it to the other one through some operation contract and client callbacks, both clients have the type for this object but we do not want the WCF service(server) to be dependent on this type.
The project is much bigger than this, but I wonder if you can send an object with an unknown type to a service and somehow receive it back on the other client. I saw this but it does not help me at all: Can WCF service transmit type (client doesn't know this type) information?
Thanks in advance.
You can do certain things with the "raw" Message data type - but it's really not pretty programming...
Read about it here:
How to pass arbitrary data in a Message object using WCF
WCF : Untyped messages on WCF operations.
Sending an "object" with unknown type is not possible in WCF because WCF requires a full compatibility with WSDL - and WSDL requires transparent type definition.
Having said that, if you use a type of object I believe there is a way for this to be loaded as a string and in WSDL it is defined as xs:anyType.
I personally would prefer defining the type as string and passing an XML which can be serialised using plain XML Serialization. I have used this in our company and it works really well, especially since we will be storing the XML as document in database.
I'm working on a simple plug-in framework. WCF client need to create an instance of 'ISubject' and then send back to service side. The 'ISubject' can be extended by the user. The only thing client knows at runtime is ID of a subclass of 'ISubject'.
Firstly, client need to get type information of a specific subclass of 'ISubject'. Secondly, client using reflection to enumerate all members to create a custom property editor so that each member can be asigned with proper value. Lastly, client create an instance of that subclass and send back to service.
The problem is how does client get the type information through WCF communication?
I don't want client to load that assembly where the subclass (of 'ISubject') exists.
Thanks
First, you need to be aware that there is no magic way that WCF will provide any type information to your client in the scenario you have descibed. If you are going to do it, you will have to provide a mechanism yourself.
Next, understand that WCF does not really pass objects from server to client or vice versa. All it passes are XML infosets. Often, the XML infoset passed includes a serialized representation of some object which existed on the sender's side; in this case, if the client knows about that type (i.e. can load the type's metadata from its assembly), it can deserialize the XML to instantiate an identical object on the client side. If the client doesn't have the type metadata, it can't: this is the normal case with WCF unless data contract types are in assemblies shared by both server and client implementations (generally not a good idea).
The way WCF is normally used (for example if the client is implemented using a "Service Reference" in Visual Studio), what happens is that the service publishes WSDL metadata describing its operations and the XML schemas for the operation parameters and return values, and from these a set of types is generated for use in the client implementation. These are NOT the same .NET types as the data contract types used by the service implementation, but they are "equivalent" in the sense that they can be serialized to the same XML data passed over the network. Normally this type generation is done at design time in Visual Studio.
In order to do what you are trying to do, which is essentially to do this type generation at runtime, you will need some mechanism by which the client can get sufficient knowledge of the structure of the XML representing the various types of object implementing ISubject so that it can understand the XML received from the service and generate the appropriate XML the service is expecting back (either working with the XML directly, or deserializing/serializing it in some fashion). If you really, really want to do this, possible ways might be:
some out-of-band mechanism whereby the client is preconfigured with the relevant type information corresponding to each subclass of ISubject that it might see. The link provided in blindmeis's answer is one way to do that.
provide a separate service operation by which the client can translate the ID of the subclass to type metadata for the subclass (perhaps as an XSD schema from which the client could generate a suitable serializable .NET type to round trip the XML).
it would also be feasible in principle for the service to pass type metadata in some format within the headers of the response containing the serialized object. The client would need to read, interpret and act on the type infomation in an appropriate fashion.
Whichever way, it would be a lot of effort and is not the standard way of using WCF. You will have to decide if it's worth it.
I think you might be missing something :)
A major concept with web services and WCF is that we can pass our objects across the network, and the client can work with the same objects as the server. Additionally, when a client adds a service reference in Visual Studio, the server will send the client all the details it needs to know about any types which will be passed across the network.
There should be no need for reflection.
There's a lot to cover, but I suggest you start with this tutorial which covers WCF DataContracts - http://www.codeproject.com/KB/WCF/WCFHostingAndConsuming.aspx
To deserialize an object the receiving side will need to have the assembly the type is defined in.
Perhaps you should consider some type of remoting or proxying setup where the instance of ISubject lives on one side and the other side calls back to it. This may be problematic if you need to marshal large amounts of data across the wire.
wcf needs to know the real object(not an interface!) which should be sent across the wire. so you have to satisfy the server AND the clientproxy side from the WCF service that they know the types. if you dont know the object type while creating the WCF service, you have to find a way to do it in a dynamic way. i use the solution from here to get the knownTypes to my WCF service.
[ServiceContract(SessionMode = SessionMode.Required]
[ServiceKnownType("GetServiceKnownTypes", typeof(KnownTypeHelper))]//<--!!!
public interface IWCFService
{
[OperationContract(IsOneWay = false)]
object DoSomething(object obj);
}
if you have something "universal" like the code above, you have to be sure that whatever your object at runtime will be, your WCF service have to know this object.
you wrote your client create a subclass and sent it back to the service. if you want to do that, WCF(clientproxy and server!) needs to know the real type of your subclass.