[Read Part
1 and Part
2 first]
Like with parts 1 and 2, I’ll stick with the “this isn’t
RPC” theme for this 3rd part of this little series and will show
how to flow free form XML from and to services. However, I will drop the “client”/”server”
nomenclature from here on and will talk about endpoints. If you look at the
contract below (along with the following explanation, of course), you’ll
quickly figure out why – both parties in the “buyer”/”seller”
conversation I am declaring in the contract below, act as client and as server at
the same time.
In contrast to the previous two examples, I am not using the raw Message
class, but I move one notch up on the messaging stack and use the XmlSerializer
formatting mode for Indigo, which allows me to flow the contents of an XmlNode
between services just like it can be done today with ASP.NET Web Services. In
addition, I show how custom message headers can be declared and flowed with (really:
inside) messages. But first things first:
The snippet below declares one contract (!) with two endpoint service
contracts. One endpoint defines the “seller” side and the other
defines the “buyer” side of a duplex conversation that two service
implementations will have about a (simplified) purchasing process. It also
defines an application-specific (SOAP-) header that is used to flow the
purchasing process identifier between the parties. That identifier can be used
to locate the process state from disk or from some in-memory location at either
side as the conversation progresses.
The seller-side service contract is defined through the ISeller interface
that is appropriately labeled with a [ServiceContract] attribute and the
buyer-side likewise defined through the IBuyer interface. The fusion of
these two interfaces into what is effectively a single contract is established
by mutually linking both interfaces by setting the respective CallbackContract
property of the [ServiceContract] attribute to the respective other
interface type. I highlighted the two places where that’s being done.
When I say “one contract”, that is not really true on the WSDL level.
In WSDL, both interfaces would indeed be represented as independent contracts.
(Which goes to show that WSDL isn’t really “the contract”,
but represents just a subset of the complete metadata model).
Each operation in these contracts is labeled with an [OperationContract]
attribute that defines the message flow as IsOneWay=true. That’s
so because in a duplex conversation, messages flow always unidirectionally and the
receiver answers not by “returning a result”, but rather by sending
a message (or multiple messages) to the other party’s endpoint. All
operation contracts also define the operation style to be DocumentBare,
which means that the infrastructure will not auto-generate body wrapper elements.
Instead, each operation defines its own body wrapper by flagging the XmlNode
typed argument for the message content with a [MessageBody] attribute
and assigning an appropriate name to it. Above the XmlNode content
argument, you can see how the custom header PurchaseProcessHeader is specified
for each operation. Custom headers are flagged with the [MessageHeader]
attribute and therefore flow in the soap:Header section of the message.
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using System;
using System.Collections.Generic;
using System.ServiceModel;
using System.Runtime.Serialization;
using System.Xml;
using System.Xml.Serialization;
namespace DuplexMessagingConversation
{
[XmlRoot(Namespace = PurchaseProcessHeader.NamespaceURI)]
[XmlType(Namespace = PurchaseProcessHeader.NamespaceURI)]
public class PurchaseProcessHeader
{
public
const string
NamespaceURI="urn:newtelligence-com:indigosamples:purchasing";
public
const string
ElementName="PurchaseOrder";
private
string orderIdentifier;
public
string OrderIdentifier
{
get { return
orderIdentifier; }
set { orderIdentifier = value;
}
}
}
[ServiceContract(Namespace
= "urn:newtelligence-com:indigosamples:seller",
Session = false,
CallbackContract = typeof(IBuyer),
FormatMode = ContractFormatMode.XmlSerializer)]
interface ISeller
{
[OperationContract(IsOneWay=true,IsInitiating=true,
Style=ServiceOperationStyle.DocumentBare)]
void
HandlePurchaseOrder(
[MessageHeader(Name=PurchaseProcessHeader.ElementName,
Namespace=PurchaseProcessHeader.NamespaceURI)]
PurchaseProcessHeader process,
[MessageBody(Name="PurchaseOrderMessage")]
XmlNode purchaseOrder);
[OperationContract(IsOneWay
= true, IsInitiating = false,
Style = ServiceOperationStyle.DocumentBare)]
void
HandlePaymentNotification(
[MessageHeader(Name = PurchaseProcessHeader.ElementName,
Namespace = PurchaseProcessHeader.NamespaceURI)]
PurchaseProcessHeader process,
[MessageBody(Name =
"PaymentNotificationMessage")]
XmlNode paymentNotification);
[OperationContract(IsOneWay
= true, IsInitiating = false, IsTerminating = true,
Style = ServiceOperationStyle.DocumentBare)]
void
HandleShippingConfirmation(
[MessageHeader(Name = PurchaseProcessHeader.ElementName,
Namespace = PurchaseProcessHeader.NamespaceURI)]
PurchaseProcessHeader process,
[MessageBody(Name =
"ShippingConfirmationMessage")]
XmlNode shippingConfirmation);
}
[ServiceContract(Namespace="urn:newtelligence-com:indigosamples:buyer",
Session = false,
CallbackContract = typeof(ISeller),
FormatMode=ContractFormatMode.XmlSerializer)]
interface IBuyer
{
[OperationContract(IsOneWay
= true, IsInitiating = true,
Style = ServiceOperationStyle.DocumentBare)]
void
HandlePurchaseOrderConfirmation(
[MessageHeader(Name = PurchaseProcessHeader.ElementName,
Namespace = PurchaseProcessHeader.NamespaceURI)]
PurchaseProcessHeader process,
[MessageBody(Name =
"PurchaseOrderConfirmationMessage")]
XmlNode purchaseOrderConfirmation);
[OperationContract(IsOneWay
= true, IsInitiating = false,
Style = ServiceOperationStyle.DocumentBare)]
void
HandleInvoice(
[MessageHeader(Name = PurchaseProcessHeader.ElementName,
Namespace = PurchaseProcessHeader.NamespaceURI)]
PurchaseProcessHeader process,
[MessageBody(Name = "InvoiceMessage")]
XmlNode invoice);
[OperationContract(IsOneWay
= true, IsInitiating = false, IsTerminating = true,
Style = ServiceOperationStyle.DocumentBare)]
void
HandleShippingNotification(
[MessageHeader(Name = PurchaseProcessHeader.ElementName,
Namespace = PurchaseProcessHeader.NamespaceURI)]
PurchaseProcessHeader process,
[MessageBody(Name =
"ShippingNotificationMessage")]
XmlNode shippingNotification);
}
}
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To illustrate the effect of these declarations on the wire (I will spare you
the XSD/WSDL goop), I’ll show an sample message (grabbed from the
debugger) as it can be seen at the ISeller endpoint’s HandlePurchaseOrder
operation when it arrives.
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<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"
xmlns:a="http://schemas.xmlsoap.org/ws/2004/08/addressing"
xmlns:r="http://schemas.xmlsoap.org/ws/2005/01/rm">
<s:Header>
<a:Action s:mustUnderstand="1">
urn:newtelligence-com:indigosamples:seller/ISeller/HandlePurchaseOrder
</a:Action>
<h:PurchaseOrder xmlns="urn:newtelligence-com:indigosamples:purchasing"
xmlns:h="urn:newtelligence-com:indigosamples:purchasing"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<OrderIdentifier>1234567890</OrderIdentifier>
</h:PurchaseOrder>
<r:Sequence s:mustUnderstand="1">
<r:Identifier>uuid:b99041bf-fab8-45dd-9235-0909d9c61d04;id=2</r:Identifier>
<r:MessageNumber>1</r:MessageNumber>
</r:Sequence>
<a:From>
<a:Address>net.tcp://localhost/buyer/reply/e01289a8-424f-4e1a-bba5-b3fb7c92a023</a:Address>
</a:From>
<a:To s:mustUnderstand="1">net.tcp://localhost/seller</a:To>
</s:Header>
<s:Body>
<PurchaseOrderMessage xmlns="urn:newtelligence-com:indigosamples:seller">
<Order xmlns="">...</Order>
</PurchaseOrderMessage>
</s:Body>
</s:Envelope>
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So … having the contract declaration in place, we can build the
service. With your knowledge from the previous
parts
of this series, the seller side is (almost) straightforward to implement. I create
a SellerService supporting the defined ISeller interface and
write all operations (methods) in a similar fashion. First I dump out the
content of the incoming message and an artificial instance identifier I use to
play with instancing. The only “magic” is in how I obtain the
callback channel that I need to be able to send my answers to the other side. To
be precise, the magic isn’t mine, it’s sitting inside Indigo. The
call IBuyer
buyer = OperationContext.Current.GetCallbackChannel<IBuyer>() yields a ready-to-use channel that is
properly configured and bound to the “other side”. Having that in
hands, I cook up an answer (or two, or none, as you can see below) and send
that to “the buyer”. The hosting class and the service host are
standard fare.
|
using System;
using System.Xml;
using System.ServiceModel;
using System.Runtime.Serialization;
namespace DuplexMessagingConversation
{
[ServiceBehavior(InstanceMode
= InstanceMode.PrivateSession)]
class SellerService : ISeller
{
Guid
instanceId = Guid.NewGuid();
public
void HandlePurchaseOrder(PurchaseProcessHeader process, XmlNode data)
{
Console.WriteLine("Seller: Purchase Order
Received\n\t{0}\n\tInstance {1}",
data.OuterXml, instanceId);
IBuyer buyer = OperationContext.Current.GetCallbackChannel<IBuyer>();
XmlDocument orderConfirmation = new XmlDocument();
orderConfirmation.LoadXml("<OrderConfirmation>...</OrderConfirmation>");
buyer.HandlePurchaseOrderConfirmation(process, orderConfirmation);
XmlDocument invoice = new
XmlDocument();
invoice.LoadXml("<Invoice>...</Invoice>");
buyer.HandleInvoice(process, invoice);
}
public
void HandlePaymentNotification(PurchaseProcessHeader process, XmlNode data)
{
Console.WriteLine("Seller: Payment
Notification Received\n\t{0}\n\tInstance {1}",
data.OuterXml, instanceId);
IBuyer buyer = OperationContext.Current.GetCallbackChannel<IBuyer>();
XmlDocument shippingNotification = new XmlDocument();
shippingNotification.LoadXml("<Shipped>...</Shipped>");
buyer.HandleShippingNotification(process, shippingNotification);
}
public
void HandleShippingConfirmation(PurchaseProcessHeader process, XmlNode data)
{
Console.WriteLine("Seller: Shipping
Confirmation Received\n\t{0}\n\tInstance {1}",
data.OuterXml, instanceId);
}
}
class Seller
{
ServiceHost<SellerService> serviceHost;
public
void Open()
{
serviceHost = new ServiceHost<SellerService>();
serviceHost.Open();
}
public
void Close()
{
serviceHost.Close();
}
}
}
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The buyer-side’s service implementation looks almost identical. The
one significant difference here is that the buyer is (in the self-hosted
scenario I have here: must be) a singleton within the scope of the
conversation. That means that the initiator of the conversation (what we
usually call “client”) will have to create a service instance and
hand that down into the infrastructure. Because I want to know when the
conversation is over and can shut down my test program, I hand a ManualResetEvent
to the service instance and have it Set it to signaled whenever the buyer’s
last expected message in the purchasing process arrives (shipping notification).
Otherwise the service implementation doesn’t have any more surprises.
More interesting is the InitiatePurchase method. It predictably creates
a service host instance for the buyer service and a channel factory that we
need to send the first message (purchase order) to the seller. From there
onwards, things are a little different than in the previous examples.
As the next step, I create a “service site”, which acts as the manager
for the duplex conversation we’re setting up. The ServiceSite is
initialized with the service host and a newly created service instance. As I
indicated in the previous paragraph, that instance is a singleton for the
conversation; it’s not a singleton per-se.
Using the service site as an argument, I can now create a duplex channel
with a call to CreateDuplexChannel on the channel factory. The resulting
channel is set up to do everything necessary to listen for answers in the scope
of the conversation and to relay the required “send answers here”
info to the other side. If you look at the SOAP message above, you’ll see
how that back reference is flowing using a WS-Addressing wsa:From header, which
is a reasonable thing to do as per WS-Addressing
(see: 3. / [reply endpoint] paragraph).
Once I have the channel in hands, I create the custom header instance and a purchase
order document (well…) and send it off to the seller side. Once that’s
done, I hang out and wait until the conversation is over and subsequently shut
down.
|
Using System;
using System.Xml;
using System.ServiceModel;
using System.Threading;
namespace DuplexMessagingConversation
{
class BuyerService : IBuyer
{
Guid
instanceId = Guid.NewGuid();
ManualResetEvent
waitHandle;
public
BuyerService(ManualResetEvent waitHandle)
{
this.waitHandle = waitHandle;
}
public
void HandlePurchaseOrderConfirmation(PurchaseProcessHeader process, XmlNode data)
{
Console.WriteLine("Buyer: Purchase Order
Confirmation Received\n\t{0}\n\tInstance {1}",
data.OuterXml, instanceId);
return;
}
public
void HandleInvoice(PurchaseProcessHeader
process, XmlNode data)
{
Console.WriteLine("Buyer: Invoice
Received\n\t{0}\n\tInstance {1}",
data.OuterXml, instanceId);
ISeller seller = OperationContext.Current.GetCallbackChannel<ISeller>();
XmlDocument paymentNotification = new XmlDocument();
paymentNotification.LoadXml("<Payment>...</Payment>");
seller.HandlePaymentNotification(process, paymentNotification);
}
public
void HandleShippingNotification(PurchaseProcessHeader process, XmlNode data)
{
Console.WriteLine("Buyer: Shipping
Notification Received\n\t{0}\n\tInstance {1}",
data.OuterXml, instanceId);
ISeller seller = OperationContext.Current.GetCallbackChannel<ISeller>();
XmlDocument shippingConfirmation = new XmlDocument();
shippingConfirmation.LoadXml("<ShipmentReceived>...</ShipmentReceived>");
seller.HandleShippingConfirmation(process, shippingConfirmation);
waitHandle.Set();
}
}
class Buyer
{
public
void InitiatePurchase()
{
ServiceHost<BuyerService>
buyerHost = new ServiceHost<BuyerService>();
using (ChannelFactory<ISeller> channelFactory = new ChannelFactory<ISeller>("clientChannel"))
{
ManualResetEvent conversationDone = new ManualResetEvent(false);
using (ServiceSite
replyTarget = new ServiceSite(buyerHost,
new BuyerService(conversationDone)))
{
ISeller channel =
channelFactory.CreateDuplexChannel(replyTarget);
PurchaseProcessHeader header = new PurchaseProcessHeader();
header.OrderIdentifier = "1234567890";
XmlDocument purchaseOrderDocument = new XmlDocument();
purchaseOrderDocument.LoadXml("<Order>...</Order>");
channel.HandlePurchaseOrder(header, purchaseOrderDocument);
conversationDone.WaitOne();
replyTarget.Close();
}
channelFactory.Close();
}
buyerHost.Close();
}
}
}
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The Program is simple and predictable; I am just posting it for
completeness and because I renamed the classes.
|
using System;
namespace DuplexMessagingConversation
{
class Program
{
static
void Main(string[]
args)
{
Seller server = new
Seller();
server.Open();
Buyer client = new Buyer();
client.InitiatePurchase();
Console.WriteLine("Press ENTER to quit");
Console.ReadLine();
server.Close();
}
}
}
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The configuration file that goes with this example is of course a bit
different from the previous ones. The <client> section and the buyerClientBinding
binding configuration apply to the buyer side, and the <services> section
and the sellerBinding are for the seller side. These sections would be
respectively split across two configuration files, if we would host the sample
in two processes.
Of course, the buyer’s <client>/<endpoint> definition
for the channel refers to the buyerClientBinding. That binding defines
three required binding elements: <reliableSession> configures the
channel to use a reliable messaging session with default values, <compositeDuplex/>
enables duplex support and <tcpTransport/> selects the TCP
transport. The order of these elements is significant and defines how these “behaviors”
are stacked in the channel. Quite special is the clientBaseAddress
attribute of the <compositeDuplex/> element; this value is used as
the base URI to dynamically construct the endpoint on which replies shall be
received by the buyer instance for this conversation. The result of that
composition can be seen in the wsa:From element in the SOAP message above.
The seller-side configuration for the <service> and its <endpoint>
is largely equivalent to what I’ve explained in the previous examples. The
only real difference is that the sellerBinding binding now also defines
the required binding elements and behaviors I just pointed out.
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<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">
<system.serviceModel>
<bindings>
<customBinding>
<binding
configurationName="sellerBinding">
<reliableSession/>
<compositeDuplex/>
<tcpTransport/>
</binding>
<binding
configurationName="buyerClientBinding">
<reliableSession/>
<compositeDuplex clientBaseAddress="net.tcp://localhost/buyer/reply"/>
<tcpTransport/>
</binding>
</customBinding>
</bindings>
<client>
<endpoint address="net.tcp://localhost/seller"
bindingConfiguration="buyerClientBinding"
bindingType="customBinding"
configurationName="clientChannel"
contractType="DuplexMessagingConversation.ISeller,
DuplexMessagingConversation"/>
</client>
<services>
<service serviceType="DuplexMessagingConversation.SellerService,
DuplexMessagingConversation">
<endpoint
contractType="DuplexMessagingConversation.ISeller,
DuplexMessagingConversation"
address="net.tcp://localhost/seller"
bindingType="customBinding"
bindingConfiguration="sellerBinding" />
</service>
</services>
</system.serviceModel>
</configuration>
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And, lastly, here’s the output:
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Seller:
Purchase Order Received
<Order xmlns="">...</Order>
Instance eb628fce-ac56-43af-9326-5bfc62a101dc
Buyer:
Purchase Order Confirmation Received
<OrderConfirmation xmlns="">...</OrderConfirmation>
Instance c1ce0c0f-fb98-4432-86fb-c81ac7243295
Buyer:
Invoice Received
<Invoice xmlns="">...</Invoice>
Instance c1ce0c0f-fb98-4432-86fb-c81ac7243295
Seller:
Payment Notification Received
<Payment xmlns="">...</Payment>
Instance eb628fce-ac56-43af-9326-5bfc62a101dc
Buyer:
Shipping Notification Received
<Shipped xmlns="">...</Shipped>
Instance c1ce0c0f-fb98-4432-86fb-c81ac7243295
Seller:
Shipping Confirmation Received
<ShipmentReceived xmlns="">...</ShipmentReceived>
Instance eb628fce-ac56-43af-9326-5bfc62a101dc
Press
ENTER to quit
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Again, the messages are free form XML, so I am using Indigo strictly as a raw
messaging platform. It’s just a bit more powerful. 
If I’d show
you a functionally equivalent application based on System.Messaging and
MSMQ, you wouldn’t be done reading, yet.