Overview of the WCF channel model with the SAP adapter

Článek
07/07/2021

To invoke RFCs, tRFCs, or BAPIs on an SAP system, or to send IDOCS to an SAP system, your code acts as a WCF client and sends outbound operations to the adapter. In the WCF channel model, your code invokes operations on the adapter by sending a request message over a channel.

To act as a tRFC or RFC server to an SAP system, your code behaves as a WCF service. That is, the adapter invokes an inbound operation on your code—for example, an RFC or the ReceiveIdoc operation (to receive an IDOC in string format from an SAP system). In this scenario, your code receives a request message for the operation over a channel from the adapter.

The topics in this section provide an overview of using the SAP adapter with the WCF channel model.

WCF Channel Model Overview

Clients and services communicate by exchanging SOAP messages. The WCF channel model is a low-level abstraction of this message exchange. It provides interfaces and types that enable you to send and receive messages by using a layered protocol stack called a channel stack. Each layer of the stack is composed of a channel, and each channel is created from a WCF binding. At the lowest layer is the transport channel. The transport channel implements the underlying transport mechanism between a service and a client and presents each message to the higher layers (and ultimately the consuming application) as a System.ServiceModel.Message. The WCF Message class is an abstraction of a SOAP message. WCF provides several channel interfaces, called channel shapes, that model the basic SOAP message exchange patterns, such as request-reply or one-way. A WCF transport binding provides an implementation of one or more channel shapes that higher layers can use to send and receive messages. For more information about the WCF channel model, see Channel Model Overview.

The SAP adapter is a WCF custom transport binding that exposes an SAP system as a WCF service.

Supported Channel Shapes for the SAP Adapter

The adapter implements the following WCF channel shapes:

IRequestChannel (System.ServiceModel.Channels.IRequestChannel). The IRequestChannel interface implements the client side of a request-reply message exchange. You can use an IRequestChannel to perform operations for which you want to consume a response, for example to invoke an RFC on the SAP system that returns data.
IOutputChannel (System.ServiceModel.Channels.IOutputChannel). This shape implements the client side of a one-way message exchange. You can use an IOutputChannel to invoke an operation for which you do not need to consume a response, for example to invoke an RFC on the SAP system that does not return any data.
IReplyChannel (System.ServiceModel.Channels.IReplyChannel). This shape implements the service side of a request-reply message exchange. You can use an IReplyChannel to implement an RFC or tRFC server or to receive IDOCs from a SAP system.

Like any WCF binding, the SAP adapter uses a factory pattern to provide channels to application code. You use a Microsoft.Adapters.SAPBinding object to create instances of:
System.ServiceModel.ChannelFactory<IRequestChannel> to provide IRequestChannel channels you can use to invoke request-response operations on the adapter.
System.ServiceModel.ChannelFactory<IOutputChannel> to provide IOutputChannel channels you can use to invoke one-way operations on the adapter.
System.ServiceModel.IChannelListener<IReplyChannel> to provide IReplyChannel channels you can use to receive request-response operations from the adapter.

Creating Messages for the SAP Adapter in the WCF Channel Model

In WCF the System.ServiceModel.Channels.Message class provides an in memory representation of a SOAP message. You create a Message instance by invoking the static Message.Create method.

There are two important parts to the SOAP message that you must specify when you construct a Message instance to send to the SAP adapter.

The message action is a string that is part of the SOAP message header. The message action identifies the operation that should be invoked on SAP adapter. The following shows the message action that is specified to invoke the SD_RFC_CUSTOMER_GET RFC on an SAP system: http://Microsoft.LobServices.Sap/2007/03/Rfc/SD_RFC_CUSTOMER_GET.
The message body contains the parameter data for the operation. The message body is composed of well-formed XML that corresponds to the message schema expected by the SAP adapter for the requested operation. The following message body contains the parameters for the SD_RFC_CUSTOMER_GET RFC on an SAP system.
```
<SD_RFC_CUSTOMER_GET xmlns=\"http://Microsoft.LobServices.Sap/2007/03/Rfc/\"> <KUNNR i:nil=\"true\" xmlns:i=\"http://www.w3.org/2001/XMLSchema-instance\"> </KUNNR> <NAME1>AB*</NAME1> <CUSTOMER_T> </CUSTOMER_T> </SD_RFC_CUSTOMER_GET>  
```
For information about the SAP adapter message schemas and message actions for operations, see Messages and Message Schemas for BizTalk Adapter for mySAP Business Suite.

The Message.Create method is overloaded and offers many different options for providing the message body. The following code shows how to create a Message instance by using an System.Xml.XmlReader to supply the message body. In this code, the message body is read from a string constant.

//create an XML message to send to the SAP system  
//We are invoking the SD_RFC_CUSTOMER_GET RFC.  
//The XML below specifies that we want to search for customers with names starting with "AB"  
string inputXml = "<SD_RFC_CUSTOMER_GET xmlns=\"http://Microsoft.LobServices.Sap/2007/03/Rfc/\"> <KUNNR i:nil=\"true\" xmlns:i=\"http://www.w3.org/2001/XMLSchema-instance\"> </KUNNR> <NAME1>AB*</NAME1> <CUSTOMER_T> </CUSTOMER_T> </SD_RFC_CUSTOMER_GET>";  
  
//create an XML reader from the input XML  
XmlReader reader = XmlReader.Create(new MemoryStream(Encoding.Default.GetBytes(inputXml)));  
  
//create a WCF message from the XML reader  
Message inputMessge = Message.CreateMessage(MessageVersion.Soap11, "http://Microsoft.LobServices.Sap/2007/03/Rfc/SD_RFC_CUSTOMER_GET", reader);

Important

You must provide a message action in your Message instance. This is typically done when the Message instance is created.

Streaming Support on the SAP Adapter in the WCF Channel Model

How you create and consume the messages that you exchange with the SAP adapter determines how the message is streamed between your code and the adapter.

Node streaming

Node streaming is the only level of streaming supported for all operations except the SendIdoc and ReceiveIdoc operations.

To perform node streaming for a message, you:

Create an outbound message using an XmlReader to supply the message body.
Consume an inbound message using an XmlReader. You get the reader by calling the GetReaderAtBodyContents method on the inbound Message.

Node-value Streaming

Because the SendIdoc and ReceiveIdoc operations contain the IDOC data in a string under a single XML node (<idocData>), the adapter supports node-value streaming on these operations.

To perform node-value streaming for these operations, you can:

Create the SendIdoc request message (outbound) using a BodyWriter that implements node-value streaming to supply the message body.
Consume the ReceiveIdoc request message (inbound) by calling the WriteBodyContents method on the message with an XmlDictionaryWriter that implements node-value streaming.

For more information about streaming flat file (string) IDOCs using the WCF channel model, see Streaming Flat-File IDOCs in SAP using the WCF Channel Model.

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