Using the AquaLogic Service Bus Console

Message Context

This section describes the BEA AquaLogic Service Bus message context model and specifically the predefined context variables that are used in the AquaLogic Service Bus message flow. It includes the following topics:

The Message Context Model

The BEA AquaLogic Service Bus message context is a set of properties that holds message context as well as information about messages as they are routed through AquaLogic Service Bus. These properties are referred to as context variables—for example, service endpoints are represented by predefined context variables. AquaLogic Service Bus also supports user-defined context variables.

The message context is defined by an XML Schema. You typically use XQuery expressions to manipulate the context variables in the message flow that defines a proxy service.

Predefined Context Variables

The following table describes the predefined context variables. The predefined context variables can be grouped into the following types: the message-related variables, the inbound and outbound variables, the operation variable, the fault variable.

For information about the element types in the message context variables, see Message Context Schema.

Message-Related Variables

Together, the message-related variables header, body and attachments represent the canonical format of a message as it flows through AquaLogic Service Bus. These variables are initialized using the message content received by a proxy service and are used to construct the outgoing messages that are routed or published to other services.

If you want to modify a message as part of processing it, you must modify these variables.

A message payload (that is, a message content exclusive of headers or attachments) is contained in the body variable. The decision about which variable's content to include in an outgoing message is made at the point at which a message is dispatched (published or routed) from AquaLogic Service Bus. That determination is dependent upon whether the target endpoint is expecting a SOAP or a non-SOAP message:

Header Variable

The header variable contains SOAP headers associated with a message. The header variable points to a <SOAP:Header> element with headers as sub-elements. If the case of non-SOAP messages or SOAP messages with no headers, the <SOAP:Header> element is empty, and has no sub-elements.

Body Variable

The body variable represents the core message payload and always points to a <SOAP:Body> element. The core payload for both SOAP and non-SOAP messages is available in the same variable and with the same packaging—that is, wrapped in a <SOAP:Body> element:

Attachments Variable

The attachments variable holds the attachments associated with a message. The attachments variable is defined by an XML schema. It consists of a single root node: <ctx:attachments>, with a <ctx:attachment> sub-element for each attachment. The sub-elements contain information about the attachment (derived from MIME headers) as well as the attachment content. As with most of the other message-related variables, attachments is always set, but if there are no attachments, the attachments variable consists of an empty <ctx:attachments> element.

Each attachment element includes a set of sub-elements, as described in the following table.

With the exception of the untyped body element, all other elements contain string values that are interpreted in the same way as they are interpreted in MIME—for example, valid values for the Content-Type element include text/xml and text/xml; charset=utf-8.

The parsing of attachments is not recursive. If an attachment has a Content-Type of multipart/..., the body element holds the original unpacked MIME content as a stream of bytes and does not contain attachment sub-elements. Because the MIME stream may contain binary data, it is represented by a <binary-content> reference element.

To learn how binary content is handled, see Binary Content in the body and attachments Variables.

Binary Content in the body and attachments Variables

In the case of both the body and attachments variables, text-, XML- and MFL-based content is placed directly inside of an XML element. For binary data, which can contain byte values that are illegal in XML, AquaLogic Service Bus does not place the binary content in the XML element. Consequently, the binary content cannot be manipulated, but it is handled efficiently.

When binary content is received, the AquaLogic Service Bus run time stores it in an in-memory hash table and a reference to that content is inserted into the XML (body or attachments) element. This reference is represented by the following XML snippet:

<binary-content ref="..."/>

where the ref attribute contains a URI or URN that uniquely identifies the binary content. This XML can be manipulated in a AquaLogic Service Bus pipeline, branch, or route node in the same way any other content can be manipulated, but only the reference and not the underlying binary content is affected.

For example:

When messages are dispatched from AquaLogic Service Bus, the URI in the reference XML is used to restore the relevant binary content in the outgoing message. For information about how outbound messages are constructed, see Constructing Messages to Dispatch.

Clients and certain transports, notably e-mail, file and FTP can use this same reference XML to implement pass-by-reference. In this case, the transport or client creates the reference XML rather than the proxy service run time. Also, the value of the URI in the ref attribute is specified by the user that creates the reference XML. For these cases in which the reference XML is not created by the proxy service run time—specifically, when the URI is not recognized as one referring to internally managed binary content—AquaLogic Service Bus does not de-reference the URI, and the content is not substituted into an outgoing message.

Inbound and Outbound Variables

The inbound and outbound context variables contain information about the inbound and outbound endpoints. The inbound variable ($inbound) contains information about the proxy service that received the request message; the outbound variable ($outbound) contains information about the target business service to which a message is sent.

The outbound variable is set in the route action in route nodes and publish actions. You can modify $outbound using the request actions you configure in routing nodes and publish actions (also in the response actions in routing nodes).

You cannot modify the outbound variable in Service Callout actions.

The inbound and outbound variables have the following characteristics:

Sub-Elements of the inbound and outbound Variables

This section describes the sub-elements of the inbound and outbound context variables, including information about whether a given sub-element is initialized at run time. To learn about how context variables are initialized, see Initializing Context Variables. The sub-elements include:

service

The service element is read-only for both inbound and outbound. Sub-elements include providerName and operation.

transport

The transport element is read-only on inbound, except for the response element, which you can modify to set the response transport headers. The sub-elements of the transport element are described in the following table.

BEA_HOME\weblogic92\servicebus\lib\sb-schemas.jar

BEA_HOME\weblogic92\servicebus\lib\sb-schemas.jar

security

The sub elements of the security element are described in the following table.

Related Topics

Adding an Action

Adding Route Node Actions

For a description of the standard HTTP headers, see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

For a description of the standard JMS headers, see http://download.oracle.com/docs/cd/E13222_01/wls/docs92/jms/fund.html#jms_features

Operation Variable

The operation variable is a read-only variable. It contains a string that identifies the operation to be invoked on a proxy service. If no operations are defined for a proxy service, the operation variable is not set and returns the equivalent of null.

AquaLogic Service Bus provides the operation variable as a stand-alone variable, rather than as a sub-element of the inbound variable to optimize performance—the computation of the operation may be deferred until the operation variable is explicitly accessed rather than anytime the inbound variable is accessed.

Fault Variable

The fault variable is used to hold information about any error that has occurred during message processing. When an error occurs, this variable is populated with information before the appropriate error handler is invoked.

The fault variable includes the errorCode, reason, details, and location sub-elements described in the following table.

The contents of the fault variable are modeled after SOAP faults to facilitate fault generation when replying from a SOAP-based proxy service. The values for error codes generated by AquaLogic Service Bus correspond to system error codes and are prefixed with BEA string.

The error codes associated with the errors surface inside the element of the fault context variable. You can access the value using the following XQuery statement:

$fault/ctx:errorCode/text()

AquaLogic Service Bus defines three generic error codes for the three classes of possible errors. The format of the generic codes is BEA-xxx000, where xxx represents a generic category as follows:

This yields the generic codes as follows:

AquaLogic Service Bus defines unique codes for specific errors. For example:

BEA-382030—Indicates a message parse error (for example, a SOAP proxy service received a non-SOAP message).

BEA-382500—Reserved for the case in which a Service Callout action receives a SOAP Fault response.

For information about these and other specific error codes, see Error Codes.

Related Topics

Error Messages and Handling

Initializing Context Variables

The message context and its variables are initialized in the binding layer when a message is received and before message processing begins. The following table summarizes how context variables are initialized.

Initializing the attachments Context Variable

The attachments context variable is initialized with any MIME attachments that accompany the message, but does not include the part representing the main message (whether it is SOAP, XML, MFL, and so on). Each <attachment> element is initialized using the MIME headers that accompany each part in the MIME package.

The contents of the <body> element in the <attachment> can be one of the following depending on the attachment's Content-Type:

Initializing the header and body Context Variables

This section describes how the initialization of header and body context variables is performed depending on the type of proxy service: SOAP Services, XML Services (Non SOAP), Messaging Services.

SOAP Services

Messages to SOAP-based services are SOAP messages containing XML that is contained in a <soap:Envelope> element. In the case that messages include attachments, the content of the inbound message is a MIME package that includes the SOAP envelope as one of the parts—typically the first part or one identified by the top-level Content-Type header. The context variables are initialized as follows:

XML Services (Non SOAP)

The messages to XML-based services are XML, but can be of any type allowed by the proxy service configuration. In the case that messages include attachments, the content of the inbound messages is a MIME package that includes the primary XML payload as one of the parts—typically the first part or one identified by the top-level Content-Type header.

The context variables are initialized as follows:

Messaging Services

Messaging services are those that can receive messages of one data type and respond with messages of a different data type. The supported data types include XML, MFL, text, untyped binary. The context variables are initialized as follows:

Performing Operations on Context Variables

You interact with and manipulate the message context through actions in the pipelines, branch, or route nodes that define a proxy service. Most actions expose the XQuery language to do so. Each context variable is represented as an XQuery variable of the same name. For example, the header variable is accessible in XQuery as $header, the body variable is accessible as $body, and so on. The examples in this section show the use of XQuery to examine and manipulate context variables.

$body

The $body variable includes the <soap-env:Body>...</soap-env:Body> element.

For example, if you assign data to the body context variable using the Assign action, you must wrap it with the <soap-env:Body> element. In other words, you build the SOAP package by including the <soap-env:Body> element in the context variable.

There is an exception to this behavior in AquaLogic Service Bus—for the case in which you build the Request Document Variable for the Service Callout action. Service Callout actions work with the core payload (RPC parameters, documents, and so on) and AquaLogic Service Bus builds the SOAP package around the core payload. In other words, when you configure the Request Document Variable for a Service Callout action, you do not wrap the input document with <soap-env:Body>...</soap-env:Body>.

For information about configuring the Service Callout action, see Service Callout.

$header

The $header variable includes the <soap-env:Header>...</soap-env:Header> element.

For example if you assign data to the header context variable using the Assign action, you must wrap it with the <soap-env:Header> element. In other words, you build the SOAP package by including the <soap-env:Header> element in the context variable. This is true for all manipulations of $header, including the case in which you can set one or more SOAP Headers for a Service Callout request. For information about configuring SOAP Headers for a Service Callout action, see Service Callout.

Extract the WS-Addressing Header—From

Extract the Payload From a Non-SOAP Message

Extract the user-header From an Outbound Response Message

When creating a body input variable that is used for the request parameter in a Service Callout to a SOAP Service, you would define that variable's contents using body/* (to remove the wrapper soap-env:Body), not $body (which results in keeping the soap-env:Body wrapper).

Assign Variable Contents for Request Parameter in a Service Callout

Related Topics

For more information about handling context variables using the XQuery and XPath editors in the AquaLogic Service Bus Console, see the following topics:

"Variables Structures" in Modeling Message Flow in AquaLogic Service Bus in the AquaLogic Service Bus User Guide.

Using the XQuery Condition Editor

Using the Inline XQuery Expression Editor

Using the XPath Expression Editor

Constructing Messages to Dispatch

When AquaLogic Service Bus publishes or routes a message, the content of the message is constructed using the values of variables in the Message Context. For example, transport headers and other transport-specific metadata are taken from $outbound/transport/request. As is the case with initialization of the context, the message content for outbound messages is handled differently depending upon the type of the target service. How the outbound message content is created depends on the type of the target service, as described in the following topics:

SOAP Services

An outgoing SOAP message is constructed by wrapping the contents of the header and body variables inside a <soap:Envelope> element. If the body variable contains a piece of reference XML, it is sent as is—in other words, the referenced content is not substituted into the message.

If attachments are defined in the attachments variable, a MIME package is created from the main message and the attachment data. The handling of the content for each attachment part is similar to how content is handled for messaging services.

XML Services (Non SOAP)

The messages to XML-based services from AquaLogic Service Bus is constructed from the contents of the body variable:

Regardless of any data it contains, the header variable does not contribute any content to the outbound message.

For examples of how messages are constructed for Service Callout Actions, see Service Callout.

Messaging Services

The messages to messaging services from AquaLogic Service Bus are constructed from the contents of the body variable.

Regardless of any data it contains, the header variable does not contribute any content to the outbound message.

For examples of how messages are constructed for Service Callout Actions, see Service Callout.

About Sending Binary Content in Email Messages

For binary messages, AquaLogic Service Bus does not insert the message content into the body variable. Instead, a <binary-content/> reference element is created and inserted into the <SOAP:Body> element (see Message-Related Variables). However, the email standard does not support sending binary content type as the main part of a message. If you want to send binary messages via email to a messaging service that accepts text or XML documents and optional attachments, you can do so as follows:

For the case in which the outgoing message type is MFL, the contents of $body is converted from XML to text or binary based on the MFL transformation:

To learn more about how binary content is handled, see Binary Content in the body and attachments Variables.

Related Topics

Service Callout

Transport Headers

Message Context Schema

Adding a Route Node

Message Context Schema

The message context schema (MessageContext.xsd) that specifies the types for the message context variables is shown in Message Context.xsd.

When working with the message context variables, you need to reference MessageContext.xsd and the transport-specific schemas, which are available in a JAR file at the following location in your AquaLogic Service Bus installation:

BEA_HOME\weblogic92\servicebus\lib\sb-schemas.jar

where BEA_HOME represents the directory in which you installed AquaLogic Service Bus. sb-schemas.jar includes the following context-related schemas:

Message Context.xsd

//depot/dev/src/wli/public/sb/schemas/MessageContext.xsd last updates @v9 6/11/05

<schema targetNamespace="http://www.bea.com/wli/sb/context"
        xmlns:mc="http://www.bea.com/wli/sb/context"
        xmlns="http://www.w3.org/2001/XMLSchema"
        elementFormDefault="qualified"
        attributeFormDefault="unqualified">
    <!--============================================================== -->

    <!-- The context variable 'fault' is an instance of this element -->
    <element name="fault" type="mc:FaultType"/>

    <!-- The context variables 'inbound' and 'outbound' are instances of this element -->
    <element name="endpoint" type="mc:EndpointType"/>

    <!-- The three sub-elements within the 'inbound' and 'outbound' variables -->
    <element name="service" type="mc:ServiceType"/>
    <element name="transport" type="mc:TransportType"/>
    <element name="security" type="mc:SecurityType"/>

    <!-- The context variable 'attachments' is an instance of this element -->
    <element name="attachments" type="mc:AttachmentsType"/>

    <!-- Each attachment in the 'attachments' variable is represented by an instance of this element -->
    <element name="attachment" type="mc:AttachmentType"/>

    <!-- Element used to represent binary payloads and pass-by reference content -->
    <element name="binary-content" type="mc:BinaryContentType"/>

    <!-- =================================================================== -->

    <!-- The schema type for  -->
    <complexType name="AttachmentsType">
        <sequence>
            <!-- the 'attachments' variable is just a series of attachment elements -->
            <element ref="mc:attachment" minOccurs="0" maxOccurs="unbounded"/>
        </sequence>
    </complexType>
    
    <complexType name="AttachmentType">
        <all>
            <!-- Set of MIME headers associated with attachment -->
            <element name="Content-ID" type="string" minOccurs="0"/>
            <element name="Content-Type" type="string" minOccurs="0"/>
            <element name="Content-Transfer-Encoding" type="string" minOccurs="0"/>
            <element name="Content-Description" type="string" minOccurs="0"/>
            <element name="Content-Location" type="string" minOccurs="0"/>
            <element name="Content-Disposition" type="string" minOccurs="0"/>

            <!-- Contains the attachment content itself, either in-lined or as <binary-content/> -->
            <element name="body" type="anyType"/>
        </all>
    </complexType>

    <complexType name="BinaryContentType">
        <!-- URI reference to the binary or pass-by-reference payload -->
        <attribute name="ref" type="anyURI" use="required"/>
    </complexType>

    <!-- =================================================================== -->

    <complexType name="EndpointType">
        <all>
            <!-- Sub-elements holding service, transport, and security details for the endpoint -->
            <element ref="mc:service" minOccurs="0" />
            <element ref="mc:transport" minOccurs="0" />
            <element ref="mc:security" minOccurs="0" />
        </all>

        <!-- Fully-qualified name of the service represented by this endpoint -->
        <attribute name="name" type="string" use="required"/>
    </complexType>

    <!-- =================================================================== -->

    <complexType name="ServiceType">
        <all>
            <!-- name of service provider -->
            <element name="providerName" type="string" minOccurs="0"/>

            <!-- the service operation being invoked -->
            <element name="operation" type="string" minOccurs="0"/>
        </all>
    </complexType>

    <!-- =================================================================== -->

    <complexType name="TransportType">
        <all>
            <!-- URI of endpoint -->
            <element name="uri" type="anyURI" minOccurs="0" />

            <!-- Transport-specific metadata for request and response (includes transport headers) -->
            <element name="request" type="anyType" minOccurs="0"/>
            <element name="response" type="anyType" minOccurs="0" />

            <!-- Indicates one-way (request only) or bi-directional (request/response) communication -->
            <element name="mode" type="mc:ModeType" minOccurs="0" />

            <!-- Specifies the quality of service -->
            <element name="qualityOfService" type="mc:QoSType" minOccurs="0" />

            <!-- Retry values (outbound only) -->
            <element name="retryInterval" type="integer" minOccurs="0" />
            <element name="retryCount" type="integer" minOccurs="0" />
        </all>
    </complexType>

    <simpleType name="ModeType">
        <restriction base="string">
            <enumeration value="request"/>
            <enumeration value="request-response"/>
        </restriction>
    </simpleType>

    <simpleType name="QoSType">
        <restriction base="string">
            <enumeration value="best-effort"/>
            <enumeration value="exactly-once"/>
        </restriction>
    </simpleType>

    <!-- =================================================================== -->

    <complexType name="SecurityType">
        <all>
            <!-- Transport-level client information (inbound only) -->
            <element name="transportClient" type="mc:SubjectType" minOccurs="0"/>

            <!-- Message-level client information (inbound only) -->
            <element name="messageLevelClient" type="mc:SubjectType" minOccurs="0"/>
            
            <!-- Boolean flag used to disable outbound WSS processing (outbound only) -->
            <element name="doOutboundWss" type="boolean" minOccurs="0"/>
        </all>
    </complexType>

    <complexType name="SubjectType">
        <all>
            <!-- User name associated with this tranport- or message-level subject -->
            <element name="username" type="string"/>
        </all>
    </complexType>

    <!-- =================================================================== -->

    <complexType name="FaultType">
        <all>
            <!-- A short string identifying the error (e.g. BEA38229) -->
            <element name="errorCode" type="string"/>

            <!-- Descriptive text explaining the reason for the error -->
            <element name="reason" type="string" minOccurs="0" />

            <!-- Any additional details about the error  -->
            <element name="details" type="anyType" minOccurs="0" />

            <!-- Information about where the error occured in the proxy -->
            <element name="location" type="mc:LocationType" minOccurs="0" />
        </all>
    </complexType>

    <complexType name="LocationType">
        <all>
            <!-- Name of the Pipeline/Branch/Route node where error occured -->
            <element name="node" type="string" minOccurs="0" />

            <!-- Name of the Pipeline where error occured (if applicable) -->
            <element name="pipeline" type="string" minOccurs="0" />

            <!-- Name of the Stage where error occured (if applicable) -->
            <element name="stage" type="string" minOccurs="0" />

            <!-- Indicates if error occured from inside an error handler -->
            <element name="error-handler" type="boolean" minOccurs="0" />
        </all>
    </complexType>
    <!-- Encapsulates any stack-traces that may be added to a fault <details> -->
    <element name="stack-trace" type="string"/>
</schema>

Related Topics

Inbound and Outbound Variables

Performing Operations on Context Variables

Constructing Messages to Dispatch