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Raise Fault policy

What

Generates a custom message in response to an error condition. Use Raise Fault to define a fault response that is returned to the requesting app when a specific condition arises.

For general information on handling faults, see Fault handling

Where

This policy can be attached in the following locations.

ProxyEndpoint TargetEndpoint
    PreFlow Flow PostFlow PreFlow Flow PostFlow    
Request    
    Response
    PostFlow Flow PreFlow PostFlow Flow PreFlow    

Samples

In the most common usage, Raise Fault is used to return a custom fault response to the requesting app. For example to return a 404:

<RaiseFault name="404">
 <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
 <FaultResponse>
   <Set>
     <StatusCode>404</StatusCode>
     <ReasonPhrase>The resource requested was not found</ReasonPhrase>
   </Set>
 </FaultResponse>
</RaiseFault>

A more complex example involves returning a custom fault response payload, along with HTTP headers and an HTTP status code. In the following example the fault response is populated with an XML message containing the HTTP status code received by Edge from the backend service, and a header containing the type of fault that occurred:

<RaiseFault name="ExceptionHandler">
 <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
 <FaultResponse>
   <Set>
     <Payload contentType="text/xml">
       <root>Please contact support@company.com</root>
     </Payload>
     <StatusCode>{response.status.code}</StatusCode>
     <ReasonPhrase>Server error</ReasonPhrase>
   </Set>
   <Add>
     <Headers>
       <Header name="FaultHeader">{fault.name}</Header>
     <Headers>
   </Add>
 <FaultResponse>
<RaiseFault>

For a list of all variables that are available for dynamically populating FaultResponse messages, see Variables reference


About the Raise Fault policy

Apigee Edge enables you to perform custom exception handling using a policy of type Raise Fault. The Raise Fault policy, which is a variation of the Assign Message policy, lets you generate a custom fault response in response to an error condition. 

Use the Raise Fault policy to define a fault response that is returned to the requesting app when a specific error condition arises. The fault response can consist of HTTP headers, query parameters, and a message payload. A custom fault response can be more useful to app developers and app end users than generic error messages or HTTP response codes.

When executed, the Raise Fault policy transfers control from the current flow to the Error flow, which then returns the designated fault response to the requesting client app. When the message Flow switches to the Error flow, no further policy processing occurs. All remaining processing Steps are bypassed, and the fault response is returned directly to the requesting app.

See Fault handling for more.

Element reference

The element reference describes the elements and attributes of the Raise Fault policy.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<RaiseFault async="false" continueOnError="false" enabled="true" name="Raise-Fault-1">
    <DisplayName>Raise Fault 1</DisplayName>
    <FaultResponse>
        <Copy source="request">
            <Headers/>
            <StatusCode/>
            <ReasonPhrase/>
        </Copy>
        <Remove>
            <Headers/>
        </Remove>
        <Set>
            <Headers/>
            <Payload/>
            <ReasonPhrase/>
            <StatusCode/>
        </Set>
    </FaultResponse>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</RaiseFault>

<RaiseFault> attributes

<RaiseFault async="false" continueOnError="false" enabled="true" name="Raise-Fault-1">

The following attributes are common to all policy parent elements.

Attribute Description Default Presence
name

The internal name of the policy. Characters you can use in the name are restricted to: A-Z0-9._\-$ %. However, the Edge management UI enforces additional restrictions, such as automatically removing characters that are not alphanumeric.

Optionally, use the <DisplayName> element to label the policy in the management UI proxy editor with a different, natural-language name.

N/A Required
continueOnError

Set to false to return an error when a policy fails. This is expected behavior for most policies.

Set to true to have flow execution continue even after a policy fails.

false Optional
enabled

Set to true to enforce the policy.

Set to false to "turn off" the policy. The policy will not be enforced even if it remains attached to a flow.

true Optional
async

Note: This attribute does not make the policy execute asynchronously.

When set to true, policy execution is offloaded to a different thread, leaving the main thread free to handle additional requests. When the offline processing is complete, the main thread comes back and finishes handling the message flow. In some cases, setting async to true improves API proxy performance. However, overusing async can hurt performance with too much thread switching.

To use asynchronous behavior in API proxies, see JavaScript callouts.

false Optional

<DisplayName> element

Use in addition to the name attribute to label the policy in the management UI proxy editor with a different, natural-language name.

<DisplayName>Policy Display Name</DisplayName>
Default:

N/A

If you omit this element, the the value of the policy's name attribute is used.

Presence: Optional
Type: String

 

<IgnoreUnresolvedVariables> element

(Optional) Ignores any unresolved variable error in the Flow. Valid values: true/false. Default true.

<FaultResponse> element

(Optional) Defines the response message returned to the requesting client. FaultResponse uses the same settings as the AssignMessage policy type. See Assign Message policy.

<FaultResponse><Copy> element

Copies information from the message specified by the source attribute to the error message.

    <Copy source="request">
        <Headers/>
        <StatusCode/>
        <ReasonPhrase/>
    </Copy>

Default:

N/A

Presence:

Optional

Type:

String

Attributes

<Copy source="response">
Attribute Description Presence Type
source

Specifies the source object of the copy.

  • If source is not specified, it is treated as a simple message. For example, if the policy is in the request flow, then the source defaults to the request object. If the policy is in the response flow, it defaults to the response object. If you omit source, you can use an absolute reference to a flow variable as the source of the copy. For example, specify the value as {request.header.user-agent}.
  • If the source variable cannot be resolved, or resolves to a non-message type, <Copy> fails to respond.
Optional String

<FaultResponse><Copy>/<Headers> element

Copies the specified HTTP header from the source to the error message. To copy all headers, specify <Copy><Headers/></Copy>.

<Copy source='request'>
    <Headers>      
        <Header name="headerName"/>     
    </Headers> 
</Copy>

If there are multiple headers with the same name, use the following syntax:

<Copy source='request'>
    <Headers>
      <Header name="h1"/>
      <Header name="h2"/>
      <Header name="h3.2"/>
    </Headers>
</Copy>

This example copies "h1", "h2", and the second value of "h3". If "h3" has only one value, then it is not copied.

Default:

N/A

Presence:

Optional

Type:

String

<FaultResponse><Copy>/<StatusCode> element

If true, copies the StatusCode from the object specified by the source attribute to the error message.

<Copy source='response'>
    <StatusCode>true</StatusCode>      
</Copy>

Default:

false

Presence:

Optional

Type:

Boolean

<FaultResponse><Copy>/<ReasonPhrase> element

If true, copies the ReasonPhrase from the object specified by the source attribute to the error message. 

<Copy source='response'>     
    <ReasonPhrase>true</ReasonPhrase>     
</Copy>

Default:

false

Presence:

Optional

Type:

Boolean

<FaultResponse><Remove>/<Headers> element

Removes specified HTTP headers from the error message. To remove all the headers, specify <Remove><Headers/></Remove>. This example removes the user-agent header from the message.

<Remove>     
    <Headers>      
        <Header name="user-agent"/>     
    </Headers> 
</Remove>

If there are multiple headers with the same name, use the following syntax:

<Remove>
    <Headers>
      <Header name="h1"/>
      <Header name="h2"/>
      <Header name="h3.2"/>
    </Headers>
</Remove>

This example removes "h1", "h2", and the second value of "h3". If "h3" has only one value, then it is not removed.

Default:

N/A

Presence:

Optional

Type:

String

<FaultResponse><Add>/<Headers> element

Adds HTTP headers to the error message. Note that the empty header <Add><Headers/></Add> does not add any header. This example copies the value of the request.user.agent flow variable into the header.

<Add>     
    <Headers>      
        <Header name="user-agent">{request.user.agent}</Header>     
    </Headers> 
</Add>

Default:

N/A

Presence:

Optional

Type:

String

<FaultResponse><Set> element

Sets information in the error message.

    <Set>
        <Headers/>
        <Payload> </Payload>
        <StatusCode/>
        <ReasonPhrase/>
    </Set>

Default:

N/A

Presence:

Optional

Type:

N/A

<FaultResponse>/<Set>/<Headers> element

Sets or overwrites HTTP headers in the error message. Note that the empty header <Set><Headers/></Set> does not set any header. This example sets the user-agent header to the message variable specified with the <AssignTo> element.

<Set>     
    <Headers>      
        <Header name="user-agent">{request.header.user-agent}</Header>     
    </Headers> 
</Set>

Default:

N/A

Presence:

Optional

Type:

String

<FaultResponse>/<Set>/<Payload> element

Sets the payload of the error message.

<Set>     
    <Payload contentType="text/plain">test1234</Payload>      
</Set>

Set a JSON payload. Notice how this example escapes the leading "{" in the payload. Otherwise, Edge would interpret the leading "{" as the beginning of a variable reference:

<Set>
    <Payload contentType="application/json">
        \{"name":"foo", "type":"bar"}
    </Payload>
</Set>

Reference a variable in a JSON payload. You cannot use curly braces to reference variables in a JSON payload. Instead, you must declare and embed the variable delimiter characters, as follows:

<Set>
    <Payload contentType="application/json" variablePrefix="@" variableSuffix="#">
        {"name":"foo", "type":"@variable_name#"}
    </Payload>
</Set>

Set a mixed payload in XML:

<Set>
    <Payload contentType="text/xml">
        <root>
          <e1>sunday</e1>
          <e2>funday</e2>
          <e3>{var1}</e3>
    </Payload>
</Set>          

Default:

 

Presence:

Optional

Type:

String

Attributes

<Payload contentType="content_type" variablePrefix="char" variableSuffix="char">
Attribute Description Presence Type
contentType

If contentType is specified, its value is assigned to the contentType header.

Optional String
variablePrefix Optionally specifies the leading delimiter on a flow variable because JSON payloads cannot use the default "{" character. Optional Char
variableSuffix Optionally specifies the trailing delimiter on a flow variable because JSON payloads cannot use the default "}" character. Optional Char

<FaultResponse>/<Set>/<StatusCode> element

Sets the status code of the response.

<Set source='request'>     
    <StatusCode>true</StatusCode>      
</Set>

Default:

false

Presence:

Optional

Type:

Boolean

<FaultResponse>/<Set>/<ReasonPhrase> element

Sets the reason phrase of the response.

<Set source='request'>     
    <ReasonPhrase>true</ReasonPhrase>     
</Set>

Default:

false

Presence:

Optional

Type:

Boolean

Flow variables

Flow variables enable dynamic behavior of policies and Flows at runtime, based on HTTP headers, message content, or Flow context. The following predefined Flow variables are available after a Raise Fault policy executes. For more information about Flow variables, see Variables reference.

Variable Type Permission Description
fault.name String Read-Only Returns the fault name in the error and if not available, an empty string.
fault.type String Read-Only Returns the fault type in the error and if not available, an empty string.
fault.category String Read-Only Returns the fault category in the error and if not available, an empty string.

Error codes

This policy defines the following error codes. For guidance on handling errors, see Fault handling.

The default format for error codes returned by policies is:

{   "code" : " {ErrorCode} ",   
    "message" : " {Error message} ",   
    "contexts" : [ ] 
}

The Raise Fault policy type defines the following error codes:

Error Code Message
RaiseFault RaiseFaultException

Schema

Each policy type is defined by an XML schema (.xsd). For reference, policy schemas are available on GitHub.

Related topics

See Fault handling

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