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Access to the
message flow variable and its properties depends on the point within
the API Proxy Flow in which it is accessed. It is available in all contexts, whereas some objects,
response are not.
The principal use case for the
message flow variable is when your proxy enters the
error flow: the
response flow variables are out of scope.
For example, in the error flow, the
response object is not available. You will not
be able to set response headers on the
if you are in the error flow. Instead, you can use one of the following:
You can use the AssignMessage policy to assign values, such as headers, to the response object. Assign Message automatically handles the switch in context from request/response flow to error flow.
Another use case for the
message variable is to log response data in the
PostClientFlow with the MessageLogging policy. If you use the
you can seamlessly log response information following both success and error conditions in the
message. For example:
The following expression, however, will not work:
In this case, the
response variable is out of scope in the
error flow. (Note that, in a trace, this is visually indicated by variables shown with an equals
sign with a slash through it.)
To set response headers for both success and error flows in a single policy, you
<faultrules> <faultrule name="invalid_key_rule"> <step> <name>SetResponseHeaders</name> </step> <condition>(fault.name = "InvalidApiKey")</condition> </faultrule> </faultrules>
In the policy, code like the following sets the error/response header in any flow context:
context.setVariable('message.header.FOO-1', 'the header value');
You can reuse this same policy on the normal ProxyResponse flow and it will succeed because
message is available from all contexts.