[Apiman-user] Is it possible blocking request after request body parsing?

[Eric Wittmann]

Yes there is a feature where apiman will parse the request BEFORE applying
the policies.  This will make the HTTP request body available to all
policies in the chain, should they need them.

You can enable this on a per-API basis in the apiman UI.

When this feature is enabled, your custom policy can access the request
body as an object found in the IPolicyContext object.  For example:

Object payload = context.getAttribute("apiman.request-payload");

The type of thing that you get depends on the API's endpoint type.  The
endpoint type might be JSON, XML, or SOAP.  I think it might be possible to
have some other kind of endpoint type, but those three are handled by the
request body parser feature.

Here is what you'll get as that payload object, depending on endpoint type:

JSON - Java Map object as a result of parsing the JSON data using Jackson
XML - org.w3c.dom.Document
Soap - javax.xml.soap.SOAPEnvelope
Anything Else - byte[]

So for example, if your endpoint type is XML, then you could do this in
your policy implementation (in the doApply() method):

org.w3c.dom.Document requestBody = (org.w3c.dom.Document) context.get
tAttribute("apiman.request-payload");

And then you could make some decision using the request data and e.g. call
doFailure().

Also note - you can *change* the request body at this point as well.  For
example you could apply a XML Transformation to the w3c Document, resulting
in a new w3c Document object, which you could store in the Policy Context
(at the same key, obviously).  That new document would then get serialized
and sent as the request body to the backing API impl.  There may be some
Content-Length issues if you do that, I can't remember...

-Eric


On Wed, Apr 25, 2018 at 1:29 AM, 林 柏廷 <btlin1025 at hotmail.com> wrote:

> Hi all,
> I would like to customize a policy, which parses the request body and
> blocks the request in case.
> in http://www.apiman.io/latest/developer-guide.html 4.2.1.2 IData policy,
> it describes:
> The request or response body will not begin streaming before the
> corresponding doApply has been called, however, it is still possible to
> interrupt the conversation during the streaming phase by signalling
> doFailure or doError.
> When I trace the transformation-policy source code, doApply() executes
> before getRequestDataHandler() which matches the description.
> In doApply() I can blocks the request via chain.doFailure() however I have
> no idea how to interrupt/block request in getRequestDataHandler().
> Besides, I found following mail group which is similar to my question.
> Eric also points it's possible to parse the body before apply in request:
>
> *On Thu, Feb 2, 2017 at 10:31 PM, Eric Wittmann <*
> *eric.wittmann at redhat.com <http://redhat.com>> wrote:*
>
> * The bottom line here is that you cannot return a Policy Failure (or*
> * customize it) based on information in the response body.  The response
> is*
> * streamed from the back-end to the client, and at the time streaming
> begins,*
> * the response code and HTTP headers have already been sent.*
>
> * It sounds to me like you're asking for a feature where you can parse*
> * the response body *before* the policy's "apply" method is invoked.  we
> have*
> * such a feature for requests, but not for responses.  I suspect core
> changes*
> * to apiman would be required to enable that.  It seems like a reasonable*
> * request to me, as long as users of the feature understand the
> performance*
> * and memory requirements of enabling it.*
>
> * -Eric*
>
> Thanks for any comments in advance.
> Kind Regards
> BT
>
>
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