APC: Abap push channel

The ABAP push channel (APC) is the ABAP implementation of websockets. It’s goal is to enable the ABAP stack to send push messages to registered web clients.

This blog will answer the following questions:

  • How to setup an ABAP push channel?
  • How to implement the ABAP push channel?
  • How to test the ABAP push channel?
  • Where to find more background and examples on ABAP push channel?

Setting up an ABAP push channel

To setup an ABAP push channel go to transaction SE80 and right click, select create / connectivity / ABAP push channel notification.

Now press the Generate Class and Service button. The classes and services will now be generated as placeholders. Save your work.

If you try to activate the service at this point in time you get this error message:

The reason is that we didn’t implement two methods of the new class yet: the ON_START and ON_MESSAGE.

Implementing the actual APC class

To do this, we go to SE24 and lookup the generated class and we select the ON_START method:

Press the redefine button to redefine the method.

Use this code in the method:

TRY.
* send the message on WebSocket connection
DATA(lo_message) = i_message_manager->create_message( ).        lo_message->set_text( |ON_START has been successfully executed !| ).
i_message_manager->send( lo_message ).
CATCH cx_apc_error INTO DATA(lx_apc_error).
MESSAGE lx_apc_error->get_text( ) TYPE 'E'.
ENDTRY.

This basically confirms the push channel registration.

Now redefine the ON_MESSAGE method:

TRY.
* create the message object
DATA(lo_message) = i_message_manager->create_message( ).
* send message
lo_message->set_text( |Hello World !| ).
i_message_manager->send( lo_message ).
CATCH cx_apc_error INTO DATA(lx_apc_error).
MESSAGE lx_apc_error->get_text( ) TYPE 'E'.
ENDTRY.

It simply pushes the message: ‘Hello World’.

Save and generate the class in SE24.

Now we can go back to the SE80 ABAP push channel we have created and activate it as well. You can run the consistency check to see all is fine:

Testing the ABAP push channel

Now you can test the ABAP push channel by hitting the test button in the SE80 screen of the ABAP push channel. The test service will launch an ABAP webdynpro screen.

If the ABAP webdynpro screen does not launch, activate in SCIF transaction the following 2 nodes: WDR_TEST_APC and WDR_TEST_APC_WSP.

Test result:

As an alternative to SE80 you can also use transaction SAPC:

Background information

Excellent blogs on ABAP push channels are:

SAP interfacing: REST

The SAP ABAP stack can also interface using REST protocol. To support this interface protocol SAP has developed special classes in the ABAP stack.

Questions that will be answered in this blog are:

  • How do I create a REST interface in ABAP stack?
  • How do I test a REST interface in ABAP stack?
  • Which tools to use to developer REST interface?

REST in ABAP

SAP delivers in the ABAP netweaver stack the ABAP REST library. The full specification can be found on the SAP help portal. The help portal also contains a small tutorial. Next to the pre-delivered REST library classes there are no tools for you available to faster develop REST in ABAP. It is coming down to SE24 and SE80.

Good reference blog is the SAP blog on usage of REST in Netweaver 7.4. This also explains the generic REST architecture implementation in ABAP.

Creating REST service in ABAP

We will create a simple Hello World REST service in ABAP. There are 2 main classes in REST ABAP: the application class handling the URL and the resource class where the logic is.

Start transaction SE24 and create a new class inheriting from the SAP delivered class CL_REST_HTTP_HANDLER:

REST create class

important here to press the inheritance button! Fill out CL_REST_HTTP_HANDLER as superclass:

REST create class as inheritance

It is mandatory to redefine the GET_ROOT_HANDLER method:

For now just leave the method empty. Save and generate.

Now create the REST resource class based on inheritance of CL_REST_RESOURCE:

REST define resource class

Now redefine the GET method:

REST resource class redefine GET method

No we add a simple implementation by simply adding the text ‘Hello World’:

REST resource class GET method implementation

Save and activate this class.

Now we go back to the previous class: the application class. In here we now edit the GET_ROOT_HANDLER implementation we left empty earlier:

REST implementation of root handler

If the URL is getting the input /hello then the handler class (our resource class) ZCL_HELLO_WORLD_RES_REST is called. This class will return the string.

Save and activate again. The coding work is done.

Runtime implementation

Now we need to make a runtime implementation. Goto transaction SICF and select the main node default_host first. Then select from the menu Service/Host the option Create Service:

REST SICF create service

Fill out the name of the service and click ok. In the next screen give a description and in the Handler List section refer to the application class ZCL_HELLO_WORLD_REST:

REST SICF handler

Save the service. The service is created but not active. To activate right click on the service and select Activate:

REST SICF activate service

Testing the service

From the previous SICF screen right click the service again and select the option Test Service. A screen will come that says “No suitable resource found”. Now modify the URL by adding /hello after the test in the URL, and press enter again:

REST SICF test service

The URL build up: the test is the name defined in SICF. The /hello was defined in the application class.

Authorizations and security

The REST library has no specifics about authorization and security. So you have to take care your self.

Business authorization security: has to be built in via AUTHORITY-CHECK statements at the correct spots.

Technical security is provided in the Logon Data tab on the SICF node. Here you can set requirements for the technical logon method and if you only allow https.

SAP interfacing: ODATA

In the previous blog we have setup RFC enabled function module. If you want to expose this function module as ODATA service you can use the wizard in transaction SEGW. This blog assumes the basis ODATA basis activation has been performed (see this blog).

Questions that will be answered in this blog are:

  • How do I generate an ODATA service based on a RFC function module?
  • How do I test if the ODATA service is properly working?

Set up of the ODATA service

Start transaction SEGW and create a new project:

Now start the RFC import wizard by right clicking on Data Model and selecting the option Import and then RFC/BOR interface:

Now select the data parameters:

And enter which field is key field:

After pressing finish the wizard will generate the needed classes.

Save your work and press the check button to validate if everything is ok:

Now we need to map the implementation to the RFC module. Right click on the GetEntitySet below ZODATADEMOENTITYSet and select Map to Data Source:

Now map the fields (you can use drag and drop):

Now you need to map the data fields correctly and press check.

Save your work.

Generation of objects

You can see that the Runtime Artifacts section is still empty.

Now press the button Generate Runtime Artifacts:

Wait for the generation to finish:

Now the runtime artifacts are generated, but the service maintenance is not done yet. Open the section Service maintenance and double click on the system:

Now press the Register Service button:

Accept settings and assign package for transport:

Now the registration status is green.

Testing the ODATA service

Press the button SAP Gateway Client (or start transaction /IWFND/GW_CLIENT directly, and then enter the correct service):

The test client starts:

Enter the correct inputdata: /sap/opu/odata/SAP/ZODATADEMO_SRV/ZODATADEMOENTITYSet(‘1’)

And check the output:

Attention points

The example above seems simple, but you will face more issues in real live implementation when you need to add tables and more complex structures. In those cases additional configuration and many times extra coding in the methods of the generated classes is required.

Nice blogs to start with:

ODATA security

The user calling the ODATA service needs a special right in SAP to be allowed to call the ODATA service.

Start transaction PFCG and create a new role. On the menu tab select the option Authorization Default. Then select type Tadir and object type IWSV gateway business suite enablement. Now you can finally search for our own developed and activated ODATA service:

Now save the role and assign it to the user(s) needing to call this ODATA service.

The application security relies on the function security authorization check inside the RFC function module.

SAP interfacing: exposing web services

In the previous blog we have created a test RFC module. We now will expose this test RFC module as web service. This blog assumes the basic SOAP web service runtime has been done according to the manual in this blog.

Questions that will be answered are:

  • How can I generate a web service design time based on an RFC module?
  • How do I activate the web service runtime via SOAMANAGER?
  • How do I test my web service?

Creating the web service based on RFC module

Goto transaction SE80 and search for the test BAPI:

Now right click on the name ZBAPIDEMO function module and select the option Create / Enterprise Service:

Fill out the name for the service definition and the description. Press Cont. to continue to the next screen:

Press Cont to go to the next step:

Press Cont. to go to the next screen:

Fill out your package and transport request.

Important here: on a sandbox you might want to use a local object ($TMP). In a development system, NEVER use the local option. A lot of data structures and coding will be generated. If you later try to move the objects from $TMP to a real package, you will be faced with a lot of issues. See note  886682 - Proxy inconsistencies on the use of repair programs SXIVERI_PROXY_HASHID_CHECK and  SXIVERI_PROXY_HASHID_CHECK_70. After the cumbersome and painfull repair you will not make the mistake again... 

Press Cont. to goto the last screen:

On the screen you can already see the next action after completion: SOAMANAGER. But first press Complete to start the generation of the objects.

After the generation, do not forget to Activate the objects!

Activation success message:

Setting up the runtime with SOAMANAGER

To setup the runtime, start transaction SOAMANAGER. It is assumed that the basis team has performed the initial SOAP runtime setup. If not done, ask the basis team to follow the steps in this blog.

On the SOAMANAGER start screen choose the option Web Service Configuration:

In the next screen search for the design time object we created and activated in the previous section (if you forgot the activate, you will not find it now…):

Select the service and on the next screen press the button Create Service:

Fill out the definition details:

Press Next and define the security settings:

Remark: in the newer versions, the default security is set to high. If you need lower security, go back to SE80 definition in the tab configuration to change the security profile (save and regenerate!):

Press next and define the SOAP protocol settings:

On the last screen of the wizard press finish:

Wait for the runtime generation to finish.

The screen returns to the generated runtime artefacts:

The most important artefact is WSDL file which you can open from here.

Testing the service

Goto transaction SE80 and select the Enterprise Services Browser (if not visible goto menu path Utilities/Settings and add the tool):

Now open your service by clicking the Open Object button and search for the service in the second tab:

Check that the WSDL file is properly showing:

If ok, press the test button (F8) to start the test tool:

On the next screen first press the XML editor button to allow the content to be changed:

Now press execute to test. The result:

Web service security

The functionality security of the web service is the same as for the generic RFC handling (see blog on this).

The technical security of web services is mainly driven from the security settings in SOAMANAGER. There you can set the transport protocol security and you can indicate if you want simple user ID / password security or work with additional certificates for server to server authentication.

The user calling the SAP web service must have the authorization object S_SERVICE. In S_SERVICE you can define the specific web service it needs to be able to call.

Troubleshooting web services security issues

For troubleshooting web services note 2321968 – SOAP Web Service Security Troubleshooting refers to a very extensive SAP site for web service security issues troubleshooting.

Monitoring web services

For monitoring web services, read this dedicated blog.

SAP interfacing: RFC

SAP has many different ways to interface. The RFC (Remote Function Call) protocol is one of the most wide used.

This blog will explain best practices around secure and correct setup of custom built ABAP RFC function modules.

Questions that will be answered are:

  • How to setup RFC enabled function module?
  • How to setup proper RFC error handling?
  • How to setup security in RFC enabled function module?
  • How strict is the S_RFC authorization handling?
  • Why is SAP_ALL not sufficient for RFC handling?

Creation of test RFC enabled function module

In SE37 you can setup an RFC enabled function module just like a normal function module. First create a function group. Activate that function group in SE80. Now you can create the function module. We will call our test module ZBAPIDEMO:

Important here in the first tab is to set the processing type to Remote-Enabled Module.

For testing we setup import and export tabs:

Important here with RFC: set the Pass by value tickbox.

For tables use a suitable table type:

And setup the correct exceptions:

Here you can see 2 very important error messages that should always be implemented:

  1. An extra authorization check
  2. An error message when no data is found

Now we can implement the following simple source code:

   DATA: zls_coms_gen_textline TYPE coms_gen_textline.
 
   AUTHORITY-CHECK OBJECT 'S_CDMC'
   ID 'CDMC_AREA' FIELD 'A'
   ID 'CDMC_ROLE' FIELD 'U'.
   IF sy-subrc EQ 0.
 
     CASE zimport.
       WHEN 1.
         zexport = 'Hello world'.
       WHEN 2.
         zls_coms_gen_textline-entry = 'Hello world table 1'.
         APPEND zls_coms_gen_textline TO ztable.
         zls_coms_gen_textline-entry = 'Hello world table 2'.
         APPEND zls_coms_gen_textline TO ztable.
       WHEN OTHERS.
         RAISE not_found.
     ENDCASE.
 
   ELSE.
     RAISE not_authorized_business.
   ENDIF. 

What is important here in this source code:

  1. The authorization check is implemented and raises an error
  2. If no data is found the NOT_FOUND error is raised

With the SE37 test suite you can test diverse scenario’s now.

Calling RFC function module from another ABAP system

If you call this RFC function module form another ABAP sytem you have to make sure you have set and check the following exceptions:

  exceptions
      not_authorized_business = 1
      not_authorized          = 2
      system_failure          = 3
      communication_failure   = 4
      not_found               = 5
      OTHERS                  = 6.

There are 2 exceptions from the BAPI definition:

  1. NOT_FOUND (nothing found)
  2. NOT_AUTHORIZED_BUSINESS (our own implemented business authorization check)

4 exceptions should be implemented as part of the RFC framework:

  1. NOT_AUTHORIZED: this is the RFC authorization, which will be explained next chapter
  2. SYSTEM_FAILURE: the coding has caused a dump and the system returns and error message (see OSS note 2484377 – Error Message: “RFC Exception SYSTEM_FAILURE Raised; No More Memory Available to Extend an Internal Tab” Upon Executing a Data Extraction Run as an example)
  3. COMMUNICATION_FAILURE: the call to the other system fails. Most likely if you go to SM59 to the RFC destination and perform a connection test you will get a failure.
  4. OTHERS: something else went wrong

The developer should take proper care of these error situations.

Dear ABAP developers: the basis team member are also humans. They will make RFC configuration errors, they rely on the authorization team to assign the correct roles and they rely on infrastructure providers to make sure systems are up and running. Also the basis team will need to perform patching and upgrades to the system, which you as ABAP developer, are calling. So please don't blame the basis team for these exceptions, but please be a good developer and implement proper error handling. If you didn't implement proper error handling, and something went wrong on basis side, that caused your code to go wrong, think twice before putting blame on basis if your code is not handling the situation properly.

For reference: OSS note 1371131 – Correct error handling of RFC calls.

Security of RFC calls

Security of RFC calls is consisting of 2 layers:

  1. The RFC layer
  2. The business application code

You should always implement both layers!

The RFC layer is protected by authorization object S_RFC:

Here you can choose between a function group or even allowing per function module. Personally I would protect by function module. Background: create, change and display BAPI’s will normally be developed inside same function group.

There is a common misunderstanding that if you give SAP_ALL to a (background) user, this would solve the RFC authorization issues. This is not true. SAP_ALL does not contain the S_RFC rights. You have to hand them out separately.

Best practice 1: you might want to start with broad authorizations at the beginning of a development to rule out authorization issues. But you must definitely limit the rights before you make the development go productively live.

Best practice 2: as first statement inside each and every RFC function module, program a relevant business authorization check statement. This is an extra safety measure that is needed to protect important business data from authorization consultants that have handed out * authorizations in object S_RFC (* means all).

More on checking the basis RFC security: read this blog.

Generic S_RFC check handling at basis level

The behavior of the S_RFC check is driven by the settings of RZ11 profile parameter auth/rfc_authorithy_check. Please make sure it has a setting of 6 or higher. Best is 9. A system with 5 or lower can be considered as insecure!

Background OSS note: 2216306 – S_RFC check and profile parameter auth/rfc_authority_check.