Server handlers

The COM library enables to intercept high-level web services operation on server side. You can now define three 4GL functions via the following methods of the web service class. They will be executed at different steps of a web service request processing in order to modify the SOAP request, response or the generated WSDL document before or after the SOAP engine has processed it. This helps handle WS-* specifications not supported in the web service API.

Method registerWSDLHandler()
Method registerInputRequestHandler()
Method registerOutputRequestHandler()

All three kinds of 4GL callback functions must conform to this prototype:

FUNCTION CallbackHandler( doc xml.DomDocument )
   RETURNING xml.DomDocument

Example 1: Modify the generation of a WSDL

CALL serv.registerWsdlHandler("WSDLHandler")

where serv is of class com.WebService and WSDLHandler is the following function:

FUNCTION WSDLHandler(wsdl)
  DEFINE wsdl Xml.DomDocument
  DEFINE node Xml.DomNode
  DEFINE list Xml.DomNodeList
  DEFINE ind  INTEGER
  DEFINE name STRING
  # Add a comment
  LET node = wsdl.createComment(
              "First modified WSDL via a 4GL callback function")
  CALL wsdl.prependDocumentNode(node)
  # Rename input and output parameter in UPPERCASE
  LET list = wsdl.selectByXPath(
              "//wsdl:definitions/wsdl:types/xsd:schema/
xsd:complexType/xsd:sequence/xsd:element/xsd:complexType/
xsd:sequence/xsd:element",NULL) 
-- first input parameter for selectByXPath above
-- one string, no spaces!
  FOR ind=1 TO list.getCount()
    LET node = list.getItem(ind)
    LET name = node.getAttribute("name")
    LET name = name.toUpperCase()
    CALL node.setAttribute("name",name)
  END FOR
  RETURN wsdl
END FUNCTION

If NULL is returned from the callback function, an HTTP error will be sent and the ProcessServices() returns error code -20.

Example 2: Change the SOAP incoming request

CALL serv.registerInputRequestHandler("InputRequestHandler")

where serv is of class com.WebService and InputRequestHandler is this function:

FUNCTION InputRequestHandler(in)
  DEFINE in Xml.DomDocument
  DEFINE ind  INTEGER
  DEFINE node Xml.DomNode
  DEFINE copy Xml.DomNode
  DEFINE tmp  Xml.DomNode
  DEFINE parent Xml.DomNode
  DEFINE name STRING
  DEFINE list Xml.DomNodeList
  # Change input parameter below myrecord in lower case 
  # to follow high-level web service
  LET list = in.SelectByXPath(
    "//SOAP:Envelope/SOAP:Body/fjs:EchoDOCRecordRequest/fjs:myrecord/*",
    "SOAP","http://schemas.xmlsoap.org/soap/envelope/",
    "fjs","http://www.mycompany.com/webservices")
  FOR ind = 1 TO list.getCount()
    LET node = list.getItem(ind)
    LET parent = node.getParentNode()
    LET name = node.getLocalName()
    LET copy = in.createElementNS(node.getPrefix(),
      name.toLowerCase(),node.getNamespaceURI())
    LET tmp = node.getFirstChild()
    LET tmp = tmp.clone(true)
    CALL copy.appendChild(tmp)
    CALL parent.replaceChild(copy,node)
  END FOR
  RETURN in
END FUNCTION

If NULL is return from the callback function, a SOAP fault will be sent (but can be changed from the output handler) and the ProcessServices() returns error code -18.

Example 3: Modify the SOAP outgoing request

CALL serv.registerOutputRequestHandler("OutputRequestHandler")

where serv is of class com.WebService and OutputRequestHandler is this function:

FUNCTION OutputRequestHandler(out)
  DEFINE out Xml.DomDocument
  DEFINE ind  INTEGER
  DEFINE node Xml.DomNode
  DEFINE copy Xml.DomNode
  DEFINE tmp  Xml.DomNode
  DEFINE parent Xml.DomNode
  DEFINE name STRING
  DEFINE list Xml.DomNodeList
  # Change output parameter below myrecord in uppercase 
  # before sending back to the client
  LET list = out.SelectByXPath(
    "//SOAP:Envelope/SOAP:Body/fjs:EchoDOCRecordResponse/fjs:myrecord/*",
    "SOAP","http://schemas.xmlsoap.org/soap/envelope/",
    "fjs","http://www.mycompany.com/webservices")
  FOR ind = 1 TO list.getCount()
    LET node = list.getItem(ind)
    LET parent = node.getParentNode()
    LET name = node.getLocalName()
    LET copy = out.createElementNS(node.getPrefix(),name.toUpperCase(),
      node.getNamespaceURI())
    LET tmp = node.getFirstChild()
    LET tmp = tmp.clone(true)
    CALL copy.appendChild(tmp)
    CALL parent.replaceChild(copy,node)
  END FOR
  RETURN out
END FUNCTION

If NULL is return from the callback function, a SOAP fault will be sent and the ProcessServices() returns error code -19.