Event Handlers

Event Handlers
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You can do more processing and customization using event handlers. Request and response event handlers are JavaScript entry points to perform user-defined actions.
API Server calls the following types of event handlers for every request:
  • Requests.
     API Server invokes these event handlers 
    after
    it receives the request but
    before
    it processes request/row mapping and reactive logic. 
  • Responses.
     API Server invokes these event handlers 
    before
    it sends the (successful) final result to the client.
  • HTTP Options.
     API Server recognizes Cross-Origin Resource Sharing (CORS) OPTIONS requests and invokes these event handler only for these requests.
In this article:
3
Create an Event Handler
There is no limit to the number of event handlers you can create.
  1. With your API open, in the Manage section, click
    Request Events
    .
  2. If your API does not have existing request and response event handlers, the Welcome to Request and Response Events page appears. If your API has existing request and response event handlers, they are listed on the Events page.
  3. Complete one of the following:
    1. If you have not defined any request and response event handlers, on the Welcome to Request and Response Events page, click 
      Create Event
      .
    2. If you have at least one request and response event handler defined, click 
      Add
      .
  4. Complete the following fields on the page, and then save your changes:
    Event type
    The type of event handler.
    Options:
     Request, Response, HTTP Options
    Default:
     Request
     
    You can create only one HTTP Options event handler per API.
     
    Event Handler name
    The name for your event handler. 
    CA Live API Creator
     invokes request and response event handlers in alphabetical order based on their name.
     
    You can have
    CA Live API Creator
    invoke the event handler in a specific order by appending the event handler name with a number sequence.
     
    Code
    The operations for this event handler. For example:
    if (“SalesResports” == req.resourceName) {
      //log.debug(‘***SalesReports Req Event - json: ' + json);
      var data = JSON.parse(json); // json from the request
      var theOrder = data[0];
      var keptItemNum = 0;
      var keptItems = [];
      log.debug(“theOrder: " + JSON.stringify(theOrder));
      for ( var i = 0; i < theOrder.Order_DetailsList.length; i ++) {
          var eachItem = theOrder.Order_DetailsList(i);
          delete eachItem[“@metadata”];
          if (eachItem.SupplierName == “Pavlova, Ltd.”) {
             delete eachItem.OrderID;
             delete eachItem.ProductID;
    ...
    Active
    Select to indicate that this event handler is active.
The event handler is created.
How API Server Invokes Event Handlers
The following section describes how API Server invokes each event handler.
Request Event Handlers
API Server invokes request event handlers using the following process:
  1. API Server performs initial authentication.
  2. API Server invokes the request event handler for every transaction, with the following variables pre-defined:
    Variable Name
    Description
    json
    The raw JSON string that the client sends, if any. Set only for POST and PUT requests. You can modify this string.
    req
    The 
    req
    object. For more information about this object, see The req Object.
    log
    The logger for the current request.
    headers
    The headers sent as part of the HTTP request. Excludes authorization headers.
  3. API Server establishes a connection to the database.
  4. API Server parses the JSON payload.
For more information about how API Server processes update requests, including how rules integrate with request event handlers, see Logic Execution.
Request Event Handler Examples
In the following example, API Server rejects all requests on
SecretData
if the request does not use HTTPS:
// Reject all requests on SecretData if they do not use HTTPS
if ("SecretData" == req.resourceName && !req.clientUsesHttps) {
  log.error('SecretData was accessed over HTTP by ' + req.clientAddress);
  throw "Use HTTPS to access this resource";
}
In the following example, API Server deletes all data from requests except the data included in the JSON payload:
// Remove extraneous data that the client sends but that is not needed.
if ( ! json) {
  // Only requests with a JSON payload are needed.
  return;
}
var data = JSON.parse(json);
if (Array.isArray(data)) {
  for (var i = 0; i < data.length; i++) {
    delete data[i].uselessData;
  }
}
else {
  delete data.uselessData;
}
// Important: Serialize the data back to a string if you want to change it
json = JSON.stringify(data);
Response Event Handlers
API Server invokes response event handlers with the following variables pre-defined:
Variable name
Description
json
The complete response object, which is sent back to the client after the response event handlers (if any) have been executed. You can (carefully) change or replace this object.
The
json
object is different from request event handlers. This variable is not a string, but rather an object or an array of objects. For a GET, this variable is a single object or an array of objects depending on the details of the request. For PUT/POST/DELETE, this variable is a single object with
statusCode
,
txsummary
,
rulesummary
elements. This variable can also be an error result. The
JSON.stringify()
method must be able to stringify the JSON object.
req
The
req
object.
For more information about this object, see The req Object.
response
The
response
object.
log
The logger for the request.
SysUtility
The
SysUtility
object.
For more information about this object, see The SysUtility Object.
Response Event Handler Examples
The Sample database illustrates preparing a partner-specific response by materializing a resource and returning it as the response message. Resource object/attribute aliases are defined to match partner expectations:
// Remove all @metadata sections from the response for a specific table/resource
// Note: This would make it difficult for the client to update the data, but this is only an example.
// This only deals with top-level resources. To remove all
// @metadata sections from a complex resource, use recursion.
// An attribute 'TheVerb' is added to each array object or the single object
// with the name of request verb - GET, PUT, POST, PATCH, DELETE
// get the name used for metadata (configurable by project).
// You CAN convert from the Java string value to a JavaScript string object here
   var metadataName = "@metadata";
   if (Array.isArray(json)) {
      // If the response is an array of objects
   for (var i = 0; i < json.length; i++) {
     delete json[i][metadataName];
     json[i].txsummary && delete json[i].txsummary[0][metadataName];
     // You MUST convert to native JavaScript string
     json[i].TheVerb = req.verb;
   }
  }
  else {
   // The response is a single object
   delete json[metadataName];
   json.txsummary && delete json.txsummary[0][metadataName];
   json.TheVerb = req.verb;
 }
 For more information:
The following code snippet adds the top 30 (by
amount_total
)
purchaseorders
where the employee is the sales rep by augmenting each employee in a GET of multiple employees:
// for a GET to an employee, add any PURCHASEORDERS where the employee is a sales rep
     if ("GET" == req.verb && "demo:employee" == req.resourceName) {
        var ordersAsSalesRep = [];
        for (var i = 0; i < json.length; i++ ) {
       // want purchase orders for this employee as sales rep
       // top thirty purchase orders by amount_total
       var detail = {
         filter: '"salesrep_id" = ' + json[i].employee_id ,
         order: '"amount_total" desc',
         pagesize: 10,
         offset: 0
       };
     if(json[i].employee_id) {
       ordersAsSalesRep = SysUtility.getResource("PurchaseOrders", detail);
       json[i].ordersAsSalesRep = ordersAsSalesRep;
     }
   }
  }
The following code snippet includes the results of a resource GET by amending the transaction summary:
// for a PUT (perhaps to update the name) of one or more employees
// add the picture into the result
    if ("PUT" == req.verb && "demo:employee" == req.resourceName) {
      var txsummary = json.txsummary;
      for (var i = 0, len = txsummary.length; i < len; i += 1) {
        var meta = txsummary[i]["@metadata"];
        if ("UPDATE" == meta.verb && "demo:employee" == meta.resource) {
          var detail = { filter: '"employee_id" = ' + txsummary[i].employee_id };
          var picInfo = SysUtility.getResource("the_employee_picture", detail);
          if (picInfo && picInfo.length > 0) {
            txsummary[i].the_picture = picInfo[0].picture;
          }
        }
      }
    }
 You can combine these examples and delete the usual transaction summary, redirecting it to be the 
getResource()
 method result. 
For more information about transaction summaries, see Transaction Summary.
HTTP Options Event Handlers
Protect your data from unauthorized access by creating an HTTP Options event handler for your API. You can get complete control over the response to CORS OPTIONS preflight requests with HTTP Options event handler.
For more information:
HTTP Options Event Handler Example
The following code snippet shows an example of an HTTP Options event handler:
return {
  "Access-Control-Allow-Methods" : "GET,PUT,POST,DELETE",
  "Access-Control-Allow-Origin" : "https://internal.acme.com,https://safe.acme.com",
  "Access-Control-Allow-Headers" : "authorization,content-type,accept,x-requested-with,X-CALiveAPICreator-ResponseFormat",
  "Access-Control-Max-Age" : 2400 ,
  "HTTPStatusCode" : 200
};
This code instructs the client web browser that this API expects calls only from the specified URLs. API Creator invokes the handler only if the request includes an 
Access-Control-Request-Method
 header or an 
Access-Control-Request-Headers
 header.
Advanced Usage
To view an advanced example of using event handlers, see Integrate Systems and Data.
Modify the JSON Response
You have full control over the result. The following is an example:
  1. Define a new 
    MyResource
     JavaScript resource, for example:
    return { Happy: ['New', 'Year']};
    For more information about how to explicitly define a JavaScript resource in API Creator, see Define JavaScript Resource Types.
  2. In the REST Lab, view the result by performing a GET request, which is a different formatting of the previous JSON. Complete the following steps:
    1. Ensure that you are functioning by defining a simple response event handler that includes the following code:
      // MUST be an object or an array, if not, it is coerced into one (and probably NOT what you want)
      if ('GET' == req.verb && 'MyResource' == req.resourceName) {
        json = ["I got what I expected"];
      }
      else {
        // this is returned on ALL other requests, make sure you delete this !!!
        json = ["Not what I wanted"];
      }
    2. Change to a more specific handler without the else condition:
      // Note double equals, as you are comparing JavaScript strings with java.lang.String objects
      if ('GET' == req.verb && 'MyResource' == req.resourceName) {
        json = SysUtility.getResource('demo:customer');
      }
The handler takes a value from the request and modifies the JSON response from the
demo:customer
 resource.
Access Request Headers
Request handlers have full access to the
headers
in the incoming request. Your handler has access to the 
headers
 object, for example:
//header names are usually lowercase
var contentType = headers["content-type"];
Modify the Response
Response handlers can modify the outgoing response in multiple ways. The
response
variable is an instance of the 
javax.ws.rs.core.Response.ResponseBuilder
Java class.
For more information about the
Response.ResponseBuilder
 Java class, see the Oracle documentation.
In the response handler, you can modify the response by adding headers, adding cookies, and setting the response code, for example:
var NewCookie = Java.type("javax.ws.rs.core.NewCookie");
var cookie = new NewCookie("MyCookie", "My cookie value");
response.cookie(cookie);
response.header("X-my-special-header", "My header value");
response.status(299);