Reference information for accessing the context object

Example code snippets access the context object in user-defined policies.

You can reference context variables in user-defined policies with the getContext() and setContext() functions and with JavaScript dot notation.

The context object is like a whiteboard for storing transactional information. Every policy in the same assembly gets the same context object for a single transaction. All of the policies can populate information into the context object and retrieve information from it. Data is categorized based on JavaScript properties. For example, all of the request related data are stored under request and response related data go to message. Pre-populated data might be read-only properties. Code that attempts to override read-only values causes an exception.

Reading payload

Request and response payload are stored in a context object. Request payload is populated into the request.body and response payload is stored in the message.body. The data type of the request.body and the message.body is determined by the value of request.content-type.

Here are examples that access the request payload.

Use dot notation to access the request.body:


var requestPayload  = context. request. body;

Use the get function to get the request.body:


var payload  = context. get(' request.body ');

Writing payload

The message.body starts with same value as the request.body, but the value can changed as the flow continues. After the policy implementation runs, the message.body becomes the payload for subsequent policies, if any, in the flow. The following table shows the correlation between the message.body data type and the request.content-type data type:

Table 1. Request body and message body data types
request.content-type	message.body
*/json	JSON
*/+json	JSON
text/*	String
*/x-www-form-urlencoded	JSON (key or value represents the HTTP form data)
*/xml	XML
*/+xml	XML
All others	Buffer

Reading headers

Request and response headers are stored in the context object. You can retrieve the headers as in the following examples:


//get header 
var requestHdr = context.get('request.headers.req-header-name');
var responseHdr = context.get('message.headers.resp-header-name');

Writing headers

Request headers are read-only headers, therefore, you cannot change them. However, you can modify headers in message.headers. The message.headers are the headers that are sent back to the client.


//set header 
context.set('message.headers.x-custom-header', 'value');
context.message.headers.myheader ='myheader';

If the header name contains a hyphen, use the get() function to retrieve it. Use brackets, [], to access this type of variable with dot-notation. For example:


var contentType = context.message.headers['content-type'];
//or
contentType = context.get('message.content-type');

Reading context

Context is transactional-wide shared variable space. For Micro Gateway policies, a context object provides access to context variables. The get() function and dot-notation are used to retrieve context values.

For example:


var verb = context.get('request.verb');
var uri = context.get('request.uri');
var path = context.request.path;

where context object is passed to the policy handler function by default.

Writing context

Similar to the get() function that reads context variables, the set() method writes context variables. For example:


context.set('acme.itemnumber', 'item1');

JavaScript dot-notation also is supported, as in this example:


context.acme.itemnumber2 = 'item2';

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