Dataservices are a dynamic component of the backend of a Zowe application. Dataservices are optional, because the proxy server might only serve static content for a particular application. However, when included in an application, a dataservice defines a URL space for which the server will run the extensible code from the application. Dataservices are primarily intended to be used to create REST APIs and Websocket channels.
sample-app repository, in the top directory, you will find a
pluginDefinition.json file. Each application requires this file, because it defines how the server registers and uses the backend of an application (called a plug-in in the terminology of the proxy server).
Within the JSON file, there is a top level attribute, dataServices:
The following attributes are valid for each dataservice in the dataServices array:
Specify one of the following values:
router: Router dataservices are dataservices that run under the proxy server, and use ExpressJS Routers for attaching actions to URLs and methods.
service: Service dataservices are dataservices that run under ZSS, and utilize the API of ZSS dataservices for attaching actions to URLs and methods.
The name of the service that must be unique for each
pluginDefinition.json file. The name is used to reference the dataservice during logging and it is also is used in the construction of the URL space that the dataservice occupies.
external unless otherwise instructed.
The name of the file that is the entry point for construction of the dataservice, relative to the application's
/lib directory. In the case of
When you use a router dataservice, the dataservice is included in the proxy server through a
require() statement. If the dataservice's exports are defined such that the router is provided through a factory of a specific name, you must state the name of the exported factory using this attribute.
true for anything in the
pluginDefinition.json file. (This setting is false only when adding dataservices to the server dynamically.)
The API for a dataservice can be categorized as Router-based or ZSS-based, and Websocket or not.
Note: Each Router dataservice can safely import express, express-ws, and bluebird without requiring the modules to be present, because these modules exist in the proxy server's directory and the NODE_MODULES environment variable can include this directory.
Router-based dataservices must return a (bluebird) Promise that resolves to an ExpressJS router upon success. For more information, see the ExpressJS guide on use of Router middleware: Using Router Middleware.
Because of the nature of Router middleware, the dataservice need only specify URLs that stem from a root '/' path, as the paths specified in the router are later prepended with the unique URL space of the dataservice.
The Promise for the Router can be within a Factory export function, as mentioned in the
pluginDefinition specification for routerFactory above, or by the module constructor.
An example is available in
ExpressJS routers are fairly flexible, so the contract to create the Router for Websockets is not significantly different.
Here, the express-ws package is used, which adds websockets through the ws package to ExpressJS. The two changes between a websocket-based router and a normal router are that the method is 'ws', as in
router.ws(<url>,<callback>), and the callback provides the websocket on which you must define event listeners.
See the ws and express-ws topics on www.npmjs.com for more information about how they work, as the API for websocket router dataservices is primarily provided in these packages.
An example is available in
Every router-based dataservice is provided with a
Context object upon creation that provides definitions of its surroundings and the functions that are helpful. The following items are present in the
The dataservice definition, originally from the
pluginDefinition.json file within a plug-in.
An object that contains the contents of configuration files, if present.
An instance of a Zowe Logger, which has its component name as the unique name of the dataservice within a plug-in.
A function to create a Zowe Logger with a new name, which is appended to the unique name of the dataservice.
A function that provides common body parsers for HTTP bodies, such as JSON and plaintext.
An object that contains more context from the plug-in scope, including:
pluginDef: The contents of the
pluginDefinition.jsonfile that contains this dataservice.
server: An object that contains information about the server's configuration such as:
app: Information about the product, which includes the productCode (for example:
user: Configuration information of the server, such as the port on which it is listening.