This post will show you how to build a policy (middleware) for your express gateway. Before creating a policy, we need to create a plugin.
Creating a plugin
To create a plugin, we need to add a folder plugins/my-plugin for it and a manifest file plugins/my-plugin/manifest.js with the following content
// plugins/my-plugin/manifest.js
module.exports = {
version: '0.0.1',
schema: {
"$id": "https://express-gateway.io/schemas/plugins/my-plugin.json"
}
}
Once this is done, we need to register the plugin in the system.config.yml file. Depending on your file structure, the file path may contain more or less ../ than this example.
# system.config.yml
plugins:
+ my-plugin:
+ package: '../../../plugins/my-plugin/manifest.js'
Creating the policy
Now that we have a plugin, we can start creating our policy. Add a policies folder plugins/my-plugin/policies and the policy itself plugins/my-plugin/policies/my-policy.js with the following content
// plugins/my-plugin/policies/my-policy.js
module.exports = {
name: 'my-policy',
schema: {
$id: 'http://express-gateway.io/schemas/policies/my-policy.json',
type: 'object'
},
policy: (actionParams) => {
return (req, res, next) => {
// TODO: Implement me
console.log('hello world');
next();
};
}
};
The policy function will be the place where you implement your specific use case.
Now we need to register the policy as part of the plugin
// plugins/my-plugin/manifest.js
module.exports = {
version: '0.0.1',
+ init: function (pluginContext) {
+ let policy = require('./policies/my-policy')
+ pluginContext.registerPolicy(policy)
+ },
+ policies: ['my-policy'],
schema: {
"$id": "https://express-gateway.io/schemas/plugins/my-plugin.json"
}
}
Using the policy
Finally, we can add the policy as any other default policy in the gateway.config.yml
# gateway.config.yml
policies:
- log
- jwt
+ - my-plugin
and use it in our pipelines
# gateway.config.yml
pipelines:
my-pipeline:
policies:
+ - my-plugin:
- log:
- action:
message: ${req.method} ${req.originalUrl}
Now we are finished with our policy, but we can still enhance it a bit.
Adding parameters
In the case, that you want to configure your policy (without changing the code) you can specify parameters. The syntax used is called Json Schema. You can have a look at their documentation for the type that you need. In this case, we add one parameter myarray with the type string[]
// plugins/my-plugin/policies/my-policy.js
schema: {
$id: 'http://express-gateway.io/schemas/policies/my-policy.json',
- type: 'object'
+ type: 'object',
+ properties: {
+ myarray: {
+ "type": "array",
+ "items": {
+ "type": "string"
+ }
+ }
+ }
},
After that, we can pass our value from the pipeline
# gateway.config.yml
policies:
- my-plugin:
+ - action:
+ myarray: ['value1', 'value2']
and use it within the policy function: actionParams.myarray.
I hope this helped you understand how to set up a policy in an express gateway pipeline.
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