Applying constraints to mocks

Overview

Sometimes, additional constraints may be required on a mock operation. Constraints related to API behaviour or semantics may be difficult, even impossible, to express with an API contract. Microcks allows you to specify such constraints by editing the properties of a Service or API operation.

This guide will introduce you to the concepts of Microcks parameters constraints, which allow you to customize the behavior and validation of your mocks. You'll learn through a simple example how to place constraints on a REST API operation.

1. Concepts

In Microcks, constraints can be put onto Query or Header parameters and are of 3 types:

• required constraints force the presence of a parameter in the incoming request,
• recopy constraints just send back the same parameter name and value into the mock response,
• match constraints check the value of a parameter against a specified regular expression.

2. Practice

To practice the setup of constraints, you can reuse the Pastry API sample that is described in our Getting Started tutorial. Now imagine you put such constraints on the GET /pastry operation of your REST API that is secured using a JWT Bearer and should be managed traceability using a correlation ID:

Now let's do some tests to check Microcks' behavior:

http http://localhost:8080/rest/API+Pastry/1.0.0/pastry

HTTP/1.1 400 
Connection: close
Content-Length: 65
Content-Type: text/plain;charset=UTF-8
Date: Fri, 13 Dec 2019 19:20:31 GMT
X-Application-Context: application

Parameter Authorization is required. Check parameter constraints.

Hum... Adding the Authorization header...

http http://localhost:8080/rest/API+Pastry/1.0.0/pastry Authorization:'Bearer 123'

HTTP/1.1 400 
Connection: close
Content-Length: 89
Content-Type: text/plain;charset=UTF-8
Date: Fri, 13 Dec 2019 19:31:01 GMT
X-Application-Context: application

Parameter Authorization should match ^Bearer\s[a-f0-9]{36}. Check parameter constraints.

Hum... Fixing the Bearer format and adding the x-request-id header:

http http://localhost:8080/rest/API+Pastry/1.0.0/pastry Authorization:'Bearer abcdefabcdefabcdefabcdefab1234567890' x-request-id:123

HTTP/1.1 200 
Content-Length: 559
Content-Type: application/json
Date: Fri, 13 Dec 2019 19:33:52 GMT
X-Application-Context: application
x-request-id: 123

[
  {
    "description": "Delicieux Baba au Rhum pas calorique du tout",
    "name": "Baba Rhum",
    "price": 3.2,
    "size": "L",
    "status": "available"
  },
  {
    "description": "Delicieux Divorces pas calorique du tout",
    "name": "Divorces",
    "price": 2.8,
    "size": "M",
    "status": "available"
  },
  {
    "description": "Delicieuse Tartelette aux Fraises fraiches",
    "name": "Tartelette Fraise",
    "price": 2,
    "size": "S",
    "status": "available"
  }
]

Yeah! That's it 🎉 You successfully configured parameter constraints on the GET /pastry operation!

Wrap-up

Constraints are easy to use and powerful for specifying additional behavior or validation rules for your mocks. Defining constraints places your consumers in a better position for a seamless transition to the real-life implementation of your API once it is ready.

It's worth noting that Operation parameter constraints are saved into the Microcks database and not replaced by a new import of your Service or API definition. They can be independently set and updated using the Microcks REST API.