Using the Mock Response middleware with Tyk OAS APIs

The Mock Response middleware allows you to configure Tyk to return a response for an API endpoint without requiring an upstream service. This can be useful when creating a new API or making a development API available to an external team.

When working with Tyk OAS APIs, this middleware is executed at the end of the request processing chain immediately prior to the upstream proxy stage. Thus, any other request processing middleware - including authentication - will be run before the request reaches the mock response.

The middleware is configured in the Tyk OAS API Definition. You can do this via the Tyk Dashboard API or in the API Designer.

The Mock Response middleware has two modes of operation:

• with manual mode, you can directly configure a response within the middleware in the Tyk extension (x-tyk-api-gateway) within the API definition. Tyk will give this response to all valid requests to the endpoint
• with automatic mode, Tyk will parse the examples and schema in the OpenAPI description and use this to generate responses automatically depending on the content of the request

If you’re using the legacy Tyk Classic APIs, then check out the Tyk Classic page.

Manually configuring the middleware in the Tyk OAS API Definition

The design of the Tyk OAS API Definition takes advantage of the operationId defined in the OpenAPI Document that declares both the path and method for which the middleware should be added.

The mock response middleware (mockResponse) can be added to the operations section of the Tyk OAS Extension (x-tyk-api-gateway) in your Tyk OAS API Definition for the appropriate operationId (as configured in the paths section of your OpenAPI Document).

For basic operation, the mockResponse object has the following configuration:

• enabled: enable the middleware for the endpoint
• code: the HTTP status code to be provided with the response (this defaults to 200 if not set)
• body: the payload to be returned as the body of the response
• headers: the headers to inject with the response

For example:

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{
    "components": {},
    "info": {
        "title": "example-mock-response1",
        "version": "1.0.0"
    },
    "openapi": "3.0.3",
    "paths": {
        "/anything": {
            "get": {
                "operationId": "anythingget",
                "responses": {
                    "200": {
                        "description": ""
                    }
                }
            }
        }
    },
    "x-tyk-api-gateway": {
        "info": {
            "name": "example-mock-response1",
            "state": {
                "active": true
            }
        },
        "upstream": {
            "url": "http://httpbin.org/"
        },
        "server": {
            "listenPath": {
                "value": "/example-mock-response1/",
                "strip": true
            }
        },
        "middleware": {
            "operations": {
                "anythingget": {
                    "mockResponse": {
                        "enabled": true,
                        "code": 200,
                        "body": "This is the mock response body",
                        "headers": [
                            {
                                "name": "X-Example-Header",
                                "value": "foobar"
                            }
                        ]
                    }
                }
            }
        }
    }
}

In this example the mock response middleware has been configured for requests to the GET /example-mock-response1/anything endpoint.

A call to GET /example-mock-response1/anything would return:

HTTP/1.1 200 OK
X-Example-Header: foobar
Content-Type: text/plain; charset=utf-8
 
This is the mock response body

The configuration above is a complete and valid Tyk OAS API Definition that you can import into Tyk to try out the mock response middleware.

Automatically configuring the middleware from the OpenAPI Document

You can direct Tyk to configure the Mock Response middleware automatically from the examples and schema defined in the OpenAPI description.

The design of the Tyk OAS API Definition takes advantage of the operationId defined in the OpenAPI Document that declares both the path and method for which the middleware should be added. Endpoint paths entries (and the associated operationId) can contain wildcards in the form of any string bracketed by curly braces, for example /status/{code}. These wildcards are so they are human readable and do not translate to variable names. Under the hood, a wildcard translates to the “match everything” regex of: (.*).

The mock response middleware (mockResponse) can be added to the operations section of the Tyk OAS Extension (x-tyk-api-gateway) in your Tyk OAS API Definition for the appropriate operationId (as configured in the paths section of your OpenAPI Document).

For basic operation, the mockResponse object has the following configuration:

• enabled: enable the middleware for the endpoint
• fromOASExamples: an object used to instruct Tyk Gateway to return a response from the OpenAPI description

The fromOASExamples object has the following configuration:

• enabled: enable the automatic configuration of mock response
• code: [optional] identifies which HTTP status code to be provided with the response (defaults to 200 if not set)
• contentType: [optional] identifies which response body type to use (defaults to application/json if not set)
• exampleName: [optional] the sample response to be returned from an examples list

The three optional fields (code, contentType, exampleName) are used to identify which sample response should be returned by the mock if multiple sample responses are declared in the OpenAPI description.

For example:

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{  
    "components": {},
    "info": {
        "title": "example-mock-response2",
        "version": "1.0.0"
    },
    "openapi": "3.0.3",
    "paths": {
        "/anything": {
            "get": {
                "operationId": "anythingget",
                "responses": {
                    "200": {
                        "content": {
                            "text/plain": {
                                "examples": {
                                    "first-example": {
                                        "value": "My favourite is pasta"
                                    },
                                    "second-example": {
                                        "value": "My second favourite is pizza"
                                    }
                                }
                            }
                        },
                        "description": ""
                    },
                    "300": {
                        "content": {
                            "text/plain": {
                                "example": "There's too much choice"
                            }
                        },
                        "description": ""
                    }
                }
            }
        }
    },
    "x-tyk-api-gateway": {
        "info": {
            "name": "example-mock-response2",
            "state": {
                "active": true
            }
        },
        "upstream": {
            "url": "http://httpbin.org/"
        },
        "server": {
            "listenPath": {
                "value": "/example-mock-response2/",
                "strip": true
            }
        },
        "middleware": {
            "operations": {
                "anythingget": {
                    "mockResponse": {
                        "enabled": true,
                        "fromOASExamples": {
                            "enabled": true,
                            "code": 200,
                            "contentType": "text/plain",
                            "exampleName": "second-example"
                        }
                    }
                }
            }
        }
    }
}

In this example, the OpenAPI description declares three possible responses: two for HTTP 200 and one for HTTP 300. We have configured the Mock Response middleware to return the value defined for HTTP 200 (code) with exampleName set to “second-example”.

If you make a call to GET /example-mock-response2/anything the response will be:

HTTP/1.1 200 OK
Content-Type: text/plain
Date: Thu, 01 Feb 2024 12:31:50 GMT
Content-Length: 8
 
"My second favourite is pizza"

If you add "code":300 in the fromOASExamples object, a call to GET /example-mock-response2/anything would instead respond as follows:

HTTP/1.1 300 Multiple Choices
Content-Type: text/plain
Date: Thu, 01 Feb 2024 12:35:45 GMT
Content-Length: 8
 
"There's too much choice"

The configuration above is a complete and valid Tyk OAS API Definition that you can import into Tyk to try out the mock response middleware.

Working with multiple mock responses for an endpoint

When the mock response middleware in your Tyk OAS API is configured to return responses from the OpenAPI description within the API definition, you can invoke a specific response, overriding the defaults configured in the middleware, by providing specific headers in your request.

To invoke a non-default response from a mocked endpoint, you must add one or more special headers to the request:

• Accept: This standard HTTP header will override the response content type (e.g. application/json, text/plain)
• X-Tyk-Accept-Example-Code: This will select the HTTP response code for which to return the example response (e.g. 400)
• X-Tyk-Accept-Example-Name: This identifies which example to select from an examples list

If an example response can’t be found for the configured code, contentType or exampleName, an HTTP 404 error will be returned to inform the client that there is no declared example for that configuration.

For example:

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{  
    "components": {},
    "info": {
        "title": "example-mock-response3",
        "version": "1.0.0"
    },
    "openapi": "3.0.3",
    "paths": {
        "/anything": {
            "get": {
                "operationId": "anythingget",
                "responses": {
                    "200": {
                        "headers": {
                            "X-Status": {
                                "schema": {
                                    "type": "boolean"
                                }
                            }
                        },
                        "content": {
                            "application/json": {
                                "schema": {
                                    "type": "object",
                                    "properties": {
                                        "lastName": {
                                            "example": "Bar",
                                            "type": "string"
                                        },
                                        "name": {
                                            "example": "Foo",
                                            "type": "string"
                                        },
                                        "id": {
                                            "type": "integer"
                                        }
                                    }
                                }
                            }
                        },
                        "description": ""
                    },
                    "300": {
                        "headers": {
                            "X-Status": {
                                "schema": {
                                    "type": "boolean",
                                    "example": false
                                }
                            }
                        },
                        "content": {
                            "text/plain": {
                                "example": "Baz"
                            }
                    },
                    "description": ""
                    } 
               }
            }
        }
    },
    "x-tyk-api-gateway": {
        "info": {
            "name": "example-mock-response3",
            "state": {
                "active": true
            }
        },
        "upstream": {
            "url": "http://httpbin.org/"
        },
        "server": {
            "listenPath": {
                "value": "/example-mock-response3/",
                "strip": true
            }
        },
        "middleware": {
            "operations": {
                "anythingget": {
                    "mockResponse": {
                        "enabled": true,
                        "fromOASExamples": {
                            "enabled": true,
                            "code": 200,
                            "contentType": "application/json"
                        }
                    }
                }
            }
        }
    }
}

In this example, the OpenAPI document declares two possible responses: one for HTTP 200 and one for HTTP 300. We have configured the Mock Response middleware to return the value defined for HTTP 200 for which the body (content) is in JSON format and a custom header X-Status which will take the default value of true.

You can trigger the mock response for HTTP 300 by adding the following headers to your request:

• X-Tyk-Accept-Example-Code: 300
• Accept: text/plain

This would return a plain text body and the X-Status header set to false.

The configuration above is a complete and valid Tyk OAS API Definition that you can import into Tyk to try out the mock response middleware.

Configuring the middleware in the API Designer

Adding a mock response to your API endpoints is easy when using the API Designer in the Tyk Dashboard, simply follow the steps appropriate to the configuration method you wish to use:

• manual configuration of the middleware config
• automatic configuration from the OpenAPI description

Manual configuration

Step 1: Add an endpoint

From the API Designer add an endpoint that matches the path and method to which you want to apply the middleware.

Step 2: Select the Mock Response middleware

Select ADD MIDDLEWARE and choose Mock Response middleware from the Add Middleware screen.

Step 3: Configure the middleware

Select Tyk Classic mock response

This takes you to the middleware configuration screen where you can:

• choose the HTTP status code that you want Tyk Gateway to return
• select the content type
• add a description for your mock response
• define headers to be provided with the response
• define the body that will be returned in the response (note that this must be defined as a JSON schema)

Select UPDATE MIDDLEWARE to apply the change to the middleware configuration.

Step 4: Save the API

Select SAVE API to apply the changes to your API.

Automatic configuration

Step 1: Import OpenAPI Document containing sample responses or schema

Import your OpenAPI Document (from file, URL or by pasting the JSON into the text editor) configuring the upstream URL and listen path, and selecting Auto-generate middleware to deliver mock responses.

Selecting this option will cause Tyk Dashboard to check for sample responses or schema in the OpenAPI description and will automatically add the Mock Response middleware for any endpoints that have suitable data.

Step 2: Edit the Mock Response middleware

Select EDIT and then the Mock Response middleware from the Endpoints tab. This will take you to the Edit Middleware screen. Note that Use mock response from Open API Specification has been selected.

Step 3: Configure the middleware

Tyk Dashboard will automatically have selected a valid HTTP response code from the drop-down. When you select a valid content-type for which a mock response is configured in the OpenAPI specification, the API Designer will display the associated response.

Here you can edit the mock response:

• modify, add or delete Response Body examples (note that this must follow the selected content-type)
• choose a default Response Body example that will be provided (unless overridden in the request)
• add a description for your mock response
• define headers to be provided with the response (note that these must be defined as a JSON schema)
• add a schema

You can create and edit mock responses for multiple HTTP status codes by choosing a different status code from the drop down.

Select UPDATE MIDDLEWARE to apply the change to the middleware configuration.

Step 4: Save the API

Select SAVE API to apply the changes to your API.