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loopback-connector-openapi

The Swagger connector enables LoopBack applications to interact with other REST APIs described by the OpenAPI (Swagger) Specification v2.0 or OpenAPI (Swagger) Specification v3.0.

We use Swagger Client and Swagger Parser internally.

Installation

In your application root directory, enter:

$ npm install loopback-connector-openapi --save

This will install the module from npm and add it as a dependency to the application’s package.json file.

Configuration

LoopBack 4 Usage

To interact with OpenAPI spec:

  1. Create a LoopBack 4 DataSource with OpenAPI connector using the lb4 datasource command.

  2. Create a service that maps to the operations using the lb4 service command.

  3. Create a controller that calls the service created in the above step using lb4 controller command.

For details, refer to the Calling other APIs and web services documentation page.

LoopBack 3 Usage

To interact with a Swagger API, configure a data source backed by the OpenAPI connector:

With code:

var ds = loopback.createDataSource('swagger', {
  connector: 'loopback-connector-openapi',
  spec: 'http://petstore.swagger.io/v2/swagger.json',
});

With JSON in datasources.json (for example, with basic authentication):

"SwaggerDS": {
    "name": "SwaggerDS",
    "connector": "swagger",
    "spec": "http://petstore.swagger.io/v2/swagger.json",
    "authorizations": {
      "basic": {
        "username": "your-username",
        "password": "your-password"
      }
    }
}

Data source properties

Specify the options for the data source with the following properties.

Property Description Default
connector Must be 'loopback-connector-openapi' to specify Swagger connector None
spec HTTP URL or path to the Swagger specification file (with file name extension .yaml/.yml or .json). File path must be relative to current working directory (process.cwd()). None
validate When true, validates provided spec against Swagger specification 2.0 before initializing a data source. false
authorizations Security configuration for making authenticated requests to the API.  
positional Use positional parameters instead of named parameters false
forceOpenApi30 Convert the Swagger 2.0 spec to OpenAPI 3.0 false
mapToMethods map OpenAPI operations to method names undefined
transformResponse Transform the response object undefined

Mapping operations to methods

By default, the connector adds the following method names to the model:

  1. x-operation-name of the operation spec
  2. operationId of the operation spec
  3. The names from 1 and 2 with <tag>_ prefix
  4. The camel case for all of the names above

For an operation with {operationId: 'get_books', 'x-operation-name': 'getBooks'} under tag BookController, the following methods are added:

  • getBooks
  • get_books
  • BookController_getBooks
  • BookController_get_books
  • bookControllerGetBooks

For tagged interfaces, the connector adds the following method names to apis.<tag>:

  1. x-operation-name of the operation spec
  2. operationId of the operation spec
  3. The camel case for all of the names above

For an operation with {operationId: 'get_books', 'x-operation-name': 'getBooks'} under tag BookController, the following methods are added:

  • getBooks
  • get_books

A custom mapToMethods can be set on the connector to override the naming conventions. The signature of the method is as follows:

/**
 * Get the method name for an operation
 * @param {string} tag - The tag. It will be '' for tagged interfaces.
 * @param {object} operationSpec - Operation spec
 * @param {string[]} existingNames - Optional array to track used names
 *
 * @returns A method name or an array of method names. Return undefined to
 * skip the operation.
 */
function mapToMethods(tag, operationSpec, existingNames) {}

Now we can configure the connector to use our custom mapToMethod.

var ds = loopback.createDataSource('swagger', {
  connector: 'loopback-connector-openapi',
  spec: 'http://petstore.swagger.io/v2/swagger.json',
  mapToMethods: mapToMethods,
});

Return value

By default, the methods return a response object with the following properties:

{
  url,
  method,
  status,
  statusText,
  headers, // See note below regarding headers
  text,    // The textual content
  body,    // The body object
}

See https://github.com/swagger-api/swagger-js#response-shape for more details.

The return value can be transformed by a custom transformResponse function configured for the connector:

function transformResponse(res, operationSpec) {
  if (res.status < 400) {
    return res.body;
  }
  const err = new Error(`${res.status} ${res.statusText}`);
  err.details = res;
  throw err;
}

Now we can configure the connector to use our custom transformResponse.

var ds = loopback.createDataSource('swagger', {
  connector: 'loopback-connector-openapi',
  spec: 'http://petstore.swagger.io/v2/swagger.json',
  transformResponse: transformResponse, // or transformResponse: true for a default transformer
});

Authentication

Basic authentication

{
  authorizations: {
    my_basic_auth: { username: 'foo', password: 'bar' },
  }
}

API Key

{
  authorizations: {
    my_query_api_key_auth: 'my-api-key',
    my_header_api_key_auth: 'my-api-key',
  }
}

OAuth2

{
  authorizations: {
    my_oauth2_token: { token: { access_token: 'abcabc' } },
  }
}

Note: The key must correspond to a security scheme declared in the Security Definitions object within the spec document.

Creating a model from the Swagger data source

The Swagger connector loads the API specification document asynchronously. As a result, the data source won’t be ready to create models until it is connected. For best results, use an event handler for the connected event of data source:

ds.once('connected', function(){
  const PetService = ds.createModel('PetService', {});
  ...
});

Once the model is created, all available Swagger API operations can be accessed as model methods, for example:

...
PetService.getPetById({petId: 1}, function (err, res){
  ...
});

How model methods are named for given Swagger API Operations:

This connector uses swagger-client which dominates the naming of generated methods for calling client API operations.

Following is how it works:

  • When operationId is present, for example:
paths: {
  /weather/forecast:
  get:
    ...
    operationId: weather.forecast
    ...

Here, as operationId is present in Swagger specification, the generated method is named equivalent to operationId.

Note: if operationId is of format equivalent to calling a nested function such as: weather.forecast, the resulting method name will replace . with _ i.e. weather.forecast will result into weather_forecast.This means you can call MyModel.weather_forecast() to access this endpoint programmatically.

  • When operationId is not provided in Swagger specification, the method name is formatted as following: <operationType (i.e. get, post, etc)> + _ + <path parts separated by underscores>

For example:

/weather/forecast:
  get:
    ...

for above operation, the resulting method name will be: get_weather_forecast.

This means you can call MyModel.get_weather_forecast() to access this endpoint programmatically.

Named parameters vs. positional parameters

The positional setting allows a method to be invoked with positional parameters based on the parameters/requestBody of the OpenAPI operation spec.

const result = await MyModel.my_operation(
  // Parameters
  '94555',
  // Request body
  {
    verbose: true
  },
  // Additional options
  {
    requestContentType: 'application/json'
  });
});

Without positional set to true, named parameters are expected:

const result = await MyModel.my_operation({
  {
    zipCode: '94555',
  },
  {
    requestBody: {verbose: true},
    requestContentType: 'application/json'
  }
});

Extend a model to wrap/mediate API Operations

Once you define the model, you can wrap or mediate it to define new methods. The following example simplifies the getPetById operation to a method that takes petID and returns a Pet instance.

PetService.searchPet = function (petID, cb) {
  PetService.getPetById({ petId: petID }, function (err, res) {
    if (err) cb(err, null);
    var result = res.data;
    cb(null, result);
  });
};

This custom method on the PetService model can be exposed as REST API end-point. It uses loopback.remoteMethod to define the mappings:

loopback.remoteMethod(PetService.searchPet, {
  accepts: [
    { arg: 'petID', type: 'string', required: true, http: { source: 'query' } },
  ],
  returns: { arg: 'result', type: 'object', root: true },
  http: { verb: 'get', path: '/searchPet' },
});

Caching

As an experimental feature, loopback-connector-openapi is able to cache the result of GET requests.

Important: we support only one cache invalidation mechanism - expiration based on a static TTL value.

To enable caching, you need to specify:

  • cache.model (required) - name of the model providing access to the cache. The model should be extending loopback’s built-in KeyValueModel and be attached to one of key-value datasources (e.g. Redis or eXtremeScale).

  • cache.ttl (required) - time to live for cache entries, the value is in milliseconds. Note that certain cache implementations (notably eXtremeScale) do not support sub-second precision for TTL.

Example configuration

server/datasources.json

{
  "SwaggerDS": {
    "connector": "swagger",
    "cache": {
      "model": "SwaggerCache",
      "ttl": 100
    }
  },
  "cache": {
    "connector": "kv-redis"
  }
}

common/models/swagger-cache.json

{
  "name": "SwaggerCache",
  "base": "KeyValueModel",
  // etc.
}

server/model-config.json

{
  "SwaggerCache": {
    "dataSource": "cache",
    "public": false
  }
}

Connector Hooks

The connector can be observed for before execute and after execute events. For example:

const ds = loopback.createDataSource('swagger', {
    connector: 'loopback-connector-openapi',
    spec: spec,
    authorizations: authz || {},
  });
  ds.on('connected', function() {
    ds.connector.observe('before execute', (ctx, next) => {
      done(null, ctx.req);
    });
    ...
  });