Frequently Asked Questions

• What are deployment modes?
• Can exposed API be asynchronous?
• Are there limitations on exposed API signatures?
• Where to put asynchronous initialization?
• Can initialization code be configured?
• How can service definition be more modular?
• How can initialisation be shared by different groups?
• How could input parameters be validated?
• How could results be validated
• Is Swagger/OpenAPI supported?
• Can endpoint method/headers/query be configured?

What are deployment modes?

µServices based on mini-service could be deployed either:

• locally: runs on the same nodejs process as the caller code

  const {getClient} = require('mini-service')
  
  // define a service
  const calc = getClient({
    name: 'calc',
    version: '1.0.0',
    init: () => ({
      add: (a, b) => a + b
    })
  })
  
  await calc.init()
  
  // invoke exposed api as async function
  const sum = await calc.add(10 + 5)
  

• remotely: runs as a dedicated HTTP server

  // server.js
  const {startServer} = require('mini-service')
  
  // define a service, start Http server
  startServer({
    name: 'calc',
    version: '1.0.0',
    init: () => ({
      add: (a, b) => a + b
    })
  })
  

  // client.js
  const {getClient} = require('mini-service')
  
  // will connect to server on demand
  const calc = getClient({
    remote: 'http://localhost:3000'
  })
  
  // invoke exposed api as async function
  const sum = await calc.add(10 + 5)
  

No need to add the service code as a dependency when using getClient() with remote url/

Can exposed API be asynchronous?

Yes, by using Promises:

const {startService} = require('mini-service')

startService({
  name: 'calc',
  version: '1.0.0',
  init: () => ({
    add: (a, b) => a + b,                    // synchronous API,
    subtract: async (a, b) => a - b          // asynchronous API, async/await syntax
    divide: (a, b) => Promise.resolve(a / b) // asynchronous API, promise-based
  })
})

Are there limitations on exposed API signatures?

Despite all our efforts, yes. Hopefully main cases are covered.

Because parameters will be stringified when sent to server:

• they could be null or undefined
• they could be booleans, numbers, strings, arrays, and plain object (contains only properties of the previous types)
• they could be of other types (Date, Error, RegExp, custom classes...) but will boils down to the output of their toString() method
• they could be Buffer or Stream (see bellow). All paremeter but the first will be ignored

In particular, don't use functions as parameters.

Same limitations applies to API returned object.

You can use destructuring, rest parameters and even default values:

async withExoticParameters ([a, b], {c: {d}} = {}, ...other) {
  return [a, b, d, ...other]
}

To use Buffer input parameter:

• decorate API with hasBufferInput
• use only one parameter (others will be set to undefined)

    const api = {
      async bufferHandling (buffer) {
        assert(Buffer.isBuffer(buffer))
        return Buffer.concat([buffer, new Uint8Array([3, 4])])
      }
    }
    // decorate
    apis.bufferHandling.hasBufferInput = true
  

To use Stream input parameter:

• decorate API with hasStreamInput
• use only one parameter (others will be set to undefined)

    const api = {
      async streamHandling (stream) {
        assert(stream instanceof Readable)
        const prefix = new BufferList()
        prefix.append('here is a prefix -- ', 'utf8')
        return multistream([prefix, stream])
      }
    }
    // decorate
    apis.streamHandling.hasStreamInput = true
  

You can return Stream and Buffer without any decoration, but don't nest them in objects (they will be stringified).

Where to put asynchronous initialization?

To serve this purpose, the init() function can be either synchronous or return a Promise.

const {promisify} = require('util')
const readFile = promisify(require('readFile').readFile)
const {startService} = require('mini-service')

startService({
  name: 'async-init',
  version: '1.0.0',
  init: async () => {
    // let's say we need to read a configuration file...
    const content = await readFile('whatever.html')
    return {
      // exposed API list
    }
  }
})

Rejecting the init() promise will prevent server to start.

Can initialization code be configured?

init() functions are invoked with a single Object parameter, populated with values from the service descriptor.

const {promisify} = require('util')
const readFile = promisify(require('readFile').readFile)
const {startService} = require('mini-service')

const config = {
  filePath: 'whatever.html'
}

startService({
  name: 'configurable-init'
  version: '1.0.0',
  // single parameter is the service definition itself
  init: async ({filePath}) => {
    const content = await readFile(filePath)
    return {
      // exposed API list
    }
  },
  // all keys in the service definition will be passed to init()
  ...config
})

If you use API groups, each group has its own configuration object stored in groupOpts[group.name].

How can service definition be more modular?

Service definition object tend to grow quickly. API groups is how mini-service makes the code more modular.

This big service definition:

const {startService} = require('mini-service')

startService({
  name: 'monolitic-service',
  version: '1.0.0',
  init: () => ({
    api1: () => {/* ... */},
    api2: () => {/* ... */},
    api3: () => {/* ... */},
    api4: () => {/* ... */},
    api5: () => {/* ... */}
  })
})

can be turned to different groups:

// server.js
const {startService} = require('mini-service')

startService({
  name: 'modular-service',
  version: '1.0.0',
  groups: [
    require('./api/group1'),
    require('./api/group2')
  ],
  groupOpts: {
    group1: {/* for group 'group1' */},
    group2: {/* for group 'group2' */}
  }
})

// api/group1.js
module.exports = {
  // must be a valid JS identifier
  name: 'group1',
  // opts comes from groupOpts[group1]
  init: opts => ({
    api1: () => {/* ... */},
    api2: () => {/* ... */}
  })
}

// api/group2.js
module.exports = {
  name: 'group2',
  // opts comes from groupOpts[group2]
  init: opts => ({
    api3: () => {/* ... */},
    api4: () => {/* ... */},
    api5: () => {/* ... */}
  })
}

Please note that groups are initialized sequentially, following the declaration order.

How can initialisation be shared by different groups?

Services are initialized sequentially. One can use orderring to perform shared initialization.

// server.js
const {startService} = require('mini-service')

let shared

startService({
  name: 'modular-configurable-service',
  version: '1.0.0',
  groups: [{
    name: 'global-init',
    init: obj => {
      // initialized shared items
      shared = { /* ... */ }
      // doesn't have to expose any API
    }
  }, {
    name: 'group1',
    // pass your shared object to your init method, as well as other options
    init: opts => require('./api/group1')(shared, opts)
  ],
  groupOpts: {
    shared: {/* for group 'shared' */}
    group1: {/* for group 'group1' */}
  }
})

// api/group1.js
module.exports = (shared, opts) {
  // initialization code, can use shared items
  return {/* exposed APIs */}
}

How could input parameters be validated?

As parameters validation is a common pattern (syntactic validation), mini-service supports it out of the box. Parameters of exposed API could be validated with Joi.

Assign an array of validation schemas to the validate property of an exposed API. Each schema will validated a given parameter (order matters).

const Joi = require('joi')
const {startService} = require('mini-service')

startService({
  name: 'validate-inputs',
  version: '1.0.0',
  init: () => {
    // declare your API
    const add = (a, b) => a + b
    // attached a schema for each parameter in an array
    add.validate = [
      Joi.Number().required(), // a
      Joi.Number().required() // b, example used in Swagger documentation
    ]
    return {add}
  }
})

Prior to any invokation of the API, incoming parameters will be matched against the validation schema. The invokation will fail with a 400 error (Bad Request) if they don't comply.

How could results be validated?

Although less common, returned results can be validated against a Joi schema by assigning to the expose API:

• a validation schemas to the responseSchema.
• true to validateResponse property.

Ommitting validateResponse property (or setting a falsy value) will disable result validation.

Results that don't match response schema will trigger a 512 Bad Response error.

const Joi = require('joi')
const {startService} = require('mini-service')

startService({
  name: 'validate-results',
  version: '1.0.0',
  init: () => {
    // declare your API
    const add = (a, b) => a + b
    // adds output documentation & validation
    add.responseSchema = Joi.number().required()
    add.validateResponse = true
    return {add}
  }
})

Is Swagger/OpenAPI supported?

Yes, but is disabled by default. It can only be used through startService().

To enable and customize it, use openApi configuration key. Documentation can be added:

• at upper level: openApi.info.title, openApi.info.description
• at group level: openApi.tags[].description (tags[].name has to match group's name)
• at api level, by attaching to the exposed API:
  • description: general description
  • notes: string or array of implementation notes
  • validate: array of Joi objects to validate incoming parameters (request body)
  • responseSchema: Joi object describing expected response

const Joi = require('joi')
const {startService} = require('mini-service')

startService({
  name: 'documented-service',
  version: '1.0.0',
  openApi: {
    // see https://github.com/glennjones/hapi-swagger/blob/master/optionsreference.md
    info: {
      title: 'Simple calculator'
    }
    /* defaults are:
    info: {version},
    documentationPath: '/documentation',
    jsonPath: '/swagger.json',
    basePath: '/api',
    pathPrefixSize: 2
    */
  }
  init: () => {
    const add = (a, b) => a + b

    // document api
    add.description = 'Sum numbers'
    add.notes = 'Only works with two numbers'

    // document parameters
    add.validate = [
      Joi.Number().required().description('reference number').example(5),
      Joi.Number().required().description('added to reference').example(2)
    ]

    // document results
    add.responseSchema = Joi.Number().required().description('number summation').example(7)
    return {add}
  }
})

See a more complete example.

Can endpoint method/headers/query be configured?

No it cannot.

Mini-service purposely hides details regarding exposed Http endpoints. Its goal is not to be another web framework, but acts more as an remote-procedure-call toolkit.

When exposing an API function, the following conventions apply:

• endpoint path is /api/${function name} (case sensitive)
• endpoint method is GET if function has no declared parameters, POST otherwise
• endpoint headers can not be configured
• endpoint query string can note be configured
• incoming request payload is always parsed as JSON
• when validate is set, and request payload doesn't comply, a 400 Bad Request error is returned with details
• when responseSchema and validateResponse are set, and response payload doesn't comply, a 512 Bad Response error is returned with details
• otherwise, endpoint always returns 200, and result (if it exists) is always serialized as JSON