micri/README.md

_**Micri** — Asynchronous HTTP microservices_

> micri is an archaic non-SI decimal metric prefix for 10−14. Its symbol was mc.

[Wikipedia - Micri-](https://en.wikipedia.org/wiki/Micri-)

[![Install Size](https://packagephobia.now.sh/badge?p=micri)](https://packagephobia.now.sh/result?p=micri)

## Features

* **Easy**: Designed for usage with `async` and `await` ([more](https://zeit.co/blog/async-and-await))
* **Fast**: Ultra-high performance (even JSON parsing is opt-in)
* **Micri**: The whole project is ~260 lines of code
* **Agile**: Super easy deployment and containerization
* **Simple**: Oriented for single purpose modules (function)
* **Standard**: Just HTTP!
* **Explicit**: No middleware - modules declare all [dependencies](https://github.com/amio/awesome-micro)
* **Lightweight**: With all dependencies, the package weighs less than a megabyte


## Usage

Create an `index.js` file and export a function that accepts the standard [http.IncomingMessage](https://nodejs.org/api/http.html#http_class_http_incomingmessage) and [http.ServerResponse](https://nodejs.org/api/http.html#http_class_http_serverresponse) objects:

```js
module.exports = (req, res) => {
  res.end('Welcome to Micri')
}
```

```js
module.exports = () => 'Welcome to Micri'
```

Next, ensure that the `main` property inside `package.json` points to your microservice (which is inside `index.js` in this example case) and add a `start` script:

```json
{
  "main": "index.js",
  "scripts": {
    "start": "micri"
  }
}
```

Once all of that is done, the server can be started like this:

```bash
npm start
```

And go to this URL: `http://localhost:3000` - 🎉

### Command line

```
  micri - Asynchronous HTTP microservices

  USAGE

      $ micri --help
      $ micri --version
      $ micri [-l listen_uri [-l ...]] [entry_point.js]

      By default micri will listen on 0.0.0.0:3000 and will look first
      for the "main" property in package.json and subsequently for index.js
      as the default entry_point.

      Specifying a single --listen argument will overwrite the default, not supplement it.

  OPTIONS

      --help                              shows this help message

      -v, --version                       displays the current version of micri

      -l, --listen listen_uri             specify a URI endpoint on which to listen (see below) -
                                          more than one may be specified to listen in multiple places

  ENDPOINTS

      Listen endpoints (specified by the --listen or -l options above) instruct micri
      to listen on one or more interfaces/ports, UNIX domain sockets, or Windows named pipes.

      For TCP (traditional host/port) endpoints:

          $ micri -l tcp://hostname:1234

      For UNIX domain socket endpoints:

          $ micri -l unix:/path/to/socket.sock

      For Windows named pipe endpoints:

          $ micri -l pipe:\\.\pipe\PipeName
```

### `async` & `await`

<p><details>
  <summary><b>Examples</b></summary>
  <ul><li><a href="./examples/external-api-call">Fetch external api</a></li></ul>
</details></p>

Micri is built for usage with async/await. You can read more about async / await [here](https://zeit.co/blog/async-and-await)

```js
const sleep = (ms) => new Promise((r) => setTimeout(r, ms));

module.exports = async (req, res) => {
  await sleep(500);
  return 'Ready!';
}
```

### Transpilation

The package takes advantage of native support for `async` and `await`, which is available as of **Node.js 8.0.0**! In turn, we suggest either using at least this version both in development and production (if possible), or transpiling the code using [async-to-gen](https://github.com/leebyron/async-to-gen), if you can't use the latest Node.js version.

In order to do that, you firstly need to install it:

```bash
npm install --save async-to-gen
```

And then add the transpilation command to the `scripts.build` property inside `package.json`:

```json
{
  "scripts": {
    "build": "async-to-gen input.js > output.js"
  }
}
```

Once these two steps are done, you can transpile the code by running this command:

```bash
npm run build
```

That's all it takes to transpile by yourself. But just to be clear: **Only do this if you can't use Node.js 8.0.0**! If you can, `async` and `await` will just work right out of the box.

### Port Based on Environment Variable

When you want to set the port using an environment variable you can use:

```
micri -l tcp://0.0.0.0:$PORT
```

Optionally you can add a default if it suits your use case:

```
micri -l tcp://0.0.0.0:${PORT-3000}
```

`${PORT-3000}` will allow a fallback to port `3000` when `$PORT` is not defined.

Note that this only works in Bash.

### Body parsing

<p id="body-parsing-examples"><details>
  <summary><b>Examples</b></summary>
  <ul>
    <li><a href="./examples/json-body-parsing">Parse JSON</a></li>
    <li><a href="./examples/urlencoded-body-parsing">Parse urlencoded form (html `form` tag)</a></li>
  </ul>
</details></p>

For parsing the incoming request body we included an async functions `buffer`, `text` and `json`

```js
const {buffer, text, json} = require('micri')

module.exports = async (req, res) => {
  const buf = await buffer(req)
  console.log(buf)
  // <Buffer 7b 22 70 72 69 63 65 22 3a 20 39 2e 39 39 7d>
  const txt = await text(req)
  console.log(txt)
  // '{"price": 9.99}'
  const js = await json(req)
  console.log(js.price)
  // 9.99
  return ''
}
```

### API

##### `buffer(req, { limit = '1mb', encoding = 'utf8' })`
##### `text(req, { limit = '1mb', encoding = 'utf8' })`
##### `json(req, { limit = '1mb', encoding = 'utf8' })`

- Buffers and parses the incoming body and returns it.
- Exposes an `async` function that can be run with  `await`.
- Can be called multiple times, as it caches the raw request body the first time.
- `limit` is how much data is aggregated before parsing at max. Otherwise, an `Error` is thrown with `statusCode` set to `413` (see [Error Handling](#error-handling)). It can be a `Number` of bytes or [a string](https://www.npmjs.com/package/bytes) like `'1mb'`.
- If JSON parsing fails, an `Error` is thrown with `statusCode` set to `400` (see [Error Handling](#error-handling))

For other types of data check the [examples](#body-parsing-examples)

### Sending a different status code

So far we have used `return` to send data to the client. `return 'Hello World'` is the equivalent of `send(res, 200, 'Hello World')`.

```js
const {send} = require('micri')

module.exports = async (req, res) => {
  const statusCode = 400
  const data = { error: 'Custom error message' }

  send(res, statusCode, data)
}
```

##### `send(res, statusCode, data = null)`

- Use `require('micri').send`.
- `statusCode` is a `Number` with the HTTP status code, and must always be supplied.
- If `data` is supplied it is sent in the response. Different input types are processed appropriately, and `Content-Type` and `Content-Length` are automatically set.
  - `Stream`: `data` is piped as an `octet-stream`. Note: it is _your_ responsibility to handle the `error` event in this case (usually, simply logging the error and aborting the response is enough).
  - `Buffer`: `data` is written as an `octet-stream`.
  - `object`: `data` is serialized as JSON.
  - `string`: `data` is written as-is.
- If JSON serialization fails (for example, if a cyclical reference is found), a `400` error is thrown. See [Error Handling](#error-handling).

### Programmatic use

You can use Micri programmatically by requiring Micri directly:

```js
const micri = require('micri')

const sleep = (ms) => new Promise((r) => setTimeout(r, ms));

const server = micri(async (req, res) => {
  await sleep(500)
  return 'Hello world'
})

server.listen(3000)
```

##### micri(fn)

- This function is exposed as the `default` export.
- Use `require('micri')`.
- Returns a [`http.Server`](https://nodejs.org/dist/latest-v6.x/docs/api/http.html#http_class_http_server) that uses the provided `function` as the request handler.
- The supplied function is run with `await`. So it can be `async`

##### sendError(req, res, error)

- Use `require('micri').sendError`.
- Used as the default handler for errors thrown.
- Automatically sets the status code of the response based on `error.statusCode`.
- Sends the `error.message` as the body.
- Stacks are printed out with `console.error` and during development (when `NODE_ENV` is set to `'development'`) also sent in responses.
- Usually, you don't need to invoke this method yourself, as you can use the [built-in error handling](#error-handling) flow with `throw`.

## Error Handling

Micri allows you to write robust microservices. This is accomplished primarily
by bringing sanity back to error handling and avoiding callback soup.

If an error is thrown and not caught by you, the response will automatically be
`500`. **Important:** Error stacks will be printed as `console.error` and during
development mode (if the env variable `NODE_ENV` is `'development'`), they will
also be included in the responses.

If the error object throw is an instance of `MicriError` the `message`,
`statusCode` and `code` properties of the object are used for the HTTP response.

Let's say you want to write a rate limiting module:

```js
const rateLimit = require('my-rate-limit')

module.exports = async (req, res) => {
  await rateLimit(req)
  // ... your code
}
```

If the API endpoint is abused, it can throw an error with ``createError`` like so:

```js
if (tooMany) {
  throw MicriError(429, 'rate_limited' 'Rate limit exceeded')
}
```

The nice thing about this model is that the `statusCode` is merely a suggestion.
The user can override it:

```js
try {
  await rateLimit(req)
} catch (err) {
  if (429 == err.statusCode) {
    // perhaps send 500 instead?
    send(res, 500)
  }
}
```

If the error is based on another error that **Micri** caught, like a `JSON.parse`
exception, then `originalError` will point to it. If a generic error is caught,
the status will be set to `500`.

In order to set up your own error handling mechanism, you can use composition in
your handler:

```js
const {send} = require('micri')

const handleErrors = fn => async (req, res) => {
  try {
    return await fn(req, res)
  } catch (err) {
    console.log(err.stack)
    send(res, 500, 'My custom error!')
  }
}

module.exports = handleErrors(async (req, res) => {
  throw new Error('What happened here?')
})
```

## Contributing

1. [Fork](https://help.github.com/articles/fork-a-repo/) this repository to your own GitHub account and then [clone](https://help.github.com/articles/cloning-a-repository/) it to your local device
2. Link the package to the global module directory: `npm link`
3. Within the module you want to test your local development instance of Micri, just link it to the dependencies: `npm link micri`. Instead of the default one from npm, node will now use your clone of Micri!

As always, you can run the [AVA](https://github.com/sindresorhus/ava) and [ESLint](http://eslint.org) tests using: `npm test`