Building a REST API with Nitric

This guide will show you how to build a serverless REST API with the Nitric framework using Dart. The example API enables reading, writing and editing basic user profile information using a Nitric key value store to store user data. Once the API is created we'll test it locally, then optionally deploy it to a cloud of your choice.

The example API enables reading, writing, and deleting profile information from a Nitric key value store.

The API will provide the following routes:

Method	Route	Description
`GET`	/profiles/[id]	Get a specific profile image by its id
`GET`	/profiles	List all profiles
`POST`	/profiles	Create a new profile image
`DELETE`	/profiles/[id]	Delete a profile

There is also an extended section of the guide that adds file operations using a Nitric bucket to store and retrieve profile pictures using signed URLs. The extension adds these routes to the API:

Method	Route	Description
`GET`	/profiles/[id]/image/upload	Get a profile image upload URL
`GET`	/profiles/[id]/image/download	Get a profile image download URL
`GET`	/profiles/[id]/image/view	View the image that is downloaded

Prerequisites

Dart
The Nitric CLI
An AWS, Google Cloud or Azure account (your choice)

Getting started

Start by creating a new Nitric project from the dart template.

nitric new my-profile-api dart-starter

Next, open the project in your editor of choice.

cd my-profile-api

The scaffolded project should have the following structure:

services/
├── api.dart
.gitignore
analysis_options.yaml
dart.dockerfile
dart.dockerfile.dockerignore
nitric.yaml
pubspec.yaml
README.md

As we will be generating IDs for each profile, add the uuid dependency by adding it to your pubspec.yaml.

dart pub add uuid

Building the API

Applications built with Nitric can contain many APIs, let's start by adding one to this project to serve as the public endpoint.

import 'package:nitric_sdk/nitric.dart';

import 'package:uuid/uuid.dart';

void main() {
  // Create an API named 'public'
  final profileApi = Nitric.api("public");

  // Define a key value store named 'profiles', then request get, set and delete permissions.
  final profiles = Nitric.kv("profiles").allow([
    KeyValueStorePermission.get,
    KeyValueStorePermission.set,
    KeyValueStorePermission.delete
  ]);
}

Here we're creating an API named public and a key value store named profiles, then requesting get, set, and delete permissions which allows our service to access the key value store.

Resources in Nitric like api and key value store represent high-level cloud resources. When your app is deployed Nitric automatically converts these requests into appropriate resources for the specific provider. Nitric also takes care of adding the IAM roles, policies, etc. that grant the requested access. For example the key value store resource uses DynamoDB in AWS or FireStore on Google Cloud.

Create profiles with POST

Let's start adding features that allow our API consumers to work with profile data.

You could separate some or all of these handlers into their own files if you prefer. For simplicity we'll group them together in this guide.

profileApi.post("/profiles", (ctx) async {
  final uuid = Uuid();

  final id = uuid.v4();

  final profile = ctx.req.json();

  // Store the new profile in the profiles kv store
  await profiles.set(id, profile);

  // Send a success response.
  ctx.res.body = "Profile $id created.";

  return ctx;
});

Retrieve a profile with GET

profileApi.get("/profiles/:id", (ctx) async {
  final id = ctx.req.pathParams["id"]!;

  try {
    // Retrieve and return the profile data
    final profile = await profiles.get(id);
    ctx.res.json(profile);
  } on Exception catch (e) {
    print(e);
    ctx.res.status = 404;
    ctx.res.body = "Profile $id not found.";
  }

  return ctx;
});

Retrieve all profiles with GET

profileApi.get("/profiles", (ctx) async {
  List<Map<String, dynamic>> profilesList = [];
  final profilesIds = await profiles.keys();

  await for (final id in profilesIds) {
    final profile = await profiles.get(id);
    profilesList.add(profile);
  }

  ctx.res.body = jsonEncode(profilesList);
  ctx.res.headers["Content-Type"] = ["application/json"];

  return ctx;
});

Remove a profile with DELETE

profileApi.delete("/profiles/:id", (ctx) async {
  final id = ctx.req.pathParams["id"]!;

  // Delete the profile
  try {
    await profiles.delete(id);
    ctx.res.body = "Profile $id removed.";
  } on Exception catch (e) {
    ctx.res.status = 404;
    ctx.res.body = "Profile $id not found. $e";
  }

  return ctx;
});

Ok, let's run this thing!

Now that you have an API defined with handlers for each of its methods, it's time to test it locally.

nitric start

Once it starts, the application will receive requests via the API port. You can use the Local Dashboard or any HTTP client to test the API. We'll keep it running for our tests. If you want to update your functions, just save them, they'll be reloaded automatically.

Test the API

Below are some example requests you can use to test the API. You'll need to update all values in brackets [] and change the URL to your deployed URL if you're testing on the cloud.

Create Profile

curl --location --request POST 'http://localhost:4001/profiles' \
--header 'Content-Type: text/plain' \
--data-raw '{
    "name": "Peter Parker",
    "age": "21",
    "homeTown" : "Queens"
}'

Fetch Profile

curl --location --request GET 'http://localhost:4001/profiles/[id]'

Fetch All Profiles

curl --location --request GET 'http://localhost:4001/profiles'

Delete Profile

curl --location --request DELETE 'http://localhost:4001/profiles/[id]'

Deploy to the cloud

At this point, you can deploy what you've built to any of the supported cloud providers. To do this start by setting up your credentials and any configuration for the cloud you prefer:

Next, we'll need to create a stack. A stack represents a deployed instance of an application, which is a key value store of resources defined in your project. You might want separate stacks for each environment, such as stacks for dev, test and prod. For now, let's start by creating a dev stack.

The stack new command below will create a stack named dev that uses the aws provider.

nitric stack new dev aws

Continue by checking your stack file nitric.dev.yaml and adding in your preferred region, let's use us-east-1.

# The nitric provider to use
provider: nitric/aws@latest
# The target aws region to deploy to
# See available regions:
# https://docs.aws.amazon.com/general/latest/gr/lambda-service.html
region: us-east-1

Cloud deployments incur costs and while most of these resource are available with free tier pricing you should consider the costs of the deployment.

We called our stack dev, let's try deploying it with the up command

nitric up

When the deployment is complete, go to the relevant cloud console and you'll be able to see and interact with your API.

To tear down your application from the cloud, use the down command:

nitric down

Optional - Add profile image upload/download support

If you want to go a bit deeper and create some other resources with Nitric, why not add images to your profiles API.

Access profile buckets with permissions

Define a bucket named profilesImg with reading/writing permissions.

final profilesImg = Nitric.bucket("profilesImg").allow([BucketPermission.read, BucketPermission.write]);

Get a URL to upload a profile image

profileApi.get("/profiles/:id/image/upload", (ctx) async {
  final id = ctx.req.pathParams["id"];

  // Return a signed upload URL, which provides temporary access to upload a file.
  final photoUrl = await profilesImg.file("images/$id/photo.png").getUploadUrl();

  ctx.req.body = photoUrl;

  return ctx;
});

Get a URL to download a profile image

profileApi.get("/profiles/:id/image/download", (ctx) async {
  final id = ctx.req.pathParams["id"];

  // Return a signed download URL, which provides temporary access to download a file.
  final photoUrl = await profilesImg.file("images/$id/photo.png").getDownloadUrl();

  ctx.req.body = photoUrl;

  return ctx;
});

You can also return a redirect response that takes the HTTP client directly to the photo URL.

profileApi.get("/profiles/:id/image/view", (ctx) async {
  final id = ctx.req.pathParams["id"];

  // Redirect to a signed read-only file URL.
  final photoUrl = await profilesImg.file("images/$id/photo.png").getDownloadUrl();

  ctx.res.status = 303;
  ctx.res.headers["Location"] = [photoUrl];

  return ctx;
});

Test the extended API

Update all values in brackets [] and change the URL to your deployed URL if you're testing on the cloud.

Get an image upload URL

curl --location --request GET 'http://localhost:4001/profiles/[id]/image/upload'

Using the upload URL with curl

curl --location --request PUT '[url]' \
--header 'content-type: image/png' \
--data-binary '@/home/user/Pictures/photo.png'

Get an image download URL

curl --location --request GET 'http://localhost:4001/profiles/[id]/image/download'