A Vercel Runtime to write serverless functions in Dart.

Usage

A serverless function file should contain a shelf handler named handler. Behind the scenes, the runtime will combine the handler with an AWS runtime and compile it into a binary file using dart2native.

Example

Create a file called api/hello.dart with the following contents.

import 'dart:io' show Platform;
import 'package:shelf/shelf.dart';

Response handler(Request req) {
  final version = Platform.version.split(" ").first;
  return Response.ok('Hello, from Dart v$version!');
}

Next, select the vercel-dart runtime to handle serverless dart functions in your vercel.json file.

{
  "functions": {
    "api/**/*.dart": { "runtime": "vercel-dart@1.1.0" }
  }
}

Demo: vercel-dart.vercel.app/api/hello

Examples

Check out the repository's api folder for more examples.

Reading Queries

import 'package:shelf/shelf.dart';

Response handler(Request req) {
  return Response.ok('Query is: ${req.requestedUri.query}');
}

Demo: vercel-dart.vercel.app/api/query

Custom Status Codes

import 'package:shelf/shelf.dart';

Response handler(Request req) =>
    Response.movedPermanently('https://youtu.be/dQw4w9WgXcQ');
    
// Response.movedPermanetly -> 301
// Response.notFound -> 404
// etc.

Demo: vercel-dart.vercel.app/api/redirect

Custom Content Types

JSON

import 'dart:convert';
import 'dart:io';
import 'package:shelf/shelf.dart';

Response handler(Request req) {
  final data = {
    'host': req.requestedUri.host,
    'path': req.requestedUri.path,
    'query': req.requestedUri.queryParameters
  };

  return Response.ok(
    jsonEncode(data),
    headers: {
      'content-type': ContentType.json.toString(),
    },
  );
}

Demo: vercel-dart.vercel.app/api/json

HTML

import 'dart:io';
import 'package:shelf/shelf.dart';

Response handler(Request req) {
  final html = '''
    <h1>Hello, World</h1>
  ''';

  return Response.ok(
    html,
    headers: {
      'content-type': ContentType.html.toString(),
    },
  );
}

Demo: vercel-dart.vercel.app/api/html

Configuration

Here are the build environment variables that you may configure for your serverless functions.

Name	Description	Default
DART_CHANNEL	The dart channel that serverless function will use.	stable
DART_VERSION	The dart version that serverless function will use.	2.10.5

Note that you need to use dart version >= 2.6 for dart2native to work.

Learn more about dart channels and versions here.

FAQ

Can I use pubspec.yaml?

Yes, just make sure it is at the same directory level as the function. The runtime will automatically run pub get before building the binary file.

Is it fast?

I'm not sure because I don't know how to benchmark. But according to my experience, it feels like it's really fast. I may be biased so help me benchmark it if you know how to.

Can I run it with vercel dev locally?

Yes, but because it won't install dart during development, make sure your machine has a working version of dart >= 2.6 installed properly.

Acknowledgement

While I was trying to build this, because I didn't any prior experience with things, a lot of open-source libraries/projects were very useful to me. The prominent ones of them are now-rust, vercel-bash, vercel-deno and aws-lambda-dart-runtime.

License

MIT © Frenco