Server-side Dart with Shelf

Setup

# pubspec.yaml
dependencies:
  shelf: ^1.4.0
  shelf_router: ^1.1.0

Basic Server

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

Response _handler(Request request) {
  return Response.ok('Hello, World!', headers: {'Content-Type': 'text/plain'});
}

void main() async {
  var handler = const Pipeline()
      .addMiddleware(logRequests())
      .addHandler(_handler);

  var server = await shelf_io.serve(handler, '0.0.0.0', 8080);
  print('Server running on http://localhost:$${server.port}');
}

Routing

import 'package:shelf_router/shelf_router.dart';

void main() async {
  var router = Router();

  router.get('/', (Request req) => Response.ok('Welcome!'));
  router.get('/hello/<name>', (Request req, String name) =>
      Response.ok('Hello, $name!'));
  router.get('/users', (Request req) => Response.ok('All users'));
  router.post('/users', (Request req) async {
    var body = await req.readAsString();
    return Response.ok('Created: $body', headers: {'Content-Type': 'application/json'});
  });

  var handler = const Pipeline()
      .addMiddleware(logRequests())
      .addHandler(router.call);

  await shelf_io.serve(handler, 'localhost', 8080);
  print('Running on http://localhost:8080');
}

Middleware

// CORS middleware
Middleware corsMiddleware() {
  return (Handler handler) {
    return (Request request) async {
      if (request.method == 'OPTIONS') {
        return Response.ok('', headers: {
          'Access-Control-Allow-Origin': '*',
          'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE, OPTIONS',
          'Access-Control-Allow-Headers': 'Content-Type, Authorization',
        });
      }
      final response = await handler(request);
      return response.change(headers: {
        'Access-Control-Allow-Origin': '*',
      });
    };
  };
}

// Auth middleware
Middleware authMiddleware(String secretKey) {
  return (Handler handler) {
    return (Request req) async {
      var auth = req.headers['Authorization'];
      if (auth == null || !auth.startsWith('Bearer ')) {
        return Response.forbidden('Unauthorized');
      }
      return handler(req);
    };
  };
}

JSON REST API

import 'dart:convert';
import 'package:shelf/shelf.dart';
import 'package:shelf_router/shelf_router.dart';
import 'package:shelf/shelf_io.dart' as io;

final _users = <int, Map<String, dynamic>>{
  1: {'id': 1, 'name': 'Alice', 'email': 'alice@example.com'},
  2: {'id': 2, 'name': 'Bob',   'email': 'bob@example.com'},
};

Response jsonResponse(dynamic data, {int status = 200}) => Response(
  status,
  body: jsonEncode(data),
  headers: {'Content-Type': 'application/json'},
);

void main() async {
  var router = Router()
    ..get('/users', (req) => jsonResponse(_users.values.toList()))
    ..get('/users/<id>', (req, String id) {
      var user = _users[int.tryParse(id)];
      return user != null ? jsonResponse(user) : Response.notFound('Not found');
    })
    ..post('/users', (req) async {
      var body = jsonDecode(await req.readAsString());
      var id = _users.length + 1;
      _users[id] = {'id': id, ...body};
      return jsonResponse(_users[id], status: 201);
    });

  var handler = Pipeline().addMiddleware(logRequests()).addHandler(router.call);
  await io.serve(handler, 'localhost', 8080);
  print('API on http://localhost:8080');
}

🧠 Quiz

Summary

Use the shelf package for server-side Dart HTTP servers. Define routes with shelf_router's Router. Chain middleware (logging, CORS, auth) with Pipeline().addMiddleware(). Return JSON with a helper that sets Content-Type: application/json. Start the server with shelf_io.serve(handler, host, port).