Dart HttpServer

last modified April 4, 2025

The HttpServer class in Dart provides functionality to create HTTP servers. It's part of the dart:io library and enables building web applications and APIs.

HttpServer handles incoming HTTP requests and manages responses. It supports features like request routing, headers, and different HTTP methods.

Basic Definition

HttpServer is a class that implements an HTTP server in Dart. It listens for incoming HTTP requests on a specified port and address.

Key features include request handling, response generation, and support for persistent connections. It forms the foundation for web applications in Dart.

Basic HttpServer Example

This example shows a simple HTTP server that responds to all requests.

import 'dart:io';

Future<void> main() async {
  final server = await HttpServer.bind('localhost', 8080);
  print('Server running on http://${server.address.host}:${server.port}');

  await for (HttpRequest request in server) {
    request.response
      ..headers.contentType = ContentType.text
      ..write('Hello from Dart server!')
      ..close();
  }
}

We create an HttpServer bound to localhost on port 8080. For each request, we send a simple text response. The server runs asynchronously using Futures.

$ dart main.dart
Server running on http://localhost:8080

Handling Different Routes

This example demonstrates basic route handling in an HTTP server.

import 'dart:io';

Future<void> main() async {
  final server = await HttpServer.bind('localhost', 8080);
  
  await for (HttpRequest request in server) {
    switch (request.uri.path) {
      case '/':
        request.response.write('Home page');
        break;
      case '/about':
        request.response.write('About page');
        break;
      default:
        request.response.statusCode = HttpStatus.notFound;
        request.response.write('Not found');
    }
    await request.response.close();
  }
}

We examine the request URI path to provide different responses. The default case handles unknown routes with a 404 status code. Each response must be closed.

$ dart main.dart

Handling POST Requests

This example shows how to process POST requests and read request bodies.

import 'dart:io';
import 'dart:convert';

Future<void> main() async {
  final server = await HttpServer.bind('localhost', 8080);
  
  await for (HttpRequest request in server) {
    if (request.method == 'POST') {
      try {
        final content = await utf8.decoder.bind(request).join();
        final data = jsonDecode(content) as Map;
        request.response.write('Received: ${data['message']}');
      } catch (e) {
        request.response.statusCode = HttpStatus.badRequest;
        request.response.write('Invalid request');
      }
    } else {
      request.response.statusCode = HttpStatus.methodNotAllowed;
      request.response.write('Only POST supported');
    }
    await request.response.close();
  }
}

We check the request method and process POST data as JSON. The request body is read asynchronously. Error handling ensures robust operation.

$ dart main.dart

Serving Static Files

This example demonstrates serving static files from a directory.

import 'dart:io';

Future<void> main() async {
  final server = await HttpServer.bind('localhost', 8080);
  final staticDir = Directory('static');
  
  await for (HttpRequest request in server) {
    final filePath = 'static${request.uri.path}';
    final file = File(filePath);
    
    if (await file.exists()) {
      await request.response.addStream(file.openRead());
    } else {
      request.response.statusCode = HttpStatus.notFound;
      request.response.write('File not found');
    }
    await request.response.close();
  }
}

We serve files from a 'static' directory matching the request path. The file contents are streamed directly to the response for efficiency.

$ dart main.dart

WebSocket Server

This example shows upgrading HTTP connections to WebSocket.

import 'dart:io';

Future<void> main() async {
  final server = await HttpServer.bind('localhost', 8080);
  
  await for (HttpRequest request in server) {
    if (WebSocketTransformer.isUpgradeRequest(request)) {
      final socket = await WebSocketTransformer.upgrade(request);
      socket.listen((data) {
        socket.add('Echo: $data');
      });
    } else {
      request.response.statusCode = HttpStatus.badRequest;
      request.response.write('WebSocket expected');
      await request.response.close();
    }
  }
}

We check for WebSocket upgrade requests and handle them separately. The WebSocket connection allows bidirectional communication with the client.

$ dart main.dart

Best Practices

• Error handling: Always handle potential I/O errors
• Resource management: Close responses properly
• Async operations: Use await for async operations
• Security: Validate all incoming data
• Performance: Stream large responses

Source

Dart HttpServer Documentation

This tutorial covered Dart's HttpServer class with practical examples showing basic usage, route handling, POST processing, static files, and WebSockets.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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