server_dart
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server dart
Alfred #
A performant, expressjs like web server / rest api framework thats easy to use and has all the bits in one place.
Quickstart:
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.get('/example', (req, res) => 'Hello world');
await app.listen();
}
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There is also a 6 part video series that walks you through creating a web server using Alfred from start to deployment, including databases and authentication. You can find that here: https://www.youtube.com/playlist?list=PLkEq83S97rEWsgFEzwBW2pxB7pRYb9wAB
Index #
Core principles
Usage overview
Quick start guide
Routing & incoming requests
Route params
Query string variables
Body parsing
File uploads
Middleware
No 'next'?
CORS
Responses
Custom type handlers
Static Files
File downloads
Error handling
404 Handling
Databases
What I want to do isn't listed
Websockets
Logging
Print routes
Multi threading & isolates
Contributions
Core principles #
A minimum of dependencies,
A minimum of code and sticking close to dart core libraries - easy to maintain!
Ease of use
Predictable, well established semantics
90%+ of everything you need all ready to go
Read about the background behind the project or why its different to shelf
Usage overview #
If you have ever used expressjs before you should be right at home:
import 'dart:io';
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.get('/text', (req, res) => 'Text response');
app.get('/json', (req, res) => {'json_response': true});
app.get('/jsonExpressStyle', (req, res) {
res.json({'type': 'traditional_json_response'});
});
app.get('/file', (req, res) => File('test/files/image.jpg'));
app.get('/html', (req, res) {
res.headers.contentType = ContentType.html;
return '<html><body><h1>Test HTML</h1></body></html>';
});
await app.listen(6565); //Listening on port 6565
}
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It should do pretty much what you expect. Handling bodies though do need an "await":
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.post('/post-route', (req, res) async {
final body = await req.body; //JSON body
body != null; //true
});
await app.listen(); //Listening on port 3000
}
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Internally dart provides a body parser, so no extra dependencies there.
The big difference you will see is the option to not call res.send or res.json etc - although you still can.
Each route accepts a Future as response. Currently you can pass back the following and it will be sent appropriately:
Return Dart Type
Returning REST type
List<dynamic>
JSON
Map<String, Object?>
JSON
Serializable object (Object.toJSON or Object.toJson) * see note
JSON
String
Plain Text
Stream<List<int>>
Binary
List<int>
Binary
File
Binary, with mime type inferred by extension
Directory
Serves static files
* If your object has a "toJSON" or "toJson" function, alfred will run it, and then return the result
If you want to return HTML, just set the content type to HTML like this:
import 'dart:io';
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.get('/html', (req, res) {
res.headers.contentType = ContentType.html;
return '<html><body><h1>Title!</h1></body></html>';
});
await app.listen(); //Listening on port 3000
}
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If you want to return a different type and have it handled automatically, you can extend Alfred with
custom type handlers.
Quick start guide #
If its all a bit overwhelming @iapicca put together a quick start guide which goes into a little
more detail: https://medium.com/@iapicca/alfred-an-express-like-server-framework-written-in-dart-1661e8963db9
Routing & incoming requests #
Routing follows a similar pattern to the more basic ExpressJS routes. While there is some regex
matching, mostly just stick with the route name and param syntax from Express:
/path/to/:id/property etc
The Express syntax has been extended to support parameter patterns and types. To enforce parameter
validation, a regular expression or a type specifier should be provided after the parameter name, using
another : as a separator:
/path/to/:id:\d+/property will ensure "id" is a string consisting of decimal digits
/path/to/:id:[0-9a-f]+/property will ensure "id" is a string consisting of hexadecimal digits
/path/to/:word:[a-z]+/property will ensure "word" is a string consisting of letters only
/path/to/:id:uuid/property will ensure "id" is a string representing an UUID
Available type specifiers are:
int: a decimal integer
uint: a positive decimal integer
double: a double (decimal form); note that scientific notation is not supported
date: a UTC date in the form of "year/month/day"; note how this type "absorbs" multiple segments of the URI
timestamp: a UTC date expressed in number of milliseconds since Epoch
uuid: a string resembling a UUID (hexadecimal number formatted as xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx); note that no effort is made to ensure this is a valid UUID
Type Specifier
Regular Expression
Dart type
int
-?\d+
int
uint
\d+
int
double
-?\d+(?:\.\d+)
double
date
-?\d{1,6}/(?:0[1-9]|1[012])/(?:0[1-9]|[12][0-9]|3[01])
DateTime
timestamp
-?\d+
DateTime
uuid
[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}
String
So for example:
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.all('/example/:id:int/:name', (req, res) {
req.params['id'] != null;
req.params['id'] is int;
req.params['name'] != null;
});
app.all('/example/:id/:name', (req, res) {
req.params['id'] != null;
req.params['name'] != null;
});
app.get('/blog/:date:date/:id:int', (req, res) {
req.params['date'] != null;
req.params['date'] is DateTime;
req.params['id'] != null;
req.params['id'] is int;
});
await app.listen();
}
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You can also use a wildcard for a route, and provided another route hasn't already resolved the
response it will be hit. So for example if you want to authenticate a whole section of an api youc
can do this:
import 'dart:async';
import 'dart:io';
import 'package:alfred/alfred.dart';
FutureOr _authenticationMiddleware(HttpRequest req, HttpResponse res) async {
res.statusCode = 401;
await res.close();
}
void main() async {
final app = Alfred();
app.all('/resource*', (req, res) => _authenticationMiddleware);
app.get('/resource', (req, res) {}); //Will not be hit
app.post('/resource', (req, res) {}); //Will not be hit
app.post('/resource/1', (req, res) {}); //Will not be hit
await app.listen();
}
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Route params #
You can access any params for routes from the req.params object as below:
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.all('/example/:id/:name', (req, res) {
req.params['id'] != null;
req.params['name'] != null;
});
await app.listen();
}
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Query string variables #
Querystring variables are exposed req.uri.queryParameters object in the request as below:
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.post('/route', (req, res) async {
/// Handle /route?qsvar=true
final result = req.uri.queryParameters['qsvar'];
result == 'true'; //true
});
await app.listen(); //Listening on port 3000
}
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Body parsing #
To access the body, simply call await req.body.
Alfred will interpret the body type from the content type headers and parse it appropriately. It handles url encoded, multipart & json bodies out of the box.
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.post('/post-route', (req, res) async {
final body = await req.body; //JSON body
body != null; //true
});
await app.listen(); //Listening on port 3000
}
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File uploads #
To upload a file the body parser will handle exposing the data you need. Its actually pretty easy
just give it a go and set a breakpoint to see what the body parser spits back.
A working example of file uploads is below to get you started:
import 'dart:io';
import 'package:alfred/alfred.dart';
final _uploadDirectory = Directory('uploadedFiles');
Future<void> main() async {
final app = Alfred();
app.get('/files/*', (req, res) => _uploadDirectory);
/// Example of handling a multipart/form-data file upload
app.post(
'/upload',
(req, res) => (HttpRequest req, HttpResponse res) async {
final body = await req.bodyAsJsonMap;
// Create the upload directory if it doesn't exist
if (await _uploadDirectory.exists() == false) {
await _uploadDirectory.create();
}
// Get the uploaded file content
final uploadedFile = (body['file'] as HttpBodyFileUpload);
var fileBytes = (uploadedFile.content as List<int>);
// Create the local file name and save the file
await File('${_uploadDirectory.absolute}/${uploadedFile.filename}')
.writeAsBytes(fileBytes);
/// Return the path to the user
///
/// The path is served from the /files route above
return ({
'path':
'https://${req.headers.host ?? ''}/files/${uploadedFile.filename}'
});
});
await app.listen();
}
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Middleware #
You can specify a middleware for all routes by using wildcards:
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.all('*', (req, res) {
// Perform action
req.headers.add('x-custom-header', "Alfred isn't bad");
/// No need to call next as we don't send a response.
/// Alfred will find the next matching route
});
app.get('/otherFunction', (req, res) {
//Action performed next
return {'message': 'complete'};
});
await app.listen();
}
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Middleware declared this way will be executed in the order its added to the app.
You can also add middleware to a route, this is great to enforce authentication etc on an endpoint:
import 'dart:async';
import 'dart:io';
import 'package:alfred/alfred.dart';
FutureOr exampleMiddlware(HttpRequest req, HttpResponse res) {
// Do work
if (req.headers.value('Authorization') != 'apikey') {
throw AlfredException(401, {'message': 'authentication failed'});
}
}
void main() async {
final app = Alfred();
app.all('/example/:id/:name', (req, res) {}, middleware: [exampleMiddlware]);
await app.listen(); //Listening on port 3000
}
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What? No 'next'? how do I even? #
OK, so the rules are simple. If a middleware resolves a http request, no future middleware gets executed.
So if you return an object from the middleware, you are preventing future middleware from executing.
If you return null it will yield to the next middleware or route.
** returning null is the equivalent of 'next' **
CORS #
There is a cors middleware supplied for your convenience. Its also a great example of how to write a middleware for Alfred
import 'package:alfred/alfred.dart';
import 'package:alfred/src/middleware/cors.dart';
void main() async {
final app = Alfred();
// Warning: defaults to origin "*"
app.all('*', cors(origin: 'myorigin.com'));
await app.listen();
}
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Responses #
Alfred is super easy, generally you just return JSON, a file, a String or a Binary stream and you are all good.
The big difference from express is you will see is the option to not call res.send or res.json etc - although you still can.
Each route accepts a Future as response. Currently you can pass back the following and it will be sent appropriately:
List<dynamic> - JSON
Map<String, Object?> - JSON
String - Plain text
Stream<List<int>> - Binary
List<int> - Binary
File - Binary, with mime type inferred by extension
Directory - Serves static files
Each type listed above has a Type Handler build in. You can create your own custom type handlers
Custom type handlers #
Alfred has a pretty cool mechanism thanks to Dart's type system to automatically resolve a response
based on the returned type from a route. These are called Type Handlers.
If you want to create custom type handlers, just add them to the type handler
array in the app object. This is a bit advanced, and I expect it would be more
for devs wanting to extend Alfred:
import 'package:alfred/alfred.dart';
class Chicken {
String get response => 'I am a chicken';
}
void main() {
final app = Alfred();
app.typeHandlers.add(TypeHandler<Chicken>((req, res, Chicken val) async {
res.write(val.response);
await res.close();
}));
/// The app will now return the Chicken.response if you return one from a route
app.get('/kfc', (req, res) => Chicken()); //I am a chicken;
app.listen(); //Listening on 3000
}
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Static Files, uploads and deleting #
This one is super easy - just pass in a public path and a dart Directory object and Alfred does
the rest.
import 'dart:io';
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
/// Note the wildcard (*) this is very important!!
app.get('/public/*', (req, res) => Directory('test/files'));
await app.listen();
}
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You can also pass in a directory and a POST or PUT command and upload files to a local directory if
you are using multipart/form encoding. Simply supply the field as file:
import 'dart:io';
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.post('/public', (req, res) => Directory('test/files'));
await app.listen();
}
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If you want to delete a file?
import 'dart:async';
import 'dart:io';
import 'package:alfred/alfred.dart';
FutureOr isAuthenticatedMiddleware(HttpRequest req, HttpResponse res) {
if (req.headers.value('Authorization') != 'MYAPIKEY') {
throw AlfredException(
401, {'error': 'You are not authorized to perform this operation'});
}
}
void main() async {
final app = Alfred();
/// Note the wildcard (*) this is very important!!
///
/// You almost certainly want to protect this endpoint with some middleware
/// to authenticate a user.
app.delete('/public/*', (req, res) => Directory('test/files'),
middleware: [isAuthenticatedMiddleware]);
await app.listen();
}
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Security? Build in a middleware function to authenticate a user etc.
File downloads #
As mentioned above - if you want to return a file, simply return it from the route callback.
However the browser will probably try to render it in browser, and not download it.
You can just set the right headers, but there is a handy little helper that will do it all for you.
See res.setDownload below.
import 'dart:io';
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.get('/image/download', (req, res) {
res.setDownload(filename: 'image.jpg');
return File('test/files/image.jpg');
});
await app.listen(); //Listening on port 3000
}
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Error handling #
You can either set the status code on the response object yourself and send the data manually, or
you can do this from any route:
app.get("/",(req, res) => throw AlfredException(400, {"message": "invalid request"}));
If any of the routes bubble an unhandled error, it will catch it and throw a 500 error.
If you want to handle the logic when a 500 error is thrown, you can add a custom handler when you
instantiate the app. For example:
import 'dart:async';
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred(onInternalError: errorHandler);
await app.listen();
app.get('/throwserror', (req, res) => throw Exception('generic exception'));
}
FutureOr errorHandler(HttpRequest req, HttpResponse res) {
res.statusCode = 500;
return {'message': 'error not handled'};
}
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404 Handling #
404 Handling works the same as 500 error handling (or uncaught error handling). There is a default
behaviour, but if you want to override it, simply handle it in the app declaration.
import 'dart:async';
import 'dart:io';
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred(onNotFound: missingHandler);
await app.listen();
}
FutureOr missingHandler(HttpRequest req, HttpResponse res) {
res.statusCode = 404;
return {'message': 'not found'};
}
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But what about Mongo or Postgres or
The other two systems that inspired this project to be kicked off - Aqueduct and Angel - both had
some sort of database integration built in.
You do not need this.
Access the dart drivers for the database system you want directly, they all use them behind the scenes:
Mongo - https://pub.dev/packages/mongo_dart
Postgres - https://pub.dev/packages/postgres
SQLLite - https://pub.dev/packages/sqlite3
You will be fine. I have used them this way and they work.
I have rolled my own classes that act as a sort of ORM, especially around Mongo. Its suprisingly effective
and doesn't rely on much code.
What I want to do isn't listed #
While there are bunch of helpers built in - you have direct access to the low level apis available
from the dart:io package. All helpers are just extension methods to:
HttpRequest: https://api.dart.dev/stable/2.10.5/dart-io/HttpRequest-class.html
HttpResponse: https://api.dart.dev/stable/2.10.5/dart-io/HttpResponse-class.html
So you can compose and write any content you can imagine there. If there is something you want to do
that isn't expressly listed by the library, you will be able to do it with a minimum of research into
underlying libraries. A core part of the architecture is to not build you into a wall.
Websockets #
Alfred supports websockets too!
There is a quick chat client in the examples
import 'dart:async';
import 'dart:io';
import 'package:alfred/alfred.dart';
import 'package:alfred/src/type_handlers/websocket_type_handler.dart';
Future<void> main() async {
final app = Alfred();
// Path to this Dart file
var dir = File(Platform.script.path).parent.path;
// Deliver web client for chat
app.get('/', (req, res) => File('$dir/chat-client.html'));
// Track connected clients
var users = <WebSocket>[];
// WebSocket chat relay implementation
app.get('/ws', (req, res) {
return WebSocketSession(
onOpen: (ws) {
users.add(ws);
users
.where((user) => user != ws)
.forEach((user) => user.send('A new user joined the chat.'));
},
onClose: (ws) {
users.remove(ws);
users.forEach((user) => user.send('A user has left.'));
},
onMessage: (ws, dynamic data) async {
users.forEach((user) => user.send(data));
},
);
});
final server = await app.listen();
print('Listening on ${server.port}');
}
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Logging #
For more details on logging click here.
Print routes #
Want to quickly print out the registered routes? (recommended when you fire up the server)
call Alfred.printRoutes ie:
import 'package:alfred/alfred.dart';
void main() async {
final app = Alfred();
app.get('/html', (req, res) {});
app.printRoutes(); //Will print the routes to the console
await app.listen();
}
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Multi threading and isolates #
You can use the app in multithreaded mode. When spawning this way, requests are evenly distributed
amongst the various isolates. Alfred is not particularly prescriptive about how you manage the isolates
just that "it works" when you fire up multiples.
import 'dart:isolate';
import 'package:alfred/alfred.dart';
Future<void> main() async {
// Fire up 5 isolates
for (var i = 0; i < 5; i++) {
unawaited(Isolate.spawn(startInstance, ''));
}
// Start listening on this isolate also
startInstance(null);
}
/// The start function needs to be top level or static. You probably want to
/// run your entire app in an isolate so you don't run into trouble sharing DB
/// connections etc. However you can engineer this however you like.
///
void startInstance(dynamic message) async {
final app = Alfred();
app.all('/example', (req, res) => 'Hello world');
await app.listen();
}
/// Simple function to prevent linting errors, can be ignored
void unawaited(Future future) {}
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Deployment #
There are many ways to skin this cat, you can upload the source code to a VPS yourself, build a binary locally and upload it to a server somewhere, but a fairly elegant way to accomplish a production level deployment is to containerize an AOT build of the server and run it on a PAAS.
Lucky there is a tutorial for that!
https://ryan-knell.medium.com/build-and-deploy-a-dart-server-using-alfred-docker-and-google-cloud-run-from-start-to-finish-d5066e3ab3c6
Contributions #
PRs are welcome and encouraged! This is a community project and as long as the PR keeps within the key principles listed it will probably be accepted. If you have an improvement you would like to to add but are not sure just reach out in the issues section.
Before you submit your code, you can run the ci_checks.sh shell script that will do many of the tests the CI suite will perform.
License:
For personal and professional use. You cannot resell or redistribute these repositories in their original state.
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