JsonClient for Dart

Is a generic async HTTP Client optimized for consuming JSON web services.

Installing via Pub

Add this to your package's pubspec.yaml file:

  json_client: 0.1.1

The current version relies on the dart:io package so only works in the Dart VM. A future update will include an identical JsonClient that wraps HttpRequest (i.e. Ajax's XMLHttpRequest) so can be transpiled to JavaScript and run in all browsers. Watch this repo or follow @demisbellot for updates.

JsonClient takes advantages of Dart's noSuchMethod language feature to offer a succinct, ruby-esque dynamic API as well as the standard get/post/put/delete HTTP Client methods found in most HTTP clients.


The only argument needed is the urlRoot which is the base Url that all relative Urls will base themselves off.

String urlRoot = "http://mono.servicestack.net/Backbone.Todos";
var client = new JsonClient(urlRoot);

The Url above points to a REST API backend for the Backbone.js TODOs demo app built with the ServiceStack .NET Webservices Framework.

With the just client and the url in-place, we can now start making API calls - Where getting the entire TODO list is no harder than:


or as a method:


This call makes a JSON request for the /todos url.

Using Futures in Dart

We use Dart's Future's API to attach your callback as a continuation on the returned Future, which looks like:

  .then((todoItems) => print("I have ${todoItems.length} things left todo"));

The dynamic API also supports optional params, any scalar variable (e.g. String, number) is combined with the urlRoot and the dynamicMethod() name to form the url like: {urlRoot}/{dynamicMethod}/{scalarParam}. Knowing this we can fetch a single todo with:

  .then((todo) => print("I still need to do ${todo['content']}"));

Which will GET the JSON at {urlRoot}/todos/1. The param can also be a String which is just appended as-is so can also include queryString params. Here's another example of making a GET request for fileInfo from the WebDav-like RestFiles Service:

var client = new JsonClient("http://mono.servicestack.net/RestFiles");
  .then((fileInfo) => print("${fileInfo['Name']} is ${fileInfo['FileSizeBytes']} bytes"));

Which just makes a JSON GET request to /files/services/FilesService.cs.txt.

If however the param is an Object or a List (i.e. Array in JavaScript) then a POST request is made instead so creating a new todo item can be done with:

client.todos({'content':'Add a new TODO!', 'order':1});

Only GET's and POST's can be made with the dynamic API. To make PUT and DELETE requests you need to fallback to the slightly more verbose HTTP Verb methods. To update an existing TODO you would do:

client.put('todos/1', {"content":"Learn Dart","done":true});

And likewise you can DELETE the above with:


Note: If you prefer the more explicit methods you can also issue GET and POST requests in the same way with client.get() and client.post().

More API

Apart from the methods described above, the JsonClient includes support for detailed logging (useful when debugging issues):

client.logLevel = LogLevel.All; //or Debug, Error, etc.

Chainging the urlRoot:

client.urlRoot = "http://host/new/base/url";

Request and response filters allowing you to decorate HTTP requests before they're sent, or HTTP responses before they're processed:

client.requestFilter  = (HttpClientRequest httpReq)  { ... };
client.responseFilter = (HttpClientResponse httpRes) { ... };

A global error handler should you wish to handle errors generically:

client.onError = (e) { ... };

Futures Example

Futures in Dart also go by the name of Promises in other languages. They're purpose is to hold a value that is yet to be determined but will still allow you to attach and compose continuation logic to be executed when the value is computed (or in our case when our response is received).

Now that we've covered the basics, lets go through a more complete demo. For this example we'll delete all the existing TODOs, create new ones from a list and re-use an existing function to mark one of them as completed.

List todos = [
    'Learn Dart!', 
    'Clear all existing todo items',
    'Add all these todos',
    'Mark this todo as done',
    'do ALL THE THINGS!'
final String completeTodo = 'Mark this todo as done';

markTodoCompleted(List createdTodos) {
    List matchingTodos = createdTodos.where((x) => x['content'] == completeTodo).toList();
    var todo = matchingTodos[0];
    todo['done'] = true;
    client.put("todos/${todo['id']}", todo);    

  .then((List existingTodos){
    Future.wait(existingTodos.map((x) => client.delete('todos/${x['id']}')) )
      .then((_) { 
        int i=0;
        Future.wait( todos.map((text) => client.todos({'content':text, 'order':i++})) )
          .then( markTodoCompleted );

You will be able to see your results after running each example at: http://mono.servicestack.net/Backbone.Todos/

More Examples

More client usage examples can be seen at Example.dart