Dart
JSON response
Learn JSON responses with shelf.
JSON responses
To return JSON from shelf, use Response.ok(jsonEncode(data), headers: {'content-type': 'application/json'}). jsonEncode comes from dart:convert; it turns Maps and Lists into JSON text.
The content-type header matters; browsers and clients parse the body as JSON. Without it, the body is treated as plain text and not auto-parsed.
Example: Response.ok(jsonEncode({'name': 'Ayşe'}), headers: {'content-type': 'application/json'}). This returns a 200 status with a JSON body.
The JSON content-type header
The headers parameter takes a Map<String, String> and sets response headers. For JSON, {'content-type': 'application/json'} is standard; it tells the client how to parse the body.
Header keys are case-insensitive; Content-Type and content-type are processed the same way. Values are sent as-is.
Multiple headers can be set: headers: {'content-type': 'application/json', 'cache-control': 'no-cache'}. cache-control controls browser caching.
Exercise Return a JSON response
Add import 'package:shelf/shelf.dart'; import 'dart:convert';. Define Response userHandler(Request r) => Response.ok(jsonEncode({'name': 'Ayşe'}), headers: {'content-type': 'application/json'});. Make main async; call the handler and add print(await resp.readAsString());.
Show example solution
import 'package:shelf/shelf.dart';
import 'dart:convert';
Response userHandler(Request r) =>
Response.ok(jsonEncode({'name': 'Ayşe'}),
headers: {'content-type': 'application/json'});
void main() async {
var resp = userHandler(Request('GET', Uri.parse('http://localhost/')));
print(await resp.readAsString());
}
Test yourself
-
JSON encode
var body = ____({'name': 'Ayşe'});
Show answer
var body = jsonEncode({'name': 'Ayşe'});
-
Match the JSON parts
- jsonEncode
- Map → String
- application/json
- Content type
- headers
- Header map
- Response.ok
- 200 response
-
Which header is required for JSON?
- content-type
- host
- accept
- user-agent
Show answer
content-type — the content-type: application/json header is required.
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