Flutter: How do I upload a JSON file to a URL? - dart

Question

I've been searching in vain for a simple way of uploading a JSON file to a specific URL but I haven't been able to find one, for Flutter.
I have implemented the code to download a simple JSON file from a specific URL. What I haven't been able to find is how to upload the same file to same location.
Do I need to do the multipart stuff? And I'm not even sure how that works.
EDIT
I'm starting with Map data (Map) and I want to upload it to a server as JSON (text file). This code is specific to binary data. And yes, I'm just writing to a URL, not an endpoint:
Upload(File imageFile) async {
var stream = new
http.ByteStream(DelegatingStream.typed(imageFile.openRead()));
var length = await imageFile.length();
var uri = Uri.parse(uploadURL);
var request = new http.MultipartRequest("POST", uri);
var multipartFile = new http.MultipartFile('file', stream, length,
filename: basename(imageFile.path));
//contentType: new MediaType('image', 'png'));
request.files.add(multipartFile);
var response = await request.send();
print(response.statusCode);
response.stream.transform(utf8.decoder).listen((value) {
print(value);
});
}

Answer 1

To upload files to an endpoint, you can use http.MultipartRequest - this allows you to upload files with binary content (images, docs, etc.) and files with regular text.
import 'package:http/http.dart' as http;
String url = // your endpoint
var req = http.MultipartRequest('POST', Uri.parse(url));
Then to upload
var request = http.MultipartRequest('POST', Uri.parse(url));
request.files.add(
await http.MultipartFile.fromPath(
'json',
filePath
)
);
var res = await request.send();