DOSpacesFileUpload.dart

import 'dart:io';

import 'package:flutter/material.dart';
import 'package:dospace/dospace.dart' as dospace;
import 'package:file_picker/file_picker.dart';

class DOSpacesFileUpload extends StatefulWidget {
  @override
  _DOSpacesFileUploadState createState() => _DOSpacesFileUploadState();
}

class _DOSpacesFileUploadState extends State<DOSpacesFileUpload> {

  dospace.Spaces spaces = new dospace.Spaces(
    //change with your project's region
    region: "nyc3",
    //change with your project's accessKey
    accessKey: "G3K3EPCZPCVRLQKOYUQE",
    //change with your project's secretKey
    secretKey: "PLpo3JZ9ARyf7Ash/wOBGRnnpnNvKFVzie86us/nNIk",
  );

  @override
  Widget build(BuildContext context) {

    return MaterialApp(
      home: Scaffold(
        body: SafeArea(
          child: Center(
            child: RaisedButton(
              child: Text('Upload File to DO Spaces'),
              onPressed: () async {

                File file = await FilePicker.getFile(
                  type: FileType.custom,
                  allowedExtensions: ['pdf','txt'],
                );

                // change with your project's name
                String project_name = "project_name";
                // change with your project's region
                String region = "nyc3";
                // change with your project's folder
                String folder_name = "taxdocs";
                String file_name = file.path.split('/').last;

                String etag = await spaces.bucket(project_name).uploadFile(
                    folder_name + '/' + file_name,
                    file,
                    'text/plain',
                    dospace.Permissions.public);
                print('upload: $etag');

                String uploaded_file_url = "https://"+project_name+"."+region+".digitaloceanspaces.com/" + folder_name + "/" + file_name;

                await spaces.close();
              },
            )
          )
        )
      )
    );
  }

}