How to save a file to Google Drive from Flutter web without a local file on disk?

Question

The example Drive API v3 code shows that to save a file to Google drive from your app you have to create a local file on disk first, then upload it.

Since I'm using Flutter for web (as well as Windows and Android) I can't save files to disk. (Nor would I want to, as it's very slow compared to just sending bytes in memory over http.)

How can I send data in memory straight to Google and have it saved as a file please (and vice versa)? I can't find any Dart code for this, nor Drive examples, anywhere that I've Googled.

Answer 1

I know your question is about flutter. I am not a flutter dev. After discussing this with you in comments it sounds like you are looking to find out if its even possible.

I went a head and tested this with C# and i can tell you that it is possible. All you have to do is turn your text into a memory stream and then upload that instead of a file stream. As it sounds like you already have the text in a memory stream you should be able to just upload it.

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Drive.v3;
using Google.Apis.Drive.v3.Data;
using Google.Apis.Services;
using Google.Apis.Upload;

namespace ConsoleApp1
{
    class Program
    {
        static readonly string CredentialsFile = "ServiceAccountCreds.json";
        private static readonly string FileName = "UploadFileString.txt";

        static async Task Main(string[] args)
        {
            Console.WriteLine("Hello World!");


            var serviceAccountCredentials = GoogleCredential.FromFile(CredentialsFile)
                .CreateScoped(DriveService.ScopeConstants.Drive);

            var service = new DriveService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = serviceAccountCredentials,
                ApplicationName = "Discovery Authentication Sample",
            });

            var uploadString = "Test";
            
            // Upload file Metadata
            var fileMetadata = new Google.Apis.Drive.v3.Data.File()
            {
                Name = FileName,
                Parents = new List<string>() {"1R_QjyKyvET838G6loFSRu27C-3ASMJJa"}
            };

            // Convert raw text to memory stream for upload.
            var fsSource = new MemoryStream(Encoding.UTF8.GetBytes(uploadString ?? ""));

            string uploadedFileId;
            
            // // Create a new file on Google Drive
            // await using (var fsSource = new FileStream(FileName, FileMode.Open, FileAccess.Read))
            // await using (var fsSource = new FileStream(FileName, FileMode.Open, FileAccess.Read))
            // {
                // Create a new file, with metadata and stream.
                var request = service.Files.Create(fileMetadata, fsSource, "text/plain");
                request.Fields = "*";
                var results = await request.UploadAsync(CancellationToken.None);

                if (results.Status == UploadStatus.Failed)
                {
                    Console.WriteLine($"Error uploading file: {results.Exception.Message}");
                }

                // the file id of the new file we created
                uploadedFileId = request.ResponseBody?.Id;
            //}
        }
    }
}

In theory any of the Flutter samples should work.