File transfer via gRPC in .NET

GrpcFileTransfer is a .NET library to transfer files between machines using protobuf & gRPC.

Getting started

To use this library, follow this three main steps:

• Install in your project from nuget
• Implement the server side service using the abstract AbstractFileTransferService class
• Register the service
• Use the FileTransferClient to up- & download files

Implementing the server class

The base class AbstractFileTransferService for the server side code is abstract and needs to be implemented to provide at least a response to the GetInfo api call in FileTransferService.proto.

A minimal implementation could look like this:

public class FileTransferService : AbstractFileTransferService
{
    protected override Task<ServiceInformation> GetInfoImplementation(Empty request, ServerCallContext context)
    {
        return Task.FromResult(new ServiceInformation
        {
            Name = "File Transfer Service",
            Description = "Transfer files over gRPC",
            Version = "1.2.3
        });
    }
}

All logic for actually handling up- & and downloads is contained in the abstract class.

To add custom logic before / after downloads, the AbstractFileTransferService offers the following virtual functions that can be overriden if required:

• ValidateHeaders, which is called before every up- or download and gets passed the gRPC headers. This can be used for custom header validation, e.g. to validate an authorization header.
• PreUploadHook called before an upload.
• PostUploadHook called after an upload.
• PreDownloadHook called before an download.
• PostDownloadHook called after an download.

For an example on how to utilize this functions, see the FileTransferServiceTestImplementation.cs in the integration tests. It demonstrates how the client does not need to be aware of the actual filepath on the server. Instead, a file token is passed as fileId to the Upload and Download functions on the client side and the overriden Pre- and PostHooks functions are used to map the token to the server file path.

Registering the service

When using asp.net core, the implemented service class needs to be registered just like any other grpc service.

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddGrpc();
        services.AddSingleton<FileTransferService>();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
            app.UseDeveloperExceptionPage();

        app.UseRouting();
        app.UseEndpoints(endpoints => { endpoints.MapGrpcService<FileTransferService>(); });
    }
}

For more information, see the corresponding Microsoft help page: https://learn.microsoft.com/en-us/aspnet/core/grpc/aspnetcore

Using the client

Using the client is straightforward - create an instance, call the up- & download functions:

var client = new FileTransferClient(grpcChannel, _logger);
await client.Upload(targetFile, sourceFile, hashVerification: true).ConfigureAwait(false);
await client.Download(targetFile, downloadedFile, hashVerification: true).ConfigureAwait(false);

See also the corresponding tests for a ready-to-run example: FileTransferIntegrationTests.cs.