Category Archives: gRPC

.Net Core Web Api Returning Binary File with No Headers Instead of Expected Response

Hey everyone,

A small issue I’ve run into while setting up a .net core web api microservice that also utilises a number of gRPC services. Symptoms were as follows:

Response Read via Fiddler
– HTTP/1.0 200 This buggy server did not return headers
– Value was binary and unable to be read

Server logs

03:59:23 DBG] Connection id “0HM01U963EUAR” accepted.
[03:59:23 DBG] Connection id “0HM01U963EUAR” started.
[03:59:23 DBG] Connection id “0HM01U963EUAR”: HTTP/2 connection error.
Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2ConnectionErrorException: HTTP/2 connection error (PROTOCOL_ERROR): Invalid HTTP/2 connection preface.
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2Connection.ParsePreface(ReadOnlySequence`1& buffer, SequencePosition& consumed, SequencePosition& examined)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2Connection.TryReadPrefaceAsync()
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2Connection.ProcessRequestsAsync[TContext](IHttpApplication`1 application)
[03:59:23 DBG] Connection id “0HM01U963EUAR” is closed. The last processed stream ID was 0.
[03:59:23 VRB] Connection id “0HM01U963EUAR” sending GOAWAY frame for stream ID 0 with length 8 and flags 0x0
[03:59:23 DBG] Connection id “0HM01U963EUAR” stopped.
[03:59:23 DBG] Connection id “0HM01U963EUAR” sending FIN because: “The Socket transport’s send loop completed gracefully.”

The issue turned out to be that in appSettings.json the default kestrel endpoint had been set to utilise http2. Removing this immediately resolved the issue. It may also be worth double checking your launch settings, startup.cs and program.cs to ensure that nothing’s been overridden.

I expect that any similar routing issues would result in similar symptoms so hopefully this post will be able to save a few people a bit time!


“protobuf” visual studio a namespace cannot directly contain members such as fields or methods

Hi everyone,

I ran into the following intellisense error while adding a new proto file:

“protobuf” visual studio a namespace cannot directly contain members such as fields or methods

This was one of many errors that were shown and appeared to be an issue with Intellisense mistaking the file for a normal class definition. The following appears to have fixed it:

1) Right click on the file and select “exclude from project”
2) Clean the solution and rebuild
3) Re-include the file in the project (you may have to toggle ‘Show All Files’ at the top of solution explorer to see the excluded item).


Automapper protobuf datetime to timestamp c#

Hi everyone,

I ran into the following error tonight while attempting to use automapper to map a datetime field to a protobuf timestamp property:

automapper missing type map “DateTime -> Timestamp”

To fix it, add the following to your mapping profile:

CreateMap().ConvertUsing(x => x.ToTimestamp());

I later hit a similar error parsing a different entity:

Type Map configuration:
Entity-> EntityDto
EntityService.Models.Entity-> EntityService.EntityDto

Destination Member:

—> System.ArgumentException: Conversion from DateTime to Timestamp requires the DateTime kind to be Utc (Parameter ‘dateTime’)

Implementing the following map appears to have resolved it:

CreateMap().ConvertUsing(x => Timestamp.FromDateTime(DateTime.SpecifyKind(x, DateTimeKind.Utc)));

If you’re planning to go the other way (timestamp -> datetime) you may also need the following:

CreateMap().ConvertUsing(x => x.ToDateTime());

I’m currently using the following base class in my library:

public class BaseMappingProfile : Profile
public BaseMappingProfile()
CreateMap().ConvertUsing(x => Timestamp.FromDateTime(DateTime.SpecifyKind(x, DateTimeKind.Utc)));
CreateMap().ConvertUsing(x => x.ToDateTime());

Google didn’t seem to turn up a lot so I thought I’d post it here in case it helps someone out!

Http gRPC with .NET Core and Docker – Error starting gRPC call. System.Net.Http.HttpRequestException: An error occurred while sending the request. —> System.IO.IOException: The response ended prematurely.

Hi everyone,

I’ve been mucking around with gRPC today while using .NET Core and Docker. I have two Microservices in the setup, one server and one client. Because these services will only be communicating internally I intended to use HTTP instead of HTTPS. Unfortunately, I hit the following error while attempting to set this up:

Error starting gRPC call. System.Net.Http.HttpRequestException: An error occurred while sending the request. —> System.IO.IOException: The response ended prematurely.

According Microsoft’s eshoponcontainers documentation there are a few extra steps for getting this to work:

Using gRPC without TLS
gRPC works with HTTP/2 only. Usually when a client connects to a server, the connection is done using HTTP1.1 and promoted to HTTP/2 only if both, server and client, support HTTP/2. This promotion is performed using a protocol negotiation, usually implemented using ALPN protocol which requires TLS.

In order to get it to work you need to add the following to your server :

.ConfigureWebHostDefaults(webBuilder =>

.ConfigureKestrel(options =>
options.Listen(IPAddress.Any, 5001, listenOptions =>
listenOptions.Protocols = HttpProtocols.Http2;

You then need to explicitly allow HTTP/2 without TLS when creating the client:

AppContext.SetSwitch(“System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport”, true);
AppContext.SetSwitch(“System.Net.Http.SocketsHttpHandler.Http2Support”, true);

// The port number(5001) must match the port of the gRPC server.
var channel = GrpcChannel.ForAddress(endpoint, new GrpcChannelOptions { LoggerFactory = loggerFactory });
var client = new CatalogService.Catalog.CatalogClient(channel);

Note that the AppContext.SetSwitch statements need to appear before the client is created to work. There’s also a bit of an overview on the following page:

The following stackoverflow post also helped with the ordering issue: