Gopherjs

In a previous post I introduced my open source project to bring GopherJS bindings to Improbable’s gRPC-Web client. I’m happy to say that the initial goal of supporting all features of the gRPC-Web client has been completed. I was initially going to leave it at that and wait for client side streaming to land in the WHATWG Streams API Standard, and subsequently added to the official grpc-web spec and probably the gRPC-Web client, but then I was sitting at the GolangUK conference and I had a brain wave....

Recently I found myself wondering how I was going to test my new GopherJS gRPC-Web bindings. Writing tests was something I had been waiting with until I had something working, mostly because I had no idea how I was going to meaningfully test GopherJS code that relies on interactions with JS and the reponses of a server. I have in the past made a small contribution to the GopherJS websocket repo, and found myself impressed with the extensive tests written for the repo....

In a previous blog series I’ve talked about how to work with a gRPC backend from the GopherJS world. It relies on the gRPC-gateway which is a great piece of tech, but unfortunately carries a couple of downsides: Clients don’t know what types are used - the interface is HTTP JSON. This can be somewhat mitigated with the use of swagger generated interfaces, but it’s still not perfect. The interface being JSON means marshalling and unmarshalling can become a significant part of the latency between the client and the server....

Putting it all together As we touched upon earlier, we generate a package from the generated JS (meta, right?), which can be served from the server. We’ll create a new file, main.go, in which we can spin up a server, serve the frontend and the gRPC backend. Much of the logic in this file is inspired by the excellent blog post put together by Brandon Philips over at CoreOS. We’re using his elegant solution to serve both the HTTP API and the gRPC API on the same port....

Implement the client GopherJS can be used in a couple of different ways, and there’s a couple of different bindings to many popular JavaScript frameworks. The GopherJS wiki has some great resources. I tried a couple of different ones and ended up using the VueJS bindings because it made it easy to prototype things quickly. I hear VueJS works well for many JS evangelisers out there, but I’ve only used it with small projects....

Implement the server I like to start by creating a struct and write a simple definition that’ll immediately fail to compile. package server import ( "github.com/johanbrandhorst/gopherjs-grpc-websocket/protos/server" ) type Server struct{} var _ server.MyServerServer = &Server{} This won’t compile, because the Server struct does not implement the server.MyServerServer interface. But it’ll also tell us what we’ve got left to implement. So lets implement the server methods: func (s Server) Simple(ctx context.Context, _ *empty....

Create the protobuf interface We’ll start by creating a folder for the package we want to create. Lets call it server. Next we type up a .proto file to define the interface between the server and the client. We’ll have to include some extra proto annotations in order to have the gRPC-gateway generate the translations methods we need. Lets define a simple service with a single HTTP GET endpoint: service MyServer { rpc Simple(google....

I’ve been using gRPC and Go a lot in the last year. At Cognitive Logic every one of our backend services is implemented with Go and gRPC, and it enables us to abstract away most of the complexities of networked micro services and keep interfaces typed and well defined using Google protobuffers. I really enjoy using both, but sometimes I need to write a frontend to a web server and I despise writing Javascript....