CORS grpc gateway GoLang

php Xiaobian Strawberry introduces you to the CORS gRPC gateway GoLang. CORS, short for Cross-Origin Resource Sharing, is a mechanism used to make cross-domain requests in browsers. gRPC is a high-performance, open source remote procedure call (RPC) framework that can be used to build distributed systems. GoLang is a powerful programming language with high concurrency and simplicity. CORS gRPC Gateway GoLang combines CORS and gRPC to implement the gateway through the Go language to implement cross-domain requests. In this article, we will introduce in detail the principles and usage of CORS gRPC gateway GoLang to help you better understand and apply this technology.

Question content

I have a vue.js 3 front end, and I call the golang backend throughgrpc-gateway. I've been doing this for a while, but I see the light at the end of the tunnel.

I'm currently facing a cors problem. However, I'm reading conflicting information on how to deal with it. Therefore, I wanted to post something that I hope will be helpful to everyone.

Here is the code for how I initialize the mux server for grpc (gateway)

func runhttpserver(server *http.server, httpendpoint, grpcendpoint, swaggerpath string) (err error) { server.addr = httpendpoint ctx, cancel := context.withcancel(context.background()) defer cancel() // register groc server endpoint mux := runtime.newservemux( runtime.witherrorhandler(func(ctx context.context, mux *runtime.servemux, marshaler runtime.marshaler, w http.responsewriter, r *http.request, err error, ) { s, ok := status.fromerror(err) if ok { if s.code() == codes.unavailable { err = status.error(codes.unavailable, errunavailable) } } runtime.defaulthttperrorhandler(ctx, mux, marshaler, w, r, err) }), ) opts := []grpc.dialoption{ grpc.withtransportcredentials(insecure.newcredentials()), grpc.withchainunaryinterceptor(), } if err = api.registerapiservicehandlerfromendpoint(ctx, mux, grpcendpoint, opts); err != nil { return } swmux := http.newservemux() swmux.handle("/", mux) serveswagger(swmux, swaggerpath) server.handler = swmux return server.listenandserve() }

Here is where I think I should add the cors configuration, but I'm not sure that's how I set it up in the server.go file..

var httpserver http.server // run http server with grpc gateway g.go(func() error { fmt.println("starting http sever (port {}) and grpc gateway (port {})", strconv.itoa(cfg.server.httpport), strconv.itoa(cfg.server.grpcport), ) return rest.runhttpserver( &httpserver, ":"+strconv.itoa(cfg.server.httpport), ":"+strconv.itoa(cfg.server.grpcport), "/webapi", ) })

Console Error:

access to xmlhttprequest at 'http://localhost:8080/v1/test' from origin 'http://localhost:9000' has been blocked by cors policy: response to preflight request doesn't pass access control check: no 'access-control-allow-origin'

I don’t know where to add something like this

func enablecors(w *http.responsewriter) { (*w).header().set("access-control-allow-origin", "*") }

I feel like there should be something built into the golang grpc gateway, but I can't find anything?

Any suggestions would be greatly appreciated.

-----Update 1-----

I've tried it

func enablecors(h http.handler) http.handler { return http.handlerfunc(func(w http.responsewriter, r *http.request) { w.header().set("access-control-allow-origin", "http://localhost:9000") w.header().set("access-control-allow-methods", "get, put, post, delete, head, options") h.servehttp(w, r) }) }

and

func enablecors(h http.handler) http.handler { return http.handlerfunc(func(w http.responsewriter, r *http.request) { w.header().set("access-control-allow-origin", "*") w.header().set("access-control-allow-methods", "get, put, post, delete, head, options") h.servehttp(w, r) }) }

and

func enablecors(h http.handler) http.handler { return http.handlerfunc(func(w http.responsewriter, r *http.request) { w.header().set("access-control-allow-origin", "http://localhost") w.header().set("access-control-allow-methods", "get, put, post, delete, head, options") h.servehttp(w, r) }) }

combine

func serveSwagger(mux *http.ServeMux, swaggerPath string) { fileServer := http.FileServer(http.Dir(swaggerPath)) prefix := "/swagger-ui" mux.Handle(prefix, http.StripPrefix(prefix, fileServer)) }

Still having the same problem.. very frustrating

Workaround

Based on the latest error you provided in the comments:

Access to xmlhttprequest at 'localhost:8080/v1/test' from origin 'localhost:9000' has been blocked by cors policy: The response to the preflight request failed an access control check: it has no http normal status.

Your browser is sending apreflight request(optionshttp method) to determine if the required cross-origin request can be made.

The server is responding with a non-2xx response.

I suspect this is because yourenablecorsfunction is propagating the request to the grpc-gateway handler, which is not happy with theoptionshttp method and returns an error status, possibly yes:

< http/1.1 501 not implemented < content-type: application/json < vary: origin < date: fri, 25 nov 2022 11:17:52 gmt < content-length: 55 < {"code":12,"message":"method not allowed","details":[]}

So to avoid this, you want tonotpropagate the request further when making a preflight request, e.g.

func enablecors(h http.handler) http.handler { return http.handlerfunc(func(w http.responsewriter, r *http.request) { w.header().set("access-control-allow-origin", "http://localhost:9000") w.header().set("access-control-allow-methods", "get, put, post, delete, head, options") if r.method == http.methodoptions { w.writeheader(http.statusnocontent) return } h.servehttp(w, r) }) }

But, the above may still not be a reasonable implementation of cors handling. You should use an existing package for this, such asgithub.com/rs/cors, which will handle this in a sensible way and handle any potential pitfalls etc.

So importgithub.com/rs/corsand then do the following:

server.Handler = cors.AllowAll().Handler(swMux)

should get you started letting everything pass. This library will allow you to tailor specific origins, http methods, etc. to your needs.

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