I am trying to create a grpc server with the hep of grpc-web wrapper. The idea is to use this grpc server both with browser based application as well as with the normal grpc client. But i am confused how can i make it work for both the applications?
package main
import (
"context"
"fmt"
"io"
"log"
"net/http"
"strconv"
"time"
"github.com/repo/test-grpc-server/greet/greetpb"
"github.com/improbable-eng/grpc-web/go/grpcweb"
"google.golang.org/grpc"
)
type server struct{}
func (*server) Greet(ctx context.Context, req *greetpb.GreetRequest) (*greetpb.GreetResponse, error) {
fmt.Printf("Greet function was invoked with %v", req)
firstName := req.GetGreeting().GetFirstName()
result := "Hello " + firstName
res := greetpb.GreetResponse{
Result: result,
}
return &res, nil
}
func (*server) GreetManyTimes(req *greetpb.GreetManyTimesRequest, stream greetpb.GreetService_GreetManyTimesServer) error {
fmt.Printf("GreetMany function was invoked with %v", req)
firstName := req.GetGreeting().GetFirstName()
for i := 0; i < 10; i++ {
result := "Hello " + firstName + " number " + strconv.Itoa(i)
res := &greetpb.GreetManyTimesResponse{
Result: result,
}
stream.Send(res)
time.Sleep(1000 * time.Millisecond)
}
return nil
}
func (*server) LongGreet(stream greetpb.GreetService_LongGreetServer) error {
fmt.Printf("LongGreet function was invoked with a streaming request\n")
result := ""
for {
req, err := stream.Recv()
if err == io.EOF {
// we have finished reading the client stream
return stream.SendAndClose(&greetpb.LongGreetResponse{
Result: result,
})
}
if err != nil {
log.Fatalf("Error while reading client stream: %v", err)
}
firstName := req.GetGreeting().GetFirstName()
result += "Hello " + firstName + "! "
}
}
func main() {
fmt.Println("Go gRPC Server")
/*lis, err := net.Listen("tcp", ":5051")
if err != nil {
log.Fatalf("Failed to listen: %v", err)
}*/
grpcServer := grpc.NewServer()
greetpb.RegisterGreetServiceServer(grpcServer, &server{})
grpc := grpcweb.WrapServer(grpcServer)
http.HandleFunc("/", func(resp http.ResponseWriter, req *http.Request) {
allowCors(resp, req)
if grpc.IsGrpcWebRequest(req) || grpc.IsAcceptableGrpcCorsRequest(req) {
grpc.ServeHTTP(resp, req)
}
})
httpPort := ":50051"
fmt.Println("HTTP server listening on", httpPort)
err := http.ListenAndServe(httpPort, nil)
if err != nil {
log.Fatal("Failed to start a HTTP server:", err)
}
}
func allowCors(resp http.ResponseWriter, req *http.Request) {
resp.Header().Set("Access-Control-Allow-Origin", "*")
resp.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
resp.Header().Set("Access-Control-Expose-Headers", "grpc-status, grpc-message")
resp.Header().Set("Access-Control-Allow-Headers", "Accept, Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, XMLHttpRequest, x-user-agent, x-grpc-web, grpc-status, grpc-message")
}
Now i am trying to call the grpc function from my client like this below. but it is not working..
package main
import (
"context"
"fmt"
"io"
"log"
"time"
"github.com/repo/test-grpc-server/greet/greetpb"
"github.com/repo/test-grpc-server/sum/sumpb"
"google.golang.org/grpc"
)
func main() {
fmt.Println("Hello I'm a client")
conn, err := grpc.Dial("0.0.0.0:50051", grpc.WithInsecure())
if err != nil {
log.Fatalf("could not connect: %v", err)
}
defer conn.Close()
c := greetpb.NewGreetServiceClient(conn)
doUnary(c)
}
func doUnary(c greetpb.GreetServiceClient) {
fmt.Println("do unary from the client")
req := &greetpb.GreetRequest{
Greeting: &greetpb.Greeting{
FirstName: "Hsn",
LastName: "Hrn",
},
}
res, err := c.Greet(context.Background(), req)
if err != nil {
log.Fatalf("error while calling Greet RPC: %v", err)
}
log.Printf("Response from Greet: %v", res.Result)
}
My .prot file look like this..
syntax = "proto3";
package greet;
option go_package="./greet/greetpb";
message Greeting {
string first_name =1 ;
string last_name = 2;
}
message GreetRequest {
Greeting greeting = 1;
}
message GreetResponse {
string result = 1;
}
message GreetManyTimesRequest{
Greeting greeting =1;
}
message GreetManyTimesResponse{
string result=1;
}
message LongGreetRequest {
Greeting greeting = 1;
}
message LongGreetResponse{
string result = 1;
}
service GreetService{
//Unary
rpc Greet (GreetRequest) returns (GreetResponse) {};
//Server Streaming
rpc GreetManyTimes(GreetManyTimesRequest) returns (stream GreetManyTimesResponse) {};
//Client Streaming
rpc LongGreet(stream LongGreetRequest) returns (LongGreetResponse) {};
}
The error logs i get are ..
Hello I'm a client
INFO: 2021/04/27 12:53:17 [core] parsed scheme: ""
INFO: 2021/04/27 12:53:17 [core] scheme "" not registered, fallback to default scheme
INFO: 2021/04/27 12:53:17 [core] ccResolverWrapper: sending update to cc: {[{0.0.0.0:50051 <nil> 0 <nil>}] <nil> <nil>}
INFO: 2021/04/27 12:53:17 [core] ClientConn switching balancer to "pick_first"
INFO: 2021/04/27 12:53:17 [core] Channel switches to new LB policy "pick_first"
INFO: 2021/04/27 12:53:17 [core] Subchannel Connectivity change to CONNECTING
INFO: 2021/04/27 12:53:17 [core] parsed scheme: ""
INFO: 2021/04/27 12:53:17 [core] scheme "" not registered, fallback to default scheme
INFO: 2021/04/27 12:53:17 [core] ccResolverWrapper: sending update to cc: {[{0.0.0.0:50051 <nil> 0 <nil>}] <nil> <nil>}
INFO: 2021/04/27 12:53:17 [core] ClientConn switching balancer to "pick_first"
INFO: 2021/04/27 12:53:17 [core] Channel switches to new LB policy "pick_first"
INFO: 2021/04/27 12:53:17 [core] Subchannel Connectivity change to CONNECTING
do unary from the client
INFO: 2021/04/27 12:53:17 [core] blockingPicker: the picked transport is not ready, loop back to repick
INFO: 2021/04/27 12:53:17 [core] Subchannel picks a new address "0.0.0.0:50051" to connect
INFO: 2021/04/27 12:53:17 [core] pickfirstBalancer: UpdateSubConnState: 0xc000021cd0, {CONNECTING <nil>}
INFO: 2021/04/27 12:53:17 [core] Channel Connectivity change to CONNECTING
INFO: 2021/04/27 12:53:17 [core] Subchannel picks a new address "0.0.0.0:50051" to connect
INFO: 2021/04/27 12:53:17 [core] pickfirstBalancer: UpdateSubConnState: 0xc000021ed0, {CONNECTING <nil>}
INFO: 2021/04/27 12:53:17 [core] Channel Connectivity change to CONNECTING
INFO: 2021/04/27 12:53:17 [core] Subchannel Connectivity change to TRANSIENT_FAILURE
INFO: 2021/04/27 12:53:17 [transport] transport: loopyWriter.run returning. connection error: desc = "transport is closing"
INFO: 2021/04/27 12:53:17 [transport] transport: loopyWriter.run returning. connection error: desc = "transport is closing"
INFO: 2021/04/27 12:53:17 [core] Subchannel Connectivity change to TRANSIENT_FAILURE
INFO: 2021/04/27 12:53:17 [core] pickfirstBalancer: UpdateSubConnState: 0xc000021ed0, {TRANSIENT_FAILURE connection closed}
INFO: 2021/04/27 12:53:17 [core] Channel Connectivity change to TRANSIENT_FAILURE
INFO: 2021/04/27 12:53:17 [core] pickfirstBalancer: UpdateSubConnState: 0xc000021cd0, {TRANSIENT_FAILURE connection closed}
INFO: 2021/04/27 12:53:17 [core] Channel Connectivity change to TRANSIENT_FAILURE
2021/04/27 12:53:17 error while calling Greet RPC: rpc error: code = Unavailable desc = connection closed
exit status 1
Someone help would be really appreciated. Thank you!
As per the comments the issue is that you are were attempting to connect to a gRPC-Web server using a gRPC client. gRPC and gRPC-Web are different wire protocols (gRPC-Web was created because web browser APIs don't provide sufficient control over HTTP/2 requests to implement gRPC). This blog post provides a good overview.
Because you are building a web-app you will need to use gRPC-Web; if you also wish to connect to your server using a go client then the preferred option is to use gRPC (the server can both simultaneously). Another option that could work would be to use a gRPC-Web client but I've not tried this (it will be less efficient).
The 'official' way of running gRPC-Web is via an envoy plugin but as you are writing this in Go improbable-eng/grpc-web provides another, simpler, option which you are already utilising (they also have a proxy but that makes deployment more complex).
Your server needs to be altered to run both gRPC and gRPC-Web. The simplest option is to run these on different ports (it may be possible to use a mux to detect the content-type but this is not something I've tried; it does work well if you want to serve html/js and gRPC-Web on a single port).
The approach I'd take to run both servers follows (please treat this as incomplete pseudo code, I have pulled bits from a few of my applications but have not compiled/tested etc; feel free to update when you discover issues!):
grpcServer := grpc.NewServer()
greetpb.RegisterGreetServiceServer(grpcServer, &server{})
// Your application is probably doing other things and you will want to be
// able to shutdown cleanly; passing in a context is a good method..
ctx, cancel = context.Cancel(context.Background())
defer cancel() // Ensure cancel function is called eventually
// Start the grpc server on port 50050
grpcTerminated := make(chan struct{})
lis, err := net.Listen("tcp", ":50050")
if err != nil {
panic(fmt.Sprintf("gRPC - failed to listen: %s", err))
}
go func() {
if sErr := grpcServer.Serve(lis); sErr != nil {
fmt.Printf("grpc server shutdown: %s", err)
}
close(grpcTerminated) // In case server is terminated without us requesting this
}()
// Start the grpc-Web server on port 5051
grpcWebTerminated := make(chan struct{})
grpc := grpcweb.WrapServer(grpcServer)
mux := http.NewServeMux()
mux.HandleFunc("/", func(resp http.ResponseWriter, req *http.Request) {
allowCors(resp, req)
if grpc.IsGrpcWebRequest(req) || grpc.IsAcceptableGrpcCorsRequest(req) {
grpc.ServeHTTP(resp, req)
}
}))
rpcWebServer := &http.Server{
Handler: mux,
Addr: ":50051"}
wg.Add(1)
go func() {
defer wg.Done()
if err := rpcWebServer.ListenAndServe(); err != nil {
fmt.Printf("Web server (GRPC) shutdown: %s", err)
}
close(grpcWebTerminated) // In case server is terminated without us requesting this
}()
// Wait for the web server to shutdown OR the context to be cancelled...
select {
case <-ctx.Done():
// Shutdown the servers (there are shutdown commands to request this)
case <-grpcTerminated:
// You may want to exit if this happens (will be due to unexpected error)
case <-grpcWebTerminated:
// You may want to exit if this happens (will be due to unexpected error)
}
// Wait for the goRoutines to complete
<-grpcTerminated:
<-grpcWebTerminated