Fix error code forwarding

Author: ryarnyah

cmd/module/module.go

@@ -16,6 +16,7 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/status"
 )
 
 type backend struct {
@@ -651,7 +652,17 @@ func init() {
 		// Create a new TLS credentials based on the TLS configuration
 		c = credentials.NewTLS(tlsConfig)
 	}
-	conn, err := grpc.Dial(os.Getenv("PKCS11_PROXY_URI"), grpc.WithTransportCredentials(c))
+	errHandler := func(ctx context.Context, method string, req, resp interface{}, info *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+		err := invoker(ctx, method, req, resp, info, opts...)
+		if err != nil {
+			s := status.Convert(err)
+			if s != nil {
+				err = pkcs11.Error(s.Code())
+			}
+		}
+		return err
+	}
+	conn, err := grpc.Dial(os.Getenv("PKCS11_PROXY_URI"), grpc.WithTransportCredentials(c), grpc.WithUnaryInterceptor(errHandler))
 	if err != nil {
 		log.Fatalf("unable to connect to pkcs11 proxy using env PKCS11_PROXY_URI %s: %s", os.Getenv("PKCS11_PROXY_URI"), err)
 	}

cmd/server/server.go

@@ -16,8 +16,10 @@ import (
 	p11 "github.com/ryarnyah/pkcs11-go-proxy/pkcs11"
 	"github.com/ryarnyah/pkcs11-go-proxy/pkg"
 	grpc "google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/status"
 )
 
 // ErrCtxNotFound raised when context can't be found.
@@ -1038,6 +1040,10 @@ func main() {
 	errHandler := func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
 		resp, err := handler(ctx, req)
 		if err != nil {
+			var pe pkcs11.Error
+			if errors.As(err, &pe) {
+				err = status.Error(codes.Code(pe), err.Error())
+			}
 			log.Printf("method %q failed: %s", info.FullMethod, err)
 		}
 		return resp, err