Map grpc error codes to http response status codes

protoc-gen-grpc-gateway/generator.go

@@ -426,7 +426,7 @@ type {{.ServiceName}}_{{.Name}}StreamChunk struct {
 func handle_{{.ServiceName}}_{{.Name}}(ctx context.Context, c web.C, client {{.ServiceName}}Client, w http.ResponseWriter, req *http.Request) {
 	stream, err := request_{{.ServiceName}}_{{.Name}}(ctx, c, client, req)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		runtime.HTTPError(w, err)
 		return
 	}
 
@@ -463,13 +463,13 @@ func handle_{{.ServiceName}}_{{.Name}}(ctx context.Context, c web.C, client {{.S
 func handle_{{.ServiceName}}_{{.Name}}(ctx context.Context, c web.C, client {{.ServiceName}}Client, w http.ResponseWriter, req *http.Request) {
 	resp, err := request_{{.ServiceName}}_{{.Name}}(ctx, c, client, req)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		runtime.HTTPError(w, err)
 		return
 	}
 	buf, err := json.Marshal(resp)
 	if err != nil {
 		glog.Errorf("Marshal error: %v", err)
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		runtime.HTTPError(w, err)
 		return
 	}
 

protoc-gen-grpc-gateway/generator_test.go

@@ -138,13 +138,13 @@ func request_EchoService_Echo(ctx context.Context, c web.C, client EchoServiceCl
 func handle_EchoService_Echo(ctx context.Context, c web.C, client EchoServiceClient, w http.ResponseWriter, req *http.Request) {
 	resp, err := request_EchoService_Echo(ctx, c, client, req)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		runtime.HTTPError(w, err)
 		return
 	}
 	buf, err := json.Marshal(resp)
 	if err != nil {
 		glog.Errorf("Marshal error: %v", err)
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		runtime.HTTPError(w, err)
 		return
 	}
 
@@ -167,13 +167,13 @@ func request_EchoService_EchoBody(ctx context.Context, c web.C, client EchoServi
 func handle_EchoService_EchoBody(ctx context.Context, c web.C, client EchoServiceClient, w http.ResponseWriter, req *http.Request) {
 	resp, err := request_EchoService_EchoBody(ctx, c, client, req)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		runtime.HTTPError(w, err)
 		return
 	}
 	buf, err := json.Marshal(resp)
 	if err != nil {
 		glog.Errorf("Marshal error: %v", err)
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		runtime.HTTPError(w, err)
 		return
 	}
 

runtime/errors.go

@@ -0,0 +1,60 @@
+package runtime
+
+import (
+	"net/http"
+
+	"github.com/golang/glog"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+)
+
+// HTTPStatusFromCode converts a gRPC error code into the corresponding HTTP response status.
+func HTTPStatusFromCode(code codes.Code) int {
+	switch code {
+	case codes.OK:
+		return http.StatusOK
+	case codes.Canceled:
+		return http.StatusRequestTimeout
+	case codes.Unknown:
+		return http.StatusInternalServerError
+	case codes.InvalidArgument:
+		return http.StatusBadRequest
+	case codes.DeadlineExceeded:
+		return http.StatusRequestTimeout
+	case codes.NotFound:
+		return http.StatusNotFound
+	case codes.AlreadyExists:
+		return http.StatusConflict
+	case codes.PermissionDenied:
+		return http.StatusForbidden
+	case codes.Unauthenticated:
+		return http.StatusUnauthorized
+	case codes.ResourceExhausted:
+		return http.StatusForbidden
+	case codes.FailedPrecondition:
+		return http.StatusPreconditionFailed
+	case codes.Aborted:
+		return http.StatusConflict
+	case codes.OutOfRange:
+		return http.StatusBadRequest
+	case codes.Unimplemented:
+		return http.StatusNotImplemented
+	case codes.Internal:
+		return http.StatusInternalServerError
+	case codes.Unavailable:
+		return http.StatusServiceUnavailable
+	case codes.DataLoss:
+		return http.StatusInternalServerError
+	}
+
+	glog.Errorf("Unknown gRPC error code: %v", code)
+	return http.StatusInternalServerError
+}
+
+// HTTPError replies to the request with the error.
+// If "err" is an error from gRPC system, the function replies with the status code mapped by HTTPStatusFromCode.
+// If otherwise, it replies with http.StatusInternalServerError.
+func HTTPError(w http.ResponseWriter, err error) {
+	st := HTTPStatusFromCode(grpc.Code(err))
+	http.Error(w, err.Error(), st)
+}