fix empty parameter fatal (#1752)

Fixes #1751

Author: danielhochman

protoc-gen-grpc-gateway/BUILD.bazel

@@ -1,4 +1,4 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library", "go_test")
 load("@io_bazel_rules_go//proto:compiler.bzl", "go_proto_compiler")
 
 package(default_visibility = ["//visibility:private"])
@@ -41,3 +41,10 @@ go_proto_compiler(
         "@org_golang_google_protobuf//proto:go_default_library",
     ],
 )
+
+go_test(
+    name = "go_default_test",
+    srcs = ["main_test.go"],
+    embed = [":go_default_library"],
+    deps = ["//internal/descriptor:go_default_library"],
+)

protoc-gen-grpc-gateway/main.go

@@ -107,6 +107,10 @@ func main() {
 }
 
 func parseFlags(reg *descriptor.Registry, parameter string) {
+	if parameter == "" {
+		return
+	}
+
 	for _, p := range strings.Split(parameter, ",") {
 		spec := strings.SplitN(p, "=", 2)
 		if len(spec) == 1 {

protoc-gen-grpc-gateway/main_test.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/grpc-ecosystem/grpc-gateway/v2/internal/descriptor"
+)
+
+func TestParseFlagsEmptyNoPanic(t *testing.T) {
+	reg := descriptor.NewRegistry()
+	parseFlags(reg, "")
+}
+
+func TestParseFlags(t *testing.T) {
+	reg := descriptor.NewRegistry()
+	parseFlags(reg, "allow_repeated_fields_in_body=true")
+	if *allowRepeatedFieldsInBody != true {
+		t.Errorf("flag allow_repeated_fields_in_body was not set correctly, wanted true got %v", *allowRepeatedFieldsInBody)
+	}
+}
+
+func TestParseFlagsMultiple(t *testing.T) {
+	reg := descriptor.NewRegistry()
+	parseFlags(reg, "allow_repeated_fields_in_body=true,import_prefix=foo")
+	if *allowRepeatedFieldsInBody != true {
+		t.Errorf("flag allow_repeated_fields_in_body was not set correctly, wanted 'true' got '%v'", *allowRepeatedFieldsInBody)
+	}
+	if *importPrefix != "foo" {
+		t.Errorf("flag importPrefix was not set correctly, wanted 'foo' got '%v'", *importPrefix)
+	}
+}