Support for Golang GRPC (Experimental) (#4082)

* support for grpc golang

* refactored grpc go generator

* added grpc-go test and refactored

* refactored idl_gen_grpc.cpp

* fixed grpc generate method name

* refactored flatc and fixed line length issue

* added codec to go lib and fixed formatting issues

* fixed spacing issues

src/flatc.cpp

@@ -33,6 +33,9 @@ struct Generator {
   const char *generator_opt_short;
   const char *generator_opt_long;
   const char *lang_name;
+  bool (*generateGRPC)(const flatbuffers::Parser &parser,
+                       const std::string &path,
+                       const std::string &file_name);
   flatbuffers::IDLOptions::Language lang;
   const char *generator_help;
 
@@ -43,45 +46,50 @@ struct Generator {
 
 const Generator generators[] = {
   { flatbuffers::GenerateBinary,   "-b", "--binary", "binary",
+    nullptr,
     flatbuffers::IDLOptions::kMAX,
     "Generate wire format binaries for any data definitions",
     flatbuffers::BinaryMakeRule },
   { flatbuffers::GenerateTextFile, "-t", "--json", "text",
+    nullptr,
     flatbuffers::IDLOptions::kMAX,
     "Generate text output for any data definitions",
     flatbuffers::TextMakeRule },
   { flatbuffers::GenerateCPP,      "-c", "--cpp", "C++",
+    flatbuffers::GenerateCppGRPC,
     flatbuffers::IDLOptions::kMAX,
     "Generate C++ headers for tables/structs",
     flatbuffers::CPPMakeRule },
   { flatbuffers::GenerateGo,       "-g", "--go", "Go",
+    flatbuffers::GenerateGoGRPC,
     flatbuffers::IDLOptions::kGo,
     "Generate Go files for tables/structs",
     flatbuffers::GeneralMakeRule },
   { flatbuffers::GenerateGeneral,  "-j", "--java", "Java",
+    nullptr,
     flatbuffers::IDLOptions::kJava,
     "Generate Java classes for tables/structs",
     flatbuffers::GeneralMakeRule },
   { flatbuffers::GenerateJS,       "-s", "--js", "JavaScript",
+    nullptr,
     flatbuffers::IDLOptions::kMAX,
     "Generate JavaScript code for tables/structs",
     flatbuffers::JSMakeRule },
   { flatbuffers::GenerateGeneral,  "-n", "--csharp", "C#",
+    nullptr,
     flatbuffers::IDLOptions::kCSharp,
     "Generate C# classes for tables/structs",
     flatbuffers::GeneralMakeRule },
   { flatbuffers::GeneratePython,   "-p", "--python", "Python",
+    nullptr,
     flatbuffers::IDLOptions::kMAX,
     "Generate Python files for tables/structs",
     flatbuffers::GeneralMakeRule },
   { flatbuffers::GeneratePhp, nullptr, "--php", "PHP",
+    nullptr,
     flatbuffers::IDLOptions::kMAX,
     "Generate PHP files for tables/structs",
     flatbuffers::GeneralMakeRule },
-  { flatbuffers::GenerateGRPC, nullptr, "--grpc", "GRPC",
-    flatbuffers::IDLOptions::kMAX,
-    "Generate GRPC interfaces",
-    flatbuffers::CPPMakeRule },
 };
 
 const char *g_program_name = nullptr;
@@ -170,6 +178,7 @@ int main(int argc, const char *argv[]) {
   bool print_make_rules = false;
   bool raw_binary = false;
   bool schema_binary = false;
+  bool grpc_enabled = false;
   std::vector<std::string> filenames;
   std::vector<const char *> include_directories;
   std::vector<const char *> conform_include_directories;
@@ -243,6 +252,8 @@ int main(int argc, const char *argv[]) {
       } else if(arg == "--version") {
         printf("flatc version %s\n", FLATC_VERSION);
         exit(0);
+      } else if(arg == "--grpc") {
+        grpc_enabled = true;
       } else {
         for (size_t i = 0; i < num_generators; ++i) {
           if (arg == generators[i].generator_opt_long ||
@@ -360,6 +371,17 @@ int main(int argc, const char *argv[]) {
               printf("%s\n", flatbuffers::WordWrap(
                   make_rule, 80, " ", " \\").c_str());
           }
+          if (grpc_enabled) {
+            if (generators[i].generateGRPC != nullptr) {
+              if (!generators[i].generateGRPC(*g_parser, output_path, filebase)) {
+                    Error(std::string("Unable to generate GRPC interface for") +
+                          generators[i].lang_name);
+              }
+            } else {
+                Error(std::string("GRPC interface generator not implemented for ") +
+                      generators[i].lang_name);
+            }
+          }
         }
       }
 

src/idl_gen_grpc.cpp

@@ -19,8 +19,10 @@
 #include "flatbuffers/flatbuffers.h"
 #include "flatbuffers/idl.h"
 #include "flatbuffers/util.h"
+#include "flatbuffers/code_generators.h"
 
 #include "src/compiler/cpp_generator.h"
+#include "src/compiler/go_generator.h"
 
 namespace flatbuffers {
 
@@ -52,6 +54,14 @@ class FlatBufMethod : public grpc_generator::Method {
     return GRPCType(*method_->response);
   }
 
+  std::string input_name() const {
+    return (*method_->request).name;
+  }
+
+  std::string output_name() const {
+    return (*method_->response).name;
+  }
+
   bool NoStreaming() const { return streaming_ == kNone; }
   bool ClientOnlyStreaming() const { return streaming_ == kClient; }
   bool ServerOnlyStreaming() const { return streaming_ == kServer; }
@@ -159,6 +169,10 @@ class FlatBufFile : public grpc_generator::File {
     return "#include \"flatbuffers/grpc.h\"\n";
   }
 
+  std::string additional_imports() const {
+    return "import \"github.com/google/flatbuffers/go\"";
+  }
+
   int service_count() const {
     return static_cast<int>(parser_.services_.vec.size());
   };
@@ -178,7 +192,47 @@ class FlatBufFile : public grpc_generator::File {
   const std::string &file_name_;
 };
 
-bool GenerateGRPC(const Parser &parser,
+class GoGRPCGenerator : public flatbuffers::BaseGenerator {
+ public:
+  GoGRPCGenerator(const Parser &parser, const std::string &path,
+                  const std::string &file_name)
+    : BaseGenerator(parser, path, file_name, "", "" /*Unused*/),
+      parser_(parser), path_(path), file_name_(file_name) {}
+
+  bool generate() {
+    FlatBufFile file(parser_, file_name_);
+    grpc_go_generator::Parameters p;
+    p.custom_method_io_type = "flatbuffers.Builder";
+    for (int i = 0; i < file.service_count(); i++) {
+      auto service = file.service(i);
+      const Definition *def = parser_.services_.vec[i];
+      p.package_name = LastNamespacePart(*(def->defined_namespace));
+      std::string output = grpc_go_generator::GenerateServiceSource(&file, service.get(), &p);
+      std::string filename = NamespaceDir(*def->defined_namespace) + def->name + "_grpc.go";
+      if (!flatbuffers::SaveFile(filename.c_str(), output, false))
+        return false;
+    }
+    return true;
+  }
+
+ protected:
+  const Parser &parser_;
+  const std::string &path_, &file_name_;
+};
+
+bool GenerateGoGRPC(const Parser &parser,
+                    const std::string &path,
+                    const std::string &file_name) {
+  int nservices = 0;
+  for (auto it = parser.services_.vec.begin();
+       it != parser.services_.vec.end(); ++it) {
+    if (!(*it)->generated) nservices++;
+  }
+  if (!nservices) return true;
+  return GoGRPCGenerator(parser, path, file_name).generate();
+}
+
+bool GenerateCppGRPC(const Parser &parser,
                   const std::string &/*path*/,
                   const std::string &file_name) {