Add printer class to wrap protobuf IO classes (googleapis#12)

* Add printer class
* Use printer, add comments
* Address PR comments

Author: michaelbausor

generator/BUILD.bazel

@@ -21,6 +21,7 @@ cc_library(
     srcs = [
         "gapic_generator.cc",
         "internal/gapic_utils.h",
+        "internal/printer.h",
     ],
     hdrs = [
         "gapic_generator.h",

generator/gapic_generator.cc

@@ -21,6 +21,7 @@
 #include "absl/strings/str_replace.h"
 #include "generator/gapic_generator.h"
 #include "internal/gapic_utils.h"
+#include "internal/printer.h"
 
 #include "google/api/client.pb.h"
 
@@ -69,7 +70,7 @@ std::vector<std::string> BuildNamespaces(
 void PrintMethods(
     pb::ServiceDescriptor const* service,
     std::map<std::string, std::string> vars,
-    pb::io::Printer* p,
+    internal::Printer& p,
     char const* tmplt) {
   for (int i = 0; i < service->method_count(); i++) {
     const pb::MethodDescriptor* method = service->method(i);
@@ -81,7 +82,7 @@ void PrintMethods(
 bool GenerateClientHeaderFile(
     pb::ServiceDescriptor const* service,
     std::map<std::string, std::string> const& vars,
-    pb::io::Printer* p,
+    internal::Printer& p,
     std::string * /* error */) {
   auto includes = BuildHeaderIncludes(service);
   auto namespaces = BuildNamespaces(service);
@@ -121,7 +122,7 @@ bool GenerateClientHeaderFile(
 bool GenerateClientCCFile(
     pb::ServiceDescriptor const* service,
     std::map<std::string, std::string> const& vars,
-    pb::io::Printer* p,
+    internal::Printer& p,
     std::string * /* error */) {
   auto includes = BuildCCIncludes(service);
   auto namespaces = BuildNamespaces(service);
@@ -174,18 +175,14 @@ bool GapicGenerator::Generate(pb::FileDescriptor const* file,
         service->full_name());
 
     std::string header_file_path = absl::StrCat(service_file_path, ".gapic.h");
-    std::unique_ptr<pb::io::ZeroCopyOutputStream> header_output(
-        generator_context->Open(header_file_path));
-    pb::io::Printer header_printer(header_output.get(), '$', NULL);
-    if (!GenerateClientHeaderFile(service, vars, &header_printer, error)) {
+    internal::Printer header_printer(generator_context, header_file_path);
+    if (!GenerateClientHeaderFile(service, vars, header_printer, error)) {
       return false;
     }
 
     std::string cc_file_path = absl::StrCat(service_file_path, ".gapic.cc");
-    std::unique_ptr<pb::io::ZeroCopyOutputStream> cc_output(
-        generator_context->Open(cc_file_path));
-    pb::io::Printer cc_printer(cc_output.get(), '$', NULL);
-    if (!GenerateClientCCFile(service, vars, &cc_printer, error)) {
+    internal::Printer cc_printer(generator_context, cc_file_path);
+    if (!GenerateClientCCFile(service, vars, cc_printer, error)) {
       return false;
     }
   }

generator/internal/printer.h

@@ -0,0 +1,56 @@
+// Copyright 2019 Google Inc.  All rights reserved
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#ifndef GOOGLE_API_CODEGEN_INTERNAL_PRINTER_H_
+#define GOOGLE_API_CODEGEN_INTERNAL_PRINTER_H_
+
+#include <string>
+#include "src/google/protobuf/compiler/code_generator.h"
+#include "src/google/protobuf/io/printer.h"
+
+namespace pb = google::protobuf;
+
+namespace google {
+namespace api {
+namespace codegen {
+namespace internal {
+
+/**
+ * Wrapper around a google::protobuf::io::ZeroCopyOutputStream and a
+ * google::protobuf::io::Printer object so that they can be used for
+ * code generation. 
+ */
+class Printer {
+ public:
+  Printer(pb::compiler::GeneratorContext* generator_context,
+          std::string const& file_name)
+    : output_(generator_context->Open(file_name)),
+      printer_(output_.get(), '$', NULL) {}
+
+  pb::io::Printer* operator->() & { return &printer_; }
+  pb::io::Printer const* operator->() const& { return &printer_; }
+
+  Printer(Printer const&) = delete;
+  Printer& operator=(Printer const&) = delete;
+
+ private:
+  std::unique_ptr<pb::io::ZeroCopyOutputStream> output_;
+  pb::io::Printer printer_;
+};
+
+} // internal
+} // codegen
+} // api
+} // google
+
+#endif // GOOGLE_API_CODEGEN_INTERNAL_PRINTER_H_