protoc-c: add string as bytes option

Allows treating proto strings as ProtobufCBinaryData to work around
limitations such as NULL characters in strings, which are allowed in
protobuf, but not allowed in 'char *' types.

Fixes #203

protobuf-c/protobuf-c.proto

@@ -67,6 +67,8 @@ extend google.protobuf.MessageOptions {
 }
 
 message ProtobufCFieldOptions {
+    // Treat string as bytes in generated code
+    optional bool string_as_bytes = 1 [default = false];
 }
 
 extend google.protobuf.FieldOptions {

protoc-c/c_field.cc

@@ -203,11 +203,15 @@ FieldGeneratorMap::FieldGeneratorMap(const Descriptor* descriptor)
 }
 
 FieldGenerator* FieldGeneratorMap::MakeGenerator(const FieldDescriptor* field) {
+  const ProtobufCFieldOptions opt = field->options().GetExtension(pb_c_field);
   switch (field->type()) {
     case FieldDescriptor::TYPE_MESSAGE:
       return new MessageFieldGenerator(field);
     case FieldDescriptor::TYPE_STRING:
-      return new StringFieldGenerator(field);
+      if (opt.string_as_bytes())
+        return new BytesFieldGenerator(field);
+      else
+        return new StringFieldGenerator(field);
     case FieldDescriptor::TYPE_BYTES:
       return new BytesFieldGenerator(field);
     case FieldDescriptor::TYPE_ENUM:

protoc-c/c_message.cc

@@ -463,6 +463,7 @@ GenerateMessageDescriptor(io::Printer* printer, bool gen_init) {
 
     for (int i = 0; i < descriptor_->field_count(); i++) {
       const FieldDescriptor *fd = descriptor_->field(i);
+      const ProtobufCFieldOptions opt = fd->options().GetExtension(pb_c_field);
       if (fd->has_default_value()) {
 
 	bool already_defined = false;
@@ -501,7 +502,7 @@ GenerateMessageDescriptor(io::Printer* printer, bool gen_init) {
 	  GOOGLE_LOG(DFATAL) << "Messages can't have default values!";
 	  break;
 	case FieldDescriptor::CPPTYPE_STRING:
-	  if (fd->type() == FieldDescriptor::TYPE_BYTES)
+	  if (fd->type() == FieldDescriptor::TYPE_BYTES || opt.string_as_bytes())
 	  {
 	    vars["field_dv_ctype"] = "ProtobufCBinaryData";
 	  }

t/test-full.proto

@@ -13,6 +13,8 @@ message SubMess {
     repeated int32 rep = 4;
     optional bytes bytes1 = 2 [default = "a \0 char"];
     optional string str1 = 3 [default = "hello world\n"];
+    optional string str2 = 5 [default = "hello\0world\n",
+			      (pb_c_field).string_as_bytes = true];
   }
   optional SubSubMess sub1 = 9;
   optional SubSubMess sub2 = 10;