Developing Microservice Plugins

Jason Coposky, Chief Technologist

The iRODS Plugin Architecture

iRODS provides 6 plugin interfaces

• Storage Resource
• Authentication
• Network
• Database
• RPC API
• Microservice

Anatomy of a Plugin

• Built as a dynamic shared object
• provides a plugin_factory method which instantiates the plugin object
• contains a class derived from a plugin interface base class:
  • ​api
  • auth
  • network
  • resource
  • database
  • ms_table_entry
• NOTE: microservices do not require a derived class, the factory can return an instance of ms_table_entry

Example Code

git clone https://github.com/irods/contrib

cd contrib/microservices/training_example/msiget_image_meta

Writing a microservice - part 1

• The microservice must use C linkage

extern "C" {

• Declare the microservice implementation as usual, following the parameters with the rule engine context

 int msiget_image_meta_impl(msParam_t* _in, msParam_t* _out, ruleExecInfo_t* rei) {
        using std::cout;
        using std::endl;
        using std::string;
        char *filePath = parseMspForStr( _in );
        if( !filePath ) {
            cout << "msiget_image_meta - null filePath parameter" << endl;
            return SYS_INVALID_INPUT_PARAM;
        }

Writing a microservice - part 2

        InitializeMagick((const char*)0);
        Image imgObj;
        imgObj.read(filePath);
        std::stringstream metaData;
        metaData << "ImageDepth=" << imgObj.modulusDepth()
                 << "%Width=" << imgObj.columns()
                 << "%Height=" << imgObj.rows()
                 << "%CompressionType=" << convertCompressTypeToStr(imgObj.compressType())
                 << "%Format=" << imgObj.format() 
                 << "%Colorspace=" << convertColorSpaceTypeToStr(imgObj.colorSpace());
        fillStrInMsParam(_out, metaData.str().c_str());
        return 0;
    } // msi_get_image_meta_impl

The plugin factory

• factory function requires C linkage and must follow the signature

    irods::ms_table_entry* plugin_factory() {

• instantiate a table entry and pass it the number of parameters of the microservice - not including the rule engine context
          irods::ms_table_entry* msvc = new irods::ms_table_entry(2);

• wire the microservice name to the name of the implementation and return the plugin
          msvc->add_operation(
              "msiget_image_meta_impl",
              "msiget_image_meta");
          return msvc;
      }
  } // extern "C"

Building a microservice plugin

• The irods-dev package is required to build plugins

GCC = g++
INC=-I/usr/include/irods/ -I/usr/include/irods/boost/ -I/usr/include/ImageMagick
all: libmsiget_image_meta
libmsiget_image_meta:
    ${GCC} ${INC} -DRODS_SERVER -fPIC "-Wl,-E" -shared -g \
        -Wno-deprecated -rdynamic -o $@.so $@.cpp -lMagick++
clean:
    @rm -f ./*.so

Questions?