PrologProtobuf

Protobuf for programs interacting with the Prolog engine.

Protobuf library

For the sake of scalability for future development and architecture quality, we thought about implementing a server for the Prolog system. The application communicates with the Server through Remote Procedure Calls (RPC). We adopted gRPC, a high-performance, open-source universal RPC framework. As Interface Description Language gRPC uses Protocol Buffers, a language-neutral, platform-neutral extensible mechanism for serializing structured data. The services and the types of messages to be exchanged between client and server are defined in a .proto file. Then, using a protobuf compiler for Scala (ScalaPB), Scala classes for the definition of the services are generated. ###Steps for the protobuf library creation

1. Created an sbt project “protobuf_classes_Prolog” on IntelliJ Idea Ultimate Edition 2018.2.4, with JDK 9.0, SBT version 1.2.6 and Scala version 2.12.7
2. Installed ScalaPB dependency for gRPC
3. To automatically generate Scala classes for messages created a file named “project/scalapb.sbt” and added instructions for the sbt-protoc plugin as described here
4. Added the following lines to “build.sbt” for generating classes in the folder “src/main/scala/validation”:

   PB.targets in Compile := Seq(
     scalapb.gen() -> (scalaSource in Compile).value )
   

5. Run the SBT task “sbt compile” to generate Scala classes and compile them
6. Added to “build.sbt” the following lines for including in the Jar the proto file:

   mappings in (Compile, packageBin) += {
     (baseDirectory.value / "src" / "main" / "protobuf"/ "validation.proto") -> "out/validation.proto"
   }
   

7. Created a file named “project/assembly.sbt” and added the following lines to it:

      addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.8")
   

8. Found deduplication error due to merge strategies in sbt assemply, for discarding them added the following lines to “build.sbt”:

   assemblyMergeStrategy in assembly := {
     case PathList("META-INF", xs @ _*) => MergeStrategy.discard
     case x => MergeStrategy.first
   }
   

9. Run the SBT task “sbt assembly” and created the jar of the project “protobuf_classes_Prolog-assembly-0.1.jar”

Important: for running on Windows, geneating Scala code requires Python 2.x to be installed on your system, so I added the following lines to “build.sbt”: PB.pythonExe := "C:\\Python27\\Python.exe"

Resources:

• https://www.beyondthelines.net/computing/grpc-in-scala/
• https://scalapb.github.io/
• https://blog.bugsnag.com/libraries-for-grpc-services/
• https://alvinalexander.com/scala/sbt-how-build-single-executable-jar-file-assembly
• https://www.scala-sbt.org/1.x/docs/index.html
• https://github.com/sbt/sbt-assembly

Project Structure

Inside the project, you can find the file prologprotobuf/src/main/protobuf/validation.proto written in the syntax of proto3 language (https://developers.google.com/protocol-buffers/docs/proto3). The file defines the grpc services and the types of messages exchanged between client and server. In the folder prologprotobuf/src/main/scala/validation there are the generated Scala classes which are emplyed to implement the communication. Finally, the assembled jar is contained in prologprotobuf/lib, along with the current version.

Built With

• SBT - Dependency Management
• IntelliJ - IntelliJ IDEA 2018.2.4 (Ultimate Edition) JRE: 1.8.0_152-release-1248-b8 amd64 JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o Windows 10 10.0
• Scala SDK version 2-12.4

Authors

• Giovanni Agugini Bassi - Master student at University of Illinois at Chicago -Initial work