Tuesday, October 19, 2021

OSGi Services with gRPC - Let's be reactive

ECF has just introduced an upgrade to the grpc distribution provider.   Previously, this distribution provider used ReaxtiveX java version 2 only.  With this release, ReactiveX java version 3 is also supported.

As many know, gRPC allows services (both traditional call/response [aka unary] and streaming services) to be defined by a 'proto3' file.  For example, here is a simple service with four methods, one unary (check) and 3 streaming (server streaming, client streaming, and bi-directional streaming)
syntax = "proto3";

package grpc.health.v1;

option java_multiple_files = true;
option java_outer_classname = "HealthProto";
option java_package = "io.grpc.health.v1.rx3";

message HealthCheckRequest {
  string message = 1;

message HealthCheckResponse {
  enum ServingStatus {
    UNKNOWN = 0;
    SERVING = 1;
    NOT_SERVING = 2;
    SERVICE_UNKNOWN = 3;  // Used only by the Watch method.
  ServingStatus status = 1;

service HealthCheck {
  // Unary method
  rpc Check(HealthCheckRequest) returns (HealthCheckResponse);
  // Server streaming method
  rpc WatchServer(HealthCheckRequest) returns (stream HealthCheckResponse);
  // Client streaming method
  rpc WatchClient(stream HealthCheckRequest) returns (HealthCheckResponse);
  // bidi streaming method
  rpc WatchBidi(stream HealthCheckRequest) returns (stream HealthCheckResponse);
The gRPC project provides a plugin so that when protoc is run, java code (or other language code) is generated that can then be used on the server and/or clients.

With some additional plugins, the classes generated by protoc can use the ReactiveX API for generating code.   So, for example, here is the java code generated by running protoc, grpc, reactive-grpc, and the osgi-generator plugins on the above HealthCheck service definition.  

Note in particular the HealthCheckService interface generated by the osgi-generator protoc plugin:
package io.grpc.health.v1.rx3;

import io.reactivex.rxjava3.core.Single;
import io.reactivex.rxjava3.core.Flowable;

value = "by grpc-osgi-generator (REACTIVEX) - A protoc plugin for ECF's grpc remote services distribution provider at https://github.com/ECF/grpc-RemoteServiceSProvider ",
comments = "Source: health.proto.  ")
public interface HealthCheckService {
     * <pre>
     *  Unary method
     * </pre>
    default Single<io.grpc.health.v1.rx3.HealthCheckResponse> check(Single<io.grpc.health.v1.rx3.HealthCheckRequest> requests)  {
        return null;
     * <pre>
     *  Server streaming method
     * </pre>
    default Flowable<io.grpc.health.v1.rx3.HealthCheckResponse> watchServer(Single<io.grpc.health.v1.rx3.HealthCheckRequest> requests)  {
        return null;
     * <pre>
     *  Client streaming method
     * </pre>
    default Single<io.grpc.health.v1.rx3.HealthCheckResponse> watchClient(Flowable<io.grpc.health.v1.rx3.HealthCheckRequest> requests)  {
        return null;
     * <pre>
     *  bidi streaming method
     * </pre>
    default Flowable<io.grpc.health.v1.rx3.HealthCheckResponse> watchBidi(Flowable<io.grpc.health.v1.rx3.HealthCheckRequest> requests)  {
        return null;

Note that it uses the two ReactiveX 3 classes: io.reactivex.rxjava3.core.Single, and io.reactivex.rxjava3.core.Flowable. These two classes provide api for event-driven/reactive sending and receiving of unary (Single) and streaming (Flowable) arguments and return values.

The ReactiveX API...particularly Flowable...makes it very easy to implement both consumers and implementers of the streaming API, while maintaining ordered delivery and non-blocking communication.

For example, this is a simple implementation of the HealthCheckService. Note how the Single and flowable methods are able to express the implementation logic through methods such as Flowable.map.
Here is a simple implementation of a consumer of the HealthCheckService.

The use of the ReactiveX API simplifies both the implementation and the consumer use of both unary and streaming services. As an added bonus: the reactive-grpc library used in the ECF Distribution provider provides *flow-control* using backpressure.

In next article I'll describe how OSGi Remote Services can be easily used to export, publish, discover, and import remote services with full support for service versioning, security, and dynamics. I'll also describe one can use tools like maven or bndtools+eclipse to generate source code (as above) from a proto3 file and easily run a generated service as an OSGi Remote Service.

Tuesday, August 03, 2021

gRPC Remote Services Development with Bndtools - video tutorials

Here are four new videos that show how to define, implement and run/debug gRPC-based remote services using bndtools, eclipse, and ECF remote services.

Part 1 - API Generation - The generation of a OSGi remote service API using bndtools code generation and the protoc/gRPC compiler. The example service API has both unary and streaming gRPC method types supported by the reactivex API.

Part 2 - Implementation and Part 3 - Consumer - bndtools-project-template-based creation of remote service impl and consumer projects

Part 4 - Debugging - Eclipse/bndtools-based running/debugging of the remote service creating in parts 1-3.

Tuesday, June 22, 2021

gRPC and OSGi Remote Services

 gRPC is a popular framework for creating high-performance remote procedure call-based microservices.  

OSGi Remote Services is a transport-agnostic specification for creating dynamic, versionable, modular, remote services.

The ECF project provides an open implementation of the OSGi Remote Services spec, and has a provider implementation based-upon gRPC.   What this means is that gRPC can be used to create and run as an OSGi remote service, with all the support for service dynamics (particularly important for network-based services), versioning, and other features provided by OSGi remote services.

The architectural fit between gRPC and OSGi Remote Services is very good, since gRPC is concerned with transport-level efficiency (i.e. http/2, binary serialization format), and OSGi Remote Services are completely transport-agnostic, and focuses instead upon service-level concerns (e.g. dynamics, versioning, and service discovery).

gRPC offers support for server and client-based streaming.   In ECF's implementation, streaming rpcs are mapped to the reactivex api.  This means that consumers and implementers of a streaming rpc can simply call methods and provide callbacks (using Flowable), and non-blocking streaming calls will be made.  In addition, the use of reactivex and backpressure will result in transport-level flow control for these streaming APIs!

Another advantage of gRPC for OSGi remote services is it's polyglot nature.   This means that if (for example) a gRPC remote service is run as an OSGi/Java server, clients can be easily implemented in any of the languages supported by gRPC.  As well, servers written in some other language can easily created and accessed from OSGi consumers.  An example of this is the ECF etcd3 discovery provider, which communicates with an etcd server (written in Go) to publish and discover OSGi remote services.

Finally, with bndtools (an Eclipse plugin for OSGi bundle development), ECF Remote Service workspace template, and it's support for generating code as part of Eclipse's incremental build, gRPC code generation can be seemlessly integrated into the Eclipse development environment so that gRPC code generation, compile, and bundle packaging can happen immediately and continuously as part of gRPC remote service development.  For a video tutorial demonstrating this, please see here.

Saturday, February 06, 2021

gRPC Code Generation using Bndtools and ECF Remote Services

There's a new video tutorial that demonstrates using ECF Remote Services, bndtools, and Eclipse to create an OSGi Remote Service.   

Bndtools has recently added the ability to run code generators as part of a bnd-based project, and with ECF's bndtools workspace template, a single proto3 file added to a project will automatically generate an entire Java remote service API and update/regenerate the API as changes are made to the proto3 file.   No command-line execution of protoc needed.

Further with ECF's project templates, the generated API can be easily implemented and exported as an OSGi Remote Service.

Please watch the video here

Thursday, January 07, 2021

ECF 3.14.19 released - simplify remote service discovery via properties

 ECF 3.14.19 has been released.

Along with the usual bug fixes, this release includes new documentation on the use of properties for discovering and importing remote services.   The docs describe the use of properties files for simplifying the import of remote services.   

This capability is especially useful for Eclipse RCP clients accessing Jax-RS/REST remote services.

Patrick Paulin describes a production usage his blog posting here.

Tuesday, December 08, 2020

Using properties to simplify discovery of OSGi Remote Services

OSGi Remote Services are discovered by ECF's Remote Services implementation in two ways:  

1. Via a network discovery protocol provider such as:  Zeroconf, jSLP, etcd, Zookeeper, or some custom protocol

2. Via an xml format known as an Endpoint Description Extender Format (EDEF)

 The EDEF format is specified by the OSGi Remote Service Admin specification.   

When importing an EDEF-defined remote service, it's typically necessary to construct the entire EDEF file 'by hand' rather than having he EDEF generated automatically.  This can be quite complicated to construct by hand as some properties are required, others are optional and it's not obvious what all of the values must be for successful import.

A new capability has been added to ECF's Remote Service Admin implementation that allows EDEF Properties to be used with the EDEF, thus simplifying the creation of remote service consumers that use EDEF for import.

This capability was added to support the usage of JaxRS Remote Services in an Eclipse RCP client.  See a description of this use case here.

Monday, September 21, 2020

Using gRPC-java code generation to create OSGi Services

OSGi Services are usually first created by declaring a java service interface class.  As an OSGi service, this interface class serves as both the name for the service in the service registry, and defines the service contract (i.e. the interface method signatures...i.e. the method name, argument types, and return types) for that version of the service.

gRPC (Google RPC) is a popular and high-performance rpc approach that allows developers to define networked services based upon protocol buffers (proto3).

By extending bndtools recently-added code generation capability, it's now possible to generate an OSGi (remote) service API from just a proto3 service declaration.  All the classes necessary for an OSGi Remote Service API (service interface, arg and return types) can be generated by bndtools within Eclipse from a single proto3 file, immediately and completely.

Ready to implement-and-consume OSGi Services can be generated by Eclipse+bndtools + a proto3 service declaration.

Further, the proto3 service declaration can be modified, and the tooling will immediately generate new service API classes, compile, and package them into a bundle, all from within Eclipse+bndtools.

To get this bndtools-grpc generation with an example see here.