The Concordant Service

The C-Service is a lightweight proxy service that can run on many kinds of devices and connect in one end C-Client instances running on edge devices (terminal or PoP) to support transactions and replication between services, and on the other end any backend server that is adapted to its drivers interface to store and replicate data.

Currently on beta version, it runs as a ServiceWorker in web browsers, using PouchDB to synchronize with a remote CouchDB server. It can also be launched as a standalone application, typically server-side, to be used by browsers that do not support Service Workers.

The C-Service exposes a REST API which should not be accessed directly, as it may not be stable; use the c-client library instead.

Note on current implementation: the C-Service beta version is a distributed database service for CRDTs of the C-CRDTlib.

Getting started

Requirements

For the next steps, you will need the following software:

• Make sure you have the latest stable version of Node.js;
• C-Service synchronizes with a CouchDB backend.
• Once CouchDB installed, use the CouchDB user panel (Fauxton) to setup a database and a user.

In addition, you will need to enable CORS in CouchDB, using Fauxton or the dedicated NPM package from PouchDB:

npx add-cors-to-couchdb [http://mycouchDBserver.org] \
    [-u myusername] [-p mypassword]
(server defaults to localhost)

Use the C-Service as a Service Worker

A Service Worker implementation is bundled with the C-Service package, in dist/c-service-worker.js.

To use it, just copy (or link) it to an appropriate location and register it as a ServiceWorker in your application. For more information, see our example applications.

This Service Worker is configured to use our demo database, so feel free to re-build it to use your own: adjust the configuration in src/config.json and run

npm install

In a future release, the C-Client will be able to provide these settings at runtime.

Start C-Service standalone

Ensure CouchDB is running before starting C-Service. If it is running on another host, set the COUCHDB_URL accordingly. You will also need to provide CouchDB credentials:

export COUCHDB_URL=my-couchdb-server.org
export COUCHDB_USER=my-user COUCHDB_PASSWORD=my-passwd

It is also possible to configure WebSocket path used by the service (default is /):

export WS_PATH=my-websocket-path

Then run the service:

npx @concordant/c-service

This launches an Express server listening on TCP port 4000 and a WebSocket server on port 8999.

Setup C-Service as a Systemd service

First ensure CouchDB is setup as a systemd service named couchdb.service (or adapt the name in c-service.service file).

Put the c-service folder in /opt/ or adapt the c-service.service file.

Put the provided file c-service.service in /etc/systemd/system/.

Create the file /etc/systemd/system/c-service.conf containing CouchDB user credentials:

COUCHDB_USER=<couchdb_id>
COUCHDB_PASSWORD=<couchdb_password>

Then start the service:

systemctl start c-service

Test C-Service using curl

The standalone C-Service exposes a REST API on /api, whose description can be found in file swagger.yml.

Once your C-Service is running you can query its REST API with curl. You can view your changes in the CouchDB user pannel.

Create the myapp database:

curl --request POST                               \
     --header "Content-Type: application/json"    \
     --data '{"appName":"myapp"}'                 \
     http://127.0.0.1:4000/api/create-app

Insert/update a PNCounter named myobject in myapp database:

curl --request POST                               \
     --header "Content-Type: application/json"    \
     --data '{"appName":"myapp","id":"{\"name\":\"myobject\",\"type\":\"PNCounter\"}","document":"{\"type\":\"PNCounter\",\"metadata\":{\"increment\":[{\"name\":\"clientid\"},{\"first\":60,\"second\":{\"uid\":{\"name\":\"clientid\"},\"cnt\":-21474836}}],\"decrement\":[]},\"value\":60}"}'  \
     http://127.0.0.1:4000/api/update-object

Get the PNCounter named myobject in myapp database:

curl --request POST                               \
     --header "Content-Type: application/json"    \
     --data '{"appName":"myapp","id":"{\"name\":\"myobject\",\"type\":\"PNCounter\"}"}'                       \
     http://127.0.0.1:4000/api/get-object

Get all objects of myapp database:

curl --request POST                               \
     --header "Content-Type: application/json"    \
     --data '{"appName":"myapp"}'                 \
     http://127.0.0.1:4000/api/get-objects

Delete myapp database:

curl --request POST                               \
     --header "Content-Type: application/json"    \
     --data '{"appName":"myapp"}'                 \
     http://127.0.0.1:4000/api/delete-app