Scope of Project:

Build an implementation of the Cloud Sync Service (CSS) storage interface that works with CouchDB, and test it with unit tests.

Background :

As of writing this, MongoDB is the only production capable database that can be configured for Cloud Sync Service storage. Mongo recently changed their licensing terms, making it harder to consume the open-horizon platform into a commercial product. This project will extend the sync service to support CouchDB as an alternative.

The storage component of the sync-service has a Golang interface that is used by the core to persist object metadata and the objects themselves. The task is to provide an implementation of that interface that works with CouchDB.

Assumptions:

• Sync service has its own notion of users, so the only kind of couch user needed is an admin. The sync service will use an admin user to talk to CouchDB.
• The relationship between object and data (using the ESS terms) is 1 to 1. In CouchDB terms, that maps to document and attachment. In CSS terms, an object is a form of a wrapper or descriptor for the data, that's why it's always 1 to 1.
• The data stored with an object is always binary data (type: application/octet-stream)
• The unit tests assume that CouchDB is installed in the dev machine and an admin user has been created with credentials - Username <username> and Password <password>. Environment variables “COUCH_USERNAME” and “COUCH_PASSWORD” need to be set with the above credentials.

Specifications:

• Golang v1.14

• CouchDB v3.1 (https://docs.couchdb.org/en/stable/)

• Kivik v3 is used as the Golang library for CouchDB. Kivik is the only library that is actively maintained, has support for CouchDB 3, and has detailed documentation.

  Required imports:

  "github.com/go-kivik/couchdb/v3" // The CouchDB Driver
  "github.com/go-kivik/couchdb/v3/chttp" // For authentication functions
  kivik "github.com/go-kivik/kivik/v3"
  

  Documentation links:

  1. https://pkg.go.dev/github.com/go-kivik/kivik/v3
  2. https://pkg.go.dev/github.com/go-kivik/couchdb/v3
  3. https://pkg.go.dev/github.com/go-kivik/couchdb/v3/chttp

CouchDB notable fundamentals:

1. To update/delete an object in CouchDB, the first step is always to GET() the object. This is because the current 'rev' i.e 'revision' is needed to perform any modifications. Due to this - there are no direct or in-built methods to delete/update objects based on queries.
2. While updating an object that has an attachment, the 'stub' value must be set as true in the object when calling PUT, otherwise, the attachment will be removed in the updated object. This is handled by kivik implicitly but is a notable behaviour.

Concepts:

A CSS object consists of metadata, binary data, and some other properties. This section documents how CSS concepts relate to CouchDB concepts.

• Documents: CouchDB database instance will store CSS objects as documents